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Calculating the ripple factor from oscilloscope

by shyta
Tags: factor, oscilloscope, ripple
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shyta
#1
Sep8-11, 07:35 AM
P: 56
Hello fellow physicists!

I have a lab about rectifying and filtering circuits and I was asked to calculated the ripple factor using an oscilloscope.

I managed to get the ripple waveform shown on the oscilloscope, but the thing is there are so many values to read off I have no idea which to use/take.

I know the ripple factor is given by the ratio of V_ac over V_dc

where V_ac is the rms of 1/2 the Vpp of the ripple waveform (am I correct here to get the Vpp and multiply this by 1/2*1/sqrt(3)) i.e. sqrt3 since this is a sawtooth waveform

and V_dc should be given by what? v_rms v_avg.. there are so many values to choose from the oscilloscope I do not know what to do!
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shyta
#2
Sep8-11, 07:16 PM
P: 56
Hi anyone? :(
berkeman
#3
Sep8-11, 07:23 PM
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berkeman's Avatar
P: 41,299
Quote Quote by shyta View Post
Hello fellow physicists!

I have a lab about rectifying and filtering circuits and I was asked to calculated the ripple factor using an oscilloscope.

I managed to get the ripple waveform shown on the oscilloscope, but the thing is there are so many values to read off I have no idea which to use/take.

I know the ripple factor is given by the ratio of V_ac over V_dc

where V_ac is the rms of 1/2 the Vpp of the ripple waveform (am I correct here to get the Vpp and multiply this by 1/2*1/sqrt(3)) i.e. sqrt3 since this is a sawtooth waveform

and V_dc should be given by what? v_rms v_avg.. there are so many values to choose from the oscilloscope I do not know what to do!
Can you post a screenshot of the oscilloscope waveform? Or maybe post a representative sketch?

I generally deal with Vpp in ripple calculations, but if your book says to use the RMS value for the "ripple factor", then go ahead and do that. I'm not sure what the Vrms is for a sawtooth wave, but you could find it online somewhere, or just calculate it with an integral.

As for the DC value, that will be the average value if the sawtooth amplitude were reduced to zero. Can you see what the average (mean) value of the sawtooth is?

shyta
#4
Sep9-11, 12:02 AM
P: 56
Calculating the ripple factor from oscilloscope

Hi berkerman. Thanks for the reply. I could possibly go find a ripple diagram when i get back home.

For the Vac do you mean that you just take it as Vpp. Meaning the ripple factor is given by Vpp/Vavg?
berkeman
#5
Sep9-11, 11:24 AM
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Quote Quote by shyta View Post
Hi berkerman. Thanks for the reply. I could possibly go find a ripple diagram when i get back home.

For the Vac do you mean that you just take it as Vpp. Meaning the ripple factor is given by Vpp/Vavg?
I typically work with the value of the ripple in Vpp (and don't ratio the ripple to the Vavge value), and haven't used a "ripple factor", so I don't know the definition of that term. You should use whatever is defined in your textbook or lecture notes.


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