power supply with two outputs having seperate RTN

I know you concerns about the the two isolated outputs. You can use PI expert to select the right PI part, core of transformer , inductance and turn ratio. But you need to modify the transformer configuration by hand, since the two outputs can not be stacked, and they should be spearated.

Thanks, can i design using PI expert as two outputs with common RTN and then make it floating in stacking option.

As you know, the PI expert recommend two outputs with same ground and stack windings for good cross regulation. Because your SPEC is two isolated outputs, you can not use stack solutions. But the transformer can be designed based on the PI expert result. The inductance, core size,  copper size, turn ratio and  turn numbers of each winding can be used for the transformer design.

Dear Sir,

I have to design a power supply using TOP256 which has dual output

Output 1: 12@1.2Amps 

Output 1: 12@1.2Amps

with individual  RTN (returns). 

Is it logically possible. if yes, can a use PI expert to desgin power supply with two outputs. 

Since both the outputs are of the same ratring, how would be the regulation on both output.

would it be nesesary to provide some load all the time on the main output.

What if main output is not loaded and i give load on the second output of the power supply. 

 These two outputs are isolated, so weight control can not be used for your design and your power supply will suffer from cross regulation issue. The output with feedback will always have very good regulation. But another output will have bad regulation since it is basically open loop. Output voltage will be higher if the one with feedabck at full load, and the output will be lower if the one with feedback at very light load or no load.

For cross regulation,  the coupling between these two outputs are very important. Try your best to improve the coupling between these outputs. And dummy load always helps improve the cross regulation. You have to test with a board first, to see where you are, and then try different transformer anddummy load to improve the performance.

regards

I have desgined a power supply with dual output ( seperate RTN) of 12V / 1.5 amps each.

I am attaching the schematic of the same. my power supply on load ( on main ouput  10ohms=1.2amps and on other output 20ohms = 0.6amps ) gets started but in 5- 10 minutes gets switched OFF with the transformer and the TOP256YN getting severly heated.

My transformer primary inductance is 333uH with leakage of around 8uH.

is my clamping circuit ok. How should i design my clamping circuit.

Please could you help me or the above.

Thanks,

Hitesh 

Dear Sir,

I have desgined a power supply with dual output ( seperate RTN) of 12V / 1.5 amps each.

I am attaching the schematic of the same. my power supply on load ( on main ouput  10ohms=1.2amps and on other output 20ohms = 0.6amps ) gets started but in 5- 10 minutes gets switched OFF with the transformer and the TOP256YN getting severly heated.

For clamping, i have used R=30K, C=2.2nF/1KV and P6ke200A, 5.1Ohms resistor and FR106 diode.

I have followed the transformer as per PIexpert.

Please let me know where is the fault.

Thanks,

Hitesh 

The RCD snubber loos good for me, but PLS double check the direction of the P6ke200A in your board, and maybe increae the cap to 10nF.

If the direction of the diode is good, I believe you have to use bigger part and bigger transformer. 

regards

Dear Sir,

I have make sure the p6KE200A direction and it is correct. I also used 10n capacitor but still the same.

I am using TOP256YN instead of what suggested by PI expert of TOP255Y.

Also the transformer is designed as per the data generated by piExpert.

Thirdly i have desinged it for 12V@1.5 amps dual ouptut i.e 36W, where as i am just loading to 7.2W each i.e 14.4W.

I am attaching my schematic.

One thing i notice is that the bias voltage is initially 13-14VDC but as transformer gets heated the bias voltage continously rises. i have seen it rise upto 20VDC. I have applied load of 20E (i.e 0.6amps, 7.2Watts per channel).

Should i desgin a Power supply with higher rating say 12V@ 1.8 amps so that the transformer has more power handling capacity..

Request to please help as i have stuck with this from a long time.

Thanks,

Hitesh 

Could you measure the voltage across the snubber capand make sure it is really  below the voltage rating of the 200V TVS? And also upload the  picture of your board,  drain waveform and current waveform of the TOP switch, and heatsink dimension of the topswitch. PLS let me know if the board is sealed into a case or open frame.

regards

The Snubber voltage is around 90VDC. 

When i try to connect ground probe of my CRO (owon make) to the drain point, the fuse blow of my isolated power supply which i use to power the oscilloscope ( this one is transformer isolated power). Please tell me the connection of the CRO probe to view drain wave forms and current. ( once again i repeat i give power to my CRO through a transformer isolated power supply. 

The voltage across the snubber cap can be tested with mutimeter. And with the ground connected to the source pin, your power supply for your scope can not be blew up. PLS upload the drain voltage and current waveform and the picture of your board.

Regards