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Bench CC/CV PSU Based on Daves uSupply (Not Anymore)
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not1xor1:

--- Quote from: Kleinstein on March 24, 2019, 07:36:31 pm ---For current limit the OP for the current loop will no necessary go down all the way. With a resistive or similar load that is just a little high the voltage would only drop a little. The usual way to check is to compare the outputs of OP1A and OP1B, e.g. with another OP/comparator.
Just an LED to V+ may not light and could be rather dim if the voltage is still rather high.

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To get CC/CV mode display by LED one may take advantage of the fact that one of the two opamps is always saturated.
So just connect the output of each opamp to the anode of a diode (1N4148) and a LED in series, then connect the cathodes of the LEDs to each other and via a resistor to the ground.
The led connected to the voltage control opamp would be ON when in CC mode and vice versa for the other opamp.
iMo:
As this is not related to your values calculation:

The IC1C opamp for the LED blinking - I would not wire inputs of 2 opamps in parallel - I would put 10k resistors in series with IC1C's inv and noninv inputs. That also gives more flexibility with different wiring then.

The shunt resistor of 1Watt would be ok (1Vx1A). I still would recommend to make two 1Watt resistor positions in parallel on the pcb available.

The T2 - the power loss could be >0.3W with 20mA load, so either you change it to a more beefy type (ie BD139), or, decrease the constant current load to 10mA or less.

jaycee:
You want the shunt resistor to heat as little as possible, as that will affect its value, so I recommend sticking with 2x1 ohm resistors.
EAGLE's transistor libraries are a mess - I ended up making my own!

If you want 5V from the TL431, there is no need for an external opamp.  The adjust pin is exactly what that is for. Use e.g two 1K resistors as shown to get 5V. You could tweak one a bit and get 4.096 if you wanted.

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.
KC0PPH:

--- Quote from: imo on March 25, 2019, 08:16:21 am ---As this is not related to your values calculation:

The IC1C opamp for the LED blinking - I would not wire inputs of 2 opamps in parallel - I would put 10k resistors in series with IC1C's inv and noninv inputs. That also gives more flexibility with different wiring then.

I will add 10K resistors

The shunt resistor of 1Watt would be ok (1Vx1A). I still would recommend to make two 1Watt resistor positions in parallel on the pcb available.
The Resistors on the board are really just for the holes. I plan on putting 1 50W 1 Ohm resistor on the bottom of the board.

The T2 - the power loss could be >0.3W with 20mA load, so either you change it to a more beefy type (ie BD139), or, decrease the constant current load to 10mA or less.

I can change that out to something in a TO-220 Package possibly. On the breadboard it did not get too warm, although I am only playing with around 5V for my regulator output currently.


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--- Quote from: jaycee on March 25, 2019, 11:24:42 am ---
If you want 5V from the TL431, there is no need for an external opamp.  The adjust pin is exactly what that is for. Use e.g two 1K resistors as shown to get 5V. You could tweak one a bit and get 4.096 if you wanted.

I most likely need to buffer the output of the Regulator no matter what, not sure if it matters where the gain is placed. In final design I will be using a high end reference which is the correct output so gain will not be required in the OA.


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jaycee:

--- Quote from: KC0PPH on March 25, 2019, 02:27:56 pm ---I most likely need to buffer the output of the Regulator no matter what, not sure if it matters where the gain is placed. In final design I will be using a high end reference which is the correct output so gain will not be required in the OA.

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Nope, the TL431 will be fine driving the setting pots without buffering. My 18V 1A bench supply uses that arrangement. The only place I had to add a buffer was on the output of the pots, and that was only because I needed to adjust the range being sent to the ADC for display.
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