GB1495661A - Voltage drop warning apparatus - Google Patents

Abstract

1495661 Detecting undervoltage or voltage failure MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 8 Jan 1975 783/75 Heading H2K [Also in Division H3] A voltage-drop indicating circuit, which can be arranged to indicate either that a voltage source Vcc has failed but subsequently been restored or that the voltage of the source is currently below a threshold value, comprises a transistor 4 and load resistor 2 forming a series circuit across the source, and a negative resistance device 1 formed by two complementary f.e.t.'s (Fig. 1, not shown) and connected between the base of the transistor 4 and an intermediate point A in the series circuit. For detecting failure and subsequent restoration of the source, the load line of Fig. 4A is chosen, so that at the normal operating point (Vcc) no current flows, but following failure and restoration of the supply the device 1 stabilizes at the point P, causing the transistor 4 to conduct. For merely detecting fall in voltage below Vt 2 a slightly steeper load line is used (Fig. 4B, not shown). Conduction of the transistor 4 is indicated, e.g. by an LED 3 in the series circuit. A change-over or shorting switch 6 resets the circuit. The f.e.t.'s in the negative-resistance device 1 may be jugfets or igfets, and the transistor 4 may be replaced by a Darlington pair. A second transistor 8 may be switched off when the first transistor conducts thereby extinguishing a corresponding lamp 7. The circuit may be used to monitor the voltage supply of clocks or data processors