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Capacitor sudden discharge time when output gets shorted

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Bjtpower

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Hello Guys,

i am trying to calculating the Fuse value when output gets short in abnormal conditions.

The attached files is off the Power integrations secondary side.

Simulations file is also attached with the same.


I am unable to do the simulations.

Can anyone let me know how to calculate the sudden current vs time accordingly choose the fuse rating only for the +27V supple denoted by +27v_CGL
capacitor timing.PNG

Regard,
Marx
 

I fear, I don't understand the purpose of the simulation setup. You need to specify a switch model to make the simulation run, everything explained in the Ltspice help.

Short circuit current and current waveform depends on capacitor ESR, short resistance, circuit series elements (e.g. wires, inductors, whatsoever). It's easy to simulate if you know the parameters.

Choose fuse rating to achieve what?
 

Hello Bjtpower,
First you need to determine the maximum current draw of your circuit, loaded and unloaded.
Lets say it draws a maximum of 1.65A, then you choose the next amperage up which would
be 2A. Thus use a 2Amp Fast-Blow type, NOT slow-blow for secondary circuits.
You should be able to get a datasheet on a 2Amp fast-blow, glass type, solid state type or
other. You will find the fuse blow over time Vs current increase.
Regards,
Relayer
 
I agree with the above, however fast blow fuses can be annoying things, for a 2A load we would normally specify a 4A fase blow fuse, under short ckt conditions - as you said in your post - it will blow fast enough, and at 4A will avoid nuisance tripping if the load is 2A for long periods .....
 
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