TOP256YN getting restarted, tik tik sound from the transformer.

Posted by: papaisou11 on 05/15/2017

Hello,

I have designed 12V 3A power supply using PI Expert 9 which uses TOP256YN.

I made a prototype PCB and the transformer myself using the design guidelines. There is an issue arrived while testing the power supply unit.

TOP256 is restarting continuously and getting tik tik sound from the transformer. Output voltage is 12V. When I am connecting a minimum load (3V LED) the voltage dropped to 4V.

I already checked the Bias Voltage across control pin of the TOP256. It is 5.75V in load, no load both condition.

I already checked for Transformer related winding issue or any circuitry related issue, but no luck.

Design file is attached here with. I am using 1N4148 instead of 1N914 and RJP15J instead of 1N4937.

Please help me to identify the issue.

Regards,

Sourav

Files

TOPSwitch-HX_PIDesign5.uds (348 KB)

Comments

Hi Sourav,

Thank you for using Power Integrations' part.

Regarding your question, I think you have inappropriate application for the power supply. Topswitch operates on Constant Voltage Mode, LED load needs Constant Current Operation since it is a constant Voltage Load. In your case your power supply regulates at 12V then you are trying to load it with 3V LED. Since your power supply don't have Constant current mode, it is hitting the over current protection. Your LED can handle the maximum current your power supply can give or else the LED will be busted. But you can still use your designed power supply for LED applications. Refer to attached file. You can compute your desired load/LED current based on resistor value. Make sure that the resistor can handle the power dissipation. This is less efficient since you are burning power on the resistor. The higher your resistor voltage, the less efficient your system is. You can't have your LED Load Voltage = PSU regulation for tolerance since LED forward voltage varies alot with temperature. At cold temp, the Vf increases and it will exceed your PSU regulation so current won't conduct and LED will not light.

The more efficient way is using Lytswitch4 in your case. The controller operates at constant current mode.

Attachment	Size
LED loading with Constant Voltage Power Supply (18.93 KB)	18.93 KB

Thanks PI-Mallora.

Although the power supply is providing 12V DC on no load condition, it's still getting restarted. Output voltage showing 11.59, 11.72, 12V and again dropped as it's restarting continuously. I was connected an OSC-COPE to see the wave... It is a Triangular/Saw-tooth Wave as it's restarting.
Also I measured the restating. It is 320mS. Also getting tic-tic sound from the Transformer.
I have connected NO LOAD in this testing case.
Is it a problem with the Transformer that making TOP256 into auto-restart mode?

Two images Attached herewith for reference.(Sorry for the Bad image quality, phone camera is good, oscope screen got damaged :P )

Thanks once again.
Regards,
SaV

Attachment	Size
Duration of the restart (2.35 MB)	2.35 MB
Output at no load condition (1.6 MB)	1.6 MB

Hi Sourav,

I can't actually figure out the waveforms. What is the voltage/division and where is the zero reference. It looks like a ripple to me. Can you give me the waveform with start-up from zero reference?

Did you follow the schematic, transformer construction and the BOM recommended on the PIExpert?

What is your input voltage when turning-ON? Is it the same behaviour when your change input voltage?

Can you also try connecting X pin to G pin?

Thanks PI-Mallora.

The issue is solved now. The opto-coulper (PC817) was faulty. Replaced it and it's working properly.

Thanks for your and Power Integration Support.

Cheers,
SaV

Hi SaV,

Good to hear that. Yes optocoupler is basically one of the weakest link in terms of reliability that is why you have to be careful on CTR IF current design. It also varies with temperature and it changes with operating time.

In your future needs, you can consider our Innoswitch family product which doesn't need optocoupler for isolation requirement of up to 25W application. We also have alot of new products in the pipeline so you can always check our website for all your power supply design needs. Thank you and good luck on your project. Thanks.

https://ac-dc.power.com/products/innoswitch-family/