RMS to DC scheme

This way to the Egress?

Hi!

I need scheme of RMS to DC converter. What is important I can`t use integrated circuits (except opamps) in this approach. Thanks for your help

LemonPL

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Hi, Lemon, or Lemone. You should have included your full name and the technical college or university you're attending, as well as the class and instructor. I'm sure your fellow students would be amused by your s.e.b. post. Your professor also might be interested, although I doubt he'd show his amusement in public.

You know, if you need a free clue (and oh yes, you do), it's sometimes good to look through the existing literature rather than just re-invent the wheel. The early manufacturers of op amps (Analog Devices, Fairchild and National Semiconductor come to mind) published application notes in the 1970s to help users of their newfangled contraption, the IC op amp. A quick search of these sites using the phrase "True rms detector" should give you some help.

But since it might actually involve work or thought to go to the National Semiconductor website and type in the search term "true rms detector", and actually scan a few of the links to see if they might have what you want (Frith forbid, you might actually learn something not connected directly with your homework assignment), retain the purity of your beautiful mind by holding your mouse and sliding it slowly until the pointer rests on the link below, to read National's LB-25, "True rms Detector". It shows a true rms detector circuit that uses five op amps, matched pair transistors, diodes and passive components. Once the pointer is resting over this link, press the mouse button.

If your newsreader isn't capable of using text links, you'll have to copy the link, paste it to the address bar of your web browser, and then click the "Go" button to the right. If you need help with that, please post again if you can, and it's not too much work.

Also, the link is in .pdf format. If you don't have the Adobe Acrobat Reader or it's equivalent (and I would guess you don't), please go to

and download and install your free Adobe Acrobat Reader (use the icon labelled "Get Adobe Reader" on the left of the page). If you have trouble with this, you should contact somebody in the computer science department. For 20 zloty, you can usually buy a clue -- they'll be happy to give you a hand and set up your computer. Also, if you don't understand the app note, please use another 20 zloty note to have one of your classmates explain it to you. It's actually a pretty elegant combination of an op amp precision rectifier, multiplier, and divider.

Good luck in your academic endeavors and career, and please call your Daddy to ask for a big pile of 20 zloty notes. I'd guess you're going to need them.

By the way, in case anyone's wondering, here's what a clue costs:

Many of the posters have assumed that you are doing a homework problem for some class. But there are a number of questions that must be answered if you are serious about this. 1. What is the bandwidth? 2. What is the maximum frequency of operation. 3. What is the PAR, peak to average ratio expected.

1. What is the voltage expected? 5. What is the dynamic range expected? 6. What are the waveshapes expected? 7. What precision is expected? 8. What speed of response is expected? 9. What transient response is required?

The scheme picked depends on answers to these questions. For example, if you know the waveform is ALWAYS a sine wave the problem is simple and is just a calibration.

use a diode? hmm, isn't their forwards voltage/current curve exponential?

Bye. Jasen