Design a simple Voltage Controlled Pulse Width Modulator

[karthik9]

I want to design a simple "Voltage Controlled Pulse Width Modulator" for my main circuit, It is possible with a 555, but the problem is It varies with the help of a varying the resistor. Is there a simple way to do this?

I tried combining V-Controlled One shot, V-Controlled Square wave generator and others but not getting the desired resuult of fixed frequency but variable duty cycle. Is there any IC similar to LTC6992 ?

 

[Tien_P]

Have a look at this KB:

http://digital.ni.com/public.nsf/allkb/EF391C48CF71AE4F862571B900644F84

[karthik9]

But you cannot vary duty cycle with voltage keeping frequency constant? 

[johnsold]

Voltage controlled pulse width modulator with constant frequency:

Oscillator: Use an op amp in a Schmidt trigger circuit charging and discharging a capacitor. This will generate a fixed frequency sawtooth waveform.

Comparator: Apply the control voltage to one input of a comparator. Connect the sawtooth waveform to the other. Scale the control voltage or sawtooth so they both have similar ranges. A small amount of hysteresis may be useful.

Output: PWM as required.

Lynn