Document Type and Number:
Japanese Patent JPS4510246
Kind Code:
B1
Abstract:
1,091,636. Switching circuits. GENERAL ELECTRIC CO. April 12, 1965 [May 18, 1964], No. 15394/65. Heading H3T. [Also in Division H2] A semi-conductor controlled rectifier is turned on only near the start of the rising part of a rectified A.C. waveform by means of a timing capacitor charged through a temperature-sensing element, so that a more precise switching action is obtained This principle is applied in Fig. 1 to the control by a thyristor of a protecting relay 13 for switching off an electric motor if the temperature sensed by a thermistor T 1 is too high. The A.C. supply 11, 12 is rectified by a diode bridge network D 1 -D 4 and used to charge up a capacitor C 1 through a resistor R 5 . If the capacitor voltage is sufficient to cause a unijunction transistor Q 1 to conduct, the capacitor discharges through R 1 and the resulting voltage pulse fires the thyristor SCR 1 . This operation occurs once per half-cycle and the resulting current is sufficient to keep the relay 13 energized. If the temperature rises above a certain point, the resistance of T 1 will fall, thus reducing the voltage on C 1 to a point where the unijunction transistor does not conduct. The thyristor is then not fired and the relay falls off. Zener diode Z 1 limits the peaks of the waveform so that C 2 charges only during the rising part of each half-cycle, giving a boost to the potential across C 1 and firing the unijunction at this point. Temperature compensation is provided by R 3 , and capacitor C 3 prevents false triggering by negative transients. If the temperatures at several points are to be sensed (Fig. 4, not shown), the various thermistors (with series resistors) are joined in parallel across the timing capacitor, and the rectifier bridge is replaced by separate diodes in series with each thermistor. Alternatively (Fig. 5, not shown), positive temperaturecoefficient thermistors are joined in series across the auxiliary CR circuit of Fig. 1, and a single diode is used in place of the rectifier bridge. In both these modifications the relay coil is shunted by a reversely-poled diode, and firing occurs only once per cycle of the applied A.C. voltage instead of once per half-cycle as in Fig. 1.
Application Number:
JP2715765A
Publication Date:
April 13, 1970
Filing Date:
May 01, 1965
Export Citation:
International Classes:
G05D23/24; H02H5/04; H03K17/72; H03K17/725