Variation in Output current

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Hello Sir!

I am working on RDR-291 150W circuit.

I have replaced LNK 420 by LYT 4228 and developed the Transformer ETD 29 using PI Expert Software.

I hace developed five prototypes and achieved the current 2.1A in both channels.

but in 5 prototypes I observed that Output current not in +-5% regulation. It is sometimes more than 10 % range.

What can I do to achieve +-5% regulation.

and also I have developed the Transformer in House so I am facing problem of one transformer giving 2.1A and same PCB with another transformer 2.3 A another transformer 1.9A .....

This type of Issue I am facing. All transformers Inductance is in within range. Leakage Inductance is also well within range.

Please provide the soution to achieve consistency in current and transformer.

Also guide for the transformer measurement techniques whether I am doing wrong?

IFB current is critical in regulation so if you have variations on the IFB, then the output current will be affected too. Please measure the bias voltage and check that the voltage does not vary from unit to unit. Use 1% resistor for the RFB.

Calculate your IFB (Vbias - VFB) / RFB. If possible, set IFB to around or near 150 uA by changing the parameters in PIXLS such as current limit mode (Reduced vs full), VOR.

Hello Sir! 

              Is there the LYT4228 is too much sensitive with heatsink??

I have observed that with adjustment in Heatsink, output current increase or decrease upto 200mA. In developed five prototypes I am facing the problem of heatasink. Linkswitch is not too much sensitive to heatsink.

I am using custom made heat sink may be this is the use. How can I fix this problem?


When you make changes to the heatsink design, please check that the temperature of the device is the same. The device has temperature coefficient so if the new heatsink make the device temperature higher, then the output current could be affected too. Please design to a temperatue < 100C if possible.

Another thing to watch out for is the layout especially the trace going to the FB. Make sure that you don't route it near the drain pin as the switching noise could get coupled with the FB.

Hello Sir!

In my RDR-290 based circuit I need to achieve THD <10%.

What changes I can do to get this value.

Currently in production I got result between 18 to 21% I need to reduce this immidiately. Please guide for this.


Please refer to my answer on the separate forum.