# Ripple voltage calculation

Discussion in 'General Electronics Chat' started by RRITESH KAKKAR, Aug 28, 2010.

1. ### RRITESH KAKKAR Thread Starter Senior Member

Jun 29, 2010
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How To Calculate Ripple voltage of Full Wave Brige rectifier Without Connecting CRO..........?

2. ### gootee Senior Member

Apr 24, 2007
447
50
Right here:

http://www.zen22142.zen.co.uk/Design/dcpsu.htm

Note that it is also a function of load current.

It is useful to calculate the ripple voltage waveform's parameters when you wish to add a regulator, so that you can make sure that the troughs/valleys/minima of the ripple voltage waveform will never excite the regulator's dropout region, i.e. so that the regulator's Vin-Vout is never less than its dropout voltage specification, where the minimum Vin is the ripple voltage waveform's minimum voltage. So don't only wory about the ripple voltage waveform's relative amplitude. Also calculate it's DC (average) level and its maximum and minimum as absolute voltage levels.

Note that you would need to use worst-case AC Mains variation for that ("voltage regulator vs ripple" calculations), or at least 10% low AC Mains voltage if you don't have actual data for it. You can also take transformer regulation into account, which usually helps mitigate things a little (i.e. raising Vin to slightly higher than expected), or you can leave it out and have a little extra safety margin.

Last edited: Aug 28, 2010
3. ### RRITESH KAKKAR Thread Starter Senior Member

Jun 29, 2010
2,831
89
As I am Calculating Ripple Factor for rectifier for It capictor is To be Connected Of XYZ value From formula c=(.47* I)/fRf
For this Rf to be calculated How.........!

4. ### gootee Senior Member

Apr 24, 2007
447
50

Rf = (0.47 * I)/fC ?

Your "Rf" equation looks very close to the delta_V equation shown at the link I gave, differing only by your 0.47 versus the 0.50 in the equation at the link, i.e. Delta_V = I / (2fC) gives C = (0.50 * I) / (f * delta_V).

delta_V is the peak-to-peak ripple voltage.

They do say that their equation is "approximate".

5. ### RRITESH KAKKAR Thread Starter Senior Member

Jun 29, 2010
2,831
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Pls tell Clearly I am not Getting, How to find delta_V with Multimeter...............?

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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It would be very difficult to measure the peak-to-peak ripple voltage with only a multimeter.

A rough estimate of the RMS ripple voltage could be obtained by connecting a multimeter [on a low AC voltage range] to the rectifier output with a series non-polarized capacitor interposed in one of the measuring leads. The series capacitor would block the rectifier DC output and pass only AC voltage to the meter. The series capacitive reactance would have to be much lower than the meter measuring resistance. For example, a 1uF capacitor has ~1.3kΩ reactance at 120Hz (the ripple frequency at 60Hz supply). So 1uF would be a reasonable series capacitor value for a meter with a >1MΩ input resistance.

The meter would also have to be able to measure quite small AC voltages - particularly if you have a DC capacitive filter at the rectifier output.

In addition when using a capacitive filter you have to have some load applied to the rectifier - otherwise the filter capacitor would charge to the AC peak voltage and there would be very little ripple - if any.

A typical multimeter is calibrated to read the RMS value of a true sine wave. Given the ripple voltage is not sinusoidal you would have to take any measured value obtained as an approximation.

Warning: Presumably you are intending to do something like this on a low voltage transformer isolated rectifier - doing such measurements with a high voltage rectifier (e.g. direct to the AC mains) could be dangerous with the risk of electrocution.

7. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
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If it's a very high ripple voltage you can isolate the DC component out of the equation and read the resulting AC component however most ripple current isn't at simple line frequency where a common multimeter would respond - most ripple current in modern electronics is a combination of many frequencies and waveforms. The only valid way of making this measurement is with a digital oscilloscope and understanding all the underlying math involved.

During the first year of college you'll eventually learn about simple line current ripple voltage as you get through the fundamentals of AC & DC circuits, the more complex components of it won't come until much later.

There's a reason electronics is taught in a very precise order just as every other subject such as nursing or accounting is taught. One has to learn how to crawl before they can walk. You weren't born then started riding bicycles two days later, did you?

8. ### RRITESH KAKKAR Thread Starter Senior Member

Jun 29, 2010
2,831
89
Ok, Pls Tell Me studying electronic with Other subject Is Important......!

9. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Yes - mathematics.

10. ### tom66 Senior Member

May 9, 2009
2,613
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Also, I highly recommend physics, so you have some background on how semiconductors work and why electrons go the "wrong way".

Without a digital oscilloscope or a true RMS AC+DC multimeter you cannot measure ripple voltage.

11. ### gootee Senior Member

Apr 24, 2007
447
50
ANALOG oscilloscopes work just fine, too!

But I thought you wanted to CALCULATE the ripple voltage parameters.

Also note that even if you could measure the ripple voltage waveform's "true RMS" value with a meter and then calculate its peak-to-peak value, or, directly meaure its peak-to-peak value with an oscilloscope, each measurement would be for only one magnitude of DC load current. But the equation that was given provides the ripple waveform's peak-to-peak voltage for _ANY_ load current, and any line frequency and smoothing capacitance value.

12. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
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Now consider that this comes after you've been through all the basics during the first two years such as english, basic physics, chemistry, math, history, government etc etc:

http://www.ece.okstate.edu/courses.php?action=view&itemID=1
Experimental Methods I :: 2011
Course Description
Basic electrical measurements and instrumentation techniques and devices. Use of voltmeters, ammeters, oscilloscopes, impedance bridges to study resistive, inductive, and capacitive circuit elements in steady state and transient operation. Reinforces ENSC 2613 and introduces design of instrumentation networks. Serves as introduction for nonmajors.
Pre-Requisites Co-Requisites
PHYS 2114 ENSC 2613

That is just your beginning, from there you go on to the 3000 and 4000 level courses just to obtain a bachelor's degree:
http://www.ece.okstate.edu/courses.php

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13. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
There must be some other courses listed under other engineering areas, I dont see one specific course listed I had a real love/hate relationship with - Thermodynamics.

It wasn't so bad learning about heat, energy & work relationships even when steam locomotives might be an examle, but the textbook presented every example and problem in a mix of units. Some were SI, some completely outdated, some older but still currently accepted etc and I mean in everything from pressures, units of force and even in to lengths. Half your time was spent getting the problem into compatible units before you could solve it.

4 credit hour course, learned a lot of stuff I've never used but couldn't do without it today when I'm trying to properly size a heat sink to a component.

Some other notes - the last digit of a course number was the amount of credit hours that course would be worthtowards your degree when successfully completed, it's also ususally the number of hours you attended that class every week. This can be deceptive though, I remember one course that required 5 hours of attendance per week just to get 2 hours of credit.

A typical BA takes 120 or more hours to graduate and that's if you stick exactly to the plan which I never did. At an average of 15 - 17 hours per semester with 2 semesters per year that works out to be 4 years although it isn't unusual for people to take 4-1/2 or 5 years because sometimes a 15 hour combination of courses which are all very diffficult can just be too much so you drop that semester down to 12.

Oh - and you can expect between to spend 1 - 2 hours on homework a week for each credit hour involved - a 15 hour semester can involve an extra 15 - 30 hours of work studying and doing problems every week.

Think very carefully before you decide on which specialty avenue to pursue when studying engineering as there are many and while most of the first two years is fairly common among them if you go to changing majors it just ends up with you having to take additional courses you missed out on and also having credits for courses that don't apply in what you switched to. When it comes to electronics there are two major avenues you can go down. One is more pure engineering while the other, Electronics Engineering Technology, is a little more geared towards hands on work than pure theory.

Luckily the first year or so gives you some time to associate with other students, teachers etc and to get into the feel of the way college works, so by the time your second year rolls around you'll have a better idea of which raod you want to go down.

I actually attended twice, my first round somewhat split between electrical engineering and engineering technology, my second round between electrical engineering and physics. Curriculums were a lot different back then so it wasn't as hard to do it that way, the way things are set up nowadays you almost have to pick one and stick through it.

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14. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
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I don't even own one of those newfangled digital wang-doodles. My trusty old Tektroniks 2245 (the plain one, not the A or B model) was only rated to 200 MHz but will cheerfully display signals in excess of 400 MHz. May be a bit harder to sync on them, accuracy suffers a little and you might encounter a small amount of internal ringing by pushing the preamp circuitry beyond their design limits but most of the time in this frequency area I don't need perfection.

Besides that less than a year ago it only set me back \$167.50 when the CRT on an older trusty one finally got too out of focus for my liking.

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15. ### beatfuse26 New Member

Aug 25, 2010
1
0
Well, when i was in school, I really tried to listened to my professor in physics but I always ended up sleeping on my desk. I always got scolded but what can I do, I just can't help myself. Therefore, I really hate mathematics. I said to my professor, why don't you <snip> instead of giving me a crap lessons.

Last edited by a moderator: Sep 2, 2010
16. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
You must have had a fairly poor teacher, or he'd been around so long he was burned out on the subject.

Physics can be a great deal of fun, even teaching it can be fun and entertaining. The problems begin when they start assuming you've already mastered the complex math courses that go along with the later years of studying it.

Last edited by a moderator: Sep 2, 2010