Topswitch TOP250Y

Posted by: dstenbro on 03/01/2013

This design is for 100 watts output. With a 75% load on the ouput at 24 volts the flyback transformer has a distinctive audio frequency. The load also creates about 170 mv of ripple. How do I eliminate the audio frequency noise?

Comments

The control loop is unstable. Send attachment of step load trasnient response and schematic of design

I will get the step response after I capture waveforms.

Per your request here are the scope captures.

Loop is definitely oscillating. Change R10 to 3.3k and add 0,1uF in series with 560 ohm in parellel to R10 for phase boost. These are tentatie values -- you may want to play around with values to optimize while looking at step response for stable response

I changed R10 to a 3.3k ohm and paralled it with a .1uf cap in series with a 560 ohm. The audible frequency did change but is still there. I want to make sure we are working with the same reference designators as the schematic I sent you. Please confirm this. I did however play around with the component values with no solution. Do you have any other recomendations?

Try placing R13 on the other side of L1. Something is seriously erroding your phase margin

I tried placing R13 with the same results.

Try replacing TL431 with simple zener type regulation.