Lookinf for options for an Absolute Magnitude" or precision rectifier circuit.

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Newsgroups: alt.binaries.schematics.electronic Subject: S.E.D: Looking for Options for an "Absolute Magnitude" or Precision Rectifier Circuit - FullWaveRectifier.pdf Message-ID:

...Jim Thompson

I did a mechanical version once. No matter which direction you turned the input shaft, the output shaft went clockwise. The MEs were stumped so I showed them how to do a rotary full-wave rectifier.

Can you post your circuit?

John

Crazy! It pulls the opamp input below ground, in violation of their own abs-max ratings! That 2 volt p-p input must be on the very edge of blowing the opamp up.

John

Planetaries and orbitals and differentials are too complicated for me, too. I used notched pulleys/belts to get counter-rotations and a pair of one-way roller clutches to rectify them into the output shaft. It actually drove a synchro for a shaft-rotaton counter on a ship. It was really silly, since ships spend so little time going backwards you'd never really miss those turns.

John

Must work over substantial range, say .01 to .6 Volts RMS.

Serious responses only. Please.

I have a working circuit now, but there is some variation between positive and negative half cycles which seems to be inherent. Must be some easy way to eliminate this. Yes?

between

between

or

Thanks Jim. I'll see if it fixes it. The circuit I used is the one in the SO291 Specification as a suggested application. Works, except as noted.

Magnitude"

Opps! OP291

turned

stumped

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Sure, But it's easier to post a link!

On page seventeen!

I read in sci.electronics.design that John Larkin wrote (in ) about 'Lookinf for options for an Absolute Magnitude" or precision rectifier circuit.', on Sat, 5 Feb 2005:

With ratchet wheels or the spring-loaded orbital idler (which looks like magic to me)?

inherent.

their

edge of

So you see why I wanted a replacement!

What a crock! Relies on rail-to-rail OpAmp with negative rail of first stage tied to ground :-(

...Jim Thompson

I read in sci.electronics.design that John Larkin wrote (in ) about 'Lookinf for options for an Absolute Magnitude" or precision rectifier circuit.', on Sat, 5 Feb 2005:

Your roller clutches are equivalent to ratchet wheels, and diodes. I saw the orbital idler solution in a Hong Kong clockwork car. It reversed the car whenever it wouldn't go further, so it was actually an inverter, but used the other way round, it's a rectifier. Unfortunately, the kid wouldn't let me steal it to see in detail how it works. (;-)

Ha! Read the "ideas for design" clips in ED or EDN. Typically nonsense.

John

ABSOLUTE MAXIMUM RATINGS 1, 2 Supply Voltage . . . . . . . .. . . . . . . 16 V Input Voltage . . . . . . . . . . . . . . . GND to VS 10 V

Is that what "GND to VS 10V" means? It looked like a misprint of "GND to VS+10V" to me. I admit I didn't study the entire datasheet, this being a newsgroup and I having real work to do of my own.

Why can't people proof datasheets?

Oh, please don't waste any of your valuable time on any of us.

John

A good roller clutch is like a schottky diode, or almost an ideal diode. They are amazing: no perceptable backlash or deadband, and very little reverse leakage.

John

Yes it's ugly, but probably works fine, provided it's DC coupled... The input stage safely draws a fraction of a mA for negative voltages (see fig 3) but is OK; the other opamp works fine inverting the signal.

But I doubt this circuit can do well at low voltages. I have another configuration I prefer for mV-level active rectification, which even works well at MHz frequencies.

Sheeesh! What have we come to? Even Fred has to resort to an alias to get read.

FuFred ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

Their abs-max input voltage rating of "GND to Vs 10V" is not clear to me; perhaps they mean you can go outside the PS rails by 10V max, or perhaps they mean the input is limited to 10V max even if the power supply is at the specified 16V max? Either way seems more than a little bit odd to me, if I were using this part I would call my AD FAE for an interpretation. Data sheet typos are not unheard of.

I would however recommend the more common precision rectifier circuit using diodes in the feedback loop of an op-amp if better performance is required. AOE discusses the half wave version in some detail, full wave is left as an exercise for the student.

Glen