Good quality LM723 LAB Power Supply

[blackdog]

Hi,

This time I show some measurement data from the tests I did on the heatsink.
This is the corrected heatsink with before testing some extra parts mounted which are removed after testing.
On top of the current measurement resistor is a 2N3904 mounted which sampled the voltage across this resistor.
The extra parts as they are applied here provide a current of about 2-Ampere.
I also hold a measure NTC here, it has a value of 5K and is connected to one of my 34461A multimeters where you can see the pictures of.
At the front of the heatsink you can just see the hole that is filled with thermal paste.
The 2SA1943 and also the cooling block have not been made extra flat before I started the measurements, but good thermal paste has been used.



NTC mounted in the hole I drilled for the fan control (100K NTC) which is exactly below the chip position of the 2SA1943.
After the thermal tests the 5K measure NTC is removed and then the 100K NTC is mounted in this hole.



You can see that I "care" about the measurement setup, a box of Qtips on the heat sink so that all air has to pass the fins.
It is also visible that the fan is about 3mm from the heat sink.



Here is visible that I now also measure the temperature of the heatsink finning.
This at 63.8-Watt and a fan voltage of 10V, desensor under 2SA1943 measured at that moment 49.7C
Another small improvement I got by the tape I used to close the 3mm space between the fan and the heat sink on two sides, this gave about 0.4C lower temperature under the 2SA1943.
I'm going to test if this is also advantageous when the heatsink is built in.



The K-Type sensor is tightly clamped between the heatsink fins.


The following measurements were taken at approximately 21C LAB temperature.
On this picture you can see that for a longer period of time there was a slightly lower temperature,
this was at the 15V fan voltage so this resulted in only a little extra cooling.
The final value of this measurement is with 12V fan voltage.



Bij 63.5-Watt, 8V Fan almost 31C higher temperatuur under the 2SA1943, the fluke meter gave here 41.2C as fin temeprature.



Here I have kept the fan voltage deliberately low at 6V and the power at 65-Watt to see what the temperature then becomes below the 2SA1943.
This is a fairly heavy test for the 2SA1943 which normally will not occur, because the dissipation limiter also helps to dissipate the power.
This also makes the heathsink's rendament better because then the dissipation power is better distributed over the heathsink.



40-Watt, 6V fan, 23c temperature increase and the Fluke measures 37C fin temperature.



30-Watt, 6V Fan, only about 17C Delta-C...



And the last one for this post.
30-Watt, 15V Fan, Delta-T =    and the Fluke measures 28.6C fin temperature.



My conclusion is that this heatsink is sufficient to use in this LM723 power supply.
I'm going to do some tests to see which "Clickson temperature" I need to mount and where.
I have to take into account that the temperature can be 38C in the box on a hot day.
So probably the mounting point will be on one of the outer fins of the heatsink.
During normal operation, the idle voltage (6V) of the fan control will be sufficient to keep the power supply cool and the fan virtually silent.

Shoot at it!

Kind regards,
Bram

[iMo]

Shoot at it!

[Wolfgang]

Off center. 

[blackdog]

Hi,

I do a lot of hard work and show it here, and the only thing i get is some form of humor?   

Kind regards,
Bram

[blackdog]

Hi,

Here two more pictures of measurements and then this time with the series resistor of 4.7 Ohm of the dissipation limiter enabled.
The dissipation in this resistor in these measurements is about 18-Watt.
The Fluke DMM that measures the fin temperature gave only small differences that, in my opinion, are covered by the measurement uncertainties.

The first picture I show now, is at the maximum power of around 65-Watt of the power section that occurs in fault situations such as short circuit.
The fan runs on 8V and the Delta-T is about 24C here and the dissipation limiter helps to reduce the temperature below 2SA1943 by about 7C.



And now the measurement with a normal fan voltage of 12V and the Delta-T is now 21.4C.
I like the performance of this part of the schematic and if the dissipation limiter also behaves well during the dynamic tests it stays in the schematic.



Also these measurements are not optimized yet, after leveling the 2SA1943 and the heatsink the chip temperature of the 2SA1943 will be lower.
This lower chip temperature of the 2SA1943 will increase the reliability of this power supply.
One of my starting points that I already indicated in the beginning of this topic, is that the power supply must be "kind" for its load.
And this is one of the ways I do this, a lot of power supplies go faulty with too slow current limits and too much dissipation in the power transistors.

Do not hesitate to ask questions or make comments.

Kind regards,
Bram

[Cliff Matthews]

Will you eventually post output stability graphs of when Q5 pulls 20w away from the output?
IMO this function at least deserves a front panel LED.

Q - Which components provide hysteresis for this?
Q2 - Does C4 provide a slow bypass "glide-in glide-out" function?
Q3 - Should this cct be off (LED on) briefly at start-up?

[blackdog]

Hi Cliff, 

Thanks for your good question.
It is my intention to show how well the disipation works more limited, if is works? 
As for the LED that shows when the dissipation limiter works, for me this is not directly necessary.
If it works well in the end, I can forget this part of the circuit under use.

But a red high efficiency LED over the 4.7 Ohm resistor with a series resistor gives at 1.8V already an indication that this function is working.
This will be around the 3-Watt disipation point in the 4.7 ohm resistor.

Q - Which components provide hysteresis for this?
The switching point of the dissipation limiter is determined by Q4 the 2N3904 and the zener at its base that sampled the output voltage.
Largely the threshold is determined by the Zener D1 which is provisionally set as 8.2V in the scheme.
Some values of resistors are not yet determined around 2N3904, this is determined during testing of this part of the circuit.

Q2 - Does C4 provide a slow bypass "glide-in glide-out" function?
Correct, the 2N3904 will have some gain and it is undesirable that "normal" variation to the output of the power supply (which will always be there,
especially with large current variations) that these variations modulate the Gate voltage of the IRF4905, and this is undesirable.

Don't forget C22 which will be mounted close to the 2SA1943.
This ensures that Q6 and Q8 see a low impedance, which is especially important when the Dissipation Limiter is working.
A high impedance at this point (Emittor Q8) deteriorates the dynamic behavior of the power supply, I tested this on another design that I measured extensively.

Q3 - Should this cct be off (LED on) briefly at start-up?
I do not understand this question very well...

But if you are talking about the current source with Q3, the RC time built up by R22 and C16, I still have to test how this finally works at boot time.
I want the "Power On Protection" to work for so long that Q3 can work normally when the set time is over.

PS,
Something went wrong in my browser again, this resulted in double last lines and a piece that was not posted.
For those who do not yet know, you can have a great advantage by mounting the power part directly on the heat sink without using insulation materials.
But beware, this means that the heat sink itself must be isolated!

I also took into account that the 4.7 Ohm resistor of the Dissipation Limiter is not mounted next to the 2SA1943.
As I said before, this is also done to improve the efficiency of the heatsink.

Kind regards,
Bram

[iMo]

FYI: I've done a simulation of your current limiter - with R21=2k2 in the current source emitter (I=860uA), shunt 0.22ohm as in your schematics v0.9 and the following resistances of your pot P-2, R32=0, output shorted with 0.1ohm:

Code: [Select]

P-2[ohm]   I_shunt
1000    0.65mA
900     0.72mA
800     0.81mA
700     200mA
600     588mA
500     976mA
400     1.36A
300     1.75A
200     2.14A
100     2.53A
With an 1N4148 in series with 560ohm wired in parallel to P-2 (anode to CL pin) and R32=100ohm, I get:

Code: [Select]

P-2[ohm]   I_shunt
1000     0.82mA
900     22mA
800     157mA
700     315mA
600     503mA
500     732mA
400     1.02A
300     1.37A
200     1.75A
100     2.14A
0       2.53A

[blackdog]

Hi imo,

Thanks for your input :-)
The first list of values you showed corresponds pretty well to the values I had with my first test print.

These values also show that the current source resistor R21 in the last schematic is chosen too low in value and therefore there is too much current for a nice control range.
This value was from the first version of this setup, in the last schematic you can also see that there is xxx at this resistor, which means that I will determine the value of those components later on.

Yesterday Farnell delivered some parts for me to test with.
This is another value for the current measurement resistor R34 which is 0.22 Ohm in the last schematic and I now have a 0.25 Ohm to test.
I hope to get closer to the Max 2.2-Ampere.

I will say something again today about the current limit and its temperature stability.
As I have already indicated several times, this is not a problem for my application.
I have already shown that I have taken a step to reduce the temperature drift of the power source, but this drift of this part is only a very small part of the whole temperature dependency.

Lets make a list!
The temperature sensitivity of the current limiting transistor in the LM723
The temperature sensitivity of the current limitation resistance R34.
The temperature sensitivity of the current source made with Q3 the BC557b, high Hfe PNP transistor.
The temperature sensitivity of the P-2 and R31 in the last schematic.
The temperature sensitivity of the copper wiring at a hot heat sink at low current settings.

The power source itself with Q3 could perhaps still be replaced by a type built with a TL431, which is more easily available for builders.
Here are two possibilities, a power source built according to an application note of the TL431, or LM336-2.5V replaced by a TL431 with a connected reference connection to the cathode.
I will use my modulable power supply to test what the differences are at a low power supply voltage to see if they have a high impedance in this situation.
Maybe you're asking yourself why?
The lower the impedance of the current source, the more the remaining ripple that is on the plus connection of C9 is injected into the current limiting transistor.
This is especially noticeable when the current limit is set to a low value.

Without using a clean reference and e.g. an opamp, it becomes difficult to provide an LM723 with a current limit that is reasonably stable over the entire current range,
such as a power supply design with two opamps.
I already knew this when I started this project, but there's nothing wrong with looking at it without using a extra opamp to make it so that it also meets your expectations a bit.

imo I will weigh/test your circuit that shows you with the extra diode and include it in the scheme if it gives an advantage.
But this will be a bit later, I want to determine the position of the Clickson on the heatsink first.
This Clickson helps with fault situations such as a defective fan and high dissipation in the cooling block.

On, off, abberations
I have some extra ideas to make this better.
This because in some circumstances this was not good enough as I have drawn it now.

What I'm going to do is the following: maintain the "control loop" as much as possible.
Q2 in the last schematic pulls pin-13 to the ground connection (pin-7) of the LM723.
And this works, but it does interrupt the control loop, and with some output voltages and currents this is not optimal.
I will place an extra resistor between the + of C14 and the plus input (pin-5) of the LM723.
And then there will be a MOSFet that goes from pin-5 (drain) to the minus of C14.
That is one of the ways to make sure that when switching on the power supply, the +input of the LM723 sees "0V".

The extra resistance that comes to the +input of the LM723 I will have to determine.
This resistance cannot be taken too high as this will cause problems with noise and bias currents.
If this resistor is taken too low, then the current from the reference output of the LM723 is too high around the maximum output voltage,
this results in a higher LM723 chip temperature which in turn results in more DC drift and this also affects the temperature stability of the current limitation.

Another way is to interrupt the top of the potentiometer P-1 with a MOSFet.
That there might still be a bit of DC on the output, is not important as this will only be a small voltage.

Electronics is fun and complex! 

Kind regards,
Bram

[blackdog]

Hi,

Yesterday and today I worked on the circuit to ensure that the power supply is switched on and off properly.
This is not all that is needed for an impeccable behavior of this power supply when switching it on and off and using the enable button.
If this part I'm showing here now works well, I'll look at what else might be needed so that no abberation occurs during a power cycle and enable use.

The first schematics were equipped with auxiliary circuits that used the compensation connection of the LM723.
If you pull this connection to Vs from the LM723, the power section will not get any current anymore and there will be no voltage on the output.
Well a little bit, this because the power source at the output brings the shootky diode over the output in alignment and there is max -0.2 a -0.3V on the output.
But I didn't think that was a big problem and I don't know if the circuit I'm showing here does a power off without abberations.
That is one of the things I still have to test.

OK, this circuit, which is visible below, is intended to prevent the switch-on abberations from occurring.
The second function is an enable switch which ensures that when the power supply is switched off with this switch, the output cannot become negative due to the 25mA current source.
Earlier I had already indicated that the "voltage loop" should be kept closed for good behaviour.

When using the compensation connection of the LM723, you interrupt this voltage loop and this always results in more abberations that you can not solve in all circumstances,
see my pictures earlier in this topic.

On the right a simple version of the LM723 schematic, I did this in order to make the changes more visible.
The power transistor is now drawn like a simple Darlington and can for know be ignored.




The diagram is drawn when the power supply is switched off and the Enable switch is on.
On none of the power lines is voltage at that moment.
If we now look at the right part of the schematic, we can see that the relay contacts are also drawn at rest.
The +input of the LM723 is connected via the 22 Ohm resistor to the "0" of the power supply.
The reference output is also connected to the power supply "0" by a 4K99 resistor, but there is still no voltage on the power supply lines.
This doesn't seem very useful, but I will explain the function of resistor (R7) later.

Now let's switch on the 230V mains voltage!
The LMM723 and the Blah-1 Power transistor get their power now quickly, I will measure later, how fast the buffer electrolytics have 90% of their charge.
While building up the voltage for the LM723 and the Power transistor, the +input of the LM723 is still at the "0".
At the moment that the LM723 starts working linear, this is from 9V supply voltage, then the +input of the LM723 is still connected to the "0" of the power supply and the output voltage is also "0 "volt.
But, where is the problem now? The point is if the LM723 is not yet linear, what does it do with the steering of the power transistor...
If I use the original uirgang of the LM723, then a resistor from connection 10 to ground will almost certainly help here.
If I am going to use the compensation connection to control the power section I will have to use an extra active component on pin-13 to get a nice behavior, we will see how it behaves.

If C1 in the left part is sufficiently charged and the SW-1 switch is closed, the relay contacts are switched over.
RE-1a switches from R7 to the potentiometer P1 and the 22 Ohm resistor is disconnected, If the potentiometer P-1 is not turned counterclockwise,
output voltage will appear at the output terminals of this power supply.
The output voltage will rise "slowly" due to the Potmeter P1 value and the R8 resistor.
C8 always filters the noise from the reference output and C8 has so two functions.
If the enable switch is turned off, the potentiometer P1 is switched off and the reference is now loaded with the resistor R7 which has the same resistance value as the potentiometer P1.
Also, C4 is now quickly discharged by the relay contact RE-1b via the resistor R9 of 22 Ohm.
This 22 Ohm resistor protects the contacts of the relay.

OK, why draw R7 in the schematic.
This is to keep the dissipation in the LM723 IC as Constant as possible, this reduces the DC drift.
The contact on the relay was free for this application, so why not! 
Now let's go back to the left part of the schematic, the enable switch has been removed and C3 shows that there is almost no bounching possible, this works together with the hysteresis of the relay.
I use the current through the relay to also control a red or green LED to see if the enable is on.

The relay used is a DIL-16 type of low power, that is completely closed.
This means that the service life will be very long.
The brands I usually use for these applications are: OMRON, Meisei and NEC in the 24V version.
To reduce the dissipation in the relay a series of resistors can be included, most of these relay types already work around 16V.
My minimum voltage at C9 is around 25V and maximum 34V as a resistor 4 a 5V reduction would be possible, but that is for later to see if this makes sense.
I also do not want to go too low in the relay coil voltage, as this also affects the speed at which the relay reacts.
Over the relay is a diode to counteract the EMF, but in series with the diode there is also a resistor that has about the value of the value of the coil itself, this resistor helps to accelerate the shutdown.

In the test shown below I took R2 loose and made it 1K, connected it to the output of one of my function generators and set it to 30Hz and a pulse width of 6mSec, 0 to 5V Top.
The blue trace is the pulse from the generator, the yellow trace is the 27V voltage which is also used for the relay coil and which goes through one of the relay contacts with a resistor to ground.
It takes almost 4mSec for the yellow trace to become positive, this delay is built up by the inertia of the relay and the 1K resistor together with the 0.1uF capacitor C3.
When the relay is switched off, it takes a little more than 2mSec if resistance R5 of 3K9 is included.


And this is the delay if the diode is switched directly over the coil, this delay is then 3.2mSec.
Furthermore, in this picture it is clearly visible that the contacts are bouncing.
This is especially the case in this picture at the rising edge.
The possible bouncing of the contacts has such a high frequency that it is well filtered by R8 and C4 at the +input of the LM723 and I don't expect any problems with that.



The trick with the series resistor is very useful here because the relay slows down a bit and is switched off by the C3 and R6 combination.
This means that no very high peak voltages are generated over the relay coil when the relay is switched off.

I want the power supply to go to "0V" as soon as possible when I set the enable switch to off.
A number of delays are added up to determine the final time.
That is this relay control and relay, the RC time of the potentiometer P1, R8 and C4 and at light loads, the 25mA current source, and the capacitors in the D.U.T that are located over the power lines.
And of course the biggest delay in "magic smoke" is my reaction speed... 

The only piece I haven't discussed yet, is the function around Q1 which is just like Q2 a small MOSFet with the type number BS170.
When the power supply is switched off, the voltage at the negative edge of C3 quickly goes towards the "0V", this lever gate control goes up for Q1 which then quickly releases RE-1.
With this I hope to get the output as good to "0V" for the power lines for the LM723 and the power transistor have dropped completely.
The timing which are determined for this function by R3, R4 and C2 I still have to test.
The 1N4148 should protect the Gate of Q1.
R3 and R4 are also chosen so that there is no more than 18V at maximum mains voltage at the gate.
Also the RC time C2 and R4 must be so long that C1 is emptied properly.

So the fine tuning of the parts values comes later, the power on delay as it is now, is about 1.5 seconds.
Which is determined by R1, R6 and the Vgs or Q2 (R2 is too small to have much influence).

Some of you may find it even more complex with the relay, but don't forget that this is a power supply for me
and I think it's important to pay attention to the detais to get the most out of this power supply regarding good behavior.

Now for the last parts I almost forgot to mention, that is an extra resistor to pin-2 of the LM723, I always thought it was already in the IC itself.
But after going through several datasheets and looking at the diagram of the structure, this resistor was never present...
This resistor is in the base of the transistor that regulates the current limitation in the LM723.

The last part is the diode1N4148 which goes from pin-4 to "0V", this protects the -input in case of a short circuit.
In case of a short circuit, the charge of C8 which 10nF in this schematic dumped into the -input.
At slightly higher output voltages, the -input may fall below the value of the -Vs connection of the LM723, this can damage this input, the 1N4148 prevent this situation.

Enough now, this was a long session to type this here, I hope you learned something.
And I'd love to hear your comments, additions and my stupid mistakes I made. 

Kind regards,
Bram

[Wolfgang]

Hi,

it probably works, but it looks a little bit too complicated for my taste.
The simplest (but extremely effective) method I have seen in an old GDR power supply was a DPDT mains switch. The "off" side drained the juice from the regulator and the output instantly via a small-value resistor and some diodes. If you dont like the switch, you could do the same via a line voltage powered relay.
After doing that, the problem left is safe startup. This could be done by the same relay as for switching off, but with a little delay for the "on" phase. While line voltage is already up but the delay is still running the resistors will shorten out any spike during this period.

[blackdog]

Hi Wolfgang, 

First, I don't find it complex, look inside a Rigol DP832 , HP6632a, DELTA Electronics ES030-5, HP6823 etc.
I have done extensive tests on "on and off" behavior of power supplies.
It is usually not easy to let the power supply behave well under different situations, as I have already explained a little and show some picture about my first setup.

Say you have for example the power supply on e.g. 3.3V and you switch it off and after two seconds it still dumps a 6V pulse in your load.   
And this one is also nice, which I have tested extensively with in another power supply, you plug the plug into the 230V socket, but you do not do that so precisely.
It is then possible that you give the power supply 5 to 10 times a power cylce within a second, and how does it behave then...
The behaviour is different for every power supply you test...
I have blown up a few circuits or damaged them by this unwanted behavior of the power supplys.

If you only use a power supply with loads that are not sensitive to voltage pulses during switch-on or switch-off, you do not need to investigate this in detail.
I do not want to have to think when I connect an LTZ1000a, or an LT1088, opamps that cost 30 euros etc, to the power supply that have on/off abberations that will damage these expensive parts.
But it's your party, you can connect every power supply to every load you test, I don't mind. 
I like to think about this kind of things en design it and when eventually 20% more parts are needed to be put into a circuit to make it perform exactly the way I want it to, who'll stop me?
I almost allway go for performance, if one of my low noise preamps need a 30€ opamp, I put it in the circuit, that gives me much more satisfaction than the behavior of "this is good enough".

Kind regards,
Bram

[Wolfgang]

... well, my "simple" solution of dumping all remaining charge after switching off prevents just that. For super sensitive stuff I always do it like this:
- power on the PSU and set params right, but let output disabled
- set limits, if paranoic install crowbars
- connect super sensitive circuit
- then enable output
- when turning off, same in reverse.

I had similar problems when trying to measure power supply output impedance with a VNA (see website).

[iMo]

A colleague of mine is testing his lab power supplies with the "red LED" method. He wires the red LED to the output terminals (none resistor in series), sets the current limit to 20mA and switches the PSU many times on/off randomly. When the LED survives he considers the PSU passed for further testing.

[blackdog]

Hi imo,

But the 10 million question is this one, on what voltage does he set the power supply?
2V, 5V, 13V, 35V?
The higher the voltage, the greater the risk that the LED will break or otherwise be damaged.
And don't forget that there are more and more LEDs made for small currents, 20mA can be too much.

What I mentioned earlier, if your colleague in my company would work and test power supplys this way, I would fire him because he draws too simple conclusions. 

Kind regards,
Bram

[iMo]

But the 10 million question is this one, on what voltage does he set the power supply?

An LED does not care about voltage but current..
What type of LED? - any one from your junkbox, even the most minuscule one, and "red"..
And sure, most PSU creators hate this test 

[blackdog]

Hi imo 

I'm afraid you didn't understand what I've written before...

The higher the voltage set on the power supply, the more energy is stored in the capacitor over the terminals of the power supply.
The energy in this capacitor is dumped into the LED and depending on the voltage and the solidity of the LED it will remain whole or will be damaged or will break down later.
Maybe it is better to understand if you see a LED as a zener diode,
above the threshold voltage of the LED, the current through the LED rises very quickly when it is connected to a voltage source (Low Ri).
This situation occurs for a certain time when the capacitor is discharged by the LED.

Even if the power supply is set to 5mA, there is still a good chance that the LED will break or get damaged.
The test your colleague does is not really intelligent, he doesn't seem to want to learn how things really work out, simple conclusions, bad technician. 

Kind regards,
Bram

[Cliff Matthews]

Nothing an always on, galvanically isolated $5 Arduino Nano and a few parts couldn't fix.. It has ADC's to quickly measure a few key points and can control fan and relays for both x-former power and output enable.

Optionally, it could be set to add brown-out/mains failure protection and have a hidden switch that turns off "auto power-up enable" if the voltage is not set below a certain threshold measured by the ADC (eg: the last guy to use the PSU forgot it was set high). This all can be done while still looking and acting like "old school".

[blackdog]

Hi Cliff,

It is not so easy to connect an Arduino to the power supply in a way that this microcontroller does not affect the operation of this power supply.
I also thought of the Arduino to control the timing of different parts in this power supply.
But don't forget that a number of things are beyond the control of the Arduino. (Think of a "brown out" lockt Arduino)

Of course I know that just like Wolfgang suggested with an extra switch contact or relay you can prevent many abberations in the different states.
But what happens, for example, when the Arduino software gets stuck?
Then I also have to think about building the electronics in such a way, that no thermo nuclear explosions wil occur. 

If you guys think think of PWM to control your fan, you don't know what a low noise power supply is...
bin there done that in one of my Electronic Dummy Loads i use a PWM fan controler.
Even with a full symetric amplifier stage that is well connected, I see disturbing pulses in my measurement signal from the PWM ventilator.
My analog control circuit in this power supply is a less efficient, but it is completely noise free and it is good.

I have already made many considerations for this power supply, such as an Arduino for the reading of voltage and current, and also as Cliff suggested to do the timing of different parts.
For the time being I will continue in the analogue way as I am currently working on, to make it as optimal as possible, nothing wrong with that...
And now and then I will process the remarks like those of Kleinstein and Wolfgang if these are good additions to the design for this power supply.

And don't forget, one transformer winding! low noise!, good dynamic behavior! low Ri!, No abberations!,  etc, etc.
The above requirement forces me to think very carefully, how can I solve it with a good 20V transformer 20VDC output voltage at 2-Ampere current
at very low noise and hum when using a LM723 and no expensive or complicated parts, without abberations in use occur, designing this, is brain candy for me.

Not only because it has to be a "old school" design, but because it has to be good, according to my specifications.
Because a measuring instrument is equipped with a processor, this does not mean that it is better. (yes the timing via a Arduino is more precies, but necessary in this power supply?)
Most of my power supply's are all analog, and 90% of the cases doing an excellent job.

And for other applications I regularly use the Rigol DP832 which is a modern power supply.
Usually these are applications where I also want to know the power consumption of the load.
I am always aware of the 470uF that is over the output terminals, even though I have set the DP832 to 3ma current limit.

Think of what Wolfgang told, in his remarks this morning, He shows that he is aware of what he is doing 
- power on the PSU and set params right, but let output disabled
- set limits, if paranoic install crowbars
- connect super sensitive circuit
- then enable output
- when turning off, same in reverse.

Kind regards,
Bram

[ZeTeX]

If you have X amount of capacitance at the output, and there is a switch from CV to CC, then I believe you could build a circuit to discharge the capacitor, so instead of the load discharging the capacitor, you would have something like a mini DC load inside the power supply. However, I believe it is not necessary and too complex for what you are trying to achieve.

I really like your design and I look forward to the finished project! you are very skillful and intelligent.
PS:
if you are using Chrome as your browser, you can add an addon called Grammarly: https://chrome.google.com/webstore/detail/grammarly-for-chrome/kbfnbcaeplbcioakkpcpgfkobkghlhen
it will fix your grammar on the spot!

[Cliff Matthews]

FWIW, the isolation I mentioned would be a small class-2 wall transformer with large enough capacitor to power the Nano, one relay coil, op-amp and maybe power an R2R driven 12-volt fan for 2 seconds (who said anything about PWM?). At least running the fan from the aux transformer would keep any fan BLDC pulses away from the main supply.

..you could opt for this second winding for that purpose, while still not invoking the Harrison curse 

[blackdog]

Hi Cliff, 

About the PWM Fan control, I don't mean that you made a comment about this, but on other forums one of the first things people start talking about is when a DC voltage needs to be regulated: PWM
In the case of power supplies, too, people immediately start talking about switching power supplies in order to improve efficiency.

Of course this is possible, but it is very difficult to get that noise and interference free.
That often results in a long design en testing time, and it is much simpler to use a transformer with multiple taps and a few relays.
You can then control the relays nicely by an Arduino, and if you solve it intelligently you can also measure the 230V mains voltage, mesaure the output voltage and the buffer capacitor voltage to determine the optimal switching point fot the relays. 

ZeTeX
Thank you for your kind words.
Chrome browser and also plugins that translate what I am typing wil not happen, but thanks for the link.
My Firewall does not allow this, more and more Microsoft, Google and social media websites are blockt here and i like it!

Dutch in my mother tongue and I have moderate dyslexia, in Dutch I can manage well with tricks, and my intelligence.
But all this quickly gets less when I get tired, or like the last few weeks that I often suffer from headaches.
So anyone who thinks there are a lot of mistakes in my English, bear with me, because posting in English is already extra difficult.
I can tell you that if I didn't already do my best now, only the schematics would be understandable.
These two things bother me daily, glasses and my dyslexia, live sucs

Kind regards,
Bram

[blackdog]

Hi!

Yesterday and today I was busy with the fan controler.
I made a little adjustments to the schematic and made it a little cleaner and some values have changed.
I decided to include the IRF540 in the schematic by default, because the differences with the IRF840 are small and a different heatsink, sensor position en the fanpower gives a bigger impact.

The modified fan controller.


I'll explain the circuit once more how it works.
First we have VR1 a 15V regulator, this is 3V higher than the rated voltage of the fan.
Most fans have no problem with that and there is only 15V present for a longer period of time on the fan in fault conditions on hot days.
Two Clickson temperature protections will disable the power supply under these extreme conditions.

Let's forget the MOSFet for a moment and only look at the fan and the resistor R3.
The fan I use is a "Low Noise" type and during testing, it already started up at 3V supply voltage.
By this I do not mean to connect the fan to 12V and then control the 12V back to the voltage that stops the fan.
I am talking about the voltage at which the fan starts reliably.

Because all the tests I did with the heatsink and transformer loose on the work bench, I have to take into account that the temperature in the closed box will be higher.
All heat dissipating parts are mounted on the heat sink, and the fan draws this heat directly out of the box.
The air coming in again partly flows through the slots in the box along the toroidal transformer.
At the top and bottom of the box are slots across the full width and the sides of the box are also heatsinks, which help to keep the temperature low.
So I chose the value of resistor R3 so that there is about 6V over the fan in the "idle" position en that is about 150 Ohm for my Fan!

As the temperature gets higher, the resistance of the NTC will get lower and lower.
With P1 and R2 you can set the point that the fan starts to run faster.
I usually measure this with a sensor close to the hottest point of the heatsink, and that is the hole I drilled, directly below the chip position of the 2SA1943.

For a good temperature control there are a number of things you need to think about to make it work properly.
Make sure you have a good coupling of your sensor, with your heat source.
Make sure your control electronics inherrent is stable.
Make sure that the heat sink and fan have sufficient capacity.
Just stick a sensor somewhere on the outside of a heat sink and assume it's good, that's not really wise.

Back to the diagram, R1 is there to keep the MOSFet HF stable, but I never really needed it, but it is there to be sure.
C3 is used when the power is switched on to ensure that the fan runs at full speed for 5 seconds and always starts.
C4 and C5 ensure that the fan always sees a low power supply impedance.

The 100K NTC next to a TO220 housing.
I put some plastic hobby glue on the white wires of the NTC, and then put the pieces of Teflon stocking on top of it and then I removed the excess glue.



Here the NTC is equipped with longer connecting wires and yellow heatshrink tubing for insulation.



In the heatsink I drilled one extra hole to mount both the NTC of the fan controler and the NTC connected to my 34461A DMM.



Yes, this extra hole is also filled with cooling paste.



Temporarily applied some PA tape to fix the wires for the measurements.
Later I do this in a neat way.



This is the fan control mounted on a piece of PCB.
Right on the vertical heatsink is the LM7815 mounted and in the middle is the IRF540.
Right next to the IRF540 is the 150 Ohm resistor mounted which determines the minimum fan speed.
Just above the IRF540 is the 50K trimpot for the set point when the fan starts to run faster.
I took some heatsinks from my storage boxes, they are almost unnecessary but to be sure I used small models.
The PCB is mounted in the cabinet on one of the walls, in a place where the air flows past.



Thats it for today, no more pictures 

Kind regards,
Bram

[ZeTeX]

Hi blackdog,
for the future, I can recommend you this fan:
https://www.arctic.ac/worldwide_en/arctic-f8-pro.html
as you see, it cost 6$ - very cheap, yet it is powerful (33 CFM / 56.1 m³/h (@ 2,000 RPM)) and very silent - 0.3sone - > 22.5dBA.
so you won't even need speed regulation since at full power it is already silent, and it is a reliable fan, with 'fluid dynamic bearing'. and in my case, it cost exactly like cheap fans I get in an electronics store that are much worse quality.

[blackdog]

Hi ZeTeX,


Thanks for the link, I think the Artic model wil not work well with my heatsink.
The fan i'am using know is also a low noise model and on 15V i kan hear it but at "normal" power levels, it is almost silent.
Other instruments in my lab have much more noise.

Lets not start talking about my Rigol DP832... 
I replaced the DP832 fan with a Low Noise type, because I found the noise level unbearable.
And when the DP832 was open, I also adjusted the wiring to improve the dynamic behavior.

A topic of mine about the Rigol DP832 on a Dutch forum: https://www.circuitsonline.net/forum/view/130740#highlight=dp832

Kind regards,
Bram