Bench CC/CV PSU Based on Daves uSupply (Not Anymore)

[not1xor1]

I've been playing with both versions a bit. Added FastCC (see a different Mike_Mike's PSU thread on that).
As an example here is the response to a "short" (from 20V) for jaycee's and not1xor1's version with identical params in compensation, parts, settings and load, LT1022A used.
Measured at the 0.33ohm 3055 emitter resistor (FastCC).

Added V(out) dropping from 20V.

Added "shorting" into 10mH, measured at the Shunt resistor.

you should also take into account things like ripple rejection (e.g. feed it with something like PULSE(35 38 0 3m 7m 0 10m)), short recovery (voltage overshot), etc...

[iMo]

This is not1xor1, 20V out, with current limit set to 3A, playing Jeremiah Clarke's "Trumpet Voluntary - Prince of Denmark's March" as the I_Load.. 

Added: Vinput=25V modulated by Trumpet, Vout=15V, Rload=15ohm (1A Iload), current limit=2A.
PS: 94dB ripple rejection?

[iMo]

Here is with jaycee version, the same setup- Vinput=25V, Vout=15V, Rload=15ohm, Ilimit=2A, Trumpet modulated Vinput.

NOTE: in both cases the modulation is applied to the power rail only. The opamps are powered from a clean 25V and -5V.

[Kleinstein]

Who needs the TRUMPet ?  It may look funny, but gives essentially no information about the regulator.

For a good test one should have a Spice current "source" as the load and do some transients, like 1 A - 10 mA - 1 A with a short rise / fall (e.g. 100 ns).

Looking at the AC analysis, with the current sink in AC mode (with some DC offset) is also a good way to analyze a regulator. The AC output voltage than directly represents the output impedance. This output impedance should not show more than 90 degreee phase shift.
This is a nice mode to adjust the compensation.

[iMo]

@Kleinstein: it was done already, see above.
If you have some typical load test pattern, you may give us the model.
I've done the Trumpet load/modulation for fun and to see how it is with the ripple rejection as well

PS: finally, the jaycee version with the common +25V power rail and V+ of the opamps (LT1022A) modulated by Trumpet.

[iMo]

Here are the simulation sources.
The baroque .wav file has to be provided yourself.
Enjoy..
 

[KC0PPH]

Got some parts in. Ill start building the latest version of this PSU on the breadboard.

[KC0PPH]

Got most of it wired up.

I used RED LED's.

For the BD139 and BC368 I used 2N3904. In place of the 2N3055 I am using a TIP-120. I have 2 2N3055 if I need a to use them, but they dont fit in the breadboard too nicely I have some TIP-35's that will be here tomorrow as well.

For the diodes I put in 1N400x.

The problem I ran into is Capacitors.

The lowest value Caps that I have are 100n. I also have some 330n

C3 and C4 are spec'ed as 470p
C5 is 330p
C6 is 10n

Can I use the 100n for these, or should I order some caps?

[not1xor1]

Who needs the TRUMPet ?  It may look funny, but gives essentially no information about the regulator.

agreed
PULSE(35 38 0 3m 7m 0 10m) is a coarse (with more harmonics) approximation of a fully rectified 50Hz AC source with 3V PP ripple.
BTW that differential amplifier with x10 gain make it advisable to add protection diode pairs to the inputs of all the opamps.

[iMo]

With the red leds use R2=220ohm (220-250ohm) for 4mA.

C3/4/5/6 are critical (compensation), do not use 100n there.
Most probably you have to play with the best values based on the parts used for an optimal performance. With a lower capacitor's values - the control loop will be unstable and may oscillate, with too high values - the control loop will be slow.

In practice setting up the optimal compensation could be a difficult exercise. You would need an oscilloscope, and watch the response to a pulsing load.

[KC0PPH]

With the red leds use R2=220ohm (220-250ohm) for 4mA.

C3/4/5/6 are critical (compensation), do not use 100n there.
Most probably you have to play with the best values based on the parts used for an optimal performance. With a lower capacitor's values - the control loop will be unstable and may oscillate, with too high values - the control loop will be slow.

OK I will wait until Tuesday to power up. I ordered an assortment of smaller value caps. Ill adjust R2.

Thank you for your assistance.

[not1xor1]

Here are the simulation sources.
The baroque .wav file has to be provided yourself.
Enjoy..
 

that's wrong
It just doesn't make sense to use the same compensation network for different feedback loops (single vs. double opamps).

Besides that LM358/324 isn't a good choice for differential amplifiers. An OP07 might be better for that purpose and is still quite cheap.
LT1056 although a bit slower than LT1022 has slightly better features regarding CMMR, PSRR, offset, etc.
LT1013 although as slow as the common LM358 has a wider input/output range and better precision than the above mentioned LT devices.
Of course there are plenty of other suitable devices.

[Kleinstein]

The TIP120 is a darlington transistor. So it would replace the 2N3055 and the BD139 directly in front.

The BD139 used for the constant load at the low side sees quite some power. So with a small 2N3904 one might have to reduce the current a little (larger resistor at the emitter).
The fast current limit shown in last Spice files is still flawed - the collector should go to the base of the darlington circuit, not just the 2N3055. One would have to do that change with the TIP120 anyway, but should also do it if BD139+2N3055 are used.

For the OPs the LM358 is not really accurate, but not that bad. For the difference amplifier at the shunt the resistors are still the larger problem than the CMRR of the LM358. The LT1013 is usually a good replacement for the LM358/324 in a simulation and the model is standard with LTspice. Usually one would not need that precision with a lab supply and the LT1013 (and OP07) are still quite slow. The LM358 has the additional cross over distortion that can be a problem, that might not be included in the simulations.

The current limiting might want a little more speed than the LM358, though no need for a really fast OP like the LT1022.
For the breadboard one could consider the RC4558 and similar OPs. 1 or 2 MHz should be fast enough.

[iMo]

Sure, a darlington pass transistor simplifies the schematics.

Here is a simulation of FastCC (set to about 4A) acting upon a "short" (Vout=15V, I_load=100mA, I_limit=1A).
The pass transistor is the TIP120.

We may simulate and discuss this wiring forever, indeed. Hopefully, there is a reader who will try with it in hardware finally

Some points to repeat/add:

1. the BD139 current source has to be put on a small heat-sink, its max loss could be 0.6W.

It is currently set to 20mA, you may lower it to 10mA (R22=120ohm) or so.

2. the max output voltage is limited by V+max of the opamps used.
 
When using a lower V+ for the opamps and a higher one for Vp, the max Vout will still be limited by the max opamp's output.

Thus, for example, a setup, where the Vp=40V and V+=15V, will work up to only Vout=13V with this wiring.

It simulates nice with 2x ADA4700 opamps, TIP122 and powered at V+=95V and V-=5V, btw.

3. the compensation - it needs to be adjusted based on the opamp's type used.

[jaycee]

I hadn't thought I'd get so much feedback on the circuit, thanks guys

The fast current limit transistor is definitely worthwhile.. it gives better current limit response and means that the compensation on the current error amp can be made faster. This will definitely be a bonus on the next power supply I'm working on.

I'm not sure why the BC368P is being chosen here, it seems to be obsolete. It doesnt seem to be shunting a lot of current, so a BC817 seems to work well too. I guess if more current and more dissipation was required, a BC639 could work.

[iMo]

BTW - this one

https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg2275563/#msg2275563

has some advantage over the one we mess with here - you can set for example 80V output with 12V opamp's Vcc
You can set the Vout and I_Limit with DACs as well.

[jaycee]

BTW - this one

https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg2275563/#msg2275563

has some advantage over the one we mess with here - you can set for example 80V output with 12V opamp's Vcc
You can set the Vout and I_Limit with DACs as well.

The output stage has gain in that version?
In my own design, Im using separate transformer taps to create a +5/-5 supply biased around the output

[KC0PPH]

I am going to continue testing the circuit you guys have worked up in this thread and see where it goes. I am pretty new with this stuff and decided to take a different approach while I am waiting on caps to arrive.

Using the latest version from iMo I have implemented the 4mA CC drive and the TIP120.

Rather than using OpAmps I am using a 5K pot. I need to do some further testing and see whats going on, but at the output of my TIP120 I can only get 3V3 with a 5V input. I was thinking I should only get .7V drop?

Also as I increase the Vout the LED begins to Dimm and eventually turns off. I have not investigated this, however I dont think that should be happening. I am wondering if I am overloading my AD2 which I am using to power this.

BTW the Emitter of the TIP120 is connected to a 100 ohm resistor to ground.

[iMo]

The stuff works such the 4ma current source produces a constant current which flows from the CCS's collector "somewhere".

Without the opamps wired the whole CCS current flows into the TIP120 base and the output voltage shall be at its Max.

You have to "redirect/steal/sink" the CCS current by pulling it off the TIP's base in order to decrease the voltage at the output.

[Kleinstein]

A darlington transistor has about 1.5 V drop, as there are 2 BE junctions. So I would expect a little more than 3.3 V, but not much. With load current there is additional drop at the shunt. The circuit shown here is never made to work with a low drop - more like good enough to get 12 V out from a 18 V source (e.g. laptop supply). The other points are keeping the circuit simple and cheap and use a high side shunt, so that it could be used in combination with an LM317 / LM7805 or similar regulator from the same raw source.

Just using a pot to set the base voltage would be only a very crude voltage adjustment. So this would be a much simpler circuit and the test on this circuit would not tell much about the final circuit.

[jaycee]

With no error amps, it wont regulate at all

[iMo]

Your TIP120 and CCS. By changing the R17 from 0(zero)..5kohm you set the output voltage from 0 to about 20V.

[KC0PPH]

The stuff works such the 4ma current source produces a constant current which flows from the CCS's collector "somewhere".

Without the opamps wired the whole CCS current flows into the TIP120 base and the output voltage shall be at its Max.

You have to "redirect/steal/sink" the CCS current by pulling it off the TIP's base in order to decrease the voltage at the output.

I believe I understood this, and to allow that current to go "somewhere" I added a Pot that gave it a path to GND. My knowledge level of transistors is pretty limited so my understanding may not be correct and the pot may not be doing the correct thing. One side is connected to V+, the other to GND and the wiper to the Transistor.

A darlington transistor has about 1.5 V drop, as there are 2 BE junctions. So I would expect a little more than 3.3 V, but not much. With load current there is additional drop at the shunt. The circuit shown here is never made to work with a low drop - more like good enough to get 12 V out from a 18 V source (e.g. laptop supply). The other points are keeping the circuit simple and cheap and use a high side shunt, so that it could be used in combination with an LM317 / LM7805 or similar regulator from the same raw source.

Just using a pot to set the base voltage would be only a very crude voltage adjustment. So this would be a much simpler circuit and the test on this circuit would not tell much about the final circuit.

I had no idea the darlington had 2 junctions in it. I always thought it was just 1 junction with a current amp. I am still lost as to why I am only getting 3V3. I will connect up to 12V here soon and see what happens.

With no error amps, it wont regulate at all

I dont understand how this circuit works, so I am trying to decompose it and test each "system" independently to learn about it. My current understanding is that I should get a constant voltage/current out of the transistor with what I have currently breadboarded up. (The 4mA current source and the TIP120 with 100 ohm to ground as a load). I understand that with varying loads and such I am going to get inconsistent results,

Your TIP120 and CCS. By changing the R17 from 0(zero)..5kohm you set the output voltage from 0 to about 20V.

What you have drawn up is almost exactly what I have breadboarded. I am hesitant to go on until I can figure out why my LED is turning off.

[KC0PPH]

Quick Update: I have everything excluding the "current limit" items wired up. I am now powering it from 12V. I get a range of 10.3V to .6V. I am thinking i need a negative supply on the op-amp now to get all the way down to zero as I was able to get to zero before I added in the op-amp. I did not put in the 10K and 470p cap on the op-amp yet (although I think that has nothing to do with the feedback of the OP, just some sort of filtering I would presume).

I might try and rig up my signal generator to a transistor and make a variable load to start playing with this.

[Kleinstein]

The small caps at the OPs are usually needed to prevent the regulator from oscillating. So they are not just for a smoother output, but really essential parts.  A main purpose of the simulations is to find the right values for the caps. This circuit is type is not that critical, but the cap value should still be about right.

How far one can go down depends on the OPs. The constant current load needs a negative supply to work - so some 0.6 V sound like a reasonable lower limit for the constant current load.