Ultra-simple PWM pulse generator

Discussion in 'General Electronics Chat' started by Alec_t, Apr 23, 2015.

  1. Alec_t

    Thread Starter AAC Fanatic!

    Sep 17, 2013
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    I may be re-inventing the wheel, but haven't come across this circuit before for generating PWM pulses using an absolute minimum of components; just one CMOS Schmitt gate (e.g. CD40106, CD4093, 74HC14) and four passives :-
    UltraSimplePWMgenerator.gif
    It can generate duty cycles voltage-controlled from ~ 10%-90% (your mileage may vary, depending on the Schmitt hysteresis). The penalty for simplicity is that the pulse frequency varies, at 50% duty-cycle being about twice the frequency at 10% or 90%. For many applications, e.g. LED dimming and motor speed control, such variation is unimportant.
    Enjoy!
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Nice little circuit. One thing - for any particular control voltage value, both the frequency and pulse width percentage vary with the temperature of the chip die, and vary from one chip to another. As you say, there are applications where this doesn't matter, but it is something to keep in mind.

    ak
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,993
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    I like that circuit. :cool:
    Can't get much simpler than that to generate a PWM signal for non-critical applications.
     
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