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

Thread Starter

Radoi

Joined May 3, 2010
3

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 ? "
-load resistance = 100 Ω.
- 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 ??




 

Bychon

Joined Mar 12, 2010
469
√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.
 

Ron H

Joined Apr 14, 2005
7,014
√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.
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.
 

Bychon

Joined Mar 12, 2010
469
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.
 

t_n_k

Joined Mar 6, 2009
5,447
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?
 

Bychon

Joined Mar 12, 2010
469
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.
 

t_n_k

Joined Mar 6, 2009
5,447
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.
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.
 
AAAAHHHHAAAA!!!!
Has to do with RMS value
I was looking for an equation to find out how much capacitance in needed in my supply
the radical2 comes from frinding rms values Vpp/rad2=Vrms
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
 
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