JPS58153177A - Voltage drop detection circuit - Google Patents

Abstract

PURPOSE:To reduce the current consumption when the power source is normal by determining the voltage of a voltage source based on a Zener voltage of a Zener diode and a voltage between the base and emitter of a transistor. CONSTITUTION:The voltage V of a voltage source when a transistor 21 is ON or OFF is determined by a Zener voltage VZ of a Zener diode 23 connected between the base of the transistor 21 and the voltage source and a voltage VBE between the base and the emitter of the transistor 21. When the voltage of the voltage source is normal, the transistor 21 turns ON by the base current Ib= (V-VZ-VBE)/R1 of the transistor 21. Then, current flowing through a collector thereof, namely current flowing through a resistance R225, is roughly V/R2. As the resistance R225 is large, only a slight change in the base current is required to turn ON or OFF the transistor 21. This eliminates the voltage difference of the voltage source between the turning ON and OFF of the transistor 21 under a very large resistance R126 thereby reducing the current comsumption when the power source is normal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that detects that a voltage is below a certain level or above a certain level.

In general, various control devices, measuring devices, etc. have their control functions and measurement functions degraded due to a drop in power supply voltage, and may malfunction. In order to know this drop in power supply voltage in advance, an emergency power supply device or the like is often equipped with a summer drop detection circuit.

Conventionally, as shown in FIG. 1, when the signal load 13 is operated by the collector current of a transistor 11 and the transistor is turned ON or OFF, the voltage of the voltage source is between the base of the transistor and the voltage source. A voltage drop detection circuit is used in which the Zener voltage of the Zener diode 12 connected to the transistor is determined by the base-emitter voltage of the transistor.In this circuit, when the voltage of the voltage source is normal, the signal load 13 is activated, and when the voltage of the voltage source drops below a desired level, the signal load 13 stops operating, thereby detecting a drop in voltage. However, in this circuit, the voltage of the voltage source is normal. In some cases, current exceeding a certain level is consumed to maintain the operating state of the signal load 13, which is uneconomical.

The present invention has been made to improve the above problems.

Hereinafter, the configuration of the present invention will be explained with reference to the drawings.

FIG. 2 shows an embodiment of the voltage drop detection circuit according to the present invention. In the figure, 21 and 22 are transistors, 23 is a Zener diode, 24 is a signal load, and 2
Reference numeral 5 denotes an element having a large resistance value, and the resistance value of this element must be such that a base current sufficient to turn on the transistor 22 when the transistor 21 is OFF flows. In this circuit, when the transistor 21 is on, the base potential of the transistor 22 becomes approximately 0.6V or less, and the transistor 22 is turned off.
When the transistor 22 is OFF, the transistor 22 is turned ON, and the signal load 24 is operated by the collector current of the transistor 22. Meanwhile, transistor 21 is turned on.
Or, the voltage V of the voltage source when turned off is the Zener voltage V8 of the Zener diode 23 connected between the base of the transistor 21 and the voltage source, and the base-emitter voltage VBE of the transistor 21. determined by.

In this circuit, when the voltage V of the voltage source is normal, the transistor 21 is turned on by the base current of the transistor 21, and the current flowing to the collector of the transistor 21, that is, the resistance R
The current flowing through 225 is approximately V/R2. Here, since the collector resistance R225 is large, the transistor 21 is
In order to turn the transistor 21 off, a slight change in the base current is sufficient, so even if the resistor R126 in FIG. The difference will disappear, and even less current will be consumed when the power supply is normal.

As described above, according to the voltage drop detection circuit of the present invention, less current is consumed when the voltage of the voltage source is normal.

[Brief explanation of the drawing]

FIG. 1 shows a voltage drop detection circuit according to the prior art. FIG. 2 shows an embodiment of a voltage drop detection circuit according to the present invention. 11, 21, 22...Transistors 12, 23...Zener diodes 13, 24...
...Signal load

Claims (1)

[Claims] When transistor 1 is ON, transistor 2 is OFF, and when transistor 1 is OFF, transistor 2 is ON, and the signal load is operated by the collector current of transistor 2. The voltage source is connected through an element having a large resistance value, and the voltage of the voltage decrease when the vapor transistor 1 is turned ON or OFF is the voltage of the transistor 1.
a voltage drop detection circuit determined by the Zener voltage of a Zener diode connected between the base of the transistor 1 and the voltage source and the base-emitter voltage of the transistor 1;