| 摘要 |
PURPOSE:To protect easily the short-circuit of a main transistor (TR) by inserting a diode and a constant voltage element in series between a base of the main TR and a base of a TR biasing reversely the main TR. CONSTITUTION:Suppose that the TR1 is turned on and the collector current of a TR6 becomes an overcurrent because of a fault such as short-circuit of load during the conducting period of the main TR6. A base-emitter voltage rises in this case and a voltage VBF exceeds a reverse dielectric strength voltage of a Zener diode 3, an Avalanche current flows to the Zener diode 3 and a TR2 is conductive. When the TR2 is conductive, a current flowing out of the TR1 is bypassed by the TR2 and the base current of the main TR is suppressed or cut off, then the main TR6 is cut or the collector current is suppressed remarkably, thereby protecting the main TR from being destroyed. |
