JPH01138467A - Voltage comparison device - Google Patents

Abstract

PURPOSE:To obtain a high precision voltage by allowing to flow various fixed capacity of an electric current which varies in accordance with whether a voltage to be measured is higher or lower than a reference voltage, to a resistance which is connected with a input side transistor of a second Darlinton connection transistor group in series. CONSTITUTION:In case an electric source voltage is high, a voltage VIN is set up by resistances R1, R2 so as to be comparing voltage VIN> reference voltage Vref. Also it is set up so as to be contact-current source I1=I3, the resistance R3=R4. At this time, a current mirror composed of Q8, Q9 is not operated because the transistor Q1, Q4 are ON, Q2 is ON, Q8 is OFF and Q9 becomes ON status, the resistance R4 is passed through by constant-current source I8 only because Q9 is OFF. Next, the electric source voltage is decreased and on changing to be VIN<Qref, the transistor Q1 is passed through by the current of the name of I4 because the transistor Q1, Q4 keep ON, the transistor Q2 is OFF, Q8 becomes ON and the transistor Q9 of the current mirror also becomes ON. Here, looking at a VR3 and VR4 against the resistance R3 and R4, the voltage of VR4 changes. After all, a Hysteresis voltage Vhys comes to be Vhys=I4.R4, then free minute value is obtained in stability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a voltage comparator with a built-in hysteresis circuit.
In particular, the present invention relates to a voltage comparator suitable for detecting power supply voltage.

[Conventional technology]

Figure 2 is a circuit diagram showing the configuration of a conventional voltage comparator.
``Q4 is a Darlington input type differential amplifier transistor that constitutes a cis voltage generation circuit, and a resistor Vref is a reference voltage.R1 and R2 are resistors for comparison voltage generation, I, ,I,
, 1. is a constant current source.

Next, the operation will be explained.

When the power supply voltage is high, it is assumed that the hexagonal voltage of the voltage comparator is set to IN n VIN > Vref. Assuming that the power supply voltage is 'tvcc.

becomes. Since VIN is Vref, Ql-Q4 is O.
N.

Q2 is ON and Q is OFF. Therefore, Q?
becomes OFF.

Next, the power supply voltage Vcc decreases, the hexagonal voltage YEN also decreases, and when VIN < Vref iC, 4 Q, @ Q
4 is ON%Q2 is OFF and Q8 is 0NiC (Z)Te&Q is also ON.

When Q is turned on, it shorts out resistor R8.

The input voltage VIN is R1) (2) VIN - Vc (IcogoF), and the hysteresis width ΔV is (from equation 11 - equation (2)).In the end, the comparison voltage is a hysteresis voltage of only ΔV. The comparison voltage when the power supply voltage VCC decreases and the comparison voltage when the power supply voltage VCC increases differ by ΔV, and the detected voltage has a hysteresis characteristic. [Problems that the invention aims to solve] Since the conventional voltage comparator with a built-in hysteresis voltage is configured as described above, the problem is that it cannot generate a minute hysteresis voltage.In other words,
When the transistor Q is turned on, the saturation voltage Vaat of the transistor remains, and this Vsat is 10 to 3
Since the voltage varies to 0 mV, it was not possible to generate a hysteresis voltage of several tens of mV with high accuracy.

The voltage comparator with a built-in hysteresis voltage according to the present invention has a built-in hysteresis voltage.

This was done to solve the problems mentioned above.
The purpose of this invention is to obtain a voltage comparator that can generate a minute hysteresis voltage with very high accuracy.

[Ninth way to solve the problem]

In the voltage comparator ri according to the present invention, the current flowing through the resistor incorporated in one input circuit of the Darlington input differential amplifier constituting the voltage comparator ri is set to a value that differs by a predetermined amount depending on whether the voltage to be compared is larger or smaller than the reference voltage. It was designed so that

[Effect]

The voltage comparator in this invention generates a stable hysteresis voltage by switching the current flowing through the resistor built into the Darlington input differential amplifier.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, Q+ -Q2. QB-Q4 is a transistor Q that constitutes a Darlington input differential amplifier.

The transistor Ql, which constitutes the Q6 constant current load circuit, is turned on together with the transistor Q2, and a current for generating pressure is generated due to hysteresis. Transistor Q for switching
g, Qs are transistors forming a current mirror, R
8, R, d Resistance for hysteresis voltage generation, R,, R2
is the comparison input terminal setting resistance, I, ,12. I.

I4 is a constant current source.

First, when the power supply voltage is high, the input voltage VINk is set using R and R2 so that VIN>Vref.

Yes.

It is set to "4".At this time, Q
,, Q4 is ON, Q2 is ON, Q8 is OFF, Q
? Since is in the ON state, the current mirror consisting of Qg and Qs does not operate, and since Q is OFF, only the current flows into R4.

Next, when the VC and power supply voltages decrease and YES < Vref, 1. of Q, , Q4UQN. Q2 is OFF', Qs is ON, and Q? becomes OFF. As a result, when Q8 is turned on, Q of the force V mirror is also turned on, so a current of I4 flows through Q9. Here, if we look at the voltage drops VR and VR between % RB and R4, VIN > Vret cv and @, VR, -I, -
R, -I, -R4 Tom VR4... (3) When ¥IN< Vref c2), VR, -I, -
R, %(I − I )−R−VR4·(4), and the voltage of VR4 changes.

In other words, the voltage difference of (VR4-V几/) becomes the hysteresis voltage of the comparator, and from equations (4) and (3), the hysteresis voltage Vhys becomes Vhys -I4・R4, and any minute value can be stably obtained. .

In the above embodiment, although the voltage comparator input to the pnp l' transistor was described, all the transistors may be of opposite conductivity type, and the voltage comparator may be used as the voltage comparator input to the npn I' transistor.

〔Effect of the invention〕

As described above, according to the present invention, since the hysteresis circuit is obtained by the product of constant current construction and resistor R4, errors due to the residual voltage of the transistor do not occur as in the conventional example, and highly accurate hysteresis voltage can be obtained. Additionally, a minute hysteresis voltage of several mV can be obtained, which is impossible to achieve in the conventional example.

[Brief explanation of the drawing]

What is the configuration of an embodiment of this invention? Circuit diagram shown, 2nd
The figure is a circuit diagram showing the configuration of a conventional voltage comparator. In the figure, Q, , Qg are the first Darlington connection transistor bQ1- (It is the second Darlington connection transistor, R8-R4 are resistors, , ~, are constant current sources, Vref is the reference voltage, and VtN tfi is the resistor. This is a comparison voltage. Note that the same symbols in Figure 1 indicate the same, t, or equivalent parts.

Claims (1)

[Claims] (1) In a differential amplifier-type voltage comparator using first and second Darlington-connected transistor groups to which a reference voltage and a voltage to be measured are respectively input, the voltage comparator is connected in series to the input side transistor of the second Darlington-connected transistor group. 1. A voltage comparator, wherein different predetermined amounts of current flow through the connected resistor depending on whether the voltage to be measured is larger than or smaller than the reference voltage.