Transformerless drive circuit for field-effect transistors

摘要

A transformerless drive circuit for operation of a switch mode regulator includes a turn-on circuit and a turn-off circuit coupled to a control terminal of the switch, respectively, for inducing a state of conduction in the switch and for terminating the state of conduction. The switch is, in the preferred embodiment, a P-channel DMOS field-effect transistor (FET) with a source electrode connected to the positive voltage terminal of a power supply, and with the drain terminal connected to load circuitry of the regulator. The gate electrode serves as the control terminal. The regulator includes a sensor of output voltage and circuitry for providing a pulse-width modulated control signal for designating the average amount of current to be passed by the switch. The turn-on circuit and the turn-off circuit share a common diode which operates alternately for conduction or turn-off. The turn-off circuit includes a bootstrap capacitor for momentarily powering the circuit for saturating a transistor therein, the relatively low saturation voltage being impressed at the control terminal for rapid turn-off. The drawing of current by the turn-on circuit pulls a gate-voltage away from the power line for rapid turn-on.