Op-Amp sawtooth generator – Miller integrator is given in figure bellow.
Op-Amp sawtooth generator is a circuit that combine Miller integrator with discharging switch – signal transistor. Output voltage oscillate from GND to VCC. From ground level to VCC voltage increases linearly, and then suddenly drops to ground again. That is why it looks like the teeth of a saw.
Input voltage is negative, and since op-amp Miller integrator is inverting, output voltage is positive. Having negative input voltage, current flows on the direction shown.
Charging current is with intensity:
This current is charging capacitor during switching period of time T (T=1/f), and output voltage is
If output voltage reaches VCC during time T, op-amp sawtooth generator goes to saturation, and output voltage is trapezoidal.
At the end of time T, discharging transistor is turned “ON” for short, and then discharging current is collector current. This discharging current is typically 500mA to 1A, so, discharging time is several hundreds of time shorter then charging time. That is how sawtooth waveform is obtained.
Sawtooth voltage is used in cathode ray tube, in analog oscilloscopes and in PWM modulators, i.e. in analog control schemes for DC-DC converters.