Variable flyback design 5-42V

Hi,

Can you please attach your Piexpert design?

Regards,

PI-NANO

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Hi Sorry for only getting back now. I didn't get a notification that there has been a response. So far, what I have done is to reduce R10 to 10k to insure adequate current flows at lower output voltages. I could then get the output down and variable between 20V and 42V. Now it seems like the voltage fed back through the bias winding becomes too low the TOPSwitch to regulate properly when I go below an output of 20V. This is as far as I have come with solving the problem. I hope you can assist further.

Regards

Gualbert

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Hi Sorry for only getting back now. I didn't get a notification that there has been a response. So far, what I have done is to reduce R10 to 10k to insure adequate current flows at lower output voltages. I could then get the output down and variable between 20V and 42V. Now it seems like the voltage fed back through the bias winding becomes too low the TOPSwitch to regulate properly when I go below an output of 20V. This is as far as I have come with solving the problem. I hope you can assist further.

Regards

Gualbert

Hi, 

When I looked at your PIExpert design, I have observed that you did the design for CV only. Can you change that CV/CC and try again.

If Bias winding voltage is becoming too low, Can you increse one or two turns on the bias winding and see if it can give you any improvement.

Regards,

PI-NANO

Hi, thank you for coming back to me. how would you suggest I impliment CC/CV? When I did my original simulation I chose CC/CV option. As I understand it you can do CC either by having a current sense resistor which you feed back or you can somehow get it from the bias winding. I couldn't find a design example of this. If you can possibly point me in a direction this will be greatly appreciated. I did add 2 windings extra to the bias winding which resulted in the voltage being set down to 13V instead of 19V so this is making an improvement. What is the maximum voltage the bias pin can handle then I can always add another 2 windings to increase my range.

Best Regards

Gualbert

Hi,

It appears that you are attempting to make a varaibvle output voltage design. In a flyback converter, all the outputs are cross regulated. The bias winding is just another output of the power supply. If the output voltage of the main regulated output is changed, the bias winding output voltage will change as well. If the bias winding output voltage becomes too low, it wil not be able to produce adequate voltage such that the optocoupler transistor can conduct. You will therefore need to adjust the number of turns of the bias winding such that even at the lowest output voltage of your main output, there is 9V at bias winding output.

Regards,

PI-Sarek

Hi,

The control pin is a current input pin and is clamped internally as indicated in the databook.

 Kindly refer to the datasheet.

Regards,

PI-Sarek