# How I can determine ripple voltage in full wave rectifier circuit ?

Discussion in 'General Electronics Chat' started by Radoi, Jun 3, 2010.

May 3, 2010
3
0

hi guys

I have problem when I wanted design DC power supply
( I used
center tap full wave rectifier with smooth capacitor and zener diode )

that problem is how I can determine
ripple voltage to find capacitor value ?

I have following values

- output voltage = 4.7 V

- input voltage from transformer = 9 V . " Is it peak or RMS value ? "
- frequency = 60 Hz .

I asked my friend , he told me you can assume it (
ripple voltage )
but how I can assume it ?? is there certain range for assumption ??

2. ### Bychon Member

Mar 12, 2010
469
41
√2 C Er F = I

The square root of 2 times the capacitance times the Ripple voltage (peak to peak) times the frequency equals the load current.

and the frequency is 120 for a full wave rectifier.

3. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Where did the √2 come from? A conservative estimate for ripple voltage of a full wave rectifier is

Vr=I/(2*F*C)

where F is the input frequency. The "2" comes from the frequency doubling of the full wave rectifier. The calculated ripple will be very close to the actual value when the ripple voltage is a small percentage of the peak input voltage. As the ripple percentage increases, the equation becomes less accurate, but the ripple will always be less than the value predicted by the equation.
BTW, this assumes that the input is a sine wave.

4. ### Bychon Member

Mar 12, 2010
469
41
Sorry, radical2 CErF=I isn't a conservative estimate. I don't know where I picked that equasion up, but it produces results that match my measurements of real parts that are actually working.

5. ### Bychon Member

Mar 12, 2010
469
41
Voltage Regulator Handbook
National Semiconductor Corporation
1982
Page 8-6
Paragraph 8.2
Line 4

6. ### kingdano Member

Apr 14, 2010
377
19
what would those guys know anyways?

7. ### Bychon Member

Mar 12, 2010
469
41
LOL! It might not be pretty, but it's functional.

8. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
I'm not sure the contributions thus far will fully answer the OP's question or lead them to think about the problem more broadly.

They are considering the design of a centre-tapped transformer, full-wave rectifier with zener regulated output. The question seems to centre on choosing a suitable rectifier filter capacitance. So what are the considerations in making an informed choice?

It's not clear whether the OP's problem is with the observed ripple on the output [at 4.7V DC] or the ripple on the rectifier section output. Do they have to meet a maximum allowable load ripple condition?

9. ### Bychon Member

Mar 12, 2010
469
41
Perhaps you can ask the O.P.

As for me, I've been wondering if "drive by questioning" is a familiar phrase in these forums.

10. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
I get your drift. I guess that's the nature of the 'game' we play.

We would possibly get bored if it were otherwise ..... and a bit of friendly banter is part of the fun of being here.

11. ### Bychon Member

Mar 12, 2010
469
41
Banter away my friend!

May 3, 2010
3
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Thanks my friends
I solved my problem ..

13. ### Hell_Bent_On_Sumthing New Member

Sep 2, 2014
1
1
AAAAHHHHAAAA!!!!
Has to do with RMS value
I was looking for an equation to find out how much capacitance in needed in my supply
Why one is an approximation and the other is exact math

ps. this thread has also enlightened me that keeping I and C the same, you get the same Vr regardless of the voltage