Hello prasad_pari,

Thank you for interested in using Power Integrations products.

I have several questions before we dig in to the solution.

1. when you mention the power supply shutdown, did you see any swicthing activity after it shuts down. You can try to reduce the load after it shuts down to see if it can come back or not

2. is you application open frame or inside an adpter

3.can you share your transformer desig. i want to if there is anything wrong with the transformer.

you can also refer to the tiny4 datasheet design example, that is also a 5V 4A design use TNY290.

Best Regards

Hello prasad_pari,

Thank you for interested in using Power Integrations products.

I have several questions before we dig in to the solution.

1. when you mention the power supply shutdown, did you see any swicthing activity after it shuts down. You can try to reduce the load after it shuts down to see if it can come back or not

2. is you application open frame or inside an adpter

3.can you share your transformer desig. i want to if there is anything wrong with the transformer.

you can also refer to the tiny4 datasheet design example, that is also a 5V 4A design use TNY290.

Best Regards

Namaste/Hi,

Thanks for your reply below is the answer for queries.

1.Yes, when  I reduce the load to less than 0,9 Amps it works fine. when I increase the load it come on for a while.

2. It is open frame. for now I tried to force cool it using fan but though there is no much heat observed on the TNY body still it shut down above 0.9 amps load

3. attaching the transformer design data.

regards,

Prasasd

Hello Prasasd,

I run the PIxls to check your transformer design. it seems that your transformer indcutance is a little bit low. Use the link below to check your design. 

https://piexpertonline.power.com/site/login

You are using the standard current limit based on your BP pin capacitor value.  the nominal inductance you should use is 975uH. 

what  is the valley voltage across capacitor C2 when you load 0.9A load. Does it trigger the undervoltage protection? you can try to remove the two 2 M resistor to disable the UV circuit to see if it can deliver the power or not.

Best Regards

Hello,

thanks for your reply.

As per your suggestion I changed the transformer to 1300uH primary inductance. it improved by 300mA that is it gives 1.2Amps now.

I removed those capacitor to disable under voltage protection, but no improvments. it is for sure not shutting down due to over heat as I am running 5600RPM contimously on it.

Please help to resolve the problem.

Thanks in advance 

Prasad

Hi,

Kindly reply, it is urgent.

thanks in  advance 

Prasad

Hello Prasad,

Do you have any voltage waveform of the Vds of primary MOSFET. I am wondering if the leakage spike is already higher than you zener diode in the primary clamp circuit when the load is higher. Can you try to change your clamp circuit as the circuit in RDK295.

https://ac-dc.power.com/design-support/reference-designs/design-examples/rdr-295-20-w-standby-power-supply/

if you can share some waveform when the power supply is loaded above 0.9A+0.3A, the drain voltage and output voltage, it will be helpful to understand the problem better.

Best Regards

Thanks for your reply,

I am afraid that I donot have isolated probe to monitor primary, But as you suggested the Zener is getting heated up heavily, So will change the ciruit with RC and will update

Thanks in advance 

Prasad

Hi,

Tested with 56K Ohms 2Watts Res, 4,7nF/2KV Cap(as only this was available with me) and 18 Ohms resistor. instead 160V TVS. but Tny290KG burnt. Hope to here from you for any other suggestion.

Thanks in advance 

Prasad

Hello prasad,

Depended on your leakage inductance of the trasnformer and clamp circuit you used, the drain to source voltage may be too high for the IC to survive. 

What we could try here is use the 160V TVS and connected a 2.2nF(or 4.7nF) capacitor in parallel and then connect a small value resistor, like 100ohms or a little smaller. Can we try this setup to see if the circuit works?

Best Regards