TOP266EG Reference design

Sir,

There are two reasons why the load voltage is higher than desired:

1. The feedback resistors R13 & R14 are incorrect.

2. The transformer has been wound incorrectly.

Could you confirm if the load voltage is within regulation as you continue to load the power supply?

I have checked R13 and R14 they seem to be correct. And the voltage at tl431's terminal is 2.55V. I have re-wound the transformer and got the same result, no change. I think i misunderstood the winding instructions. Correct me if I'm wrong. If i start to wind with 3, 5, 8 and 2 in order and end with 2, 4, 7 and 1 in order then i should wind in the same direction. Is this right? I mean i start with 3 and end with 2. Start with 5, end with 4. Start with 8, end with 7. Start with 2, end with 1 and i always wind in the same direction. Do I understand right?

It seems that load the supply the output voltage decreases slightly. E.g. 1V decrease @ 500mA

Your explaination of winding methodology is correct:

1. Maintain the same winding direction.

2. Split Primary: Start at 3 / End at 2 || Start at 2 / End at 1.

3. Bias: Start at 5 / End at 4.

4. Secondary: Start at 8 / End at 7.

5. Ensure that you have the corrent number of wires per layer as described under the winding instructions. 

Could you describe the variations (if any) in the load voltage as the load current is increased to full load please? 

I have done more or less the same design just with a little less power rating and with the TOP264KG package, but I get exactly the same result as you did, did you ever resolve this issue.

Thanks 

Unfortunately, i tried to wind transformer several times and checked the circuit but didn't get a result and i gave it a break because i had other jobs to do. I'll look it in my spare time again soon i hope. If you get a result please inform me too.

mvdeventer,

I noticed the following in your design file:

1) When the file is first opened, under Design Results-->Primary Winding Section 1-->NP1=44turns and NS=10turns; however, under Transformer Construction-->Electrical Diagram-->NP=55turns and NS=10turns. This discrepancy in winding should however not affect your output voltage.

2) Can you make sure the CTR of the optocoupler you have used in the circuit matches with the one that is specified in the PI Expert design? The CTR of the optocoupler in the design file is 300. Is this number the same for the optocoupler used in your circuit?

mustafaag,

Can you make sure the CTR of the optocoupler you have used in the circuit matches with the one that is specified in the PI Expert design? The CTR of the optocoupler in the design file is 300 (PC817D). Is this number the same for the optocoupler used in your circuit?

Hi mustafaag

After playing around with the circuit I did realize that the opto coupler I used is not the same as the one specified in die PI design file, instead of using the PS2501-1-K, I used the PS2561 wich have a CTR of  min of 50 the same as for the one specified, but after realizing that the CTR actually playes a great role in the output voltage, I started to change the value of R8(15K Ohm) to a higher value of 19K to decrease the current throught the voltoge reference U3(TLV431). This actually cuased my output voltage to decrease from 40V output to 30V. Connecting this to an load of about 1A did cause the output to drop by more or less 500mV- 1V, but at least I could connect a load of about 1A wihout the circuit restarting itself. I also removed R3, witch is the current limiting resistor for the circuit and conneted the X pin of the TOP device directly to return of the circuit as suggested in the datasheet of the TOP device.

In a second test I connected the circuit to a purely resistive load of about 35W(1.2A, 30V out)and everything worked like a charm. Connecting the same circuit to an inductive load of 35W was not that sucsessfull though. This was caused due to the fact of the peak inrush current of the load actually exceeding the the max current value of the TOP264 and causing the circuit then to self restart. By decreasing the value of R3 will get you a better maximum output current, but the peak current rating of the TOP264 is just to small to drive such a heavy inductive load. By choosing a higher current rating TOP devise like the TOP268 solved this problem for me and I can drive a pure inductive or resistive load of about 40W-45W(1.5A 30V output)

Hope this help you guys

Thanks for the tip. I did not notice that. I've checked the optocoupler it is pc817 but i could not be sure but it seems to be B version and it CTR is from 130 to 260.

I've changed optocoupler and now it seems to work, thanks.

Dear Sir,

 How to  get a reference schematic for top266eg ic

What's your output Power Spec's? However we have design with TOP267 with High Efficiency 40 W Output Power. You Can use with TOP266 device for your output Power Spec's. Below is the reference design and Application Note Guide for TopSwitch Based designs:

https://ac-dc.power.com/sites/default/files/PDFFiles/der276.pdf

https://ac-dc.power.com/sites/default/files/product-docs/an47.pdf

Output Power Specification is 10V/4A.

I am using TOP266EG controller.Output Power Specification is 10V/4A 

I need above controller & mentioned specification reference schematic.

thanks

As we don't have referenc schematic for your spec's. However, you can use our PI Expert, enter the IC number and your specifications. it will provide your optimised design and reference schematic.

thanks sir.