Power Supply TNY274

Posted by: nanosun on 01/11/2012

Hi PI,
The attached file is my PS schematic using TNY274GN. Now, there are the problems as follows :
1/ Just power on then RF1(10 Ohm/2W)is burned and TNY274 shorted.
2/ Sometime it runs about 5 minutes then happens the same problem.
I have changed a few devices as RF1 to 30 Ohm/3Watt, adding more clamp circuit RCD,shorting R2(4.7M). But failed.
Please give me some advice. Thank you.
nanosun

Files

Schematic_PSTNY274GN.jpg (60.83 KB)

Comments

Please support with any idea, 5 chips TNY274GN have died.
Thanks

why did you use RF here? The current limit of the RF you are using is too low.. I thing if you put NTC( Negative Temperature coefficient ) resistor with serial 1A fuse it will be ok...

Hi,

Please use NTC thermistor in series with a fuse in place of RF1. In order to debug the issue and to protect the devices limit your bench power supply source current. turn on the converter on no load and see if everything comes up fine. Start probing the drain waveform then slowly increase the load on the output. At some point of load your input voltage might fluctuate because of your source current limitation. Increase the source current by a small amount in order to make the input voltage stable. Lets see if anything looks suspicious on drain waveform. please capture the
drain voltage and share it with us so that we can understand the issue better.

Meanwhile could you please send the PCB layout file so that we can review the layout.

Regards,

PI-NANO

Hi Kemred & PI-NANO,
Thank you for your advices. I will test the PS board again but now I'm waiting the devices from a new order.
Regards.
nanosun

This issues happens because you are using a wrong pulse rated resistor.

during startup the inruch current is about Vpeak/Rf this current should not exceed the maximum pulse current rating (or maximum instantaneous Power) of the resistor.

When the resistor got burned during start up it'll interrupt the current through the inductor of the line filter which will generate and over voltage.

using NTC is good solution but it'll slow your start up to more than 15 sec.

regards

Mohamed