Solving Voltage Ripple Formula: Get the Right Answer!

In summary, Rafeng404 has a problem with the formula for voltage ripple peak to peak, and has attempted to solve it without success.
  • #1
Rafeng404
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Poster has been reminded to use the Homework Help Template when starting threads in the schoolwork forums
Hi lads,

Working through my HND course books and I have come across a formula that I cannot get to give me the same answer as the book. Nor can some of my engineering student friends.

Values are:

F=50
C=500^-6
Rl = 100
Vc=31.03

The formula is

=(1/(2FsCRl))*(Vc-(Vr/2))

Inputting the values to make it look clearer it becomes

= (1/5)*(41.03-(Vr/2))

Solve for Vr.

My attempt:

=0.2(41.03-(Vr/2))
=8.206 * 0.1Vr
Vr= 8.206/0.1
Vr = 82.06

Clearly we have missed something stupid here and transposed it wrong. I am a bit rusty but I have lent my maths bible to someone else.

The right answer according to the uni is 7.46.

Have I completely forgotten how to do maths?

Thanks in advance
 
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  • #2
Rafeng404 said:
Hi lads,

Working through my HND course books and I have come across a formula that I cannot get to give me the same answer as the book. Nor can some of my engineering student friends.

Values are:

F=50
C=500^-6
Rl = 100
Vc=31.03

The formula is

=(1/(2FsCRl))*(Vc-(Vr/2))

Inputting the values to make it look clearer it becomes

= (1/5)*(41.03-(Vr/2))

Solve for Vr.

My attempt:

=0.2(41.03-(Vr/2))
=8.206 * 0.1Vr
Vr= 8.206/0.1
Vr = 82.06

Clearly we have missed something stupid here and transposed it wrong. I am a bit rusty but I have lent my maths bible to someone else.

The right answer according to the uni is 7.46.

Have I completely forgotten how to do maths?

Thanks in advance
Hello @Rafeng404,

It would greatly help if you clarified a few things:

  • Your values for F, C, Rl, and Vc don't have any units. I can assume that they're all in SI units, but it's good to specify.
  • In your formula, "=(1/(2FsCRl))*(Vc-(Vr/2))", there's nothing on the left hand side of the equation. What is all that equal to? You can't solve for Vr with nothing on the left-hand-side. It doesn't make any sense unless it is equal to something.
  • Where did this formula come from? Was it given to you like that or did you derive it in an intermediate step?
  • In my experience with these types of problems, I would expect there to be a [itex] \pi [/itex] in your formula, usually between the 2 and the [itex] F_s [/itex]. I find it curious that it's not present. Do you have any comments on this?
  • When specifying your constants, you stated that Vc = 31.03. But when plugging it into your formula it became 41.03. I don't know what to make of that.
  • In your attempted solution, I'm not sure how you solved for Vr since there was nothing originally on the left-hand-side of the equation. This goes back to an earlier bullet.
 
  • #3
It is difficult to understand the formula. Usually s is the operational parameter but then you don't need F. If s=pi then the parameters are in complex Xc=-j1/(2*pi()*F*C). If the formula represents the current in a [mesh?] circuit the circuit diagram could be useful in order to solve the problem.
 
  • #4
Lads,

Apologies, perhaps I should not have done this on my phone after a back shift.

1. F= frequency, C= capacitance, Rl = Load resistance, Vc = Peak voltage across capacitor, Vr = voltage ripple peak to peak.
2. The formula is for Vr ( see attached)
3. The formula is in our books, you need to transpose to get Vr (see attached)
4. I agree, normally I would expect to see Pi in a formula like this, perhaps this is where the uni has buggered up??
5. Vc is 41.03, the 31.01 is a typo

Hope this helps, Vr is what I am looking for.

I am sure there is something obvious that I am missing but I cannot seem to make it work for 7.46Volts.

Many thanks

upload_2017-8-31_7-25-41.png
 
Last edited:
  • #5
Rafeng404 said:
My attempt:

Vr = 0.2(41.03 - (Vr/2))
.....⤴
=8.206 * 0.1Vr
Try simplifying that again, moving all Vr terms to the left side.
 
  • #6
"ALL Vr terms" head slap! Bloody hell! cheers mate i realize what I haven't been doing now. I have been negating the first Vr term. I am such a spanner sometimes.

Thank you all.
 

1. What is voltage ripple?

Voltage ripple is the fluctuation in voltage that occurs in an electrical circuit. It is caused by the switching on and off of components, such as diodes and transistors, and can result in unwanted noise and interference.

2. Why is it important to solve for voltage ripple?

Solving for voltage ripple is important because it allows us to understand and minimize the impact of voltage fluctuations on our electrical circuits. This is especially important in sensitive electronic devices, where even small changes in voltage can cause malfunctions or damage.

3. How do you calculate voltage ripple?

The formula for calculating voltage ripple is VR = I/(2*f*C), where VR is the voltage ripple, I is the current, f is the frequency, and C is the capacitance. This formula takes into account the key factors that contribute to voltage ripple and provides an accurate estimate of the fluctuation.

4. What is the right answer for solving voltage ripple formula?

The right answer for solving voltage ripple formula is a value for VR in units of volts. This value represents the maximum fluctuation in voltage that can be expected in the circuit.

5. What are some ways to reduce voltage ripple?

There are several ways to reduce voltage ripple, including using a higher quality power supply, adding additional filtering components such as capacitors or inductors, and minimizing the load on the circuit. Proper design and layout of the circuit can also help to reduce voltage ripple.

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