| 摘要 |
<p>Control impulses or variable delays are generated in a part tied to a cold earth. Only the input, driver and switching circuit are powered directly by a rectifier connected to the supply. Four foward biased diodes in series connected to the power transistor emitter provide passive security by blocking the transistor in the absence of a control signal. Control signal input isolation is provided by a pulse transformer or opto-isolator. The phototransistor or pulse transformer output transistor has an anti-saturation diode connected to its collector which is connected to the base of the first of the driver transistor pair. A secondary winding of the power transformer is connected by diodes and a limiting resistor to the power transistor to provide self-drive in the saturated state. Turing the control transistor on blocks the driver transistors switching on the power output transistor. The emitter diodes are bridged by a long time constant capacitor reservoir. The two diodes in series providing regenerative feedback are connected by resistor to the supply to lower the level necessary to start saturation using the feedback winding and by an anti-saturation diode to the collector of the output transistor. This limits the base voltage to within five times the forward biasses diode voltage drop.</p> |
