A simple sawtooth generator using a GTO and a Zener diode is shown in figure.
When the supply is switched on, the GTO will turn on, resulting in the short-circuit equivalent from anode to cathode. As a consequence the capacitor C will begin to charge toward the supply voltage, as illustrated in figure. As the voltage across the capacitor C exceeds the Zener potential, there will be a reversal in gate-to-cathode voltage resulting in a reversal of gate current. Eventually, the negative gate current will be large enough to turn the GTO off. Now the capacitor C will begin to discharge through resistor R„ because turning off of GTO results in the open-circuit equivalent from anode to cathode. The discharge time will be determined by the circuit time constant T = CR2. The proper choice of R2 and C will result in the sawtooth waveform shown in figure. Once the output voltage Vout drops below Zener voltage VZ the GTO will turn on and the process will repeat.