Help regarding 12v 3A SMPS using TOP244

If the design is working fine in all areas except for output current, I would suspect that the controller has hit its max duty cycle and current limit.


Does this problem happen at low-line, high-line or both? If it's only happening at low-line, then you might only need to increase your bulk cap size. If your bulk cap is undersized, at low-line the bulk cap voltage will drop to a point where the TOP device cannot deliver enough power to keep the output in regulation. If the design works fine at high-line, this is likely your culprit.

-The Traveler

I found a reference design that might be helpful:
http://www.powerint.com/sites/default/files/PDFFiles/di43.pdf

-The Traveler

I have already checked the reference design you have provided. But it is for 30W o/p @12v i.e. 2.5A. But I need 36W o/p i.e. 3A, so I created the circuit using PI Expert.

I checked this o/p at 230V AC. So, it doesn't seem that this is because of Bulk Capacitor.

Please suggest me some other changes. Also, I am suspecting that Transformer may be creating the problem as I get it made by a Local Manufacturer. Could this be the real problem ?

It's a possibility that there could be a problem with the transformer. Did you verify that it was built correctly?


I'm still curious if you've checked to see if the controller has hit max duty cycle...have you taken and drain voltage/current waveforms?


The reason I brought up the reference design was because, yes, it's for only 30W but the design uses a 100 uF cap whereas your design is running a 68 uF cap. A really simple test would be to add on an extra cap (or run it from a high voltage DC source) and see if the problem still exists.


If you want to send in your PI Expert design files as well as your PCB layout, I'd be happy to look at it. I would definitely recommend verifying the transformer design from your vendor though.

-The Traveler

Thnx for your replies

I am not able to see the waveforms as I don't have an CRO :(

I have asked my local transformer vendor to check the design again.

I have attached the PI expert design file with this message.

I don't know how much help I'm going to be able to provide if you don't have some of the basic but necessary bench equipment to debug a power supply.


Off the top of my head, I'm noticing the following:
- You're using a smaller PI device in your design than in the PI Expert design (TOP244 vs TOP245).
- I also notice that the PI Expert design is calling for a 100 uF input bulk cap and you're using a smaller 68uF cap.
- I'm also noticing that the output bulk caps in the PI Expert design are quite a bit larger than in your design.


I would start looking at these areas first.

-The Traveler

I will surely make the mentioned changes and post the results.

Hello Friend, can I vary your output voltage from 12 v to 15v. If yes what changes do i have to do in this circuit?

The output voltage may be adjusted by adjusting the voltage divider (R9 and R10). They should be calculated such that the output voltage is at 15V with the TL431 reference voltage of 2.5Vtyp.

I would suggest redesigning your transformer because by changing the output voltage you will increase the output power from 30W to 37.5W. It is recommended that you use PIExpert to redesign the transformer.

Hi
How to designe amps transformer for 1500ma and 40v

Application for 50watt led driver circuits
Wanted to designe plz help me thanks

Hi Ashish23june,

It would be my pleasure to help you on your LED Driver design. Can you give me more details of your design specs (please input below):

Input Voltage Range:
Output Voltage:
Output Power: 50W
PF Requirement:
%ATHD Requirement:
Efficiency:

Thanks and Regards.

-Dukat