Using several discrete electronic components can be designed a very simple DC DC converter which converts a positive voltage of 5 volts to a negative voltage of 15 volts. The negative voltage converter is different than most other similar circuits.
Works as a multivibrator IC1 provide an output signal with a relatively high duty cycle. LM311 is designed to work with a single supply of 5 V and allows a high current output for command switching of transistor T1. Duty cycle of the output signal is determined by voltage divider R2-R3, and the oscillation frequency of the C2-R4. Transistor T2 is part of a control loop to change the duty cycle of the oscillator and maintain a value of -15 V to converter output. Maximum output current isabout 200mA (transistor T1 to be installed on a radiator).