Top 243NY restart when the temperature increases.

Can you post a PDF or photo of your layout. This may be due to noise pick up - is the L pin PCB trace routed close to the Drain trace?

Cheers

PI-Chekov

Dear Sir/Madam

According to pages 5 & 6 of AN-32, there are 4 types of feedback circuits for TOPSwitch. The function of Opto/Zener & opto/TL431 is clear for me, because they get sample from Vo & transfer it to pin C. However, the function of pri/basic & pri/enhanced  isn't clear for me, because they don't get any sample from Vo . Would you please explain how these pri feedback circuits work & regulate the output voltage?

Hi Ahja,

Thank you for your interest in Power Integrations' part.

Regarding your question, basically the Vo is in proportion with bias feedback winding regulation since they are both in flyback with the primary winding. We usually called this cross regulation. This is indirect sensing of Output voltage that is why it has wider tolerance regulation compared to opto-zener feedback circuti which directly sensed the output. I hope this answers your question. Thank you.

Hi Mallora
Thanks for your prompt reply.
In an electronic board, TOP243YN was used as switching power supply. The power section has become defective due to fluctuation of input voltage (220vac, 50hz). The board has been checked; all related components (diode, zener, transistor, capacitor, and resistor) have been checked. It seems all of them are ok. It seems TOP243YN is faulty, since the drain- source resistance (Rds) is zero. TOP243YN is dismounted from board & Rds is measured between PIN 4 & 7.
I tried to buy TOP243YN but it wasn’t available in our market. So, TOP245YN has been used instead of TOP243YN!
When input power (220vac) is turned on, nothing happens. Schematic diagram of the power section could be found in the attached file. Some measured voltages have been marked-up in the attached file in RED.
You are kindly requested let me have your valuable commends & recommendations in this regard.
Best Regards
Ahmad Javid

Hi Ahmad Javid,

Thank you for your interest in usipng Power Integrations' part.

Regarding your question, using TOP245YN instead ot TOP243YN should work.  The only possible scenario is the maximum power capability of your power supply will increase due to increase in size of your part used.  The problem you might encounter is that your other components are not designed with higher power capability like possible saturation of the transformer before you reach your new power limit or your current rating of the output diode might be not enough.  

About your problem with power-up, I can't figure out if your power supply is switching already.  It seems that there is/are other parts that is also damaged or there might be some loose or lost connection in your circuit.  What you measured using your Voltmeter is just the RMS value of your rectified AC.  You really need to use Oscilloscope to see if the MOSFET is switching.  Or you can try to measure frequency at the VDS if you can measure kHz frequency range.  Thanks.