I need your help in one SMPS problem

[MohamedRagab]

Hi gents
I need your help in one SMPS problem
It is rectifier module supply 48V/50A for telecom equipment and the issue as below:

when I powered on the SMPS there is a 48V for seconds then output decreases gradually till reach Zero.

I isolate the switching transformer and run the voltage test method all the primary volts are OK and when connect the transformer problem happen again, which part suspected to be faulty

The PWM IC is UCC3895DW
The Off-Line SMPS Current Mode Controller is 2A280Z
The shottcky diode is V30200C
The optoisolator is A6N137

 

[treez]

overload on output?

 

[chuckey]

Seconds? Eh, not a catastrophic voltage over load then? Some sneak leakage/discharge path? does anything get warm/ hot?
Frank

 

[c_mitra]

when I powered on the SMPS there is a 48V for seconds then output decreases gradually till reach Zero.

Check:

1. What is the load (if connected)
2. What is the output filter cap (value)
3. Can you estimate the voltage decay time constant?
4. Does it work without load?

 

[MohamedRagab]

hi
1-load not connected (load is 50A/48V DC) and module power is 3000W
2- output filter cap is 63V/470MF
3- the estimated decay time for volt to reach Zero is 4Sec
4- no it doesn't work without load

 

[max.wangxin.sh]

1) you can connect a small load for example, 48ohm and then try to start the SMPS.
2) Check the start process if the output voltage would reach your setting.
3) run some time if the output voltage would be stable at your setting and check if there is any component hot.
4) increase your load slowly and check if there is any component hot.
5) Monitor the current signal of the primary winding and check if there is any over current.

good luck.

 

[c_mitra]

Perhaps something is getting overheated and shutting down the SMPS? In particular, does it work with reduced load?