CONTROL CIRCUIT FOR SELF-OSCILLATION DC/DC CONVERTER

PURPOSE:To obtain a small and sophisticated control circuit for self-oscillation DC/DC converter by providing a constant voltage circuit and a comparator, maintaining the base voltage of a switching transistor at a low level, and controlling the output voltage of the comparator to a prescribed level. CONSTITUTION:Upon rising of input voltage Vin from 0, a constant voltage circuit 1 starts at first to rise. When the output of the constant voltage circuit 1 approaches to 0.7V, current is fed through a resistor 6(Rsink) to the base of a transistor 5(Qsink) to maintain the base voltage of a switching transistor at a low level. When the constant voltage circuit 1 rises to operate a bias circuit 2, a switching circuit 4 is operated to feed a starting current IG to the switching transistor, while simultaneously a comparator 3 functions to turn the transistor 5(Qsink) OFF thus starting oscillation of the comparator 3. Consequently, abnormal output from the comparator can be prevented.