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

[iMo]

If I was designing the board, I would arrange the ref for ie 431 (with those 3 resistors and cap) and design the pcb for the noninverting amp (with those 2 resistors creating fb) - that allows to use

a) TL431 set for 5V/4.096V/2.5V and buffered or unbuffered,
b) LM329 or any other 1.25/2.5/5V precision 2 terminal Vref source buffered or unbuffered,
c) to use 78L0x buffered or unbuffered,
d) to use a zener buffered or unbuffered.

as the holes, pads and tracks will simply be there.

If you intend to offer the pcb to others I would put those 2 1w shunt resistors as well. It is also expected the pass transistor will be placed on an external heatsink, as the heatsink you plan can hardly dissipate 3W.

[Kleinstein]

The CC/CV indication would with a 50% chance not work with the OPs inputs directly parallel. The usual way is to compare the outputs of the 2 regulating OPs.

For the shunt even a 1 W type can be a little on the small side.  To keep self heating low the power rating should be more like 10 times the actual power used.
One may not need the extra resistors for the fast current Limit - the shunt could be used for this purpose too.

For the reference there is no real need to plan with an 78L05 - it's normally lower stability than the cheaper TL431. The LM329 is 7 V.

[iMo]

Frankly, using an 1ohm resistor as the shunt is rather rare, afaik.
Normally people use something like 0.1/0.15/0.18/0.22ohm.
With 0.22ohm and 3A the loss would be 2W, with two 0.39ohm in parallel =1Watt each.

For the reference there is no real need to plan with an 78L05 - it's normally lower stability than the cheaper TL431. The LM329 is 7 V.

Nope, no plans for 780x. Plans are for the TL431 with 3 resistors and cap only. All the other Vrefs can be wired there as a Bonus

[Kleinstein]

The board shown is also a rather odd combination with THT resistors and SMD electrolytic caps.  The more usual way is using SMD resistors - maybe except for the shunt and other higher power resistors and THT for the power transistor,  large caps and foil caps if needed. The filter caps tend to need a larger foot-print.

D2 and D3 can be smaller (e.g. 1N4148 class diodes). It may be a good idea to wire a diode emitter to base at the power transistor, so that the reverse voltage is limited. This also gives the supply a limited (by the OP) sink capability in addition to the current sink.

The original plan was for a low current version (e.g. 0.5 - 1 A) and the TO220 case transistor is also only good for low power, like some 30 W - so maybe 1.5 A at most. One could still use the TO220 food-print to solder wires for an external higher power transistor (e.g. TIP140).

Similar I would see the pot food-print more like a place to but wires toa pot at the front panel.

[KC0PPH]

This board is just to play around with, not my final PSU. The TH is due to the fact that I have TH. The SMD Caps are because Id like to verify Footprints before I go for the final rev. Final project will be pretty much all surface mount and I will use 1206 components for everything.

I figured screwing around on a Breadboard, or order a set of boards for $7.

I think my end goal will to build a PSU with 3 of these circuits on them to provide 3 outputs in addition to  5V 3V3 2V5 1V8 1V2 fixed supplies (say 100ma max)

 

[KC0PPH]

Ill post the schematic and layout later tonight.

Once again thanks for all the input. I have made some significant changes to the board due to size creep. I am hoping to keep the board to the size that it currently is.

As for schematic changes. I added R33 and R34 to IC1C (OA Powering CC LED) as it was suggested that connecting the inputs together was a bad idea.

I added 2 resistors to the Voltage REF. I set the Lower one to 50K and the upper one to 0R so I should still get the 2.5V output (I need to verify on the datasheet).

I also changed the OA power source to be on the other side of the 10 ohm resistors as it was suggested to do that for isolation and filtering.

Q4 Will be changing to a larger SMD device. I need to google some good alternatives.

So a few questions:

1) Is my V_SENSE voltage divider correct? If not where did I go wrong?

2) Is my resistor networks for IC1B Correct? I believe I should get 0-5 on inverting input (Based on 0-15Vout). I am guessing I need a 0-1V signal on I_SET for 0-1A but I am pretty sure I am wrong.

3) Are my Pots Correct? Assuming I want a 0-5V and 0-1V on the wipers.

I Will post the schematic later tonight, although none of the values I am talking about in points 1-3 have changed.

[KC0PPH]

Here are the files.

[not1xor1]

edit: AS others have said about the current limit LED, you can simply connect the cathode of the LED to I_SENSE and use a suitable limiting resistor. When the current limit is not in operation, the output of the opamp will be close to the +V rail, and the LED wont light. When it is operating, it will be somewhere near the -V rail and thus the led will light.

IMHO this is much simpler and provides both CV and CC monitoring.
Notice that the opamp are ... criss-crossed as the voltage regulation opamp drives the CC LED and vice-versa.
It is a sort of OFF indication and since either of those 2 opamps has to be ON... 

[iMo]

The TL431 has to be wired this way when used as a Vref:

[iMo]

..So a few questions:

1) Is my V_SENSE voltage divider correct? If not where did I go wrong?

2) Is my resistor networks for IC1B Correct? I believe I should get 0-5 on inverting input (Based on 0-15Vout). I am guessing I need a 0-1V signal on I_SET for 0-1A but I am pretty sure I am wrong.

3) Are my Pots Correct? Assuming I want a 0-5V and 0-1V on the wipers.

Your resistor's values:

The Vout will be the voltage on the Vset pot's wiper multiplied by the divider's ratio, in your case 51k/25k=3.04, therefore Vout = 3.04 x Vset.

The SLowCC will be set to 1A with 1V on the Iset pot's wiper when all 4 resistors around the Isense opamp IC1B will have the same value AND the Rshunt will be 1ohm.

Note: above is valid when the 560k resistors are not populated.

The pots and resistors in series with them look ok.

Because of the 560k resistors there will be a small nonlinearity in the pot's scales.

Also the Iset's pot wiper voltage will be influenced by the network around the Isense opamp.

PS: the I_set's setting looks to be an issue 

The setting is heavily influenced by the resistor's values in the Isense IC1B diff amplifier and the Vout.

The I_set has to be either
a) pretty low impedance, or
b) the resistors around IC1B have to be pretty large values.

It seems you need to buffer the I_set.

[iMo]

As the simulation confirms the I_set issue I would recommnd to change the schematics such you buffer the I_set with an opamp, and the CC limit blinking has to be done by the schematics above.
I would also recommend to buffer the TL431 with an opapm as it is now in your schematics (mind there is a wiring error around the TL431 - see above).

[Kleinstein]

The resistors for the current regulation (IC1B) should be more in a way that the resistors towards the shunt are smaller that the resistors to ground. This helps to reduce the sensitivity to errors and gives away less signal from the shunt. So more like 2 K to the shunt side and 50-100 k to ground and the set voltage. This works with a relatively high set voltage range (e.g. 0-10 V).  Ideally there should be a buffer for the set voltage to keep the impedance constant - a changing impedance directly from the pot would cause an error.

The CC/CV indication with just the diodes would give a variable intensity and may not work at very high or low voltage.

[iMo]

As I wrote above, the usual way is to use a shunt with 0.1-0.22 ohm value. With two 0.22ohm in parallel you get 0.11ohm total.

At, say, 1A current it creates 0.11V drop on the shunt resistor. This voltage drop needs to be amplified by the IC1B (diff) such it fits your pot setting range.

In order to get, say, 1.1V / 1A (through the shunt) with your pot setting, you have to amplify that drop 10x.

The resistors at IC1B have to be 1:10 therefore, for example 2x2k2 at the shunt and 2x22k to the GND and Iset (or any other values you wish).

Those resistors have to be as precise as possible.

[KC0PPH]

edit: AS others have said about the current limit LED, you can simply connect the cathode of the LED to I_SENSE and use a suitable limiting resistor. When the current limit is not in operation, the output of the opamp will be close to the +V rail, and the LED wont light. When it is operating, it will be somewhere near the -V rail and thus the led will light.

IMHO this is much simpler and provides both CV and CC monitoring.
Notice that the opamp are ... criss-crossed as the voltage regulation opamp drives the CC LED and vice-versa.
It is a sort of OFF indication and since either of those 2 opamps has to be ON... 

I did this on the breadboard and it was inconsistent at best. I used RED LED's.

I need to breadboard the way I have it on my schematic

[KC0PPH]

The TL431 has to be wired this way when used as a Vref:

Corrected. Thank You. I was planning on RTFM but you beat me to it.

Your resistor's values:

The Vout will be the voltage on the Vset pot's wiper multiplied by the divider's ratio, in your case 51k/25k=3.04, therefore Vout = 3.04 x Vset. That is what I calculated so perfect. For final design Ill need to modify a tad as I want a bit more than 12V and my ref will be 4.096V. 15V was just a nice even number. 13.5V should be enough but Ill adjust those resistors on the final board and not on this one.

The SLowCC will be set to 1A with 1V on the Iset pot's wiper when all 4 resistors around the Isense opamp IC1B will have the same value AND the Rshunt will be 1ohm.
Once again I think my calculations are correct if I understand you right.

Note: above is valid when the 560k resistors are not populated.
I believe the 560K resistors are there if for some reason the SET lines ever loose their connection to the pot. I am not sure this would be a common failure point and it might be worth removing them.

The pots and resistors in series with them look ok.


Because of the 560k resistors there will be a small nonlinearity in the pot's scales.
I think these should be removed unless there is a good reason to keep them.

Also the Iset's pot wiper voltage will be influenced by the network around the Isense opamp.

I will buffer it as you suggested.


PS: the I_set's setting looks to be an issue 

The setting is heavily influenced by the resistor's values in the Isense IC1B diff amplifier and the Vout.

The I_set has to be either
a) pretty low impedance, or
b) the resistors around IC1B have to be pretty large values.

It seems you need to buffer the I_set.

[Kleinstein]

edit: AS others have said about the current limit LED, you can simply connect the cathode of the LED to I_SENSE and use a suitable limiting resistor. When the current limit is not in operation, the output of the opamp will be close to the +V rail, and the LED wont light. When it is operating, it will be somewhere near the -V rail and thus the led will light.

IMHO this is much simpler and provides both CV and CC monitoring.
Notice that the opamp are ... criss-crossed as the voltage regulation opamp drives the CC LED and vice-versa.
It is a sort of OFF indication and since either of those 2 opamps has to be ON... 

I did this on the breadboard and it was inconsistent at best. I used RED LED's.

I need to breadboard the way I have it on my schematic

The way with sensing across the one OPs inputs has an about 50% chance to work, depending on the OPs offset. So unless there are high resistors used to make sure the offset is defined sign the breadboard would not give a reliable answer. It still is near 50% chance, depending on the chip.

The better way is to compare the outputs of the two regulating OPs instead.

[KC0PPH]

edit: AS others have said about the current limit LED, you can simply connect the cathode of the LED to I_SENSE and use a suitable limiting resistor. When the current limit is not in operation, the output of the opamp will be close to the +V rail, and the LED wont light. When it is operating, it will be somewhere near the -V rail and thus the led will light.

IMHO this is much simpler and provides both CV and CC monitoring.
Notice that the opamp are ... criss-crossed as the voltage regulation opamp drives the CC LED and vice-versa.
It is a sort of OFF indication and since either of those 2 opamps has to be ON... 

I did this on the breadboard and it was inconsistent at best. I used RED LED's.

I need to breadboard the way I have it on my schematic

The way with sensing across the one OPs inputs has an about 50% chance to work, depending on the OPs offset. So unless there are high resistors used to make sure the offset is defined sign the breadboard would not give a reliable answer. It still is near 50% chance, depending on the chip.

The better way is to compare the outputs of the two regulating OPs instead.

Something like this?

[KC0PPH]

Added all of the feedback into the schematic.

I will be replacing the Diodes with SMD ones. I also made the board smaller. We will see how things go when I route it. The autorouter is not having much difficulties doing it, although the via count has slowly increased from 0 to 40.

First batch of boards will be 2 layer. I will hand route the important things (high current and sense lines) and let the auto-router do the rest. For the final board it will be 4 layers which should make life much easier.

[KC0PPH]

Was curious if JLC charges extra for lots o holes. Set Via to 0.2mm drill and 0.45mm dia and went crazy. Still $2USD for 10 boards.

So I can do a decent job of via stitching the Top and bottom GND planes together.

[not1xor1]

edit: AS others have said about the current limit LED, you can simply connect the cathode of the LED to I_SENSE and use a suitable limiting resistor. When the current limit is not in operation, the output of the opamp will be close to the +V rail, and the LED wont light. When it is operating, it will be somewhere near the -V rail and thus the led will light.

IMHO this is much simpler and provides both CV and CC monitoring.
Notice that the opamp are ... criss-crossed as the voltage regulation opamp drives the CC LED and vice-versa.
It is a sort of OFF indication and since either of those 2 opamps has to be ON... 

I did this on the breadboard and it was inconsistent at best. I used RED LED's.

I need to breadboard the way I have it on my schematic

I only tested it in simulation, but I do not see how it can't work in the real world (I can't test it before may-june), provided you wired it properly and did not swap LED or diode polarity.

Even if the individual opamps saturate to a slightly different high voltage, that voltage would always be higher than that of the unsaturated one otherwise the PSU would not be able to switch between CV/CC mode.
It works (in LT spice) even with different LEDs (one green and one red) and different diodes in series (one 1N4148 and 4102) and with the voltage and current set on the verge of the switch (i.e. max out voltage min current over the limit).

Just check the current through the LEDs vs. output current/voltage in the attached LTSPICE sim.

[not1xor1]

The way with sensing across the one OPs inputs has an about 50% chance to work, depending on the OPs offset. So unless there are high resistors used to make sure the offset is defined sign the breadboard would not give a reliable answer. It still is near 50% chance, depending on the chip.

The better way is to compare the outputs of the two regulating OPs instead.

are you kidding?
The LEDs in my schematic diagram are connected to the outputs of the regulating opamps!!!
and the output of the regulating opamp has to be at least 0.6V less than that of the saturated one otherwise the CC/CV mode switch would just not work. That voltage difference would be enough to switch on the LED connected to the saturated opamp (it is a sort of OFF indicator) while the other diode+LED pair would either be reverse polarized or have just not enough voltage to get any sensible current through.

[iMo]

@not1xor1: Kleinstein is referring to the blinking version with the opamp which inputs are wired in parallel to the IC1B opamp.

I would add 100nF ceramics in parallel to the 2x1000uF as well as to the output capacitor.

With 8 opamps it seems the PSU is a bit over-engineered

My simulation also shows the not1xor1's blinking works, there is a region where the both may lit (Iout pretty close to the SlowCC limit) but that situation is rather rare.

With Vout from 124mV to 25V (30V V+) the current of each LED is always 0mA or 1.6mA with 15k resistor while blinking - see below.

I would also leave the 560k there, you may or may not populate them. If somebody decided to use cheap potentiometers the resistors could become handy.

I would go back to the 4opamps version, with the buffer for the I_set, buffer for the Vref, and the CC and CV opamps. And blinking according to not1xor1.

PS: doublecheck the labels on your opamp power. Looks like both are V-. Use better names for the labels.

PPS: Why your previous main V+ is now called V- in your schematics?
That is weird..weird..

I would highly recommend you to rename it back to V+.

Or better, when you are getting confused by too many sources with 2 chars long names, use the appropriate long names like for example:

Code: [Select]

Vpower+  or  Vpower_P        for the main 18V power
Vpower-  or  Vpower_N        for the -1.3V created on the 2 diodes
Vopamp+  or  Vopamp_P        for the opapm's positive power
Vopamp-  or  Vopamp_N        for the opamp's negative power
otherwise you may easily create a big mess on your PCB.
Also do use underscores instead of spaces in the label names.
73

[Edd]

KCOPPH . . . . .
Not so much that you made the PCB smaller . . .but MORE importantly was that you made that schematic of

=https://www.eevblog.com/forum/projects/bench-cccv-psu-based-on-daves-usupply/?action=dlattach;attach=688722;image

Smaller . . . so much that the alpha numerics aspects  are now too small to reliably be able to read.

You were so image density stingy /limiting, that your whole schematic page came out as ~ 805 X 621 pixels.
Best that you doubled  . . 2X'd that size . . . to then be fully  readable.

73's de Edd

I KNOW the speed of light  . . . .So, what is the speed of dark?

[KC0PPH]

@not1xor1: Kleinstein is referring to the blinking version with the opamp which inputs are wired in parallel to the IC1B opamp.

I would add 100nF ceramics in parallel to the 2x1000uF as well as to the output capacitor.
Easy enough to do.

With 8 opamps it seems the PSU is a bit over-engineered

I agree its getting a bit complicated.

My simulation also shows the not1xor1's blinking works, there is a region where the both may lit (Iout pretty close to the SlowCC limit) but that situation is rather rare.

I checked my wiring and it was wrong on the breadboard. I did notice the issue at low voltage (around 400mV) that the LED's did not light up. But I dont plan on really using it that low.

With Vout from 124mV to 25V (30V V+) the current of each LED is always 0mA or 1.6mA with 15k resistor while blinking - see below.

I would also leave the 560k there, you may or may not populate them. If somebody decided to use cheap potentiometers the resistors could become handy.
Ill put them in the schematic as 100Meg and not populate them.

I would go back to the 4opamps version, with the buffer for the I_set, buffer for the Vref, and the CC and CV opamps. And blinking according to not1xor1.
Too Easy

PS: doublecheck the labels on your opamp power. Looks like both are V-. Use better names for the labels.
Opamps are Powered by OA_V+ and OA_V-

PPS: Why your previous main V+ is now called V- in your schematics?
That is weird..weird..

I think the issue is I am doing both a Print to PDF and a Screen Capture. I believe you are looking at the screen capture and its not very clear. If you look at the PDF you will see everything is correct. I agree its a bit odd that its not showing up correctly.

I would highly recommend you to rename it back to V+.

Or better, when you are getting confused by too many sources with 2 chars long names, use the appropriate long names like for example:

Code: [Select]

Vpower+  or  Vpower_P        for the main 18V power
Vpower-  or  Vpower_N        for the -1.3V created on the 2 diodes
Vopamp+  or  Vopamp_P        for the opapm's positive power
Vopamp-  or  Vopamp_N        for the opamp's negative power
otherwise you may easily create a big mess on your PCB.
Also do use underscores instead of spaces in the label names.
Eagle does not let you use Spaces in Net Names, plus the programmer in me always uses underscores. Once again I think the screen capture is not working correctly. PDF shows this clearly.
73

73's

[Kleinstein]

With no variable load, there is no need for an extra buffer of the reference. So one could use 4 OPs as.
1 x CC mode regulator
2 x CV mode regulator
1 x Current set buffer
1 x CC/CV indication  between the outputs of the first 2 OPs.

Just using the LEDs with no OP between the outputs of the OPs would give a variable intensity and would not work with voltage near the upper limit.  The CC limit can also be reached at a relatively high voltage.

The TL431 itself can do some amplification like 2.5 V to 5 V or 7 V. The LM329 would be 7 V directly. So no extra OP is needed to buffer the reference.