# Ripple Voltage

#### david mendes

Joined Mar 23, 2006
6
Hello
Does anyone know how to calculate the Ripple Voltage on a half-wave rectifier circuit and on a full-wave?
I found the following formulas but when I compare them with what I get on the oscilloscope, the difference is huge!

Ripple (half-wave)= 4,5 x I(mA)/C( μ F)

Ripple (full-wave)= 1,7 x I(mA)/C( μ F)

Cheers

David Mendes

#### Papabravo

Joined Feb 24, 2006
21,022
Originally posted by david mendes@Mar 23 2006, 02:03 PM
Hello
Does anyone know how to calculate the Ripple Voltage on a half-wave rectifier circuit and on a full-wave?
I found the following formulas but when I compare them with what I get on the oscilloscope, the difference is huge!

Ripple (half-wave)= 4,5 x I(mA)/C( μ F)

Ripple (full-wave)= 1,7 x I(mA)/C( μ F)

Cheers

David Mendes
[post=15349]Quoted post[/post]​
The problem could be the constant or it could be the units that you are mixing. That is mA and uF. The approximations are derived from the following equation
Rich (BB code):
dV/dT = - I/C

where

dV/dT is the voltage sag from one rectified peak to the next. dT will be 8.33 milliseconds for the full wave case and 16.67 milliseconds for the half wave case.

I is the current in Amperes

C is the capacitence in Farads.

In a less tha rigorous fashion this leads to

dV = dT*(I/C)
So using 0.00833 or 0.01667 for dT and I in amperes and C in Farads do you get more consistent results?

#### david mendes

Joined Mar 23, 2006
6
>So using 0.00833 or 0.01667 for dT and I in amperes and C in Farads do you get more consistent results?

Where do the 8.33msec and the 16.67 msec come from?

Cheers
david

#### Papabravo

Joined Feb 24, 2006
21,022
Originally posted by david mendes@Mar 28 2006, 08:43 AM
>So using 0.00833 or 0.01667 for dT and I in amperes and C in Farads do you get more consistent results?

Where do the 8.33msec and the 16.67 msec come from?

Cheers
david
[post=15522]Quoted post[/post]​
8.33 msec is the time from one peak to the next peak of a full wave rectified 60 Hz. sine wave, and 16.67 msec is the time from one peak to the next peak of a half wave rectified 60 Hz. sine wave.

Naturally if you are outside North America your sine waves will be 50 Hz. and not 60 Hz., and if you are on an airplane they will be 400 Hz.

Joined Oct 26, 2008
2
PapaBravo, is the 'I' in that equation based on the RMS voltage or the peak voltage? Is the 'I', Irms or Ipeak?

#### Papabravo

Joined Feb 24, 2006
21,022
In a somewhat ironic fashion for a thread which died 2 1/2 years ago it is neither. It is instantaneous.