OVERCURRENT PROTECTING CIRCUIT FOR DC STABILIZED POWER SUPPLY CIRCUIT

摘要

PURPOSE:To reduce the rating level and the cost of parts of a DC stabilized power supply circuit by using a switching element which is turned off when the load is short-circuited together with reduction of the output voltage level. CONSTITUTION:When an output terminal B of a voltage regulator 3 is short- circuited, the potential of the terminal B is set at the same level of that of the cathode of a light emitting diode D of a photocoupler 7. Thus the diode D is turned off and therefore a phototransistor PT is also turned off. Then the conduction is broken between a common terminal C of the regulator 3 and an earth E. Thus the regulator 3 loses its control input and is turned off and therefore the output of the regulator 3 is equal to zero. Here a Zener diode 5 is turned on again owing to the difference of potential between an input terminal A and the terminal B of the regulator 3. Thus a current flows from a non-stabilized DC power supply 1. However the short circuit current can be reduced by setting previously the value of a resistance 4 at a high level.