# Calculate Capacitance

Discussion in 'General Electronics Chat' started by wkumtrider, Jun 3, 2009.

1. ### wkumtrider Thread Starter Member

Jun 3, 2009
14
0
Hello,

I'm new here. I am designing a simple circuit to run 6 LEDs off AC current (110 - 120V, 60hz). The LEDs have a Vf of 3.3 and 30ma. I want to use a capacitor to limit the voltage to the LEDS. How do I calculate the size of capacitor I need? I have seen the formula C=1/(2*pi*f*X). Is X the resistance needed in the circuit? So I just find out what resistance I need using R=V/I, plug that in for X, and solve for C?

Thanks for the help.

Apr 5, 2008
15,798
2,384
Hello,

Using leds directly on the mains can be unsafe.
The mains power can be leathal.

Greetings,
Bertus

3. ### wkumtrider Thread Starter Member

Jun 3, 2009
14
0
I am actually going to use them in a lamp.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Use a step down transformer. No circuit running off the line can be made safe - it always presents a lethal shock hazard.

5. ### wkumtrider Thread Starter Member

Jun 3, 2009
14
0
Ok, I'll look into a transformer. Thanks for the info.

However just for my knowledge, is the formula I asked about in my first post correct?