boylesg
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May be slightly similar, but surely quite different. You don't want to short the voltage regulator output but change the feedback resistor ratio. "Impossible" BC556 configuration in any case.I copied the idea from a LM317 circuit that was using a similar method.
I agree.with resistor divider, the you can inject a DC current into the voltage reference node
Hi,
Q1 is not involved in the feedback circuit at all.
It just controls the load current.
And if you see no change in the output voltage, that just means that the buck controller works perfectly.
Klaus
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Added:
For further discussion please give each of your schematics a "name" which we can refer to.
I'm not sure if you realized the mistake:I tried connecting the bottom of R3 to the feedback terminal
Hi,
I'm not sure if you realized the mistake:
You didn't connect R3 or Q1 to the feedback node...you connected it to the output node, and thus it doesn't modify the output voltage.
--> Connect Q1 to the feedback node and it will work.
Klaus
I would expect a schematic where the voltage feedback is varied by a control signal, but so far I haven't seen any in this thread.
I miss to understand how the post #5 schematic should be related to adjusting a voltage regulator.
If the purpose is just turning the MOSFET on and off, neither of the circuits provides sufficient gate swing to turn the MOSFET fully on. Supplying the MOSFET drain form 12V is useless in so far. May it's not intended to switch the 12V to MOSFET source, but in this case we are missing a specification of circuit purpose.
No, what you say is not cirrect.You missed the bit where I said I had given up on the digitally controlled LM2576 idea because it just doesn't work and this seems to have been confirmed by multiple experts.
Hi,
No, what you say is not cirrect.
Digital feedback control does work,
But you made a mistake in your circuit, thus your circuit does not work.
Correct your circuit and it does work
Klaus
Hi,
Read post#2, read post#6.
Klaus
No need for a true LM2576 component.Klaus the schematic I showed you is improvised in Multisim because I cannot find an LM2576 component.
I used a 'stand in' device that happened to have 5 pins like the LM2576.
But I have no real idea what that device is nor the function of its pins, other than the obvious ones.
Please read the posts again.So I have probably connected the middle of the voltage divider to the wrong pin since I guessed the function of each pin.
Yes, as already written. You need to disconnect Q1 from VOUT and connect it to the feedback path = middle of the voltage divider.I tried connecting the transistor (with a 120R resistor) from the Vout to the middle of the voltage divider in order to short out R2. (schematic from LM2576 datasheet)
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