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

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not1xor1:

--- Quote from: not1xor1 on March 28, 2019, 06:27:34 am ---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  ;D, 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.  :-//

--- End quote ---

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  :palm: -  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.

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