Help to avoid the start up problem IN top switch based battery Charger

Dear Friends

I have designed the Circuit from The power Integrations which i have attached in the Mail

My problem is when i switched on the supply on direct ac with 50% load. my TOPSWITCH is blasting.

When i am trying to turn on With the help of Variac it is working properly and taking 1.4 amp of load.

At startup waveform i have captured and attached here with the post.

Input Voltage Range:150-265VAC

output voltage: 28V/1.4A

Any necessary information i will provide
Pls help me to solve this.

Regards
Marx

View attachment Battery_charger_230516_1000.pdf

Hi,

I assume an overcurrent problem.

Do you have any overcurrent protection?
Maybe inductor goes into saturation.

Klaus

Klauss:

I am using an NTC 5E/5W at input side before Bridge.

And how to avoid if Inductor is saturated..??

When i try to Turn on at Direct ac it is blowing topswitch250 Having voltage rating of Bvdss=700V.

which is actually going near by 700VDC at no load so with load it can cross above 700v which is killing the TOPSWITCH 250

any ways to avoid topswitch to be failed.

Hi,

Could you add a soft start or a delay circuit somewhere in there?

I agree that DS overvoltage is the most likely way to kill the IC. Transformer leakage inductance and parasitic circuit inductance are causing overvoltage, and it's directly proportional to load current. Thus it's expectable that device failure happens above a certain load current level.

Soft start may be a way to get around it, but the real problem is transformer design, circuit layout and suitable voltage clamping.

d123 said:

Hi,

Could you add a soft start or a delay circuit somewhere in there?

Click to expand...

Where Exactly are you talking about..??
Input section and Output Section

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Here i am attaching a waveform of the input and the Output waveforms at no Load

FvM said:

Soft start may be a way to get around it, but the real problem is transformer design, circuit layout and suitable voltage clamping.

Click to expand...

FVM
If you check the schematics, then Q5 section is for the Output softstart.
I dont know why the Drain to source voltage exceeds above the Bvdss.

Also, for clamping we have the RCDZ Snubber
D=1.5KE200A
C=4.7nF and R ACROSS Snubber is 100K
D=UF5408
R=22E

i am doubting on the output softstart and how to avoid it.
View attachment Battery_charger_230516_1000.pdf

Hi,
Your soft starter turns Q3 on which turns Q2 off, and Q2 being off means that Q4 is off…..that is a problem because Q4 is what you rely on to “brake” your smps.
Also,I don’t see a RC snubber across your sec diode.
I think what you need to do is just first of all set it up as a simple 28vout smps, and put a load on of 28v/1.4a…then when you have it working like that you can go forward.
So go back into “power calc”, (or whatever powerint call it), and do a design for 28vout and 1.4a out, and solder that circuitry in and then go from there….it will probably give you a tl431 circuit.

I woudl put your bjt based soft starter and current (amps) regulator circuit into ltspice and check it out in there.

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Also, is your c14 too big?......what is its value....what does your control pin voltage look like...is it rising up quick enough?......if not then youre into max peak current threshold territory

Hi
C14 is 100nF recommend by the PI

I would like to understand the soft start circuit at output and how it work..
I boxed soft start circuit in the pdf attached but you are talking for the Q3,Q2 and Q4 are there for the cc functions if you read the application note of PI

Also your point is good if Q3 gets turn on at the start up does it mean like PI application is wrong and we have to report to the POwer integration's...

Regards
Marx

well, if Q3 is hard on and the soft start cap is fully charged up, then theres nothing to "brake" the smps except the overvoltage circuit.
I think the bjt stuff needs simulating to verify.
I am surprised they do current regulation like that as it is inaccurate and relies on the vbe of a bjt...there are cheap currrent monitors that you can use instead

Ohk..
Can I know how to proceed ahead
All of manufacturing boards are ready