Control circuit for a switching transistor

Abstract

Abstract A circuit for controlling a switching transistor (1), in which a control circuit (7), in particular an integrated circuit chip, is connected via a capacitor (3) to the base of the switching transistor (1) and a resistor (4) is connected between the base and emitter of the switching transistor (1). Control circuits for switching transistors are known. All these known circuits attempt to keep the power loss dissipated in the switching transistor as low as possible. To keep turn-on losses low, the transistor (1) must be turned on as quickly as possible, i.e. the collector-emitter voltage must fall rapidly to the saturation voltage, i.e. the voltage drop in the equilibrium turned-on state. The object of the invention is to find the simplest possible control circuit that will produce low losses in the switching transistor. The circuit arrangement in accordance with the invention, of the type mentioned initially, is characterised by the fact that it ensures, by the combined action of the control circuit (7), the coupling network consisting of the resistor (4), the capacitor (3), and the switching transistor (1), that when the transistor is turned on, the base current has an excessive value, which means that the turn-on time is short, that, while it is turned on, the switching transistor (1) is saturated, that further, at the end of the turn-on state, the switching transistor (1) is operating in the quasi-saturated range and that finally, at turn-off, initially both a high negative base current (which may be very large during turn-off from the quasi-saturated range and does not need to be precisely set) can flow and a large negative voltage is also available. <IMAGE>

Inventors

• 👤 Horst Dr. Ebhardt
• 👤 Reinhard Dipl.-Ing. Ruff

Bibliographic Details