GB1358687A - Power supply systems - Google Patents

Abstract

1358687 Inductive signalling; transponders; time delay switching circuits PLESSEY CO Ltd 24 Aug 1971 [24 Sept 1970] 45470/70 Headings H4L, H4U and H3T In a power supply system of the type which receives, rectifies and stores radiated energy, e.g. to energize a transponder carried by a vehicle or person for identification purposes, the energy is released from the store for power supply purposes only in response to a reduction in the radiated energy received thus enabling a reasonable quantity of energy to be stored before it is utilized. In one arrangement, Fig. 1 (not shown) a transmitter is coupled to an aerial via a switch which is closed for short periods. The power supply system includes a receiving aerial coupled to a storage device via a rectifier, the output of the store being connected to a switch which is responsive to a reduction in output from the rectifier to apply power from the store to a device. In a further arrangement, Fig. 2, for providing power for a moving device 10 which carries a power supply of the type described, a stationary power source 11 feeds a loop 12 comprising a high output section A and a low output section B. When the device moves from A to B a reduction of input energy to the store of the power supply for the moving device will cause energy to be supplied via the switch to a transmitter (not shown) to cause it to transmit an identification signal. The weaker signal from section B provides a reference signal, for example. Details of power supply, Fig. 3.-Signals received by aerial 14 are rectified at 15 and supplied via integrator 16, 17 and diode 18 to a capacitor store 19. Diode 18 is shunted by a transistor 20 which feeds the base of a transistor 26, which with transistor 23 forms the switch controlling power supply from the store 19 to the device 27. Initially, capacitor 19 is discharged and transistor 20 is off. As capacitor 19 charges, the voltage V 2 follows the voltage V 1 across capacitor 16, differing by the voltage drop across diode 18. When V 1 drops, a point will be reached when the voltage V 2 -V 1 , is sufficient to make transistor 20 conductive, followed by transistors 23, 26, the switching-on time being largely determined by the time constant of circuit 16, 17. The circuit is arranged so that transistor 26 remains on when transistor 20 is turned off until the voltage across transistor 23 falls to a predetermined value. A Zener diode 28 prevents the voltage across device 27 from exceeding a predetermined value.