JPH0583872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a voltage detection circuit that detects a change in power supply voltage with respect to a reference voltage.

[Technical background of the invention]

Conventionally, as shown in FIG. 1, this type of voltage detection circuit has two transistors 1 and 2 whose emitters are commonly connected to a constant current source 3, and whose collectors are connected to a power supply line via resistors 4 and 5. A differential amplifier is constructed by applying a power supply voltage V _CC to the collector of a transistor 6 whose base and collector are connected via a resistor 7, and a reference voltage V _A to the connection point between the resistor 7 and the collector of the transistor 6. The reference voltage V _A is applied to the base of the transistor 1, and the resistors 8 and 9 and the diode 10 are
are connected in series and the power supply voltage is applied to the connection point between resistors 8 and 9.
By generating a detection voltage V _B by dividing V _CC and applying this detection voltage V _B to the base of transistor 2, the difference voltage between the reference voltage V _A and detection voltage V _B is extracted from the collector of transistor 1. , this differential voltage is applied to the base of the transistor 11, and if the differential voltage is greater than or equal to the threshold value of the transistor 11, it is detected from the connection point between the collector of the transistor 11 and the resistor 12 that the power supply voltage has become greater than or less than a predetermined value. There is something like this. In this case, the diode 10 is provided to match the temperature characteristics of the reference voltage V _A and the detection voltage V _B in relation to the transistor 6 for forming the reference voltage.

[Problems with background technology]

However, in the above-mentioned conventional circuit, since there are large variations in the resistance elements for forming the reference voltage and the detection voltage, these variations directly appear as variations in the detection voltage, and there is a drawback that the detection accuracy of the power supply voltage is poor.

[Object of the Invention] An object of the present invention is to solve the above-mentioned drawbacks and provide a voltage detection circuit that can detect the power supply voltage with high accuracy.

[Summary of the invention]

The present invention provides a second source in addition to the constant current source for differential amplification.
A constant current source is provided, and a constant current is caused to flow from this second constant current source to a diode-connected transistor to generate a reference voltage.Furthermore, the constant current flowing to this transistor is also transmitted to a detection voltage generation section by a current mirror effect. The above object is achieved by reducing the relative error between the reference voltage and the detected voltage.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 2 is a circuit diagram showing one embodiment of the present invention, and all the same parts as in FIG. 1 are represented by the same symbols. The difference between this figure and FIG. 1 is that a second constant current source 13 is provided, and a constant current is passed from this constant current source 13 through a resistor 14 to a transistor 15 having a diode-connected configuration. A reference voltage V _A is generated at the connection point with the source 13, and this reference voltage V _A is applied to the base of the transistor 1. Further, a transistor 16 controlled by the transistor 15 is provided, a current mirror circuit is configured so that its collector current is equal to the collector current of the transistor 15, and a detection voltage V _B is generated at the connection point with the collector resistor 17. The reason is that the voltage is applied to the base of transistor 2. In this case, transistors 15 and 16 are selected to have the same characteristics.

Here, the constant current source 13 is configured to output a constant current _I.sub.O (= _K.V.sub.T / _R.sub.S ) proportional to absolute temperature by utilizing a band gap in semiconductor manufacturing. Here, K is a proportionality constant, V _T is the PN junction forward voltage, and R _S is the internal resistance of the band gap.

Therefore, in such a configuration, the transistor 15
The collector voltage of is V _BE , the resistance value of resistor 14 is R ₁ ,
If the resistance value of the resistor 17 is _R2 , the reference voltage V _A and the detection voltage V _B are calculated by the following equations (1) and (1), respectively.
It is expressed by equation (2).

V _A = R ₁・I _O +V _BE =K・R ₁ /R _S V _T +V _BE ……(1) V _B =V _CC −R ₂・I _O =V _CC −K・R ₂ /R _S V _T ...(2) Since the detection output passes through an inflection point when V _A = V _B , the power supply voltage V _CC at this time becomes the detection target. Therefore, from the above equations (1) and (2), V _CC =K·R ₁ +R ² / _RS V _T +V _BE (3).

Therefore, within the integrated circuit, the balance between the resistors can be achieved with high precision, so that the reference voltage V _A and the detection voltage
The relative error with V _B becomes small, and changes in the power supply voltage V _CC can be detected with high accuracy. in this case,
The first term in equation (3) indicates a positive temperature coefficient, and the second term indicates a negative temperature coefficient, so the resistance value R ₁ + R ₂
By appropriately selecting the values of V and collector voltage V _BE , it is possible to construct a voltage detection circuit with a temperature coefficient of zero.

In addition, although the transistor is configured as an NPN type in the embodiment, it can also be configured as a PNP type.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a second constant current source is provided, a constant current is caused to flow from the second constant current source to a transistor having a diode connection configuration, and a reference voltage is generated. Since the constant current flowing through the transistor is also passed through the detection voltage generation section using a current mirror configuration to reduce the relative error between the reference voltage and the detection voltage, changes in the power supply voltage can be detected with high accuracy. Further, when a bandgap type is used as the second constant current source, it is possible to realize a voltage detection circuit with a temperature coefficient of zero.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional voltage detection circuit, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1, 2, 15, 16...transistor, 3, 1
3... Constant current source, 4, 5, 14, 17... Resistor.

Claims (1)

[Claims] 1 A differential amplifier consisting of a first and a second transistor whose emitters are commonly connected to a first constant current source, and a second constant current source connected between a power supply line and the base of the first transistor. And this second
is connected to a connection point between the constant current source and the base of the first transistor, generates a reference voltage at the connection point and applies it to the base of the first transistor, the base and collector are connected, and the emitter is grounded. a series branch consisting of a third transistor and a first resistor connected to the collector of the third transistor; connected to the power line through the resistor of
and a fourth transistor that generates a detection voltage at a connection point between the second resistor and the collector and applies it to the base of the second transistor, and receives a change detection signal of the power supply voltage with respect to the reference voltage from the differential amplifier. A voltage detection circuit characterized by outputting.