Linear lab power supply

[perieanuo]

hi,
for me the 2 transformers are a little on the edge for superior current limit.
Translation, I doubt they can take 1A for long time.
But for first PSU it's fine, if you want to power arduinos it will do fine.
Anyway changing them is 15' job, continue with pcb and all.
regards, Pierre

[JuanGg]

hi,
for me the 2 transformers are a little on the edge for superior current limit.
Translation, I doubt they can take 1A for long time.
But for first PSU it's fine, if you want to power arduinos it will do fine.
Anyway changing them is 15' job, continue with pcb and all.
regards, Pierre

On the wall - warts they came from said 15 V 1 A, but who knows. I am aiming at 500-600 mA anyways. I can always upgrade the transformers later. I'll make a PCB with the rectifier, cap, tap-switching relay and maybe an lm 317 for a 10 V rail (to power the Arduino, fans relays, etc.)Any thoughts on this?

Juan

[perieanuo]

hi,
for me the 2 transformers are a little on the edge for superior current limit.
Translation, I doubt they can take 1A for long time.
But for first PSU it's fine, if you want to power arduinos it will do fine.
Anyway changing them is 15' job, continue with pcb and all.
regards, Pierre

On the wall - warts they came from said 15 V 1 A, but who knows. I am aiming at 500-600 mA anyways. I can always upgrade the transformers later. I'll make a PCB with the rectifier, cap, tap-switching relay and maybe an lm 317 for a 10 V rail (to power the Arduino, fans relays, etc.)Any thoughts on this?

Juan

Me,I always put a minimum 10 amps rectifier screwed to the bottom case, then main capacitors on separate pcb or glued to the case with 2-face adhesive like 3M stuff, the control board itself separate pcb.but you can do your thing
Of course fuses for every transformer output and 220V input.those days on outputs I tend to put rearmable fuses (ptc) for currents like 0-2 Amps, tired of fuse stocking...
Regards,pierre


Envoyé de mon iPad en utilisant Tapatalk

[cdev]

1 amp is a lot of power for low voltage stuff, most of the times I use my triple bench supply I use MUCH less than its rated 7v@6a and 20v @ 3 amps x2 . However, lots of the time I need two voltages at the same time with current limiting. If I were you I would make two identical supplies and make them well regulated with adjustable current limiting and some kind of notification (LED and/or beeper would be best) when the current draw reaches that limit. A nice multiturn pot for voltage and a digital 4 digit display of the voltage and current (so you can set the voltage + current limiting easily) with a floating decimal point (around $3 on ebay) is nice too.

You could probably get away with multiple common fixed voltages but make sure you have a nice pot to adjust the current limit.

[fsr]

hi,
for me the 2 transformers are a little on the edge for superior current limit.
Translation, I doubt they can take 1A for long time.
But for first PSU it's fine, if you want to power arduinos it will do fine.
Anyway changing them is 15' job, continue with pcb and all.
regards, Pierre

On the wall - warts they came from said 15 V 1 A, but who knows. I am aiming at 500-600 mA anyways. I can always upgrade the transformers later. I'll make a PCB with the rectifier, cap, tap-switching relay and maybe an lm 317 for a 10 V rail (to power the Arduino, fans relays, etc.)Any thoughts on this?

Juan

And did the wall-warts had a bridge rectifier with capacitive filter? Because the maximum current output, ripple, and other characteristics varies with different rectifier circuits. Take a look:

[JuanGg]

And did the wall-warts had a bridge rectifier with capacitive filter? Because the maximum current output, ripple, and other characteristics varies with different rectifier circuits. Take a look:

No, they were ac ones, just the tranformer. Thank you for the very informative sheet.

[JuanGg]

Me,I always put a minimum 10 amps rectifier screwed to the bottom case, then main capacitors on separate pcb or glued to the case with 2-face adhesive like 3M stuff, the control board itself separate pcb.but you can do your thing
Of course fuses for every transformer output and 220V input.those days on outputs I tend to put rearmable fuses (ptc) for currents like 0-2 Amps, tired of fuse stocking...
Regards,pierre

I was thinking of making a separate pcb with rectifier, cap, relay, even fan controller. I won't do it just for now, as I may be needing more voltage rails for the regulating pcb. The big transformer already has fuses on every winding, but I may add some more.

1 amp is a lot of power for low voltage stuff, most of the times I use my triple bench supply I use MUCH less than its rated 7v@6a and 20v @ 3 amps x2 . However, lots of the time I need two voltages at the same time with current limiting. If I were you I would make two identical supplies and make them well regulated with adjustable current limiting and some kind of notification (LED and/or beeper would be best) when the current draw reaches that limit. A nice multiturn pot for voltage and a digital 4 digit display of the voltage and current (so you can set the voltage + current limiting easily) with a floating decimal point (around $3 on ebay) is nice too.

You could probably get away with multiple common fixed voltages but make sure you have a nice pot to adjust the current limit.

That's precisely what I want to do. Dual 0-25 V @ 0.5 A. Arduino controlled, with filtered 12-bit pwm as DAC. I will be using the arduino's ADCs (10 bit) to measure voltage and current, showing the readings on 4-digit 7 segment displays or on an LCD. I can also display the set values as well.

I don't really know what to do now. I may start breadboard the circuit in #37.
      Juan

[perieanuo]

37 may not work, missing reverse output diode, me I don't like it.
my favs are sokolsky one and mine course
regards,pierre

[JuanGg]

37 may not work, missing reverse output diode, me I don't like it.
my favs are sokolsky one and mine course
regards,pierre

Well that diode can be easily added.
I can't do the sokolsky one as-is as I don't have another transformer to derive the +-5V referenced to the output.Any ideas?

Juan

[JuanGg]

Connecting only the 15 Vac transformer, I had the raw PSU running at 1 A for 20 minutes, using my electronic load. The rectifier got warm, so did the transformer. Not too hot to keep one's hand on it for a while, so I guess it will be fine. DC voltage out dropped from 17 to 15 V and I was getting about 1 Vpp ripple.

Juan

[perieanuo]

37 may not work, missing reverse output diode, me I don't like it.
my favs are sokolsky one and mine course
regards,pierre

Well that diode can be easily added.
I can't do the sokolsky one as-is as I don't have another transformer to derive the +-5V referenced to the output.Any ideas?

Juan

Dcdc converter (1.5 euros ebay) with capacitors aside or rcd to generate -5V from AC branch.see my schematic as guide,I use 24V and 12V outputs from transformer.
I doubt #37 works...


Envoyé de mon iPad en utilisant Tapatalk

[fsr]

And did the wall-warts had a bridge rectifier with capacitive filter? Because the maximum current output, ripple, and other characteristics varies with different rectifier circuits. Take a look:

No, they were ac ones, just the tranformer. Thank you for the very informative sheet.

You're welcome.
If the wall-wart was AC, then it probably listed the transformer's AC output current, so if you use a diode bridge and capacitive filter, you can get about 620 mA of current from the 1A rated transformer. Any more current than that would be going over the maximum.

[JuanGg]

Dcdc converter (1.5 euros ebay) with capacitors aside or rcd to generate -5V from AC branch.see my schematic as guide,I use 24V and 12V outputs from transformer.
I doubt #37 works...

Will look into that. As I previously said, I'll go with whatever you guys recommend.

     
If the wall-wart was AC, then it probably listed the transformer's AC output current, so if you use a diode bridge and capacitive filter, you can get about 620 mA of current from the 1A rated transformer. Any more current than that would be going over the maximum

As they were sealed up in a plastic enclosure, I suppose they would be able to handle a bit more. I am aiming for 500-600 mA output current anyway, so no problem there.

Juan

[cdev]

Try an old ATX power supply as your power source. Do you have one?

[JuanGg]

Try an old ATX power supply as your power source. Do you have one?

I have two in fact. But they are mains earth referenced, so not suitable for my purpose. One of them is fitted with some binding posts, and that's what I have been using for a while.
Plus, I already have the transformers mounted and the enclosure half made. I am not changing that unless I have to.

Juan

[JuanGg]

Some of the stuff I ordered just arrived, including 7-segment displays, 0.1 power resistors, some perfboard etc. I have been playing around with some of them, towards making the "easy" digital part. Who writes a 7-segment display library and doesn't support decimal points? .
So far I have managed to write a function that displays a decimal number. Also I've made a simple test program that lets you set the value on the display via a rotary encoder. My idea is to have two of this displays per chanel, showing voltage and current.
(I know I should focus on the analog side first, just wanted to get something working)
    Juan

[JuanGg]

Any thoughts on this schematic? (https://dangerfromdeer.com/2016/04/06/bench-power-supply-build-part-ii/). It seems simple enough and has 0-5 V inputs to set voltage and current, which can be easily changed from pots to DACs. No auxiliary transformers are needed as well. Current sensing can be changed.

    Juan

[xavier60]

It looks mostly fine to me.
I would do some experimenting with the compensation to reduce the size of C4 which would be causing slow reaction to sudden current overloads. The AC gain of the op-amps would have to be reduced with local feedback.

[JuanGg]

It looks mostly fine to me.
I would do some experimenting with the compensation to reduce the size of C4 which would be causing slow reaction to sudden current overloads. The AC gain of the op-amps would have to be reduced with local feedback.

Ok. I can breadboard the thing and try several capacitor values, loading it with my electronic load in pulse mode.
I suppose local feedback to reduce AC gain can be added by putting capacitors in the feedback loop, just between the output and the non inverting input of the op-amps.
I will order the current sense ic and the Darlington transistor, and maybe some DACs. I suppose I can use 2n3904's and 2n3906's instead of the BC337 and  BC327.
    Juan

[xavier60]

Any thoughts on this schematic? (https://dangerfromdeer.com/2016/04/06/bench-power-supply-build-part-ii/). It seems simple enough and has 0-5 V inputs to set voltage and current, which can be easily changed from pots to DACs. No auxiliary transformers are needed as well. Current sensing can be changed.

    Juan

I mocked up just the voltage regulation loop with different parts. I used a TIP35C and BC337 with 100Ω and 1KΩ B-E resistors for the Darlington. And a TLC072 op-amp.
The presence of C4 encourages the Darlington to oscillate at certain conditions. A 100Ω series Base resistor fixed that.
The loop was stable with C4 removed and a 1000pF compensating capacitor added to the op-amp, with or without an output capacitor.
The loop became unstable when I reduced the compensating capacitor to try to improve the load transient response.
This was mainly caused by high frequency phase reversal at Q2(BC548) caused by more signal being coupled through the Base to Collector capacitance than the expected  amplified inverted signal.  Bypassing R3 with 22pF made a big improvement.
I got the best load transient response of 5us by configuring Q2 as  Common Base and swapping the op-amp inputs.
I can't do any testing of the current loop as I don't have the INA196  handy.

[JuanGg]

I mocked up just the voltage regulation loop with different parts. I used a TIP35C and BC337 with 100Ω and 1KΩ B-E resistors for the Darlington. And ...

Thanks a lot. I will draw a schematic with the changes you made and try it myself. Not sure about Q2 as common base, is it base to 3, emitter to 2 and collector to 1, as drawn on the schematic?
    Juan

[xavier60]

This shows Q2 configured as a Common Base amplifier. It is very good at transferring fast signals from ground referenced circuitry to circuitry referenced to a higher voltage.
Because the Base is tied to the 8V rail which is regarded as a signal ground, the Base acts like a shield between input and output. The Emitter is the signal input in a Common Base amplifier.
https://en.wikipedia.org/wiki/Common_base

[xavier60]

Q2 as a Common Base amplifier causes a possible complication.
Because it's non-inverting, the op-amp inputs had to be swapped.
When reference voltage  is connected to the inverting input and the feedback divider to the non-inverting input, the op-amp can't ever function as a true Miller Integrator. The minimum gain can never be less than unity.
For the voltage regulation loop, a small amount of proportional gain can and does improved stability.
For the current loop it is an uncertainty.
With Q2 as a Common Emitter amplifier again and a bit of tweaking, the response and stability are near as good as the Common Base version.
 

[JuanGg]

Q2 as a Common Base amplifier causes a possible complication.
Because it's non-inverting, the op-amp inputs had to be swapped.

Thank you very much. I'll try to prototype it myself as soon as I can.

[xavier60]

Because I don't have the IC for high-side current sensing. I have added low-side sensing.
I know it's not ideal because control circuit current flows through the shunt. It's only a few milliamps.
As expected, there is a massive current spike when the output is short circuited.
I do have a solution for this that is currently working in a bench supply that I had previously completed.
I'm trying to adapt it to the present design.
I have made small changes to the CV loop which is working very well.