# Capacitor voltage rating with rectifier

Discussion in 'General Electronics Chat' started by mendiola_loyola, Nov 12, 2010.

1. ### mendiola_loyola Thread Starter New Member

Sep 18, 2010
16
0
Dear All:

I'm rectifying a 12V rms AC voltage using a diode bridge.

I want to know how to calculate the capacitor voltage rating.

Do I have to multiply 12 * 1.5 or 12*2 ?

Thanks.
Alfredo Mendiola Loyola
Lima, Perú

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
The multiplier to go from RMS to peak is 1.404. The voltage on the caps will be a bit less, due to the conduction drops across the diodes. For a good safety margin, use a capacitor voltage rating of about double the calculated voltage.

So, 12 VRMS * 1.404 = 16.85 VDC. Use a capacitor rated for 35 volts.

3. ### mendiola_loyola Thread Starter New Member

Sep 18, 2010
16
0
Thank you for your Help

Alfredo Mendiola Loyola
Lima, Perú

4. ### BillB3857 Senior Member

Feb 28, 2009
2,400
348

Hey Beenthere,

When did they change the value of the square root of two? I missed it. How do I update the programming on my TI calculator?

Just kidding of course. My fat fingers frequently get me, too. At least yours are consistent.

5. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Wow, I've been dropping the 1 out of the value for years. For the record, it's 1.4142136 on my TI.

Let's see, that's 16.97 volts.

6. ### BillB3857 Senior Member

Feb 28, 2009
2,400
348
Olde age tends to let us lock in pre-conceived notions. From your avitar, I can only guess tht I have a couple of years head start on you.