JP3343920B2 - Voltage detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detection circuit, and more particularly to a voltage detection circuit for detecting that a power supply voltage has dropped below a predetermined voltage.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional voltage detection circuit.

[0003] In the figure, the power supply voltage Vcc inputted from the input terminal 5 is inputted is divided by resistors R _6, R ₇ to a differential amplifier 7. On the other hand, bunt gap Zener diode Dz which is known temperature compensation, the power supply voltage vcc is supplied with current from current source I ₃ supplied to generate a reference voltage V _REF = 1.25V at one end. Differential amplifier 7
Compares the _divided voltage of the power supply voltage Vcc with the reference voltage _VREF, and outputs the detection voltage _VDET to the output terminal 6 when the current voltage Vcc falls below a predetermined threshold voltage. Since the reference voltage _VREF is temperature-compensated, a drop in the power supply voltage Vcc is detected stably with respect to a change in temperature.

[0004]

However, the conventional voltage detection
In the output circuit, temperature compensation is performed to improve the temperature characteristics.
Using a band gap zener diode Dz
You. Therefore, the reference voltage V _REF= 1.25V
Therefore, the threshold value of the power supply voltage Vcc must be 1.25 V or more.
However, there is a disadvantage that the detection operation cannot be performed.

On the other hand, although the threshold value if the reference voltage a forward voltage drop V _F of the diode can be less of a low-voltage 1.25V, the reference voltage will have a negative temperature characteristic.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described drawbacks, and has been made in view of the above circumstances. A voltage capable of detecting a drop in power supply voltage at a low voltage of 1.25 V or less and operating stably even with temperature changes. It is an object to provide a detection circuit.

[0007]

In order to solve the above problem, the present invention is configured as shown in the principle diagram of FIG.

That is, a constant current is generated from the power supply voltage Vcc.
Constant current circuit 2 and the constant current generated by the constant current circuit 2.
PN junction element 1 which is supplied with a current and generates a PN junction voltage
And a reference voltage generating means 3 for generating a reference voltage VREF according to the PN junction voltage , and comparing an input voltage VI according to the power supply voltage Vcc with an output reference voltage VREF from the reference voltage generating means 3. Detecting means 4 for outputting detection voltage VDET
In the voltage detection circuit provided with the said reference voltage generating hand
The stage 3 is connected in parallel to the PN junction device 1 and
The N junction voltage is divided and the output base of the reference voltage generating means 3 is divided.
A voltage dividing resistor supplied to the detection means 4 as a reference voltage VREF
R1 and R2, and the detecting means 4 has first and second transistors Q2, Q2, Q3, whose emitters are connected in common and whose current density ratio is set to a predetermined value to obtain a desired temperature characteristic.
Q3 and current mirror circuits Q4 and Q5 for controlling the collector current of the second transistor Q3 to be equal to the collector current of the first transistor Q2 according to the collector current of the first transistor Q2. A differential amplifier is provided, wherein the output reference voltage VREF of the reference voltage generating means 3 is input to the base of the first transistor Q2, and the input voltage VI is input to the base of the second transistor Q3.

[0009]

According to the above arrangement, the reference voltage VREF has a well-known negative temperature coefficient (-2 mV / ° C.) of the PN junction voltage, and the divided voltage connected in parallel to the reference voltage generating means 3. Usually
Temperature coefficient can be set to any negative value by anti-R1 and R2
You. Hand, the detection signal VDET output of the differential amplifier is inverted
Is output, the temperature coefficient of the input offset voltage is arbitrarily set. The current density ratio B /
Since it is proportional to the logarithm of A, it works so that it can be set to any positive or negative value or zero by selecting the value of B / A.

[0010]

FIG. 2 is a circuit diagram of an embodiment of the present invention. As shown in the figure, the power supply voltage Vcc from the input terminal 5 is equal to the resistances R ₃ and R ₃ connected in series between the input terminal 5 and the ground.
_The voltage is divided by V ₄ into V _I (input voltage), which is input to the detection means 4. On the other hand, the output detection voltage V
_DET is output to the output terminal 6 via the transistor Q _6.

The reference voltage generating means 3 is a PN junction element.
Transistor Q₁And resistance R₁, R _TwoIs a constant current circuit.
Current source I₁Consists of Transistor Q₁Ha
Connected as a diode
You. Transistor Q₁Emitter connected to ground
And the base and collector are current sources I₁Supply voltage V through
It is connected to an input terminal 5 to which cc is supplied. Also,
Transistor Q₁Between the base collector and ground
Resistance R₁, R_TwoAre connected in series.

As a result, the power supply voltage Vcc is
Q₁Base-emitter forward drop
Lower voltage V_F(≒ 0.6 V) or more, the transistor Q
₁Turns on and the resistance R₁, R_TwoBy V_FDivided voltage
Is the reference voltage V_REFIs output to the detection means 4. Real truth
In the example, V_REFResistor R so that it becomes ≒ 0.2V₁, R _Two
Is chosen.

The detecting means 4 comprises a differential amplifier comprising a current power supply I ₂ , a transistor Q ₂ (first transistor), a transistor Q ₃ (second transistor), and transistors Q ₄ and Q ₅ . Commonly connected emitters of the first and second transistors are connected to the input terminal 5 to which a power supply voltage Vcc through a current source I ₂ is supplied. The collectors of the transistors Q ₂ and Q ₃ are
It is connected to the collectors of transistors Q ₄ and Q ₅ which are connected in a current mirror.

[0014] Thus, the detection means 4 receives the divided reference voltage (V _REF ≒ 0.2V) the base-emitter junction voltage of the transistor Q ₁ to the base of the transistor Q _2, the base of the transistor Q ₃ the power supply voltage Vcc to input divided by the input voltage V _I is compared to. The difference between the input voltage V _I to decrease each of the base voltage transistors Q _2, Q
₃ base-emitter junction voltage difference (offset voltage Δ
When the V _B), the detection voltage of a high level, the transistor Q ₃ is turned on is output to the base of the transistor Q _6.

Subsequently, the transistor Q ₆ is turned on, and a low-level detection voltage is output to the output terminal 6.

Incidentally, the input offset voltage ΔV _B is ΔV _B = V _BEQ2 −V _BEQ3

[0017]

(Equation 1)

## EQU1 ## Here, k is the Boltzmann constant, T is the absolute temperature, q is the electron charge amount, A is the emitter area of the transistor Q _2, B is the emitter area of the transistor Q _3, Is is the reverse saturation current, I _CQ2 transistor Q ₂ , I _CQ3 is the collector current of the transistor Q ₃ , and Is is the forward saturation current. (Note that the DC current amplification factor β is β≫1.) If I _CQ2 = I _{CQ3 in the} equation (1), ΔV _B = (kT / q) · ln (B / A) (2) . Therefore, the temperature coefficient of the offset voltage ΔV _B is

[0019]

(Equation 2)

## EQU1 ##

On the other hand, the reference voltage V _REF is

[0022]

(Equation 3)

## EQU2 ##

In the equation (4), the temperature coefficient ΔV _BEQ1 / ΔT of the base-emitter junction voltage of the transistor Q ₁ shows a negative value of −2 mV / ° C. as is well known. Therefore, in equation (3), B> A and the offset voltage Δ
The V _B temperature coefficient [Delta] V _B / [Delta] T is a positive value,

[0025]

(Equation 4)

By selecting the emitter area ratio B / A of the transistors Q ₂ and Q ₃ and the values of the resistances R ₁ and R ₂ so that the temperature coefficient of the reference voltage V _REF and the offset voltage ΔV _B are equalized, It can operate stably with respect to temperature changes.

As described above, according to the present embodiment, 1.25 V
From the following low voltage power supply voltage Vcc, the transistor Q₁of
Resistance R according to base-emitter junction voltage₁, R_TwoSet in
Fixed reference voltage V_REFAnd the current ratio is determined
Of the transistor Q _Two, Q_ThreeError amplification with
Input voltage V obtained by dividing power supply voltage Vcc by_ICompare with
And a stable detection of a drop in the power supply voltage Vcc against a temperature change.
Can be issued. Also, the reference voltage V_REFTemperature coefficient of
Is the resistance R₁, R_TwoValue can be any negative value, off
Set voltage ΔV_BThe temperature coefficient of transistor Q_Two, Q_Three
Any positive or negative by choosing the emitter area of
Value, or zero, so that any temperature
It is possible to have the nature.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

2, the same components as those of FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the input voltage V_Iof
Voltage dividing resistor R_FourResistor R on the ground side of _FiveAre connected in series,
Resistance R_Four, R_FiveThe reference voltage V_REFOf the voltage dividing resistance R
_TwoAre connected on the ground side. This
Then, the transistor Q_TwoWhen the base voltage of
And the resistor R_FiveThe voltage drop across the transistor decreases
Q_ThreeLowers the base voltage of the transistor Q_TwoIs saturated
Prevents entering state.

The PN junction element is not limited to a transistor, but may be a diode. Further, even when the respective transistors are configured to have the opposite polarities, it is needless to say that the same effect as in the above embodiment can be obtained.

[0032]

As described above, according to the present invention, a reference voltage generator is provided.
The temperature of the reference voltage is set by a voltage-dividing resistor connected in parallel with the
Set the degree coefficient to any negative value, input the voltage according to the power supply voltage and the reference voltage divided by the voltage- dividing resistor and compare them. The output of the differential amplifier is inverted and the detection signal is output. The first temperature coefficient of the input offset voltage is set arbitrarily.
In addition, by setting the current density ratio to an arbitrary value according to the current density ratio of the second transistor, the overall temperature characteristic can be set to an arbitrary characteristic, and, of course, the temperature characteristic can be set to have no temperature characteristic. .

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a circuit diagram of one embodiment of the present invention.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of an example of a conventional voltage detection circuit.

[Explanation of symbols]

1 PN junction element 2 constant current circuit 3 reference voltage generating means 4 detecting signal Vcc supply voltage V _REF reference voltage V _I input voltage V _DET detection voltage Q ₁ transistor (PN junction element) Q ₂ transistor (first transistor) Q ₃ Transistor (second transistor) I ₁ current source (constant current circuit)

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01R 19/00-19/32 H02H 3/02-3/253 H02J 1/00

Claims (1)

(57) [Claims] (1)A constant current circuit that generates a constant current from the power supply voltage
And a constant current generated by the constant current circuit.
A PN junction element for generating an N-junction voltage,The PN contact
Reference voltage generation means for generating a reference voltage according to the combined voltage
And an input voltage corresponding to the power supply voltage to the reference voltage generating means.
Detection that outputs the detection voltage in comparison with the output reference voltage
And a voltage detection circuit comprising:The reference voltage generating means is connected to the PN junction element in parallel.
And divides the PN junction voltage to generate the reference voltage.
A partial voltage supplied to the detection means as an output reference voltage of the means
Have resistance,  The detecting meansIsEmitters are connected in common, each current
The density ratio was set to a predetermined value to obtain the desired temperature characteristics.
First and second transistors; and the first and second transistors in accordance with a collector current of the first transistor.
2 is connected to the first transistor.
Karen controlled to be equal to the collector current of the star
And a differential amplifier including a first mirror and an output reference voltage of the reference voltage generating means.
The input voltage is applied to the base of a transistor in the second transistor.
Voltage detection circuit characterized by being input to the base of a transistor
Road.