JPS6290574A - Voltage detection circuit - Google Patents

Abstract

PURPOSE:To detect a voltage with good accuracy by eliminating the effect of temp. and power source voltage on input threshold voltage, by adjusting the values of first and second resistors connected to the first transistor TR, which is connected to the input terminal of a voltage detection circuit, and connected to the second transistor TR connected between said first transistor TR and the earth. CONSTITUTION:A first transistor TR1 is connected to the output point 43 of the current mirror circuit 30 connected to the power source 50 of a voltage detection circuit and an input terminal 41 is connected to the base of the first transistor TR1. The collector of a second transistor TR2 is connected to the emitter of the first transistor TR1 through a first resistor 11 and the emitter of the second transistor TR2 is connected to earth through a second resistor 12. Further, a third transistor TR3 is connected to the base of the second transistor TR2 and the common connection point of the base and collector of the third transistor TR3 is connected to the output point 44 of the circuit 30 and the emitter thereof is earthed. A fourth transistor TR4 of which the collector is connected to the output terminal 42 is connected to the collector of the transistor TR2 and the emitter thereof is earthed. Then, the values of the resistors 11, 12 are controlled to remove the effect of the variation of temp. and the power source 50.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for detecting whether an input voltage exceeds a threshold value.

[Conventional technology]

A conventional voltage detection circuit is shown in FIG. In Figure 2,
20 is a reference voltage generation circuit that generates a reference voltage; 21 is a comparator that compares the reference voltage with an input terminal; 41 is an input terminal to which a voltage to be measured is input; and 42 is an output voltage from the comparator 21. It is an output terminal.

The operation of the circuit configured in this way will be explained. The reference voltage generation circuit generates a voltage that is independent of temperature and power supply voltage. By inputting this generated voltage to a child terminal of the comparator 21 and inputting the voltage to be measured to one terminal of the comparator 21, the voltage to be measured is detected. Comparator 21 outputs a comparison voltage to output terminal 42 .

[Problem that the invention seeks to solve]

However, in such a circuit, the function of generating the reference voltage and the function of comparing the voltages are performed in separate circuit blocks, so there is a problem that a large number of elements are required.

The present invention has been made in view of these points, and its purpose is to integrate the functions of reference voltage generation and voltage comparison, and whose operation is independent of temperature and power supply voltage.
Another object of the present invention is to provide a voltage detection circuit with a simple circuit configuration.

[Means for solving problems]

To achieve this purpose, the present invention includes a first transistor whose base is connected to an input terminal, whose collector is connected to the emitter of the first transistor through a resistor, and whose emitter is connected to ground through a resistor. a third transistor whose collector and base are connected to the base of the second transistor and whose emitter is connected to ground; and whose collector and base are connected to the base of the second transistor and whose emitter is connected to ground and whose base is connected to the collector of the second transistor. and a current mirror circuit whose input point is connected to the collector of the first transistor and whose output point is connected to the collector of the third transistor.

[Effect]

In the present invention, the values of the first resistor between the emitter of the first transistor and the collector of the second transistor, the second resistor between the emitter of the second transistor and ground, etc. are set appropriately. If selected, the temperature dependence of the input threshold voltage will disappear.

〔Example〕

An embodiment of a voltage detection circuit according to the present invention is shown in FIG. In FIG. 1, I is a first transistor whose base is connected to an input terminal 41, and 2 is a transistor whose collector is connected to the emitter of transistor 1 through a first resistor 11 and whose emitter is connected through a second resistor 12. 3 is a third transistor whose collector and base are connected to the base of transistor 2 and whose emitter is connected to earth; 4 is a third transistor whose collector and base are connected to the base of transistor 2 and whose emitter is connected to earth; and 4 is a transistor whose collector and base are connected to the base of transistor 2 and whose emitter is connected to earth; A fourth transistor connected to the collector; 30 is a current mirror circuit that outputs an output current proportional to the input current; 30a and 30b are transistors forming the current mirror circuit 30; 43 is a current mirror circuit that outputs an output current proportional to the input current; Input point for input, 4
4 is an output point for outputting current from the current mirror circuit 30, and 50 is a power source for operating this circuit.

Next, the operation of this embodiment configured as described above will be explained. When the input voltage at input terminal 41 is low, the emitter potential of transistor 1 is at a low potential, so 1-
The collector potential of transistor 2 is also low, and transistor 4 is in an off state. Conversely, when the input voltage at input terminal 41 is high, the emitter potential of transistor 1 is at a high potential, so the collector potential of transistor 2 is also high, and transistor 4 is in an on state.

Next, the input threshold voltage at which the transistor 4 changes from the off state to the on state will be explained.

At this threshold, transistors 1.2, 3.4 are in the active region and their base currents can be ignored provided hFE is high enough, so in the following description it is assumed that there is no base current.

Assuming that the current mirror circuit 30 generates a current m times as much as its input current as an output current, the relationship between the collector current ICI of the transistor 1 and the collector current rc3 of the transistor 3 is expressed by the following equation (1). holds true.

IC3=m・ic+ (1) The emitter area of transistor 2 is n of the emitter area of transistor 3
+RZ is the resistance value of resistor 12, k is Portzmann's constant, and T is the absolute temperature.

When q is an electronic charge, the following equation (2) holds between the emitter current 1tt of the transistor 2 and the emitter current IE3 of the transistor 3 based on Shockley's equation.

Rt-IEZ= (kT/q) 7! n (n IE3
/IEz)... (2) In this example, it is assumed that there is no base current, so the collector current of transistor 1 is the emitter current of transistor 1, the collector current of transistor 2,
Equal to the emitter current of transistor 2. Further, the collector current of transistor 3 is equal to the emitter current of transistor 3. Therefore, the following equation (3) holds true.

Rz・Icz= (kT/q)12 n (m-n)
(3) Therefore, the voltage drop Vll+ across the resistor 11 is determined by the following equation (4), assuming that the resistance value of the resistor 11 is R1.

V +z = R+ ' I t□ -(R+/RzL(kT/q)l n (m-n)・
... (4) From this equation (4), the input threshold voltage VINTH is the voltage between the base and emitter of transistor 1 as vgt+, and the voltage between the base and emitter of transistor 4 as V B E 4
Then, the following equation (5) is obtained.

VINTH=VREl +VB! .

+ (R+/Rz)・(kT/q)1 n (m −
n)... (5) VBEI+VBE4 has a negative temperature coefficient, and is expressed as the following equation (6).

Vlltt +v! 14” 2 (Vgo-αIT-
α4T)・・・・・(6) ■Since 9°-1,25, equation (5) becomes the following equation (7).

■1.4□n=2.5V (α, +αa) T+ (
R+/Rz)・(kT/q)in (m-n)...
・ (7) Therefore α, +αa= (R+/Rz)・(k/ (1)
If R, , R, , m, and n are set so that i n (m−n), the input threshold voltage becomes a temperature-independent threshold voltage of about 2.5 V. Furthermore, since equation (7) is not a function of the power supply voltage, there is no dependence on the power supply voltage.

〔Effect of the invention〕

As explained above, in the present invention, the first resistor is placed between the emitter of the first transistor and the collector of the second transistor, and the second resistor is placed between the emitter of the second transistor and the ground. Since the values of these resistors are adjusted, the effects of temperature and power supply voltage on the input threshold voltage can be eliminated, and the voltage can be detected with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a voltage detection circuit according to the present invention, and FIG. 2 is a block system diagram showing a conventional voltage detection circuit. 1.2,3,4,30a,30b・-) transistor, 1
1.12...Resistor, 30...Current mirror circuit, 41...Input terminal, 42...Output terminal,
43...Input point, 44...Output point, 50...
·power supply.

Claims (1)

[Claims] a first transistor whose base is connected to the input terminal;
a second transistor whose collector is connected to the emitter of the first transistor through a first resistor and whose emitter is connected to ground through a second resistor; and whose collector and base are connected to the base of the second transistor. a third transistor whose emitter is connected to ground, a fourth transistor whose collector is connected to the output terminal, whose emitter is connected to ground and whose base is connected to the collector of the second transistor, and whose input point is the first transistor. and a current mirror circuit whose output point is connected to the collector of the third transistor.