bridge rectifier and fuse blows when powered up

[electrophysics]

Hi. I'm making a circuit for switching supply. first of all I thought to test its input section which consists of emi filters and bridge rectifier. when I give power to it, the fuse blows up due to short circuit that is created of one ac pin to -ve output pin of bridge rectifier. how to resolve this issue? when I look at wiring all things look ok. the circuit diagram is attached.

 

[barry]

Is it a very-fast-blow fuse? Maybe the input capacitor surge is causing the failure. Try a slow-blow fuse just for testing. And did you actually measure a short from ac to bridge output with an ohmmeter?

 

[electrophysics]

As you can see no load is connected to 100uF capacitor. If I increase the fuse from 2A to 3A then still it blows. and at the same time bridge rectifier shows short between its one ac pin and -ve pin.

 

[barry]

Then you've got a blown diode in your bridge.

 

[kak111]

Have you checked that the input grounding and dc grounding is not connected together.
Neutral supply wire in power grid is in earth potential.

 

[mrarslanahmed]

the fuse blows up due to short circuit that is created of one ac pin to -ve output pin of bridge rectifier. .

i dont think fuse blow due to this reason.....

may be you need some resistance in series with c1 but i am not sure about that...

 

[betwixt]

I'm with kak111 on this. It looks like you have the chassis ground and AC input grounds connected. As there is no isolation on the AC lines, you are connecting the bottom right diode in the bridge directly across the 230V. Please check there is no resistance betwen the negative side of C5 and pin 2 of J1.

Brian.

 

[FvM]

The other explanation would be a defective rectifier. Unfortunately your description is somewhat cryptic:

and at the same time bridge rectifier shows short between its one ac pin and -ve pin.

What means "at the same time". Either there's a short in the rectifier, then it's permanently and easily detectable with an ohmeter. Or an insulation fault in your wiring. Or an external short like the said grounding problem.

A healthy rectifier shows by presence of all four diode forward voltages in an ohmmeter test.

 

[Tipu606]

remove C2 and C4, especially the junction connection to "earth"
Then check the bridge rectifier diodes
Now hopefully the fuse should not blow

 

[electrophysics]

I have checked the wiring thoroughly but no fault was seen. The only thing come in mind is whether the bridge is not capable of handling starting surge (although NTC is limiting the current) or there is something wrong with common mode choke.

 

[electrophysics]

it was bridge rectifier which was faulty. I replaced it with another bridge rectifier which is lower in voltage (600V) and lower in current (4A) and is working fine now. the new bridge no. is PBL405. i'm astonished of the behavior of previous bridge rectifier as I had properly tested it before inserting in board.

 

[milind.a.kulkarni]

First off all check the diodes ....there meight be short circuit in diode even.....just check one of the diode may be faulty even.....

Good Luck