| 摘要 |
PURPOSE:To protect a circuit from overcurrent by providing a short-circuit in parallel with a photodiode and a resistor in series with the collector/emitter of a transistor (TR) controlled by a sensing resistor. CONSTITUTION:When a switch S turned off, a photocoupler C1 is turned off and an output TR TRT1 is turned off and a load L is also turned off. No voltage drop exists in an overcurrent resistor R6, a TRT3 is turned off, the PC2 is turned off and a thyristor THY is turned off. With the switch S turned on, the THY1 is turned off, the PC1 is turned on, the TRT2 is turned on and the load L is turned on. When a constant current flows to the load L, the TRT3 is turned on and the THY is turned off by a voltage drop across the resistor R6. When an overcurrent or a short-circuit current flows to the load L, a voltage drop is generated in the resistor R6, the TRT3 is turned on, the PC2 is turned on, the THY1 is turned on, the PC1 is turned off, the TRT2 is turned off, the TRT3 is turned off and the PC2 is turned off, but the THY1 keeps the on-state until the switch S is turned off by a current from an input power supply Ein. Thus, the circuit is protected from an overcurrent. |
