voltage controlles duty-cycle

7-08 elektor july/august 1980 The principle behind this circuit is the fact that the average voltage of a squarewave is proportional to its duty-cycle. The circuit consists quite simply of an integrator (A1) and a Schmitt-trigger (A2), together for- ming a squarewave oscillator. If the output of the Schmitt-trigger is low the output of Al will gradually decrease until the lower threshold of A2 is reached. The output of A2 will then go high (just less than the supply voltage) causing the integrator out- put to rise until the upper threshold is reached and the Schmitt-trigger output goes low again. By altering the voltage level on the inverting input of Al the integrator"s characteristics can be altered. As the trigger thresholds of A2 are fixed, the result is a change in duty-cycle. The average voltage of the squarewave output will always be equal to the input voltage, but the frequency will remain constant. In this way the duty-cycle can be varied between 0% uin • 11:111 11 volt...