| 摘要 |
A surge protection device 130 for use with a three wire power source 105 comprising surge protection units S1, S2 and S3, photocoupler units P1 and P2, resistors R11, R12, R13 and R14 and low pass filter comprising resistor R1 and capacitor C1. Each of the surge protection units S1-S3 further comprise a fuse F, varistor VAR and monitor terminal Tm. Each of the photocoupler units further comprise a light emitting component 110a or 120a and a light detecting component 110b or 120b and emitter and collector terminals Te and Tc coupled to a bipolar transistor. The collector terminal of the first photocoupler P1 is connected to a voltage source VDD. The varistors VAR in the surge protection devices S1-S3 dissipate excess currents within a rated threshold and the light emitting components in the photocoupler units P1 and P2 emit light, which is detected by the light detecting components and produce electrical signals indicating normal operation. Above rated current thresholds, the fuses F in affected surge protection units are blown and power to the light emitting components of the photocouplers is cut, thereby cutting the electrical signals in the light detecting components, and an abnormal indication signal is output from the emitter terminal of the second photocoupler unit P2. The arrangement thus provides a more inexpensive surge protection for a three-wire power source and also a means of detecting when the surge protection fails. |
