Re: simplified converter needed for duty cycle to voltage (SEB)

I need to simplify a 'duty cycle to voltage' circuit. The range it has

>to cover are a varying 5 volt square wave pulse with a frequency range >of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while >the duty cycle of the square wave is varied within the set time period. > >The idea is to use a voltmeter as a percent duty cycle indicator. ie: >10.0 volts = 100 percent duty cycle. If the frequency was always >constant I think I could get away with a resistor and capacitor and just >measure the average voltage. Things become more difficult with the >variable frequency thrown in. > >Any help would be welcome. > >mike

Somewhat outside the box thinking...

Generate a master ramp synchronized to the input frequency, but amplitude "AGC'd" to be 1V peak by a controlled current source.

Replication of this same current into same value capacitor, but switched by the duty cycle, presents a peak voltage proportional to duty cycle... 1V = 100%, irrespective of frequency.

AGC method shown is a crude "quicky"... in actual practice corrections are by "dollop" ;-)

First used this scheme in the summer of 1968 when I was at Philco-Ford, Santa Clara, for an automotive inductive storage ignition system timing:

Turn on charging of inductor. When it reaches 5.5A go into regulation mode, holding 5.5A until firing.

System senses at firing time, was inductor into regulation already... delay timing by a dollop before beginning next charging cycle.

If inductor current was not yet at 5.5A, make timing a dollop earlier.

(Scheme minimizes/optimizes switch power dissipation.)

I used to scare my bosses (Bob Rutherford/John Welty) by driving (1968 Ford Thunderbird 429CID) up and down 101 with my legs crossed Yoga-style and drive only using the cruise control buttons up to 100 MPH, to see if I could out-run such a timing scheme... I couldn't ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson
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Here's some outside the box thinking for 21st century: get a real multimeter. The Extech EX330 measures ( and displays ) duty cycle over 0.1 to 99.9% range with resolution of 0.1% and accuracy of +/- 1.2% reading and 0.5Hz - 150KHz fequency. And this meter is cheap, even Lowes sells it, although not at the best price.

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