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

--- Quote from: not1xor1 on March 28, 2019, 06:06:41 am ---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  ;D) 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.

--- End quote ---
Well, there is always a probability that you walk through a concrete wall. Pretty small, but there is.. :)
not1xor1:

--- Quote from: KC0PPH on March 27, 2019, 08:48:25 pm ---
--- Quote from: Kleinstein on March 27, 2019, 05:04:21 pm ---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.

--- End quote ---

--- Quote from: Kleinstein on March 27, 2019, 05:04:21 pm ---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.

--- End quote ---

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.

--- End quote ---

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
8) 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.

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