PMP10531: TIDA-00199: Split IGBT power supply

Dear Vivek Nirmal,

First of all make sure the transformer phase is correct. When varying VIN from 15V to 20V there should be not much change of the output voltage at light load (30mA). Use oscilloscope to verify that the transformer output voltage is negative when output switching voltage of LM5160 is positive (VIN). When output switching voltage of LM5160 is zero then you should see the positive output swing at the transformer (energy flows from C15 to secondary side). 

The topology is fly-buck. Fly-bucks degrade the regulation when VPRI (the voltage across your C15/C16) is more than 60% to 70% of VIN. With VIN=15V and VPRI=10.5V you are at the very limit. Your VIN undervoltage is set to around 11.5V and as per our experience this is not sufficient for nominal power at 10.5V VPRI.

For healthy and cosy operation you would want to set VPRI to VIN/2 (8V is still fine) and the winding ratio to 3.2 giving bit more than 25V. In this case change the secondary side Schottky to SS36 (VBR>((VIN(max)-VPRI)*N)+VOUT which is more than 50V).

For operation at the limit it is important to have low leakage in the transformer. The Dongguan has a low leakage of 300nH (1%) which is good. For the other transformer this is not specified.

There two more things to change:

---- Each output rail needs one ceramic cap of 0.1uF up to 1uF from VEE tor REF and REF to VCC. It has the purpose to receive the peak current from transformer, to block the reverse diode current during switching and also to deliver the peak current for the gate driver of the IGBT.

---- C21 in your circuit should be a low ESR type like a ceramic 1uF

For your tests you can virtually increase the primary voltage by operating the transformer in series resonance of leakage inductance and C15/C16. For this you could remove C16 and reduce C15 to 1.5uF ceramic (300nH leakage inductance) in total and try. Also you need to have very tight control over the leakage inductance and regulation becomes slightly soft.

Kind regards, Ingolf

Dear ingolf Frank,

Thanks for your Detail Explanation.

1.First of all, make sure the transformer phase is correct. When varying VIN from 15V to 20V there should be not much chance of the output voltage at light load (30mA). Use an oscilloscope to verify that the transformer output voltage is negative when the output switching voltage of LM5160 is positive (VIN). When the output switching voltage of LM5160 is zero then you should see the positive output swing at the transformer (energy flows from C15 to the secondary side).

• For This, I've checked as per your guidance, and it is quite well as expected. I checked the transformer output with respect to the IC switching and it's showing exactly as it needs to be. for your reference, I am attaching the photos as well.

2.The topology is fly-buck. Fly-bucks degrade the regulation when VPRI (the voltage across your C15/C16) is more than 60% to 70% of VIN. With VIN=15V and VPRI=10.5V you are at the very limit. Your VIN Undervoltage is set to around 11.5V and as per our experience, this is not sufficient for nominal power at 10.5V VPRI

1. I know that Flybuck worked most efficiently when Duty Cycle is at/below 50%. Now as per the requirement, Vin=15V is fixed and according to you, I just have to set the Vpri under the 8V or nearby 8V so that it will not affect the Load regulation as well.
2. My question is, How to set the Vpri voltage to 8 Volt? should I have to modify the UVLO level or Transformer turn ratio or Both of them?
3. Also, If I want to go ahead with this existing transformer, Is that possible, or Transformer change is necessary?
4. if I only change the UVLO level with the existing hardware setup, will it work? 

Also as per your Suggestion,

I changed the C21-1uF, All the VEE or REF and REF to VCC capacitor to 1uF ceramic and Diode changed to SR306 shotkey with same transformer 2.33:1

I hope you understand my requirement, VIN is 15Volt and I want to have this kind of 8 Output at secondary. Suggest me necessary changes in this design.

Waiting for your response.

Image.1,2 Yellow (C1) = Diode PRRV voltage  & Green (C2) = Switching Waveform from IC (Consider Values at 1:10)

Please Someone from the Ti team Reply on this as I am chasing it for the last many weeks.

Is there anyone who can reply on this matter as I am waiting for the last 30 days?

I wanted to change my input supply to 15V with having 25volt@ output side to all 4 secondary. I am planning to change the turn ratio to 1:3.3.

Do I have to modify any other thing in the schematics? I already attached the schematics in the first thread.

Please guide me through this. Waiting for the respective response.

You can reach me out at 0903.vivek@gmail.com for faster communication.