# 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.

2. ### bertus Administrator

Apr 5, 2008
18,512
3,570
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
293
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?

Apr 5, 2008
18,512
3,570