simplified converter needed for duty cycle to voltage (SEB)
 

On Sun, 08 Jun 2014 14:22:20 -0600, m II wrote:

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...

http://www.analog-innovations.com/SED/DutyCycle%28SEB%29.pdf

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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