POWER SUPPLY CIRCUIT

摘要

1468899 AC/DC power supply circuits; converting smoothing; pulsating currents NIPPON ELECTRIC CO Ltd and HITACHI Ltd 10 June 1974 [11 June 1973] 25653/74 Headings H2H and H2F A power supply circuit comprises an A.C. power supply, a D.C. power supply, a rectifier circuit 4 and an active filter circuit 7 including series connected resistors 16, 17, a transistor 16 being connected in parallel with the resistor 18 and being switched off when the A.C. supply is connected to the circuit but being switched on when the D.C. supply is connected to the circuit. The circuit supplies smoothed D.C. to a load 11 such as a television receiver and when a plug 1 connected to the A.C. supply is inserted in a socket 2, leads 6, 9 are interconnected. The voltage at the base of the transistor 18 is less than its emitter voltage so that the transistor is non-conductive and the voltage between the input and output terminals of the filter circuit 7 equals the voltage across the resistors 16, 17 due to the base current of the transistor 13 plus the base-emitter voltage of the transistor 13. When the D.C. supply is connected to the circuit via a plug 12 and the socket 2, the leads 6, 9 are not interconnected and the transistor 18 conducts so that the inter-terminal voltage of the filter 7 is determined by the voltage across the resistor 17. By reducing the inter-terminal voltage of the filter unnecessary power consumption of the D.C. supply is avoided. In a modification, Fig. 3 (not shown), regulation of the voltage across the load is provided.