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Top-Switch SMPS is stopping after 5 sec

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Gomez

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i have built power supply alike from
**broken link removed** page 23.
The SMPS works fine, but after 5sec with a power of 100W
the P6KE200 is defective. The next greater (P1.5KE600) only
works 10sec.
The leakage inductance from my transformer is 3uH.

What can i do??

Gomez
 

purpose of p6ke200 in power supply

hi,do you parallel two 68K 2W resistor and the 4.7nf capacitor?maybe you need two 68k or 56k 5w resistor and a 4.7nf or just a 10nf capacitor!
maybe your transformer is not so good,for example,the leakage inductence can not extend 2% of primary inductance.if so ,try to reduce the leakage inductence.
hope it can be useful.
 

topswitch problem

Try to split the primary winding. The power of your SMPS is not low (for a flyback topology), so the influence of the leakage inductance is important. It is not enough to use only a transil without a clamp RCD snubber, at this power, because the energy stored in the leakage inductance is important.
 

topswitcher smps

OK. I have reduce the soft clamp R (2 x 10K) and the SMPS works fine.

I have a another problem.

I have make a short circuit :-(( in primary side and now the top switch goes to fail save if i make power up.

Only if i make power up slowly (transformer with regulation) the top switch is running.

Gomez
 

clamp smps

Gomez

Difficult to say what has been damaged.
Maybe optocoupler, start-up capacitor or TOP itself.
Have you tried to replace P1.5KE200 ? Often this is the problem.

Maybe the P1.5KE200, though you have used snubber resistors, got still very hot before you made short. Value of 10K//10K you have used sounds quite low. This could says that you have not solved the main problem; the primary leakage inductance.

3uH seems good over, let say, 250/350uH of primary inductance, however have you measured output trace inductance ?

Trace inductance will have big impact over primary leakage, as it increases the secondary inductance and secondary inductance will be transferred to primary multiplied by the square of tourns ratio.

For instance, if primary wounds are 40 tourns and secondary are 4 tourns (low voltage output) the ratio is N=10. Should the trace + secondary indunctance be equal to 50nH, (i.e. long tracks of your PCB), you will have 5uH of additional leakage on primary.

As MADURAN said, energy stored with this power is terrific bigger. So, though before you made the short your SMPS seemed working, it doesn't means it works nice.

When fixed the fault I suggest:

1) split primary. about 50% reduction of primary leakage.
2) get measured the trace inductance in your application.
3) use snubbers resistor and
4) get monitored the temperature over clamp's body. Temperatures greather then 100°C will not allow for any safety margin.
5) split P1.5KE200 in two P1.5KE100 in series. It works, and helps to reduce a lot the temperature over the clamp.
6) use multi-wounds technique to reduce loss in copper. It doesn't matter if you have used wire greather then 0.4mm. The skin effect at 100-130kHz will reduce useful sectional area.
 

topswitch smps

the solution is to use low esr caps allround

you will find you use normal 85 or 105 types
these are no good

8)

forinstance c9 c10 c11 in parrallel
wont like high esr type

and will be a higher reluctance value
{lots slower}
 

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