Mosfet not switching ON

Posted by: vasanthkumar_ng on 08/22/2013

Dear Sir,

I am designing 9v 5amps smps.

I have problem with my design while implementing. When I implement it, my Vds is 275v(dc) and my control pin voltage is fluctuating between 5.1v to 5.6v so my control circuit and mosfet in topswitch is not getting activate, what should I do to increase my contol pin voltage to 5.8v. (Note: I implemented as per the design of PI). I have used 6.8ohm resistor at the control pin, if I use 6.2ohm resistor at the contorl pin, will this work out? will control pin voltage increase to 5.8v?. For your reference I have attached the schematic of my design and also i designed the transformer as per the specification mentioned by PI Expert.

Please help me in sorting out this problem.

Thanks,

V K Gunalan

Files

TOPSwitch-GX_PIDesign(EF25 or EE25).jpg (104.48 KB)

TOPSwitch-GX_PIDesign(EF25 or EE25).xls (46 KB)

TOPSwitch-GX_PIDesign(EF25 or EE25)Trans.xls (645.5 KB)

Comments

Hi,

Thanks for contacting PI.

I checked your schematic, do you have a specific reason to put 3 * 2200uF capactors on the outputs? These capacitors value are very big, it takes long time to build the output.

Would you remove 2 * 2200uF cap, and try it again. If still not working, try to put one cap like 680uF. If you really need to use very big value of capacitor, then you will need to apply a soft starter circuit.

Hope this will be helpful.

Thanks

Dear Sir,

Thanks a lot for your reply,

I tried both the ways you said, first i removed 2*2200uF caps and tried with 1*2200uF, then I tried with 670uF cap, but still my problem not yet solved. My control pin voltage is just 4.4volt and its goes on discharging till 2 v, its not going up till 5.8volt. I do no where the problem actually. I tried everything which I could.

Please help me to solve this problem.

Thanks

V K gunalan

Dear Sir,

Thanks a lot for your idea. Now its working fine(I used 2nd method which you said)... sorry for my previous post, I found the problem with my top246yn, so replaced it and then the problem got solved.

Thanks,

V K Gunalan

Hi,

Sorry, I have a little bit confused. In you second post, seems you found the issue and get it solved. Then the issue came back?

If the issue still existing, could you record the waveforms of drain voltage, drain current, C pin voltage at power up? Without this information, will be hard to know what exactly happened.

Thanks

no no no, I am sorry for your confusion. My second post is my final one. my problem got solved. I am getting the output voltage as expected. Now i am about to check my current ratings.. once I get it, i will ping you sir.. Thanks a lot for the help.