Output Voltage Less Than Expected

Posted by: mahshid on 02/15/2009

Hello Dear PI Expert,

I am trying to build a 36V,2.2A power supply with TOP224Y. I have a circuit design (the attached file) which used to work without any problem, every thing was tested (even in full load) and was great. But suddenly output voltage reduced to about 17V and poor regulation was observed.
Reference pin voltage is fixed at 2.5V but the voltage drop on Rup is about 14V which is less than what expected. It seems that some current flows out of the TL431 reference pin!!!!! Very Strange!!!
Most of the components were replaced with new ones but nothing changed and still output voltage is less than expected.
Would you please tell me where the problem can be? I am completely mixed up.

I look forward to your answer.
Best regards.
Mahshid Yaghmaee.

Comments

Can you attach a copy of your schematic and PI Expert design file?
Which components did you change? Is it regulating at 17 V? As in does the voltage change with change in line voltage and or load?

Hi Spock, Actually, I could repair it (One off the component was out of order). Power supply is now working without any problem. Your Topswitch is great.Thank you. The next project we have is to build a 300W CV power supply (+60V@5A).We need it for a 250W Class D audio power amplifier. Is it possible to make it with TOP261Y or TOP262Y (In open frame mode)? Thank you very much. Mahshid

Honestly, at such a high power level you should be considering a forward converter topology. Beyond about 5 A or beyond 200 W power, Flyback should'nt really be the choice.

supposing they were doing 60V, 4A flyback, would this then be OK by your "5A/200W" rule?

You have to understand that this is a "guideline". Its certainly not black and white. Ultimately what matters is the ripple current on the output caps. But to answer your specific question, 60V, 4 A violates 200 W but even so because output current is relative low we can still *consider* using Flyback - although you are really in the Forward converter region for this power range.