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Feedback on power supply 0-30V 0-4A
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xavier60:

--- Quote from: d4n13l on July 27, 2019, 07:58:21 pm ---I just connected the a L7805 in parallele with C2.. I didn't realize before that this causes the voltage to come down.. guess I'll try to connected it somehow to B2

--- End quote ---
You still have options with B3 by using a full bridge split rail rectifier or a 2 diode doubler to give + and - rails depending on how much voltage is needed.
Another option with the CC adjustment is to use a Logarithmic potentiometer which will allow fine adjustment for the low end of the range and coarse for the high end. Most audio Pots are this type.
To find out, turn the Pot to the middle of its range and measure the resistance on each side of the wiper. There will be a large difference with a log Pot.
xavier60:
One more option for the current control is to add a range  switch.
David Hess:
For those not familiar with this design, a simplified example is shown below.

The idea is that the operational amplifier, configured as an instrumentation amplifier (notice the 4 equal valued resistors), copies the voltage across R7 as shown below which is always 1.25 volts as maintained by the regulator, inverts it, and then applies it to the bottom of the resistive divider which sets the output voltage.  So with -1.25 volts applied to the bottom of the divider, the regulator's output can reach zero volts.  R8 helps the operational amplifier sink the current through the resistive divider.


d4n13l, your idea is sound but the implementation of that current control loop has at least one problem.

1. The voltage reference for control of the current is unregulated so the output current is going to follow the ripple voltage at the input of the regulator.  Maybe that is acceptable though.

2. 50 kilohms worst case impedance at the non-inverting input of IC1B may be a problem.  Pin 5 should be bypassed to the bottom of the potentiometer (the node where VR1 and R2 connect) and *not* ground as drawn in the schematic.

3. I think the current regulation loop will be stable but if it is not, Circlotron is wrong about the gain but right about how to add external frequency compensation of IC1B if necessary.  C5 severely limits the bandwidth of IC1B which should make it stable albeit slow.

4. IC1B should be able to to sink the roughly 5.7 milliamps coming from R4.

5. The bottom of R6 should be connected to ground as shown below and not the negative supply.
d4n13l:
Hi David,

Thanks for the reply. About your simplified schematic, you're right R7 voltage is always 1.25V however after some thought I realized that the voltage copied by the op amp is not this 1.25V but the output voltage minus 1.25V, thus allowing the voltage to go to zero. Great! now I can delete the voltage regulator from the second transformer in my schematic.

As for your other comments, from

1. You're right it's unregulated, I don't know a good and efficient way to get 1V regulated from 34V input, I'd love suggestions.
2. If I understood correctly, and you meant to simply delete the connection from the bottom of the pot VR1 to ground, that wouldn't work because the pin 5 would see the voltage from the voltage divider R1-R10 (0-1V) , and I wouldn't be able to regulate the current with VR1.

The current regulation part works and is stable but I get coarse instead fine tunning (I'm not happy about it).
Also the voltage/current meter that I have works with 3-30 input voltage, but I get 34V from B1, I fixed it with a transistor as in shown in the schematic, but I'm not sure how good of a solution it is.
xavier60:
It's likely that the meter should be fully referenced to GND. The brand and model of the meter will be helpful.
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