Please help me with this circuit . I have to create thư schematic and PCB circuit but I don't know the funtion of this circuit . Please show me all your knowledge about this circuit and analysis this circuit . I really need your help . Thank you every one so much

 

That is apparently supposed to deliver a constant DC output for a varying AC input, but it is a very wierd circuit and I don't really see how it can work.
It feeds DC to the primary of the transformer and then apparently tries to chop/regulate it with the transistor with feedback from the secondary DC voltage through the optocoupler.
I see no way that it can actually work, however.
Where did you get that circuit?

 

The chopping/regulation is ISO1 chopping via Q1, controlled by DZ1 to keep it at 12V. The entire purpose of the chopper appears to be to control the step-down transformer. Transformer needs a changing field to work. At least that's my take on it.

 

The secondary of the transformer makes it hard to tell what it is supposed to be. The phasing suggests it is a forward converter with the top half of the secondary as the main output, but the lack of discrete inductance on the secondary side suggests it it a flyback converter and the upper half of the secondary doesn't do much, perhaps providing a discharge path for leakage inductance. It is clearly intended to be self-oscillating, presumably relying in part on transformer saturation.

When Q1 starts to turn on, positive feedback through the lower winding on the primary side, C2 and R2 will turn it on harder. What is not clear to me is how it is supposed to begin turn-off. The opto coupler would have to be driven quite hard to pull the base of Q1 down hard enough to get turn-off started. Once turn-off is underway, the auxiliary winding on the primary side will assist. My suspicion is that the optocoupler current essentially raises the point at which the feedback via the auxiliary winding is able to sustain the base drive to the Q1.

 

That is apparently supposed to deliver a constant DC output for a varying AC input, but it is a very wierd circuit and I don't really see how it can work.
It feeds DC to the primary of the transformer and then apparently tries to chop/regulate it with the transistor with feedback from the secondary DC voltage through the optocoupler.
I see no way that it can actually work, however.
Where did you get that circuit?

It's my homework bro . I study CAD/CAM

 

The chopping/regulation is ISO1 chopping via Q1, controlled by DZ1 to keep it at 12V. The entire purpose of the chopper appears to be to control the step-down transformer. Transformer needs a changing field to work. At least that's my take on it.

thanks bro

 

The secondary of the transformer makes it hard to tell what it is supposed to be. The phasing suggests it is a forward converter with the top half of the secondary as the main output, but the lack of discrete inductance on the secondary side suggests it it a flyback converter and the upper half of the secondary doesn't do much, perhaps providing a discharge path for leakage inductance. It is clearly intended to be self-oscillating, presumably relying in part on transformer saturation.

When Q1 starts to turn on, positive feedback through the lower winding on the primary side, C2 and R2 will turn it on harder. What is not clear to me is how it is supposed to begin turn-off. The opto coupler would have to be driven quite hard to pull the base of Q1 down hard enough to get turn-off started. Once turn-off is underway, the auxiliary winding on the primary side will assist. My suspicion is that the optocoupler current essentially lowers the point at which the feedback via the auxiliary winding is able to sustain the base drive to the Q1.

thanks bro

 

Hi,

This looks like a *highly modified* Joule Thief circuit. The mod's include sophisticated voltage regulation and output isolation. I built such a circuit several years back for use in an automobile but used a simpler method for voltage regulation and used a center tapped secondary so i would only have to use two diodes for rectification to get full wave rectification.

How well it works would have to be tested. A good idea might be to try using the LT Spice simulator.
Unfortunately it looks like we dont have any spec's for the transformer though, so that would be a little bit of a guessing game, but if it works it should work to some degree in simulation anyway.

If you are going to be doing these kinds of circuits a lot and you have to be able to analyze them, then you should get familiar with a circuit simulator so you can see how they work.

 

You can look at my description here
https://forum.allaboutcircuits.com/threads/is-this-a-class-c-amplifier.132927/page-2#post-1107738