LIGHT RESPONSIVE SEMICONDUCTOR SWITCH WITH SHORTED LOAD PROTECTION

摘要

An improved light responsive semiconductor switch with shorted load protection capable of successfully interrupting a load overcurrent. The swit ch is includes an output transistor which is triggered by a photovoltaic element t o connect a load to a power source thereof, and an overcurrent sensor which provides an overcurrent signal upon seeing an overcurrent condition in the load. A shunt transistor is connected in series with a current limiting resistive element across the photovoltaic element to define a shunt path of flowing the curren t from the photovoltaic element through the current limiting resistive element away from the output transistor. A latch circuit is included to be energized by the photovoltaic element and to provide an interruption signal once the overcurrent signal is received and hold the interruption signal. The interruption signal turns on the shunt transistor so as to flow the current from the photovoltaic element through the shunt path, thereby turning off the output transistor for interruption of the overcurrent. The current limiting resistive element is connected in seri es with the shunt transistor to limit the current from the photovoltaic element when the shunt transistor is turned on, thereby providing a supply voltage from t he photovoltaic element to the latch circuit. Thus, the latch circuit is enable d to keep providing the interruption signal for reliable interruption of the overcurrent.