Circuit for detecting an excess-discharge of a battery

Claim 1

A circuit for detecting a decrease in voltage level of a DC voltage source supplying current to a load and receiving a load control signal, said circuit comprising: first, second, third and fourth transistors (4, 10, 11, 15) each having an emitter, a collector and a base; first, second, third, fourth and fifth resistors (9, 16, 14, 12, 13); a capacitor (8); and a reference voltage device (17); said second resistor (16) and said reference voltage device (17) forming a series circuit; said first transistor (4) being of a first polarity and having the control signal connected to the base thereof, the collector of said first transistor being connected to one electrode of the DC voltage source, said second transistor (10) being of said first polarity, the emitter of said first transistor being connected through said capacitor (8) to the base of said second transistor (10), the base of said second transistor being connected through said first resistor (9) to the other electrode of said DC voltage source, said third transistor (11) being of a second polarity, the collector of said second transistor being connected to the base of said third transistor (11), the emitter of said third transistor being connected to said one electrode of said DC voltage source, the collector of said third transistor being connected through said series circuit of said second resistor (16) and said reference voltage device (17) to said other electrode of said DC voltage source, said fourth transistor being of said first polarity, a junction between said second resistor and said reference voltage device being connected to the base of said fourth transistor (15), the collector of said fourth transistor being connected through said third resistor (14) to the collector of said third transistor, the collector of said fourth transistor being connected through said fourth resistor (12) to the base of said second transistor, the emitter of said second and fourth transistors being coupled together, and there being a junction therebetween connected through said fifth resistor (13) to the other electrode of said DC voltage source, the supply of current to the load being controlled by said third transistor (11), said third transistor being turned ON or OFF by the control signal, and said third transistor being turned OFF when a voltage between said two electrodes of said DC voltage source becomes lower than a predetermined voltage determined by said reference voltage device (17).