Problem with secondary side of the LLC converter - 200W AC-DC power supply

Thread Starter

Piotar.M

Joined Feb 19, 2019
3
Hello everyone,

I am designing a AC-DC (200W) power supply.
I was trying to figuring out, that everything is working properly, but instantly everything drops down.
The issue is that, when I powered the schemе, NMOS transistors on the secondary side of LLC converter got shorted. They are rated for 40V/21A, so they should handle with max output consumption (14.4V/13.8A). Other way is to generate so high voltage on gate, but they are +-20V, so it also should be Ok.
So, how can I understand and solve this issue? Can anyone help?

Regards,
Petar
AC_DC_Power.JPG
 

Alec_t

Joined Sep 17, 2013
10,354
Welcome to AAC!
Isn't the diode across the regulator the wrong way round?
 

Thread Starter

Piotar.M

Joined Feb 19, 2019
3
Welcome to AAC!
Isn't the diode across the regulator the wrong way round?
Hello Alec,

Do you mean the D800 diode? I think, that it is the right way.
During start-up, diode D800 provides an inrush current path to the output capacitor C802,
bypassing the switching inductor L803 and PFS device U800 in order to prevent a resonant
interaction between the switching inductor and output capacitor
 

Thread Starter

Piotar.M

Joined Feb 19, 2019
3
The diode D800 is on the top of the scheme above.
About the input voltage, it should handle with 85~250. For the test, I am using 220V/50Hz
 
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