caps in line

[Volter]

If there is a cap, 470uF, 200V, in line where 117V is coming into the power supply, what is it there for?
Thanks.

[Janitor Tzap]

If there is a cap, 470uF, 200V, in line where 117V is coming into the power supply, what is it there for?
Thanks.

Are you sure that it is on the 117Vac line?
Or is it just after the rectifier diodes?

If it is after the rectifier diodes.
Then it is acting as a filter to smooth out the DC for very little ripple going to the rest of the circuit.

Plus....
What is this Capacitor in?

Normally, a AC type Capacitor will be with a choke coil, or transformer.
To form a EMI, or RFI Filter before going to a dropping transformer, or rectifier.

If this is off of an AC Motor.
Then it could be a Start-up Capacitor.
But 470uf would be a rather high value for that.

Need more information please.


Signed: Janitor Tzap

[Volter]

It is a computer power supply and there are chokes and voltage regulators and a transformer but the cap negative is connected to 117V wire line and then there are a couple of diodes. The main rectification is after a transformer. I'll unsolder some of the parts and see the values of the regulators.

[Bigglez]

If there is a cap, 470uF, 200V, in line where 117V is coming into the power supply, what is it there for?

All AC to DC circuits use capacitors to store energy, usually to
reduce the ripple present in the DC output.

If you trace more of the circuit you may discover this is part
of a voltage doubler, typically used to give the circuit 'universal'
inputs that cover 100 - 240V AC for worldwide deployment.

Try to avoid personal injury or property damage. Directly connected
to the AC line circuits are hazardous and require additional caution
for safety.

[sofaspud]

I'll WAG it and say you'll find +/-5V and +/-12V and possibly even +3.3V regulators.
The capacitor is there to provide input filtering of the line voltage. Don't confuse
a switched-mode topology with a linear supply topology, even though at
some level they may share design concepts.