EEVblog #259 - PSU Rev C Schematic - Part 12

[caroper]

I like it, living in Africa and, as I do, in a village that suffers fairly frequent power outages, a battery operated variable supply would be worth its weight in gold. And that would be from Murphy's Pot of Gold too as Murphy generally arranges the Power outages right at a critical phase of the project.


I think the improved Voltage range at the cost of precision is a viable trade off.
Seeing as most of the measurements in modern electronics that require low noise and high precision would probably happen in design's that are running between 2V0 and 3V8 anyway, so the switching regulator is off.


Two things I would like to see, to make it really shine.


1) Ability to supply burst currents of up to 2 Amps, common when working with Cellular modules and other Radio devices.


2) A Analogue or Digital link between two boards to allow for Serial/Parallel/Independent operation of 2 supply's. Many modern designed need dual supply, i.e. 3V3 for the MCU but 3V8 for Cellular/GPS or possibly separate supplies for the Digital and Analogue portions. Serial tracking would also be a great benefit for those who still wish to experiment with split rail op amps etc.


All in all an excellent device, versatile and expandable.


You beauty 


Cheers
Chris

[BravoV]

Great series, learned a lot of in design change and modification in the building a circuit, thanks a lot Dave.

Noob questions :

- I saw there are 2 x LM358 op-amps there, will this save even for few cents by replacing it with LM324 ? Since they're almost identical by spec. Just checked Digikey, the cost of single LM358 is almost identical with LM324 which has 4 op-amps instead of 2.
- Correct me if I'm misinterpreting Dave's explanation, is that pre-regulator control loop is now handled by the mcu (cpu cycles) instead of linearly controlled like the front end linear section ?

[FreeThinker]

Hi Dave
You asked for input on the latest design so here goes.
First I love it, the increased range is a winner for me.
During vid you mention mounting the pcb on the top and using a pcb to mount the lcd. Please don't do what I did and forget that this would make the display upside down  . I can laugh about it now....Just

[markus_b]

What is the link to the pdf file of the schematic ?

[firewalker]

If you haven't already thought it, place a female header for the Tx,Rx pins on the board, not only to the rear of the enclosure.

Alexander.

[EEVblog]

1) Ability to supply burst currents of up to 2 Amps, common when working with Cellular modules and other Radio devices.

You can never satisfy everyone's power requirements. Give them 2A and they want 3A...
This is deliberately a low power PSU.

2) A Analogue or Digital link between two boards to allow for Serial/Parallel/Independent operation of 2 supply's. Many modern designed need dual supply, i.e. 3V3 for the MCU but 3V8 for Cellular/GPS or possibly separate supplies for the Digital and Analogue portions. Serial tracking would also be a great benefit for those who still wish to experiment with split rail op amps etc.

I don't see much point in tracking.
If you want dual supplies, just use two supplies.

Dave.

[caroper]

You can never satisfy everyone's power requirements. Give them 2A and they want 3A...
This is deliberately a low power PSU.

This is true, and if anything I worded it incorrectly, it is more a matter off can the device tolerate such a spike rather than current limit at it or sustain 2 Amps and it looks like the specifications of the parts can indeed handle it for short peaks. It would be a software option to turn off current limiting. In reality I find that just having a 1000uF 16V cap across the Celuller modules supply pins is sufficient to meet that occasional 2A spike.

I don't see much point in tracking.
If you want dual supplies, just use two supplies.

Dave.

Also valid, and with the expansion capability's you have provided or allowed for already with SPI, ICSP and optional Ethernet, Tracking etc. becomes a software rather than hardware feature anyway.

I haven't seen the schematic yet but it should be easy enough for a daughter board, that plugs in place of the Ethernet Module, to provide optically isolated communications with 2 or more of your boards. So that, allong with any other wild ideas can become a challenge for the community rather than you having to satisfy every possible request.

Keep it up Dave,

I wan't 2 at least (Just for myself) and I think several of my mates will want them too, so I look forward to final design and production.


 

[tnt]

I don't really get how the battery is connected ... it seems like it's connected in "series" on the schematics.

[sacherjj]

Timing of this is funny.  Last week I was looking at linear regulators and wondering how tough it would be to make a hybrid switching and linear to minimize cooling required for a large voltage range supply.  The difficulty seemed to be making it variable.  I'll be learning a bunch from rev C.

[Bored@Work]

- Correct me if I'm misinterpreting Dave's explanation, is that pre-regulator control loop is now handled by the mcu (cpu cycles) instead of linearly controlled like the front end linear section ?

I am also surprised about that. Actually I was surprised on several accounts.

While a slow digital control loop should work for a per-regulator I was excepting an analog feedback loop. More precisely, something along the examples in the LT3080 data sheet. There they use a simple transistor to keep the pre-regulator output above 0.6V of the LT3080 output. And the transistor should be cheaper compared to the digital pot. But that feedback loop would offset the current measurement.

Still, the digital pot bugs me. Simple DACs have been used instead for controlling regulators for ages For amusement I have attached a 37 year old application note I rediscovered on some datasheet collection site. They use a current DAC in a little bit convoluted way. Kids these days always think digital stuff was just invented yesterday

This more recent article http://electronicdesign.com/article/power/an-easy-way-to-roll-your-own-programmable-power-su uses a voltage DAC, some math (which they got wrong), and a resistor to do the same with a switching regulator. The schematic (Figure 1)  http://www.electronicdesign.com/files/29/20515/fig_01.gif is dead simple. Although startup can be a problem in some application, it starts with full output. But when used as a pre-regulator this shouldn't be too big of a problem.

I didn't check if Dave has a spare (PWM) DAC in the circuit. If yes, this would be an additional way to shave of some cost.

[Rufus]

To me the power input circuitry and battery have given a power supply with a continuous power limit through the input of about 4W which will be more like 3W at the output.

You are going to have to jump through mechanical and thermal hoops to prevent U2 running steaming hot and in thermal current limit all the time which would further reduce the power limit.

Maybe the ?Supply title is more descriptive than you would think.

[FreeThinker]

Schematic C up now here http://www.eevblog.com/files/uSupplyBenchRevC.pdf
Battery connector fixed and 5v Reg mysteriously has reappeared 

[kkp]

U12A (buffer LM358) will be running outside of common mode input range. Which will ruin your happiness.
Suggestion:
Add 1 ohm in the short vertical wire between R1 and R19. Then remove the buffer.
With the 1 ohm added, the current in R17 and R23 will cause equal drop on the inputs to the INA219, and also cancel in the differential amplifier.
Now you have a free opamp.

/Kasper Pedersen

[hans]

Just my thoughts:

I don't remember battery support was mentioned earlier. It's unique, but very specific. I would have no use for it, and rather power it via a plug pack only. Doesn't matter, it's Dave's power supply

I would have used a DC-DC converter with wider input range, though. Maybe even buck-boost so really low voltage applications can be powered effieciently.

Oh by the way, a high frequency regulator is by essence not more efficient. There is a trade off between that as higher frequency equals in more switching losses. Take a look at the datasheet of LT3505, it clearly says that the programmable frequency set should be used so the power supply can be very efficient or very small (in PCB dimensions).

Also, you mentoined in the video that the tracking regulator will be +2V of the output voltage. What happens in a long period short circuit operation? All the output power would go into the LT3080, which would be dissapating 12W (12V 1A) or more.. maybe make it so that it follows the live output voltage instead (or only if the output voltage deviates alot from the input).
I wonder how stable the power supply is with a constantly adjusting input voltage on the LT3080. I also wonder if the update speed is good enough , because now all is being controlled through I2C.

I like I2C for it's bus capability, but it's so slow. C'mon 400kHz, you can't even get 30kB/s over that. Whatever, it saves a ton of I/O space and makes the design simpler.

I see you also power the whole system with a LDO. How much would the screen+backlight+control circuitry draw? If it's like 100mA, you're probably dissipating 5V*100mA=500mW in the LDO there..

I really like the new INA209 chip. I think it's a great choice over the microcurrent. Also measuring high-side current is so much better than putting a 1 ohm resistance in series. It also makes the power supply stable for applications with low-current sleep but high current bursts when operational (like sensor terminals sending data over GSM network).
The LM358 opamp is not rail-to-rail btw, you have to pick one which is.
I also have concerns regarding the maximum output voltage of a typical R-R opamp, as it sometimes is 10mV or even more under V+, which means that opamp is constantly reading 10mA current draw, on top of the input offset voltage!

I find it disappointing to see the 'ultra high resolution' thing removed though. I really was looking forward to modding or expanding the PSU design with an even more precise measurement capability (as I have a design back from project that had 16-bit resolution auto-ranging from several mA up to 2Amps). But I guess that would be my own spin-off, as I hate Arduino and still don't understand you're putting up with after all the trouble you've had with it

The ethernet control thing is cool feature tho, especially an expansion board is a great idea to integrate.

Going for complete SMD kinda spoils the fun as it's not a kit anymore in sense you'd have to solder the PCB, but I guess you're right for being able to pick so much more and better components.

[sacherjj]

After looking through the INA219 data sheet, I'm wondering if it would be possible to move the shunt to the output.  The sense would still compensate for the voltage drop.  However, you would have to go with a 0.25 ohm shunt to get full range current.  It would allow you to measure Vin- as the actual output voltage, with the 12 bit DAC in the ship.  It would also calculate output power.  This sacrifices 1/4 of your resolution with current measurement, but is probably more accurate than ADC on the Atmel for output voltage.  Hard to say without a schematic to pour over, I'm probably missing something.

[FreeThinker]

After looking through the INA219 data sheet, I'm wondering if it would be possible to move the shunt to the output.  The sense would still compensate for the voltage drop.  However, you would have to go with a 0.25 ohm shunt to get full range current.  It would allow you to measure Vin- as the actual output voltage, with the 12 bit DAC in the ship.  It would also calculate output power.  This sacrifices 1/4 of your resolution with current measurement, but is probably more accurate than ADC on the Atmel for output voltage.  Hard to say without a schematic to pour over, I'm probably missing something.

See my previous post for link to schematic

[McMonster]

I didn't see anyone mentioning it, but there are actually more pins on AVR available than you think Dave. The Rev C schematic shows a DIP-28 ATmega168A-PU chip, while the SMD version, ATmega168A-AU is in TQFP-32 package. The "missing" 4 pins go for additional power pins and two dedicated ADC pins (no I/O capability, internally tied to the ADC). So you may replace the chip in the schematic with the proper part, move two of your channels to the dedicated pins and still have two free I/Os for greater flexibility or you can just route them to some I/O header for people to use as they want.

Magic!

[McMonster]

By the way, I think Rev C is much better than previous versions, much simplified, much less ICs (like an entry for a "how many digital/mixed ICs can you stuff into a linear PSU?" contest). Having a mixed SMPS/linear kind of design sounds a bit strange, so I think first thing you should do is to fully characterize the PSU once you build it (and post a video of course), I'm really curious what's the total efficiency of this device. And now that we really know the "big secret" (not that the battery connector wasn't screaming it out in previous revisions) I must say I'll reconsider buying it. I was absolutely sure I can't justify it before, but I could use a battery powered PSU of that size actually. So I'll wait until the price is known and just hope the shipping to Poland won't double it.

Now waiting for Rev D.

[sacherjj]

I didn't see anyone mentioning it, but there are actually more pins on AVR available than you think Dave. The Rev C schematic shows a DIP-28 ATmega168A-PU chip, while the SMD version, ATmega168A-AU is in TQFP-32 package. The "missing" 4 pins go for additional power pins and two dedicated ADC pins (no I/O capability, internally tied to the ADC). So you may replace the chip in the schematic with the proper part, move two of your channels to the dedicated pins and still have two free I/Os for greater flexibility or you can just route them to some I/O header for people to use as they want.

Magic!

Based on Dave's comments on YouTube for this video, I believe he is sticking with a socket DIP-28 based processor, to allow replacement if someone screws up programming it.

[ModernRonin]

I realize Dave said he didn't want to do this in the video, but I'm seriously thinking that using a 0.1 ohm current shut (10 x 1 ohm 0.1%) might be a good idea. Several reasons...

First, with a 12 bit ADC on the INA219B (*great* choice on that chip, BTW) you're not hurting for resolution. Go ahead and use a smaller shunt!

Second, that would allow reading up to 320 / 0.1 = 3.2 amps. Makes it super easy for someone to drop the LT3083 reg in there and get a full 3 amp PSU with very little trouble.

Seems like the only problem would be that the voltage going into U12A would be ten times smaller. But to fix that, U12A could act as a x10 voltage multiplier (just add 2 resistors around the negative feedback path). Or we can change the gain resistor on U12B (R24) to make it an x10 diff amp. Everything else can stay the same.

The only downside to using opamp gain is that the output voltage error is (input offset) * (gain). So we might have to go to a more precise opamp for U12A or U12B, depending on where the gain is done.

[McMonster]

I didn't see anyone mentioning it, but there are actually more pins on AVR available than you think Dave. The Rev C schematic shows a DIP-28 ATmega168A-PU chip, while the SMD version, ATmega168A-AU is in TQFP-32 package. The "missing" 4 pins go for additional power pins and two dedicated ADC pins (no I/O capability, internally tied to the ADC). So you may replace the chip in the schematic with the proper part, move two of your channels to the dedicated pins and still have two free I/Os for greater flexibility or you can just route them to some I/O header for people to use as they want.

Magic!

Based on Dave's comments on YouTube for this video, I believe he is sticking with a socket DIP-28 based processor, to allow replacement if someone screws up programming it.

Didn't catch that from the video, thanks. But then... Most of the people would probably go with using Arduino or some other bootloader, so there's no room for screwing up the chip. So I think using SMD micro is worth it if it's going to be SMD desing after all.

[m12lrpv]

So I think using SMD micro is worth it if it's going to be SMD desing after all.

Yes I would agree go for the SMD version and the extra pins. I don't see how you can screw up the chip, they are pretty robust and it would take a lot less PCB space. Not to mention that they are probably cheaper too.

Having screwed up a chip in my own adventures and reading about others having done the same I believe the current choice is better than the smd version.

It's also a hell of a lot easier to program if you can just swap the chip in and out of a commercial board.

You can guarantee that someone is going to want to reprogram the fuses to clock it differently and that's another great way of bricking the chip.

[EEVblog]

U12A (buffer LM358) will be running outside of common mode input range. Which will ruin your happiness.

Damn, you are quite right. I must have been thinking I was still using the rail-rail opamp.
Thanks.

Suggestion:
Add 1 ohm in the short vertical wire between R1 and R19. Then remove the buffer.
With the 1 ohm added, the current in R17 and R23 will cause equal drop on the inputs to the INA219, and also cancel in the differential amplifier.
Now you have a free opamp.

I can't see how that would work. There would only be a fixed extra current current flowing through that extra 1ohm resistor, so it can't compensate the variable current flowing through R17 and R18 as the load current changes.

Dave.

[EEVblog]

Also, you mentoined in the video that the tracking regulator will be +2V of the output voltage. What happens in a long period short circuit operation? All the output power would go into the LT3080, which would be dissapating 12W (12V 1A) or more.. maybe make it so that it follows the live output voltage instead (or only if the output voltage deviates alot from the input).
I wonder how stable the power supply is with a constantly adjusting input voltage on the LT3080. I also wonder if the update speed is good enough , because now all is being controlled through I2C.

I like I2C for it's bus capability, but it's so slow. C'mon 400kHz, you can't even get 30kB/s over that. Whatever, it saves a ton of I/O space and makes the design simpler.

The update speed of the tracking pre-regular doesn't really matter.

I see you also power the whole system with a LDO. How much would the screen+backlight+control circuitry draw? If it's like 100mA, you're probably dissipating 5V*100mA=500mW in the LDO there..

The whole design takes about 15mA I think, and the backlight will only add 5-10mA on top of that. I would not be silly enough to run it at 100mA per LED.

Dave.

[EEVblog]

After looking through the INA219 data sheet, I'm wondering if it would be possible to move the shunt to the output.  The sense would still compensate for the voltage drop.  However, you would have to go with a 0.25 ohm shunt to get full range current.  It would allow you to measure Vin- as the actual output voltage, with the 12 bit DAC in the ship.  It would also calculate output power.  This sacrifices 1/4 of your resolution with current measurement, but is probably more accurate than ADC on the Atmel for output voltage.  Hard to say without a schematic to pour over, I'm probably missing something.

I briefly considered that, but the LT3080 driving sense would need to be on the output to compensate, and that might screw up the stability somehow. It would have to be tested.
But that would now fix the LM358 issue I've got...

EDIT: 2nd thought, no it wouldn't work the regulator response time would now to terrible due to the RC on the set pin.

Dave.

[EEVblog]

Hi Dave, did you reverse the +/- inputs on the U3B opamp, isn't ADC-IOUT suppose to go the - side? and the PWM output to the + side?

No, it is correct. Rev B was wrong.

Dave.

[EEVblog]

Also, you mentoined in the video that the tracking regulator will be +2V of the output voltage. What happens in a long period short circuit operation? All the output power would go into the LT3080, which would be dissapating 12W (12V 1A) or more.. maybe make it so that it follows the live output voltage instead (or only if the output voltage deviates alot from the input).

The software knows that the output voltage is and if it's in constant current limit, so it can adjust the input as required.

Dave.

[kkp]

I can't see how that would work. There would only be a fixed extra current current flowing through that extra 1ohm resistor, so it can't compensate the variable current flowing through R17 and R18 as the load current changes.

The current is not fixed (it varies with V+).
As long as U12B is not out of regulation*, the U12B inputs are at the same voltage. Therefore the current in R17 and R23 is almost identical. If you consider the case where U1 is removed (no output current, the difference should be 0), the negative terminal is fed with 18001 ohm, the positive 18000 ohm. So 'almost'. Once you add 1 ohm, they are identical. And thus the current in the shunt due to R17R18 should be suppressed with the matching of the real and dummy 1 ohm shunt.
It does mean that your shunt is effectively 1 ohm || 18k ohm, but that will be well below the resistor tolerance.

I will find a pen and paper, if required.

/Kasper

*I have my reservations about using LM358 with the output this close to ground. I recall it has problems below 0.6V. My first thought was LMV358, but it cannot handle your input voltage.

[EEVblog]

I can't see how that would work. There would only be a fixed extra current current flowing through that extra 1ohm resistor, so it can't compensate the variable current flowing through R17 and R18 as the load current changes.

The current is not fixed (it varies with V+).
As long as U12B is not out of regulation*, the U12B inputs are at the same voltage. Therefore the current in R17 and R23 is almost identical. If you consider the case where U1 is removed (no output current, the difference should be 0), the negative terminal is fed with 18001 ohm, the positive 18000 ohm. So 'almost'. Once you add 1 ohm, they are identical. And thus the current in the shunt due to R17R18 should be suppressed with the matching of the real and dummy 1 ohm shunt.
It does mean that your shunt is effectively 1 ohm || 18k ohm, but that will be well below the resistor tolerance.

I think you are missing the point here.
The residual current is "zeroed" out by the user at a fixed output voltage.
The current through R17/R18 then changes with the output current, and that's the problem.
The current through R23/R24 and your new 1R resistor will however remain the same, and will not change with the output current. So it cannot be used to compensate for the changing current through R17/R18

Dave.

[IanB]

I only got part way through the video but I was a little puzzled at the battery charger chip and typical circuit. There did not seem to be a center tap on the battery or any cell balancing control. If the cells age and become mismatched that might lead to one cell being charged to 4.3 V while the other is at 4.1 V. It this a good idea, and do other integrated charger ICs behave the same way?

[EEVblog]

I only got part way through the video but I was a little puzzled at the battery charger chip and typical circuit. There did not seem to be a center tap on the battery or any cell balancing control. If the cells age and become mismatched that might lead to one cell being charged to 4.3 V while the other is at 4.1 V. It this a good idea, and do other integrated charger ICs behave the same way?

Yes, that is common for low-ish current two cell chargers like this. Cell balancing is not used as it would be for say a high current LiPo pack.

Dave.

[Psi]

I only got part way through the video but I was a little puzzled at the battery charger chip and typical circuit. There did not seem to be a center tap on the battery or any cell balancing control. If the cells age and become mismatched that might lead to one cell being charged to 4.3 V while the other is at 4.1 V. It this a good idea, and do other integrated charger ICs behave the same way?

also you may have missed the bit where he said the lithium batteries he plans to use have built in protection. They wont allow themselves to charge up past max or discharge below min volts.

[sacherjj]

After looking through the INA219 data sheet, I'm wondering if it would be possible to move the shunt to the output.  The sense would still compensate for the voltage drop.  However, you would have to go with a 0.25 ohm shunt to get full range current.  It would allow you to measure Vin- as the actual output voltage, with the 12 bit DAC in the ship.  It would also calculate output power.  This sacrifices 1/4 of your resolution with current measurement, but is probably more accurate than ADC on the Atmel for output voltage.  Hard to say without a schematic to pour over, I'm probably missing something.

I briefly considered that, but the LT3080 driving sense would need to be on the output to compensate, and that might screw up the stability somehow. It would have to be tested.
But that would now fix the LM358 issue I've got...

It would also lower the shunt loss and allow you to run the tracking pre-regulator a little closer.

[IanB]

also you may have missed the bit where he said the lithium batteries he plans to use have built in protection. They wont allow themselves to charge up past max or discharge below min volts.

I didn't miss that. But it depends a little on the batteries you actually have in the device and the quality of the protection circuit--individual 18650 cells with protection circuits are an "after market" item that are not available from the big name manufacturers and do not have any standardization on the level of protection.

If the protection circuit tripped on one cell in the pair while charging it would block the whole charging circuit and I'm not quite sure what would enable it to reset. Usually you would have to take the cell off the charger and then put a load on it.

I think the integrated charging ICs may expect a two cell protection and charge control circuit to be present on the battery with some internal cell balancing. I am unsure about this area but I don't quite see how having unbalanced cells in a pack is a good idea.

[IanB]

Dave,

I noticed how your schematic divides the circuit into separate functional blocks for clarity. Does the tool (Altium?) also then have the capability to produce a separate system block diagram showing the high level view of how those functional blocks are interconnected? I can see that being useful in more complex design.

[EEVblog]

I noticed how your schematic divides the circuit into separate functional blocks for clarity. Does the tool (Altium?) also then have the capability to produce a separate system block diagram showing the high level view of how those functional blocks are interconnected? I can see that being useful in more complex design.

Not automatically, no. But kinda can manually, with things like harnesses.
The functional block thing is purely visual, it can be done in any CAD package, nothing special about Altium here.

Dave.

[IanB]

Not automatically, no. But kinda can manually, with things like harnesses.
The functional block thing is purely visual, it can be done in any CAD package, nothing special about Altium here.

Oh. I thought that might be one of the "added value" features of a package like Altium. It definitely seems like it would be a useful feature when designing complex systems.

[TerminalJack505]

The battery powered feature is pretty cool.  Are shipping the batteries with the product going to be a problem?  Although I don't know for certain, some countries might consider them hazardous material and restrict shipping methods.  (Ground only, for example.)

Also, I noticed a possible issue with the schematic.  See attached.  Does ERC not catch that?  Or maybe that's not the actual net name coming from the connector.

Edit: I guess the two pins across the cap are just two passive pins to the ERC checker so I guess it might be hard for it to find issues like that.

[EEVblog]

The battery powered feature is pretty cool.  Are shipping the batteries with the product going to be a problem?  Although I don't know for certain, some countries might consider them hazardous material and restrict shipping methods.  (Ground only, for example.)

Yep, I won't be able to ship them.

Dave.

[timelessbeing]

Isn't it possible to let a switcher IC handle all the regulation? (I am not an EE)

Also, is there a ballpark total cost for this device?

[jshonw]

I have experimented with the INA219 a few years back.  From my foggy memory, I believe the dV/dt protection resistors  caused problems with the accuracy and I removed them while playing with it.  Then again, I was doing this with a breadboard, so take it with a grain of salt.

[ModernRonin]

Isn't it possible to let a switcher IC handle all the regulation?

You can, but switching supplies are notoriously noisy. If you need clean power (like for high gain or high precision analog circuitry), running the power rail through a good linear regulator to clean up the noise is considered good practice.

[timelessbeing]

Can't the noise be removed with filters?

[Psi]

Can't the noise be removed with filters?

kinda, but it's complicated and it only reduces the noise, doesn't remove it entirely.

[kkp]

I think you are missing the point here.
The residual current is "zeroed" out by the user at a fixed output voltage.
The current through R17/R18 then changes with the output current, and that's the problem.

Quite possible. I would have thought the 'size of the problem' would be 1 ohm / (1 ohm+18k), so the changing current in R17  causes a gain error of only 55 uA/A(at output), and 1/36001=27 uA/V(at V+) of offset.

The 1 ohm I suggested is purely for suppression of this offset going into the INA219. When V+ is 10V, R17/R18 current contributes 277uV across the shunt. Let's say the user zeroes here, then adjust so V+ becomes 20V.
The R17/R18 current now contributes another 277uA, so even if U1/U4/D3 have unchanging leakage to ground, the INA219 readout changes 277uA.  But one can also fix this in software.

/Kasper

back of envelope check: 1A output change, the shunt drops 1V, the opamp output rises 1V, 2V across 36k, 55uA, 55 ppm.

[vk6hdx]

Are the Li-ion cells in series or parallel?  The choice of the charge controller (MCP73213) with its 8.4V VREG output seems to indicate they are in series, however the 3v3 LDO MCP1700 seems to have a max VIN of 6v.

Edit:  Without knowing how much space the current code takes up, is it worth going to the ATMega328?  AFAIK its pin compatible & Arduino compatible and would double the programming space available.  Around 50c more.  Then in addition to all the PSU smarts we may even have enough space left to program in a game of pong on the 20x2 LCD

Cheers,
Troy

[A Hellene]

Damn it, Dave! You made me finally decide to upgrade my lab PSU that I built in the early eighties! Especially now, that my time is very, very limited...

It is a 350W linear PSU (0.0-32.0V/0.00-10.00A) based on the legendary LM723, whose circuit I redesigned from scratch a couple of years after its initial construction, and it still goes strong with few recent minor losses (the 20 years old output filtering capacitors!) after having it used to debug crude switching power supplies! All these years it did never complain, even when I used it to be charging my motorcycle and car batteries!

Thanks to you, the LT3080 got my attention and I found it to be an excellent voltage follower for the upgrade of my lab PSU, even though I might need to change the power stages (2 x 2N3772) with faster ones. I initially intended to add a few exotic features like, a deep memory to be storing real time the output voltage and current history and to display or send the data to a graphics display or over a serial line, and a few hundred steps of arbitrary output waveform programmability. Now, I think that adding a switching tracking pre-regulator stage would not be that irrational...

Anyway, I have made a few drafts that simulate perfectly well, in a hope that you will find them useful for the PSU you are constructing. I am using the AD8628, this lovely Analog Devices's chopper, that does not only have one of the best offset values in the market but it also needs only a few micoseconds time to recover from an I/O saturation or overload condition, instead of the usual 50ms most choppers need. There is also the AD8616, if you need any faster solutions.

Linear PSU v1

This, above, was my first attempt. Kelvin connections for the I/V sense resistors and dividers. R4 adds to the output voltage the shunt resistor voltage drop (= <Vout-> * R2/R4), while V_Set has a gain of R2/R3; R1 balances the overall gain of U1, adding to the output an amount of 0V * R2/R1. My initial thought was to keep my current shunt configuration as it was (low-side current sensing), but I ditched that idea because this way I insert extra stages to the regulation loop, compromising LT3080's accuracy and speed. Next, I used a current-sense IC but the overall stability is not of the standard I expect it to have. But the voltage regulation loop seems to be flawless:

Linear PSU v2

This is only a draft, but the solution you might be seeking for your PSU is the U3 stage, above: Personally, I need 5.0V for the 16-bit, <1 LSB INL ADCs/DACs and, possibly, for the graphics LCD; otherwise, everything can run on 3.3V. Vcc can be anywhere between 3.3-5.0V while Vee=0.0V. If you are paranoid about the ground level accuracy, set Vcc=3.3V and Vee=-1.0V and you are done! You can use any low voltage op-amp to drive the LT3080 voltage follower by using an extra high voltage (>40V) MOSFET with an Rds of 100 milliohm or better: See the U3 stage. Additionally, if your LT3080 drives a power stage instead of the load directly, R8 shuts the power stage off, providing the first milliampers to the load by the LT3080 itself and after that the power stage takes over; R9 ensures that the LT3080 will never provide more than 40mA, keeping it always cool on the PCB -no need to mount it in the hot heat-sink and have its characteristics drift off.

I hope that the above could be of some help; of course, any ideas are welcome!


-George

[Psi]

Are the Li-ion cells in series or parallel?  The choice of the charge controller (MCP73213) with its 8.4V VREG output seems to indicate they are in series, however the 3v3 LDO MCP1700 seems to have a max VIN of 6v.

Give this man some points!
That does look to be a critical error

[tomwulf]

Hello folks, hello Dave,

I have a little question about the op amp U12A in the PSU REV C schematic. This op amp is powered from V+ and the input pins are also connected to a potential close to V+. But the LM358 common-mode-range does not include V+. This op amp has a maximum input common mode range approximately 2V below the positive supply rail. Is this right ? I didn't understand the reason of the correct function under these conditions.

Thank you for answering.

Great blog- Dave.

Best regards,

Thomas

[EEVblog]

back of envelope check: 1A output change, the shunt drops 1V, the opamp output rises 1V, 2V across 36k, 55uA, 55 ppm.

Yes, without the opamp it would be 5 LSB's error or so for a load change of 1A.
With the opamp in there there is zero load change with output current.
Adding a resistor V+ side does not compensate for that change, because V+ is fixed.

Dave.

[EEVblog]

Are the Li-ion cells in series or parallel?  The choice of the charge controller (MCP73213) with its 8.4V VREG output seems to indicate they are in series, however the 3v3 LDO MCP1700 seems to have a max VIN of 6v.

Give this man some points!
That does look to be a critical error

Yep, points hereby awarded!
The MCP1700 was originally powered from the +5V reg, so I missed rechecking that.
Thanks.

Dave.

[Stephen Hill]

Are the Li-ion cells in series or parallel?  The choice of the charge controller (MCP73213) with its 8.4V VREG output seems to indicate they are in series, however the 3v3 LDO MCP1700 seems to have a max VIN of 6v.

Give this man some points!
That does look to be a critical error

Yep, points hereby awarded!
The MCP1700 was originally powered from the +5V reg, so I missed rechecking that.
Thanks.

Dave.

Easily fixed with two resistors

[robrenz]

Center tap the battery holder and power it  with one cell?

[tom66]

Dave, if the boost converter has a minimum output of 9V, how is the LT3080 going to cope when the load is a short circuit @ 1A? Or even a low voltage? That could be 9W dissipation. I hope it has thermal shutdown.

Do you need a SEPIC converter to provide the lower ranges? Or maybe an isolated flyback supply? (good fun to design, trust me!)

[SuperFungus]

Wow.  I must say your original design didn't really excite me too much, but after all these Rev. C design decisions I'm pretty damn excited.  I thought every single thing you changed was for the better and now I'd actually buy one.

Since you asked, I did have a few comments

1) Why not move the battery measurement divider to the 'system' side (pin 3) of the switch rather than the 'battery' side (pin 2) of the switch to save the quiescent current when the supply is turned off?  Not that it's really a big deal, if your battery is about 3AH I back of the envelope around 2 years to discharge the batteries into that 44k. Doesn't cost anything to change either though.

2) You've probably considered this, but at 20V out and ~7 Volts nominal on the battery string to get 1A out of the output you'll need close to 3A at the batteries.  Can your cells handle that?  You mentioned they were about 3AH capacity so 1.5AH each?  That would be a 2C discharge rate? Sounds a little quick to me. Maybe a good candidate for a firmware fix, just drop the maximum current limit for high voltages.

3) Looks like the 100pF compensation capacitor from Vo to the feedback pin on the switcher is missing from your schematic.  I also notice that the digital pot seems to have around 16pF of output capacitance.  I haven't gone through the math but could you be introducing a stability issue?  The series 820 ohms helps, but 16pF seems close enough to that 100pF to be worth a second look. Maybe another argument for some kind of analog control loop for the pre-regulator?

One last note: THANK YOU for using Ethernet comms and not USB/GPIB.  (Why isn't GPIB dead yet?)  Ethernet is perfect for test equipment: isolated, completely ubiquitous, run long lengths with no problem etc.  But it seems like all sorts of gear just still targets USB or GPIB and not Ethernet and I just don't get it.

[IanB]

Just a quick observation to the above poster that two cells in series at 3 Ah each is 3 Ah total.

[SuperFungus]

Whoops!  Of course you're right!  I always think about AH as the capacity of the battery which isn't strictly true. 1C discharge is much more reasonable, ignore that part of my post. Good catch, thanks!

[oPossum]

Are the Li-ion cells in series or parallel?  The choice of the charge controller (MCP73213) with its 8.4V VREG output seems to indicate they are in series, however the 3v3 LDO MCP1700 seems to have a max VIN of 6v.

Yep, points hereby awarded!
The MCP1700 was originally powered from the +5V reg, so I missed rechecking that.
Thanks.

Dave.

MCP1702 goes up to 13.2 V

[robrenz]

Dave,  I know that design euphoria feeling you were describing when a few inspired design changes cascade into many design refinements that satisfy your personal design sensibilities and you know "this is it".  Except mine occur in mechanical design. My life path was similar to yours except I was machining at 12 years old instead of electronics.  I think this "design euphoria" can only be experienced fully when you have sole control of a project and there are basically no constraints.  Probably why many may be unfulfilled at work where deadlines and costs and the boss may prevent that from happening.  Also may explain why personal projects can be so fullfilling.  Now because of your inspiration I may someday experience some "electronic design euphoria"

Thanks for all you do,

Robin

[inderpreet]

Any chance of getting a connector in there for an Xbee? Would be cooler than the ethernet since the battery powered supply would then be wireless. Also, There is some example code out there on how to get arduinos to upload wireless-ly over the Xbee. Just a connector...

[curiousbob]

Center tap the battery holder and power it  with one cell?

This would work... until the battery voltage drops below (3.3V+dropout voltage)
For a few more cents, the MCP1702 will do the job as oPossum suggests.

[chavotronic]

Can someone explain to me the purpose of C24? Its between the Arduino reset and the CN3 FTDI Connector. I personally would have tied the other side of the cap to ground to build a lowpass together with R44, and then paralleled the lines. But i am probably wrong on the understanding of this way of connecting it.

[A Hellene]

C24 is needed for the good operation of the AVR microcontroller (see its data sheet), in order to decouple any possible noise that could be randomly resetting the AVR. Of course, it should be connected between the nRESET pin and the ground.


-George

[chavotronic]

So george, so you also think this could be a mistake in the schematic?

[A Hellene]

I think that it is rather about what it actually is than what I think it is!

Kidding aside, yes, of course it is one of the countless oversights or mistakes that could be introduced in any new design. This is one of the side effects of one's overly self-confidence, I usually also excel in...


-George

[oPossum]

The schematic is correct. That cap will reset the AVR on the falling edge of the handshake line. This is an ugly hack that has been in the Arduino from the start.

[A Hellene]

If the case is this, then I fail see any components that discharge the coupling capacitor C24, or any other components that decouple the AVR nRESET line noise, or that use the same capacitor for this task.


-George

[oPossum]

The internal pull-up resistor on the reset line will discharge the cap. It also provides some limited noise immunity - the pin isn't floating.

[A Hellene]

Yes, of course the AVR nRESET line has an equivalent of a >50 kohm silicon pull-up resistance built in on the die. But, when the component manufacturer strongly suggests the use of an external low-pass filter for enhanced noise immunity in ther engineering application notes, I will ostentatiously disregard any quick-and-dirty hacks of non-engineering communities like the aforementioned one; of non-engineering communities that introduced that imbecile baby-talk by renaming the add-on PCBs to "shields" and the programs to "sketches"...


-George

[curiousbob]

Not sure if someone has already mentioned it but  the LM7805 5V regulator requires VBATT>7V.
Now that Dave will use only 2 18650 batteries, this will be a problem once each battery goes below 3.5V.

[oPossum]

Yes, of course the AVR nRESET line has an equivalent of a >50 kohm silicon pull-up resistance built in on the die. But, when the component manufacturer strongly suggests the use of an external low-pass filter for enhanced noise immunity in ther engineering application notes, I will ostentatiously disregard any quick-and-dirty hacks of non-engineering communities like the aforementioned one; of non-engineering communities that introduced that imbecile baby-talk by renaming the add-on PCBs to "shields" and the programs to "sketches"...
-George

It's not hard to find poor design practices in the Arduino - both hardware and software.

I prefer the Microchip Microstick or TI Launchpad for simple DIY projects. They both have a full featured IDE with source level debugging and cost less than a genuine Arduino.

[oPossum]

Not sure if someone has already mentioned it but  the LM7805 5V regulator requires VBATT>7V.
Now that Dave will use only 2 18650 batteries, this will be a problem once each battery goes below 3.5V.

LD1117V50 would solve that problem

[A Hellene]

Yes, oPossum, that is right! However, Dave's PSU being compatible to the Arduino platform does not necessarily mean that it will be of that non-quality, also. Dave, as well as many other members of this community, is a seasoned designer. I would not expect him to adopt poor practices. After all, I cannot find a better quality for someone to have, other than their reputation as effective designers.

By the way, Dave, on the battery matter I would rather prefer to restore the third battery cell back in order to increase the PSU's autonomy by more than 50%, with the insignificant additional burden of swapping the two-cells battery charger with a three-cells one and restoring the SEPIC pre-regulator that will reduce the thermal losses dramatically. I would also take BaW's advice to ditch the ee-pot in favour of a faster regulation loop, a better power efficiency, a lower CPU load and, most importantly, of a better overall autonomy and, thus, efficiency of the device.


-George

[Shale]

Question about microcontroller choice?

Dave. why have you chosen to use the standard arduino 168 micro vs, the 328 or the one on the arduino Mega? After you changed the entire design to smd i would have thought you would change the micro as well, but i seem to be wrong. with all the people wanting to mod your design seems like the extra pins could just connect to headers and be left for people who might want them. as I am not yet an engineer I would like to know what drove those decisions.

Thank You

[IanB]

I think Dave wants the micro to be socketed so it's easy to swap out if necessary.

[Shale]

I think Dave wants the micro to be socketed so it's easy to swap out if necessary.

I was thinking something like this
http://parts.digikey.com/1/parts/295966-ic-socket-32pos-plcc-smd-w-post-8432-21a1-rk-tp.html


http://search.digikey.com/us/en/products/ATMEGA328P-15MZ/ATMEGA328P-15MZCT-ND/2477178

couldn't you get the 328 chip to fit in something like this? would this be a solution? if not then why?

[m12lrpv]

The only pin difference offered by your suggestion is the two ADC pins (ADC6 and ADC7) which isn't much. The extra memory afforded by the 328 can be had in a dip replacement that the user can otherwise do themselves.

[FreeThinker]

I think Dave wants the micro to be socketed so it's easy to swap out if necessary.

I was thinking something like this
http://parts.digikey.com/1/parts/295966-ic-socket-32pos-plcc-smd-w-post-8432-21a1-rk-tp.html


http://search.digikey.com/us/en/products/ATMEGA328P-15MZ/ATMEGA328P-15MZCT-ND/2477178

couldn't you get the 328 chip to fit in something like this? would this be a solution? if not then why?

Well It would cost around $4 more for little extra functionality

[alm]

But, when the component manufacturer strongly suggests the use of an external low-pass filter for enhanced noise immunity in ther engineering application notes, I will ostentatiously disregard any quick-and-dirty hacks of non-engineering communities like the aforementioned one; of non-engineering communities that introduced that imbecile baby-talk by renaming the add-on PCBs to "shields" and the programs to "sketches"...

Do they really strongly suggest a low pas filter on the reset pin? I'm surprised, since that would interfere with debugWire.

From AVR042:

The recommended pull-up resistor is 4.7kOhm or larger when using STK500 for programming. For debugWIRE to function properly, the pull-up must not be smaller than 10kOhm.

To protect the RESET line further from noise, it is an advantage to connect a capacitor from the RESET pin to ground. This is not directly required since the AVR internally have a low-pass filter to eliminate spikes and noise that could cause reset. Applying an extra capacitor is thus an additional protection. However, note that this capacitor cannot be present if debugWIRE is used.

Not exactly a strong recommendation in my opinion, more a suggestion that it might be useful if your environment is very noisy. A lower value pull-up might be a good idea, but this would probably interfere with the capacitively coupled reset circuit.

[EEVblog]

Dave. why have you chosen to use the standard arduino 168 micro vs, the 328 or the one on the arduino Mega? After you changed the entire design to smd i would have thought you would change the micro as well, but i seem to be wrong. with all the people wanting to mod your design seems like the extra pins could just connect to headers and be left for people who might want them. as I am not yet an engineer I would like to know what drove those decisions.

The 168 and 328 are the same pinout, you can use either.
The 168 has plenty of code space and is cheaper.
The 328 might be handy if you want Ethernet though, but don't know, haven't tried Ethernet yet.

I just feel like having the micro in socketed through hole might be an advantage to some down the track. Just like the new UNO still has a DIP chip.
I don't need any extra I/O capability in this, it's feature-laden enough as it is.
The 328 means it looks like an Arduino Pro/Uno. To get something else "standard" you have to go up to an Arduino mega 2560, and that's a big price difference.
There are other ways and other chips you can use, but its in the standard Arduino build.

Dave.

[A Hellene]

[...]
Do they really strongly suggest a low pas filter on the reset pin? I'm surprised, since that would interfere with debugWire.
[...]
Not exactly a strong recommendation in my opinion, more a suggestion that it might be useful if your environment is very noisy. A lower value pull-up might be a good idea, but this would probably interfere with the capacitively coupled reset circuit.

Alm, the debugWire is a fairly new addition. When the reset pin did not have that functionality, the standard recommendation for the reset pin protection from external noise was a 100 nF capacitor to ground and a 10 kohm pull-up resistor.

Since I adopted the AVR family almost from their beginnings in '98, I can still remember another standard recommendation of that era, not to use the first EEPROM location (at address 0x00) in the absence of an external reset supervisor because the chip could execute random instructions when power was low during start up and power down that could (and did!) erase that memory location; this changed when the next AVR family with an internal brown-out detector and a more complex programming algorithm arrived.

I realize that the AVR nRESET input might now be hardened against external noise but I am still taking that simple precaution. I can remember like it was yesterday my first prototype without that 100 nF noise filter that worked flawlessly on the bench but it could not even boot properly up in automotive environment, where it was destined to operate. This is the reason why my opinion is so strong on this matter.


-George

[markus_b]

If we change the micro then I would go to an xMega like the xMega32A4U. It features an fast 12-bit ADC and DAC, making external ones superfluous. It also has USB on board and enough ports, so you need no i2c I/O. The Arduino support is unofficial, though.

An interesting application of the chip is the xprotolab MSO, Gabotronics have published the schematics and the source code.

Another thing: There was talk that the LM358 is not rail-to-rail. I propose to use the OPA4171, it is rail to rail and goes to 36V, like the LT3080.

Markus

[McMonster]

XMegas are a bit obscure comparing to other AVRs, much less resources available online on how to program this thing and they're not available in DIP packages. And it requires a different programming hardware (for programming the bootloader in at least), either Atmel's JTAG or something supporting interface called PDI. Last but not least, I think it's not Arduino compatible.

I think that if Dave wants Arduino-compatible PSU, the Mega168 is the best choice. And there's a whole range of pin compatible chips from 4/1 kB Flash/RAM to huge 128/16 kB with Mega1284, all in DIP packages.

[markus_b]

XMegas are a bit obscure comparing to other AVRs, much less resources available online on how to program this thing and they're not available in DIP packages. And it requires a different programming hardware (for programming the bootloader in at least), either Atmel's JTAG or something supporting interface called PDI. Last but not least, I think it's not Arduino compatible.

I think that if Dave wants Arduino-compatible PSU, the Mega168 is the best choice. And there's a whole range of pin compatible chips from 4/1 kB Flash/RAM to huge 128/16 kB with Mega1284, all in DIP packages.

Yes, xMegas are relatively new and they had a bad start to boot (plenty of errata, like a broken ADC). But they have matured and the second generation U-devices are good. Programming is using PDI, not ISP but even a dragon can do PDI these days. But using the USB bootloader is the easiest way.

There are Arduino libraries for it, but not supplied by the official Arduino people.

Personally I don't care much for a DIP package, they are getting mighty big if you need a bunch of ports. Yes, if you put is into a socket (you do ?) you can remove it to reprogram it using a stk500 (do you have one ?). Nah, is not worth the trouble and waste of board space.

[markus_b]

One more thing about microcontroller choice: This is Daves design and he has the say. I can see that taking a micro which is out of the box Arduino-compatible is interesting for him. The over all design as he presents it here is very interesting, but does not fulfill my needs. So I started to stray off, taking the things I like (the linear power and current regulation part is pure genius) and replacing the things who not fit my ideas.

However, maybe it is better if I shut up here on everything out of scope (and and another micros is) and discuss that in another thread.
Here: Dave's power supply mods.
or here: General Purpose Power Supply Design

Markus

[EEVblog]

One more thing about microcontroller choice: This is Daves design and he has the say. I can see that taking a micro which is out of the box Arduino-compatible is interesting for him. The over all design as he presents it here is very interesting, but does not fulfill my needs. So I started to stray off, taking the things I like (the linear power and current regulation part is pure genius) and replacing the things who not fit my ideas.

That's the thing, it can't be all things to all people, that's impossible for any design or any prodct. So I'm not even going to try, I'm building this for me.

Dave.

[Shale]

I have another question for you dave. Did you ever think about making your power supply like a shield for the arduino? if so why or why not and what would be disadvantages to that idea?

Thanks

[EEVblog]

I have another question for you dave. Did you ever think about making your power supply like a shield for the arduino? if so why or why not and what would be disadvantages to that idea?

Not even considered for a second.
Why?
Because it would be a very poor choice from a physical design perspective.
How do you fit the Arduino + shield in the case nicely? What about the heatsink and front panel switches?
It would be:
a) Ugly
b) more expensive
c) require more wiring
etc

You have to do a custom PCB either way, so doing a shield gives you absolutely no advantages what so ever.

Good product design can be mostly about (or driven by) the physical implementation.

Dave.

[Shale]

Good product design can be mostly about (or driven by) the physical implementation.

Thats something I hadn't thought about. Thank you for answering all my questions, and keep up the great work on the videos.

[king.oslo]

Dave, on multimeters, I know you do not like protruding range-switches. They are a weakness despite their low profile. If they fall on their face, damage may be inflicted.

Unfortunately, I spot a weakness on the PSU. The rotary encoders look nice, and I like them, but they are the first to sheer off when the power supply is transported. I would find some switches with a good feel.

Marius

[markus_b]

Unfortunately, I spot a weakness on the PSU. The rotary encoders look nice, and I like them, but they are the first to sheer off when the power supply is transported. I would find some momentary switches with a good feel.

I understand your concern about the robustness of these rotaries, but I find those an excellent feature. *Much* better than momentary switches. I have a digital power supply with momentary switches and I would very much prefer rotary switches to operate it.

[EEVblog]

Dave, on multimeters, I know you do not like protruding range-switches. They are a weakness despite their low profile. If they fall on their face, damage may be inflicted.
Unfortunately, I spot a weakness on the PSU. The rotary encoders look nice, and I like them, but they are the first to sheer off when the power supply is transported. I would find some switches with a good feel.

Yes, I have deliberately traded off robustness for the sake of having knobs. I like knobs.

However, I am working on another PSU design that has switches instead of knobs, as I consider ruggedness more important for this one.

Dave.

[king.oslo]

However, I am working on another PSU design that has switches instead of knobs, as I consider ruggedness more important for this one.

Where may we learn more about this?

M

[EEVblog]

However, I am working on another PSU design that has switches instead of knobs, as I consider ruggedness more important for this one.

Where may we learn more about this?

In due course.
At the rate the battery PSU is going, this one could come out first...

Dave.

[EEVblog]

Dave, on multimeters, I know you do not like protruding range-switches. They are a weakness despite their low profile. If they fall on their face, damage may be inflicted.
Unfortunately, I spot a weakness on the PSU. The rotary encoders look nice, and I like them, but they are the first to sheer off when the power supply is transported. I would find some switches with a good feel.

Yes, I have deliberately traded off robustness for the sake of having knobs. I like knobs.

And of course, as soon as I say that, I mock up the front panel, and the knob usability kinda sucks. Not as good as I thought.
Either top or bottom PCB orientation isn't working that great.
I may have to ditch my beloved knobs for switches  , to gain space and more sensible vertical mounting of the binding posts.



Dave.

[king.oslo]

I may have to ditch my beloved knobs for switches  , to gain space and more sensible vertical mounting of the binding posts.

Dave, I know the unpleasant feeling. I love knobs too, but on the contrary, I think switches are a mature decision. This is my suggestion:

Free up space, cost and ruggedness with switches in stead of knobs. With the new space it is possible to move the TO-220 to the back of an aluminium front panel (sexy aluminium where you can see it) and plastic back panel. I think stubby shorty binding posts which protrude less, rather then full size binding posts. The new aluminium front panel will reinforce the new binding posts. That way, the binding posts will no more look like a pointy protruding weakness which breaks off. You can get chamfer holes for the switches which will feel  luxurious for the finger

I hope you like the idea. I like knobs too, but these changes will move the sweet PSU into a new league. I am really enthusiastic about these changes

Kind regards,
Marius

[Andy]

Free up space, cost and ruggedness with switches in stead of knobs. With the new space it is possible to move the TO-220 to the back of an aluminium front panel (sexy aluminium where you can see it) and plastic back panel.

Is it really a good idea to make the front panel a heatsink. What if it gets hot...

[T4P]

Free up space, cost and ruggedness with switches in stead of knobs. With the new space it is possible to move the TO-220 to the back of an aluminium front panel (sexy aluminium where you can see it) and plastic back panel.

Is it really a good idea to make the front panel a heatsink. What if it gets hot...

That's why you know the thermal performance   
And Dave's using a tracking pre-regulator .

[jerry507]

What is the obsession with the analog tracking loop? It adds a lot more circuit complexity to the design, likely saves no money, and reduces the flexibility Dave has in writing the software to implement various features like voltage tracking current limits etc that he talks about in the video.

Analog dogma is usually a bad idea.

[amspire]

With the switching pre-regulator, think the worst case heat into the front panel is about 3W, and that is only the case when you have left the output shorted with the current limit at maximum. I really cannot see that as being a problem.

For "normal" voltages - ie above 2V out - the maximum power into the front panel will get under 2W, if Dave sets a switching regulator to supply out differential of 3V or less.

Richard.

[samarkh]

I know that there is a PDF of the project, but is there any chance of the original altium files being posted? I would find this useful to show my students some of your workings and 'what ifs' using the live cad file.

Yours Simon M.

[Kevin.D]

Are you going to finish this off Dave. ?  Your 90% there to a finished project.
I really could have done with one of these small portable supply's the other day.

[MarSik]

Hi Dave,

I was trying to design a supply for my needs and used your videos as inspiration. But I have noticed one issue which haven't been mentioned in the forums (I think..) yet.

The issue with your rev C schematics is the power supply for your U3A (voltage control). The LM358 datasheet states Output voltage swing to be 26V with Vcc = 30V and only 5mV when Vcc is 5V.

In the digital case, it changes the calculations a bit as you have to account for the limit in the DC-DC control algorithm.

However, when combined with your attempt at analog control loop for the SMPS preregulator part, it would not allow the supply to start, am I right?

(Vbat = 3.7V, Vset doesn´t really matter here => V+ = 3.7V, LT3080 adj pin is less than 5mV => SPMS control transistor is less than 2.005V which is less than battery voltage and will stay that way => V+ = 3.7V)

This all means that in both cases the power dissipation of lt3080 will be a bit higher (V+ needs to be about 5V higher than the desired voltage) than expected. I suppose it is a limitation of the used opamp and is solvable by using a rail-to-rail one though.

[wrayman]

Hello all,

I am new, and since Dave's vBlogs are extensive, I don't think I have time to catch up....

On this PSU I don't understand why there can't be an option to run this off the power supply that will charge the battery.

Please let me know (you die hard fans that have followed this from the beginning) I watched the Rev C blog and it wasn't covered, or I missed it,.

Would an idea of running if off your notebook power supply be stupid??  I have used my notebook supply as a base for other projects before. You can make or buy a splitter for your notebook (mine is a 5.5 mm 2.1) but on your splitter you could always make one that has the size for your notebook and the standard 5.5 on the Y, which it seems to be a "standard". 4

Here a One Hung Lo brand concept photo:

[wrayman]

Thanks for the warm smartass welcome....

It is a appreciated.

Like I can't read a data sheet or I don't know the voltage.

Components are coming and going so I suppose, duh, another part could be used, but I guess I should check with you first to see if I am allowed to have an opinion or suggestion.

I suppose your the type that has to police the conscious of all so that one singular set of conformal behavior can be had for all.

I think your advice should be heeded. Check before you speak, you might piss someone off.

[baljemmett]

Check before you speak ...

Maybe you missed the bit where this is the thread about the big boys' PSU project, not the USB one...

[nathancrum]

Is this project dead?  Dang - I finally got through all 12 videos in detail and was hoping something more had been brewing elsewhere for the last 11 months. 

Here's to hoping Dave makes another video installation on this project...

[EEVblog]

My current effort is going into the battery powered "USB" version.

Dave.

[inderpreet]

I was wondering if the LTC3115 can be used instead of the Micreal. I was hoping to get a suggestion based on LTC devices since my experience with their sample service is great.

In the Battery powered version of the PSU i was hoping to use an external USB type battery/ power pack solutions available in the market and use the one best suited to my power requirements. This means that i can use the PSU with
a. The USB port of my PC/Laptop
b. Use the Battery power pack solution used to charge mobiles and stuff during travel
c. Use the USB type chargers that come with cellphones.

Additionally I would like to keep the option for a 12V adaptor and use the LTC3115 to buck the voltage in that case.

Please suggest.
Many Thanks in advance.

[Pilot3514]

"What's a SOC4?" Answer: To keep your foot warm.

You need to be and old fart (like me) to get that one.

[Pilot3514]

I'm no engineer and but I feel I am leaning a lot from the video blog (Thanks you crazy Auzzie).

In many places, such as R30-R32, you are using 0.1% resisters.  They are in circuits that are either controlled or send data to the microcontroler.  I would think that you could have "calibration constants" stored in the controller to compensate for the variations in resistor values.  I would think the the more important aspect is consistency over time and temperature.

I started thinking about this when I watched the teardown video on the HP multimeter and the comment was made that if the battery were disconnected, the calibration values would be lost.

I'm cheap and I don't want to spend extra on resistors if I can use a few bytes of EEPROM and a little code to get the same results.

[KuchateK]

I'm cheap and I don't want to spend extra on resistors if I can use a few bytes of EEPROM and a little code to get the same results.

With this method you need to calibrate each unit, spend extra time on coding. Calibration equipment is required, often with custom made jigs. For small run it may be cheaper to use more precise components and skip labor intensive coding and calibration. If you'll look at the whole picture sometimes expensive parts are the cheapest and certainly quickest solution.

[Pilot3514]

With this method you need to calibrate each unit, spend extra time on coding. Calibration equipment is required, ...

So then my assumption is correct, that you could use lower tolerance (read 'cheaper') components and compensate in software.

Without a micro this is not an option.  I recall a blog where Dave was ranting mentioning that he received components that were out of spec from his supplier.  If the unit had a microcontroller, the errors  could have been accounted for in sortware.

I agree that this calibration could be difficult.  I wonder if you could build a test/calibration jig that could work with software in the PS.  The PS could talk over it's serial bus telling what voltage it is sending and the test jig could tell what voltage it is getting.  The PS could then log that bit of information.  Do this for several voltages.  Then make an other pass, this time with adjustment factors applied.

After the voltage then do current in much the same way.

I would think that this sort of calibration could be performed in about the same amount of time as a functional test would take.

I have not thought this all the way through but just off the top of my head.  Therefore, there may be large problems that I have not considered.

[wigman27]

Hi Dave,

It's been a while on this topic I know so its all probably gone out of your head now, did you end up building it? and where you happy with it? I have notice a few videos lately that you a re working on the rev C board but haven't yet seen it done.

A couple of questions, did you do a video on the board design for the rev C? and is there somewhere I can download the software you programmed to Micro with?

Thanks Mate, Great job!

[wigman27]

Just a little bump to hopefully get someone that may not have seen the post. Any ideas??

[mwilson]

Something I noticed between the Rev B and Rev C schematic as I start planning on designing my own PS and find this video series extremely educational (thanks, Dave!):

Starting with RevC, the Vcontrol pin of the LT3080 is tied to V+ instead of Vin. I assume that decision was to improve the dropout voltage of the LT3080. However, according to Page 8 of the LT3080 datasheet, "the current flow into this [Vcontrol] pin is about 1.7% of the output current." Does that mean that since you're still just measuring the current into the Vin pin, the current measurement of the supply is going to be 1.7% low?

[wigman27]

Hi mwilson.

They have discovered a bit of an issue with the Lt3080 in this design. May want to check it out.

https://www.eevblog.com/forum/projects/lt3080-wierdness-dave%27s-power-supply-%28eev224%29-gone-mad/

[robbag]

Hi

Does anyone know if there has there been anymore progress with this great project?

Cheers

[mos6502]

If you're running off batteries, I think it would be wise to use a switching regulator. Your energy will be very limited, and you don't want to waste most of it on heating the surrounding air. Check out these buck-boost modules available on eBay:

http://www.ebay.com/itm/DC-DC-Auto-Boost-Buck-Step-Down-Converter-Module-Solar-Voltage-LM2577-S9-/141053316479?pt=LH_DefaultDomain_0&hash=item20d76ecd7f

Being Buck-Boost, they can create an output voltage that is either higher or lower (or indeed the same) than the input voltage.

If you need low noise, you could use a linear low drop regulator and set the switcher voltage just 1V higher than the voltage you need. That way you have the best of both worlds: high efficieny and low noise linear regulation.

Now, a neat project would be to have a uC control the voltage setting for both the switcher and the linear reg so you don't have to fiddle with two knobs.

[kizzap]

If you're running off batteries, I think it would be wise to use a switching regulator. Your energy will be very limited, and you don't want to waste most of it on heating the surrounding air. Check out these buck-boost modules available on eBay:

http://www.ebay.com/itm/DC-DC-Auto-Boost-Buck-Step-Down-Converter-Module-Solar-Voltage-LM2577-S9-/141053316479?pt=LH_DefaultDomain_0&hash=item20d76ecd7f

Being Buck-Boost, they can create an output voltage that is either higher or lower (or indeed the same) than the input voltage.

If you need low noise, you could use a linear low drop regulator and set the switcher voltage just 1V higher than the voltage you need. That way you have the best of both worlds: high efficieny and low noise linear regulation.

Now, a neat project would be to have a uC control the voltage setting for both the switcher and the linear reg so you don't have to fiddle with two knobs.

Last time I checked, he was...

[boffin]

Eagerly awaiting the next instalment.  It's just what my bench needs...

[mvdswaluw]

The PSU was the trigger for
me to join the forum and subcribe to the youtube channel. Read and watched a lot since and I did buy a ucurrent, but still no supply :-(

[timofonic]

Any news? Does using a switching power supply make ripple greater? I see people are obsessed with linear adjustable power supplies because of that.

I lost half information because my spoken English is quite bad, I would love to have subtitles
and I would want to help to translate them to Spanish!

[boffin]

Dave;  having re-watched a little bit, I'll add my suggestions/comments

Heatsink:
You're still going to have significant heat across the 3080 when you're using lower voltages.  If you run 2v @ 1a, you're dropping 6.4v (and hence 6.4W) across the regulator as the lowest you'll get on the source is the 8.4 off the LiIons

Controls:
I'd rather see a SINGLE control, one nice rotary encoder & knob (with finger hole) you press and spin to switch between V/A/mode select. One nicer knob rather than two cheap ones and a  bunch of buttons.  That also frees up some front panel space.  The only push button I think might make sense is a load on/off.

Layout of front case:
KNOB (multifunction) --- DISPLAY --- JACKS (vertical)