The output voltage changes approximately linearly up to 20 KV as the input voltage is varied from 0 to 5 V. The oscillator is tuned by a 5-0 potentiometer to peak the output voltage at the frequency of maximum transformer response between 45 and 55 kHz. The feedback voltage is applied through a 100-KO resistor, an op amp, and a comparator to a high-voltage amplifier. A diode and varistors on the primary side of the transformer protect the output transistor.
The transformer is a flyback-type used in color-television sets. A feedback loop balances between the high-voltage output and the low-voltage input.