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Resistor in parallel with inductor on mains input to SMPS.

Robotnik

Mar 12, 2016
3
Joined
Mar 12, 2016
Messages
3
Hi
My first post here, hello all.
I have a burnt out resistor on the mains input to a small low power switch mode supply which powers the microprocessor board on a dehumidifier.

The resistor it totally burnt out, open circuit, value unknown.

I've searched online for the circuit, but nothing found, it is a 'Silvercrest SLE420-A1 Dehumidifier', resistor R5.

The resistor in question is right on the mains input of the circuit between the mains fuse and the bridge rectifier and in parallel with an 1100uH inductor, the resistor is in line with the live mains and all current used by the SMPS must pass through this component.

I've looked at some smps circuits online to get an idea of what sort of value to try but all the circuits I have found don't have anything except a fuse and a thyrstor before the mains rectification.

I feel it must be part some sort of filter along with the inductor and is probably fairly low value, about 10 ohm or less but I don't know much about switching power supplies, any clues folks?
Thanks
Neil
 

Anon_LG

Jun 24, 2014
453
Joined
Jun 24, 2014
Messages
453
When attempting to identify damaged components, a picture is the most helpful source. Please provide a clear, focussed, well lit image with the circuit board aligned with the camera. Please also provide a closer image of the area around the damaged component.

Thank you,
 

BitHead

Mar 2, 2012
34
Joined
Mar 2, 2012
Messages
34
Hi. I see the inductive reactance of that choke coil is about .4 ohms at 60Hz. I usually add that to the coil wire resistance and make my snubber resistor = x5 that - so 10 ohms would be the ballpark. But, there is some reason why so much current took that fork in the road - I usually find a micro-crack at the perimeter of a a solder pad. The coil wire is usually OK but check it first. Good luck!
 

Robotnik

Mar 12, 2016
3
Joined
Mar 12, 2016
Messages
3
Hi Bithead, thanks for the reply.
I've made a bit of a mistake, I fell into the trap of expecting a low resistance so that is what I looked for but on taking another look at it, it does actually measure 1.3megohms, it's black and burned but it's not open circuit.
The inductor is open circuit though.
By the way it's 50Hz where I live. :)
Thanks
Neil
 
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