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

[KC0PPH]

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?

Correct, the PNG is not a high res version.

I will make it full screen before i do a capture again and see if that fixes it.

[KC0PPH]

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.

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.

I am starting to agree with you on the not buffering of the VREF.

First I dont like the idea of introducing additional temp-co's to the ref- I am sure a lot will disagree with me here.
Second the VREF is only tied to the 2 Pots. The total resistance is 25K for one and 50K for the other.
Through the 25K Pot I get a current of 0.1mA and through the 50K pot I get a current of .05mA
This is well within spec for the Voltage Reference. (There is also the SET voltage divider with 0.5mA.

On the final design I will have a single high end VREF that will most likely be buffered due to how much will be using it (Still need to determine for sure). This makes less "Rework" for this design as the VREF buffer does not need to be removed.

[not1xor1]

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.

Really??? I've just checked my simulation (with unmatched LEDs/diodes) and while the current limit appears to be 1.9989A, if I set the constant current load to 1.999A only the CC LED is on, if I set it to 1.9988A the CV LED current drops from 2.1247mA to 2.1059mA, while the CC LED current stays at 2.1039pA.

If both LED are on then the problem would not be a LED one, but that the PSU is in an undetermined state (a Schrödinger PSU  ) with both CC and CV opamps active or in an unregulated state where the input voltage is too low for the programmed output voltage and current.

[not1xor1]

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.

I can't see how it can't work even at low voltages. It does down to about 9mV in simulations, and should go below that if you manage to to drive it in CC mode at those low voltages (your load should be less than a few mΩ inicluded contact and wire resistances).

BTW please correct your quoting.
Please make use of the quote tag (it is next to the # icon in the toolbar).

[not1xor1]

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.

It looks like you haven't grasped the working of the circuit. The current through the LED is roughly constant in any situation.
And yes both LEDs are on if the input voltage is too low, but that is not a bug  , but rather a feature as that would clearly point to an under-voltage problem
If you drive the LEDs through an opamp comparator, in case of input under-voltage, just one of them, randomly depending on the offset voltage, would be on.
I just can't see any advantage in that. 

[iMo]

If both LED are on then the problem would not be a LED one, but that the PSU is in an undetermined state (a Schrödinger PSU  ) with both CC and CV opamps active or in an unregulated state where the input voltage is too low for the programmed output voltage and current.

Well, there is always a probability that you walk through a concrete wall. Pretty small, but there is..

[not1xor1]

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.

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.

I am starting to agree with you on the not buffering of the VREF.

First I dont like the idea of introducing additional temp-co's to the ref- I am sure a lot will disagree with me here.
Second the VREF is only tied to the 2 Pots. The total resistance is 25K for one and 50K for the other.
Through the 25K Pot I get a current of 0.1mA and through the 50K pot I get a current of .05mA
This is well within spec for the Voltage Reference. (There is also the SET voltage divider with 0.5mA.

On the final design I will have a single high end VREF that will most likely be buffered due to how much will be using it (Still need to determine for sure). This makes less "Rework" for this design as the VREF buffer does not need to be removed.

The reference voltage is just fed to the inputs of the regulation opamps so its impedance (at worst pot value/2 + input resistors) would affect a bit just the linearity of the regulation (due to the opamp bias current). But the intrinsic non linearity of most potentiometers would probably be higher.

In any case the drift caused by an additional opamp would probably be less than that of a cheap voltage reference and of that of the potentiometers.
Both the opamp and the reference temp. drift are non linear so it is hard to calculate the respective contribution, but the maximum specified offset drift of a LM324 through its working temperature range is about an order of magnitude less than that of a TL431. Of course each real device may display a different behaviour..

Regarding the current through the potentiometers you should care about the specified power (in some case as low as 125mW, 250mW in most cases of carbon or polymer pots) which might add to the drift (but in your case it is just a matter of mW or less). Regarding the Vref current it has to be higher than the specified minimum (1mA for TL431) so you have just to ensure that the current through the reference at the minimum input voltage less the current through the pots is above 1mA.

[iMo]

The tempcos of the LM324-N (TI datasheet, at 5Vcc, typically) are 7uV/degC and 10pA/degC. At Vcc=18V probably more.

TL431 is around 100ppm/degC (250uV/degC @2.5V), LM431 50ppm/degC.

[KC0PPH]

It seems like this subject on CC/CV indication has been beat to death. I have included the proposal without the Opamps. We I get the boards I will give a detailed review of how it works.

My To-Do list is now down to the following items before I order the prototype boards.

1) Finalize all Calculations and Document all Equations Used
2) Replace Resistors with standard E144 values
3) Re-Do Equations and verify any error is tolerable
4) Replace 1N400X diodes with SMD versions. (I will keep the 1N540X as TH). For a final supply I may use a real negative regulator as the diodes are pretty wasteful.
5) Finalize Schematic. Make placement of all attributes consistent
6) Finalize Board Layout - Make sure Silkscreen will look nice
7) Manually Route the following Nets
7a) V+
7b) Vout
7c) Bypass Caps for OA
Click on AutoRouter
9) Drink a beer for the 7.3 seconds it takes to do the work
10) DRC -> Fix Errors, Order Boards
11) Order Components


So a few questions I still have:

First I am only getting a difference of 400mV on IC1B. I have put my calculations on the schematic. I would like this to be 1V Can I use different value resistors for the Inverting and Non Inverting inputs?

Second I have been searching around on the internet on how to calculate the Current of the current sources. Could anyone provide some literature on how this circuit works and how to calculate the current?

Rev4 should be the final version before I order boards. I will make Rev5 after what I spoke about in the list above is complete.

Once again thank you guys for helping out with this.

[iMo]

The IC1B is a differential amplifier, where R10/R8=R16/R9.

For best operation R8=R9 and R10=R16 (your schematics).

The amplification of the differential amplifier is set by R10/R8.

For your requirement 1A_shunt/1V_output (1ohm shunt) the amplification shall be R10/R8=R16/R9=1.0

The current sources in your schematics work such the constant current flowing off the collector of Q2 transistor is:

Ic = (Vb - Vbe) / R1, where Vb (voltage at the base) is the voltage at the LED1 (1.6V-1.8V with red led).

The above voltages are referenced to V+.

It is expected the voltage at the LED is stable. Also it helps when tempco of the V_LED and of Vbe of the transistor compensate each other.

For example: Ic = (1.8V - 0.65V) / 220ohm = 5.23mA.

[not1xor1]

It looks like you haven't grasped the working of the circuit. The current through the LED is roughly constant in any situation.
And yes both LEDs are on if the input voltage is too low, but that is not a bug  , but rather a feature as that would clearly point to an under-voltage problem
If you drive the LEDs through an opamp comparator, in case of input under-voltage, just one of them, randomly depending on the offset voltage, would be on.
I just can't see any advantage in that. 

when in a under-voltage event the current is shared between both LEDs but due to the small difference in the forward voltage drop and opamp saturation voltage one might look brighter than the other.
I'll see if I can manage to run a few tests on a breadboard.

[Kleinstein]

To a large part the circuit looks good now. A few more comments:

1) R2 and R12 could be combined - the 2 LEDs could use the same current.
2) The diodes D2 and D3  are probably better faster 1N4148 instead of large 1N4001 - the foot-print is small already
3)  R3 may not be needed - 50 Ohms may be on the high side already
4) It could be a good idea to have a small diode across Q3 ( emitter to collector) to prevent a large reverse voltage during transients. This would give the OP some power to pull down the voltage. This can also help with some transients. The current would be still limited by the OP internal limit.

5) The resistor values for the current sense part (R8,R9,R10,R16) would be better off with R8 = R9 way smaller than R10 = R16. This way less of the small voltage at the shunt is lost and the accuracy of the resistors is less critical. The buffer for I_set is missing the connection to the OPs output. As a consequence R24 would be smaller, possibly even to 0.

6) The 4 th, currently not used OP could be used as an additional differential amplifier for the shunt voltage, just to read the current. The current I_sense  signal is not sensing the actual current, but more like the output voltage.

The layout looks a little odd with the OP so far to the side.

[jaycee]

Regarding the CC/CV leds... i overcame the intensity problem in my design in a rather simple fashion...
This could be configured to provide 0-5V signals to a microprocessor too. V_REG and I_REG are the outputs of the error amps.

[iMo]

Except the Iset buffer missing wire the LED's resistor is not connected as well.

I messed with simulation yesterday and I found out there are regions where the not1xor1 led signalling does not work. Try with I_Set=30mA, and smaller output voltages (2V-8V) and loads.
EDIT: I messed up something in my schematics.. Blinking still works..

And, yes, the diodes in the control loops should be fast one (ie 1n4148).

I would leave the R24 there it gives more flexibility when playing with I_Set.

The 560k resistor I still recommend there could be used (with a value like 5k) to make the I_set scale "log".

The pass transistor and the heatsink will get most probably hot - I would move the TL431 into very lower right side corner of the board. Also the large elyts are too close to the heatsink, imho.

[iMo]

I've tried harder with a simulation where the V+ (input voltage) is switched on and off periodically.
V+ (25V) rising edge is 10ms, falling edge is 10ms.
The load is a Red_LED with 10ohm in series.
The current limit set to 20mA, Vout set to 17.2V.

With the "2 diodes negative supply" the output voltage and currents shoot up to the roof during switching off.
EDIT: Again, an issue in my schematics  -  2diodes negative looks ok.

With a separate negative 3V, with same pulsing and edges as the V+, the output looks much better during switching off.

See below.

[Kleinstein]

Against turn on / turn off transients it might be a good idea to have something like a 12 V zener in series with R2. So the current source is off when the supply is too low or not yet low enough for the OP to work.

[iMo]

  Again a small issue in my schematics - I grounded the 2200uF cap into the ground instead to the -1.3V..
I've replaced the picture in my above post. The switching off looks ok with "2 diodes" negative supply..
Better, you may doublecheck..

PS: below a more realistic scenario - switching on/off (200ms on, 4sec off) the AC before the diode bridge, "2diodes" negative supply.

[KC0PPH]

Just wanted to give an update. I have been busy with work and school, and so this took a back seat.

I had my first board populated, and had issues trying to get it to actually regulate. It tuns out the resistor that limits current into the OpAmp Outputs for Voltage or Current Control was 51.1K not 51.1 Ohm... So that explains why I could not get it to regulate.

I gave that one to my father, and am in the process of populating another one. I have been doing it slowly and powering it up to keep an eye on things. So far it is looking like it will work, the problem I have is missing parts. I only ordered 1 TL431 thinking I had a handful. What I do have is 4040's. With that I will be waiting on the postman again.

One question for everyone though.

In the attached picture I am trying to figure out why that LED does not stay lit. It only turns on when I short out the Collector of that transistor to ground (through a 51 Ohm Resistor). I thought this was wrong and did it up on the proto board with same results???

I have also been racking my brain trying to figure out the Fast CC calculation. I have .15 ohm as the shunt resistor and need to figure out how to do that math? Could anyone give me a starting place so I can calculate the fast CC based on my requirements?

Once again Thanks in Advance!

[iMo]

The LED does not lit because of a wiring issue (doublecheck the transistor type and its wiring).
The current through the LED should be 4-5mA when the collector is sourcing the current.
When the collector is floating the I_LED is around 0.5mA.
With shorted collector to gnd the I_LED is around 5mA.

The Fast CC calculation (aprox):

I_fcc_limit = 0.6V / Rsense = 0.6 / 0.15 = aprox 4A