Micropower Linear PWM
Pulse width modulators are a fundamental building block. Among other things, they are used for remote sensing, DC motor control, and switch-mode power supply controllers.
This circuit uses a rail-to-rail OpAmp to linearize the pulse width of the classic, dual 555 Pulse Width Modulator. The first timer is set to run as a 10Khz oscillator. The square wave output from this section is latched by the D Flip Flop. The Q output then triggers the second 555 timer which is acting as a one-shot. The output pulse clears the latch (which allows output pulses shorter than the trigger width) and is also integrated by the combination of R4 and C6. This integrated, or averaged signal is compared to the input voltage on the OpAmp. The OpAmp will drive the control voltage of the one-shot until the average voltage of the output is equal to the input voltage.