Hi all,

I give up for a linear PSU, with 2N3055 and 0 > 20 VDC 2A, bulky heatsink mainly, and efficiency.

Now, i'm trying to understand Switching Power Supplies, and the learning curve is steep, so reading and reading....


In sketch, beneath, i want to get 0V output, with Op-Amp.
Right or wrong?




As always, thanks a lot.

jm

 

U1 has no ground connection. Pin-3.
D2 is a slow diode for 60hz. You need a fast diode. Maybe a uF5401.
The op-amps have no power.
I do not understand why the op-amps.
It is hard to make any power IC output less than the reference voltage. (1.23V)
-----edited-----
You could add a switch to the on/off pin. Pulling it down will cause the IC to stop. I know that is not what you want.

 

The LM2576 can't work with its pin 3 open circuit.

 

Right or wrong?

Apparently wrong.
Don't see how that circuit can work as the FB input is what controls the output voltage and the amps aren't even connected to that(?).

Below is the LTspice sim of a similar switching regulator (I don't have the model for the LM2576) that adds the TL431 voltage reference to buck the FB feedback (reference) voltage and allow adjustment of the output voltage to zero:

Thus with the U3 adjustment pot at the top of its setting, the pot output voltage from the TL431 (2.5V) is slightly larger than the 2.21V FB reference voltage, so the output goes to zero (green trace).
(The regulator always tries to adjust the output voltage to keep the FB voltage at its reference level.)
The plot shows four other settings of the adjustment pot giving outputs of approximately 5V, 10V, 15V, and 20V.

Note that this regulator has an FB feedback voltage of 2.21V while the LM2576 has a feedback voltage of 1.23V so the values of R1, R2, and pot U3. along with the possible addition of another resistor, would have to be adjusted accordingly to use this technique with that regulator.
Alternately a 1.25V reference IC could be used, but that would still likely require tweaking of some of the resistor values to get the output voltage range you want.

 

Below is the LTspice sim of a similar switching regulator

Good job. That is simple and better than what I had.

 

Wrong;
The LM380 is an audio amplifier. Why is its output even connected to the regulator output?

 

Wrong;
The LM380 is an audio amplifier. Why is its output even connected to the regulator output?

Interesting point.
But whether it's an op amp or an audio amp, the circuit makes little sense either way.

 

Hi all,

Thanks for your replies, first.

I tried to draw with LM380, as i found it in my Kicad library, with others and wrong choice..

Power was not designed, but the entire draft is bad.

Thanks to Crutschow to take time with his soft.

Nice day.

jm