JP2000056841A - Voltage limiter circuit - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To execute a voltage limit accurately and with a small number of elements. SOLUTION: A first transistor Q1 and a second transistor Q2 having a diode connection structure form a differential pair, and the emitter current densities of the first transistor Q1 and the second transistor Q2 are set substantially equal to each other. The base-collector voltage of the second transistor Q2 connected to the output terminal of the control target circuit 2, that is, the output voltage of the control target circuit 2, is applied to a limit voltage VLi applied to the base of the first transistor.
When it becomes larger than m, the second transistor Q2 operates and the output voltage is fixed to the limit voltage VLim. Further, by setting the emitter current of the first transistor Q1 to be smaller than the emitter current of the second transistor Q2, the current consumption is reduced without lowering the limit accuracy of the voltage limiter circuit 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of a voltage limiter circuit for limiting an output voltage of a control target circuit to a certain voltage or less.

[0002]

2. Description of the Related Art As a voltage limiter circuit for limiting an output voltage from a control target circuit such as an operational amplifier or a comparator to a predetermined voltage or less, as shown in FIG. 6, an output terminal of the control target circuit, a reference power supply [Vref], A simple configuration in which a diode D1 is provided in the forward direction between them is known. In this circuit configuration, the output voltage of the control target circuit is equal to the reference power supply voltage Vref.
+ Diode operating voltage Vf
1 turns on, the voltage at the output terminal becomes Vref + Vf
Limited to not be larger.

As another configuration of an output limiter circuit, a configuration is known in which a limiter circuit using an amplifier Amp1 dedicated to a limit is connected to an output stage of a circuit to be controlled, as shown in FIG. In this limiter circuit, the amplifier Am
As p1, a circuit having a sufficiently higher driving capability than the circuit to be controlled (for example, an operational amplifier) is used. When the output voltage of the circuit to be controlled becomes higher than VLim applied to the negative input terminal of the amplifier Amp1, the amplifier Amp1 becomes NPN. The transistor is operated, and the output voltage is limited so as not to become larger than VLim.

[0004]

FIG. 6 shows a simple circuit configuration, which can be provided at a low cost. However, since the diode D1 has temperature dependency, the limit voltage fluctuates according to the environmental temperature. Therefore, there is a problem that the output voltage cannot be accurately maintained below the predetermined voltage. For example, in various sensor output circuits for vehicles and the like, the environmental temperature in which the circuit is placed changes remarkably, and it is inappropriate as a limiter for such a circuit. Also, each diode D by the wafer manufacturing process
The characteristic variation of 1 is also large. Therefore, the limiter circuit of FIG. 6 cannot be used for a circuit that requires a high-precision voltage limit regardless of a temperature change.

On the other hand, the limiter circuit shown in FIG. 7 uses the limit amplifier Amp1 and can accurately control the limit voltage. But such a dedicated amplifier
Amp1 is provided with a phase compensation capacitor or the like that requires a large number of elements and requires a large area. Therefore, IC
In this case, there is a problem that an increase in the chip area inevitably occurs and the circuit becomes expensive.

[0006] Therefore, the present invention is to reduce the number of elements,
It is another object of the present invention to provide a voltage limiter circuit that limits an output voltage with a simple circuit configuration and with high accuracy.

[0007]

According to the present invention, there is provided a voltage limiter circuit for limiting an output voltage from a control target circuit to be higher than a limiter voltage, wherein the limit voltage is based on A first transistor to be applied, a second transistor having a diode connection configuration connected in a forward direction, or a second transistor having a diode connection configuration, which constitutes a differential pair with the first transistor and is connected to an output terminal of the control target circuit; And a diode, wherein the emitter current density of the first transistor and the emitter current density of the second transistor or the forward current density of the diode are set substantially equal.

[0008] Since the first transistor and the second transistor (or diode) having a diode connection configuration form a differential pair, the voltage limiter circuit of the present invention includes a base voltage of the second transistor (or an anode voltage of the diode). ) Operates so as to be equal to the limit voltage applied to the base of the first transistor. Further, the base and collector of the second transistor (or the anode of the diode)
Is connected to the output of the control target circuit. For this reason, when the output voltage of the circuit to be controlled becomes higher than the limit voltage, the second transistor (or diode) is accordingly operated.
Operates to discharge the current from the output terminal, and as a result, the output voltage is fixed at the limit voltage. Here, the first transistor and the second transistor (or diode) forming a differential pair cancel characteristics variations due to temperature changes and variations due to fluctuations in element manufacturing conditions. It is not affected by the variation. Therefore, the electric power limiter circuit of the present invention can limit the output voltage with high accuracy by a simple circuit configuration.

According to the present invention, in the voltage limiter circuit, an emitter current of the first transistor is set smaller than an emitter current of the second transistor or a forward current of the diode. .

By reducing the emitter current of the first transistor, the current consumption can be reduced without lowering the voltage limiting accuracy of the voltage limiter circuit even when the first transistor is constantly operating.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a voltage limiter circuit according to the present embodiment. The control target circuit 2 whose output voltage is limited by the voltage limiter circuit 1 is, for example, an operational amplifier or a comparator, and the output terminal thereof is connected to the voltage limiter circuit 1 of the present embodiment. In addition,
The output stage of the control target circuit 2 has, for example, a general configuration in which the output current I0 is controlled according to the input applied to the base of the transistor Qc, as shown in FIG.

The voltage limiter circuit 1 has a limit voltage VLi
It has a first transistor Q1 to which m is applied to the base, and a second transistor Q2 in a diode connection configuration in which the base and collector are short-circuited. The diode connection of the second transistor Q2 is connected to the output stage of the control target circuit 2 in the forward direction.
A collector is connected to the output stage. The first transistor Q1 and the second transistor Q2 form a differential pair, and both emitters are both connected to a second constant current source 20 that draws a constant current I2. The constant current I1 is supplied from the first constant current source 10 to the collector of the first transistor Q1. When the current output from the control target circuit 2 is I0, the constant current I2 flowing from the second constant current source 20 is I2 = I0 + I1.

The emitter area of the first transistor Q1 is A1, and the emitter area of the second transistor Q2 is A2.
Then, the circuit is configured so that A2 / A1 = I0 / I1.

In such a voltage limiter circuit 1,
The limit voltage VLim applied to the base of the first transistor Q1 is a voltage division of the power supply Vcc which can be arbitrarily set by the voltage dividing resistors R1 and R2, and the limit voltage VLim is applied to the first transistor Q1. , A current substantially equal to the constant current I1 is constantly supplied to the second constant current source 20. Note that the limit voltage VLim is determined by dividing the voltage dividing resistors R1 and R2.
The reference voltage Vref generated by a predetermined reference power supply circuit or the like may be applied to the base of the first transistor Q1 as the limit voltage VLim.

In such a configuration, when the output voltage of the control target circuit 2 becomes higher than the limit voltage VLim,
As a result, the second transistor Q2 operates, and the current I0 output from the control target circuit 2 flows. Here, in the present embodiment, in the operation state of the second transistor Q2, the emitter current density of the first transistor Q1 and the emitter current density of the second transistor Q2 are set to be substantially equal. Therefore, VBE1 of the first transistor Q1 and VBE2 of the second transistor Q2 are accurately equalized. As a result, even when the output voltage from the control target circuit 2 is higher than VLim, the output voltage generated at the output terminal is the limit voltage VLim. It will be fixed to.

Although the operating characteristics of the transistor change due to the temperature change of the environment where the circuit is placed, and individual differences exist due to the fluctuation of the circuit manufacturing conditions, these transistors Q1 and Q2 of the differential configuration have these differences. Limit voltage VLi against output voltage to cancel changes and variations
m is accurately maintained without being affected by temperature changes or variations during element manufacturing.

FIG. 3 shows a configuration of a control target circuit 2 to which the voltage limiter circuit 1 of FIG. 1 can be applied and a control characteristic of an output voltage. The control target circuit 2 in FIG. 3A is a circuit such as an operational amplifier whose output changes according to the input, and by connecting the voltage limiter circuit 1 of the present embodiment to the output terminal, the control target circuit 2 in FIG. ), When the output voltage that changes according to the input signal to the control target circuit 2 exceeds VLim,
The voltage obtained at the output terminal is fixed at the limit voltage VLim. When the control target circuit 2 is a circuit such as a comparator that generates a difference output between the reference voltage Vref and the input signal voltage as shown in FIG. 3B, the voltage limiter circuit 1 of the present embodiment is connected to the output terminal. By connecting, when the differential output from the control target circuit 2 exceeds VLim as shown in FIG. 3D, the output voltage obtained at the output terminal becomes the limit voltage VLim.
Fixed to

Note that the voltage limiter circuit 1 of the present embodiment
When the input impedance of the next stage connected to the output terminal of the control target circuit 2 is relatively high, the output voltage can be very accurately limited to the limit voltage VLim or less. However, it is not impossible to apply the present invention to a case where the circuit input impedance of the next stage is low, although the limit accuracy is somewhat lowered.

In the voltage limiter circuit 1 of the present embodiment, a diode connected in the forward direction to the control target circuit 2 can be used instead of the diode-connected second transistor Q2. Also in this case, it is necessary to set the forward current density of the diode so that the emitter current density of the first transistor Q1 becomes substantially equal. When a diode is used, the accuracy of the limit voltage VLim with respect to the output voltage is lower than when a diode-connected transistor is used.

(Circuit Configuration Example 1) Next, a more specific circuit configuration example of the voltage limiter circuit 1 according to the above embodiment will be described with reference to FIG. In the following, portions corresponding to the above-described configuration are denoted by the same reference numerals, and description thereof is omitted. Further, the transistors indicated by “× 2” and “× 3” in the figure indicate the emitter area ratios to the unmarked transistors.

The voltage limiter circuit 1 shown in FIG. 4 has an appropriate configuration for limiting the output voltage when the output stage of the control target circuit 2 has a constant current output as shown. In this voltage limiter circuit 1, the first constant current source 10 in FIG. 1 is configured by a transistor Q3, and the second constant current source 20 is configured by transistors Q4 and Q5 and a current mirror circuit 22. Also, the transistor Q
The transistor 3 and the transistor Q4 are connected in parallel with the output transistor Q0 of the current mirror circuit 4 in the output stage of the control target circuit 2, and flow a current equivalent to that of the input transistor of the current mirror circuit 4.

In the configuration example of FIG. 4, the emitter area A1 of the first transistor Q1 is set to be smaller than the emitter area A2 of the second transistor Q2.
Specifically, the emitter area A1 of the first transistor Q1
Is 1, the emitter area A of the second transistor Q2
2 is set to, for example, twice. The ratio of A1 to A2 is not limited to 1: 2, but satisfies A2 / A1 = I0 / I1, and the output voltage generated at the output terminal exceeds the limit voltage VLim, and the second transistor Q2 operates. In this case, the emitter current density of the first transistor Q1 and the second transistor
It is necessary to set such that the emitter current density of the transistor Q2 becomes substantially equal. The emitter area A2 of the second transistor Q2 corresponds to the emitter area (twice) of the transistor Q0 of the current mirror circuit 4 of the control target circuit 2. However, the emitter area A2 of the transistor Q0 and the second transistor Q2 do not necessarily have to match. The emitter area A2 is determined by the current transmitted from the transistor Q0 when the output voltage of the control target circuit 2 (the voltage between the transistor Q0 and the transistor Qc) exceeds the limit voltage VLim.
2 should be large enough to flow out. Further, the emitter area A1 of the first transistor Q1
It is preferable that the first transistor Q1 reduce the emitter current that always flows to the current mirror circuit 22 and reduce the emitter current to such an extent that the effect of reducing current consumption can be obtained.

The transistor Q3 forming the first constant current source 10
Is set to one half of the emitter area of the transistor Q0, and the constant current I
A constant current I1 of one half of 0 flows out. Also, the emitter area of the transistor Q4 is set to one half of the emitter area of the transistor Q0 similarly to the transistor Q3, and supplies the current mirror circuit 22 with the same amount of current as the transistor Q3.

As described above, the constant current I0 in the circuit to be controlled is
By setting the constant current I1 of the voltage limiter circuit 1 smaller than that of the first transistor Q1 and setting the emitter area of the first transistor Q1 smaller than the emitter area of the second transistor Q2, the emitter current density of the first and second transistors Q1 and Q2 can be reduced. Are reduced, and the current consumption of the voltage limiter circuit 1 is reduced.

The current mirror circuit 22 in the second constant current source 20 includes mirror-connected transistors Q6 and Q7.
It is composed of Transistor Q on the input side
6, a current equal to the constant current supplied from the transistor Q4 via the transistor Q5 flows, and the collector of the output side transistor Q7 is connected to the first and second transistors Q1 and Q2. Further, the emitter area of the transistor Q7 is set to be three times that of the transistor Q6, and the total maximum emitter current (I0 + I1) of the first and second transistors Q1 and Q2 flows as the constant current I2.

The base of the PNP transistor Q5 is connected to the emitters of the first and second transistors Q1 and Q2, and the voltage of the collector of the transistor Q4 is changed from the emitter potential of the transistors Q1 and Q2 to VBE.
Only fixed at a higher voltage. Since the transistor Q5 fixes the collector voltage of the transistor Q4 in this manner, the Early effect in the transistor Q4 is reduced. In addition, due to the presence of the transistor Q5, the amount of current supplied to the current mirror circuit 22 is reduced by the power supply voltage V
It is less susceptible to cc fluctuations.

In the above-described circuit configuration, when the output voltage of the control target circuit 2 exceeds the limit voltage VLim, the second transistor Q2 operates to supply the current I0 supplied to the output terminal to the second constant current source 20. Discharge toward. Then, at this time, since VBE1 of the first transistor Q1 and VBE2 of the second transistor Q2 are aligned, the output voltage is fixed to the limit voltage VLim.

(Circuit Configuration Example 2) FIG. 5 shows another example of the circuit configuration of the voltage limiter circuit 1 according to the above embodiment. Note that, similarly to FIG. 4, parts corresponding to the above-described configuration are denoted by the same reference numerals, and description thereof will be omitted. Further, the transistors indicated by “× 2” and “× 3” in the figure indicate the emitter area ratios to the unmarked transistors.

The voltage limiter circuit 1 shown in FIG. 5 limits the output voltage when the output stage of the control target circuit 2 has a configuration in which a resistor R0 is connected to a power supply as a pull-up resistor as shown in the figure. Has an appropriate configuration. In the voltage limiter circuit 1, the first constant current source 10 uses a resistor R3 connected to a power supply instead of the transistor Q3 in FIG. 4, and the second constant current source 20 uses a resistor R4 connected to a power supply and a transistor Q8 and the current mirror circuit 24.

The emitter area A1 of the first transistor Q1
Is smaller than the emitter area A2 of the second transistor Q2. Here, as in the configuration example 1, the second transistor Q2 is smaller than the emitter area A1 of the first transistor Q1.
Is set to be twice as large. The current mirror circuit 24 provided on the emitter side of the first and second transistors Q1 and Q2 is connected to a power supply.
A transistor Q9 connected via a resistor R4 and a transistor Q8, and a transistor Q10 mirror-connected to the transistor Q9, the emitter area of the transistor Q10 is tripled for the same reason as the transistor Q7 of FIG. It is set and the constant current I2 flows out.

In the circuit configuration as shown in FIG.
0, R3, and R4 are set so that R3 and R4 are larger than R0, for example, so that 2R0 = R3 = R4 is satisfied. The ratio of the emitter areas A1 and A2 and the resistance value R0,
The ratio of R3 and R4 is not limited to the above example, but also in the case of the present circuit configuration example 2, A2 / A1 = I0 / I1 is satisfied, and the output voltage generated at the output terminal exceeds the limit voltage VLim. When the transistor Q2 is operating, the first
It is necessary to set the emitter current density of the transistor Q1 and the emitter current density of the second transistor Q2 to be substantially equal.

The base of the PNP transistor Q8 is connected to the emitters of the first and second transistors Q1 and Q2. The potential of the resistor R4 on the low voltage side is higher than the emitter potential of the transistors Q1 and Q2. The value is set to be higher by VBE8 to prevent fluctuation of the constant current I2 of the current mirror circuit 24.

With the voltage limiter circuit 1 having such a configuration, as in the case of the circuit 1 of FIG. 4, when the output voltage of the control target circuit 2 exceeds the limit voltage VLim, the second transistor Q2 operates to output. Current I0 at the second constant current source 2
The output voltage is fixed to the limit voltage VLim because the voltage VBE1 of the first transistor Q1 is equal to the voltage VBE2 of the second transistor Q2.

Here, when the output voltage from a certain circuit becomes larger than a predetermined limit voltage, the cause of the voltage excess is a predetermined reason (for example, a disconnection of a circuit, a short circuit, a device failure, etc.). It has been considered to introduce a control method for determining the above. This is because, when the circuit to be controlled has an abnormality in the output value, for example, the output of a hydraulic pressure sensor of a vehicle brake, whether the abnormality is caused by the abnormality of the sensor, the failure of the brake, or The present invention can be applied to a system in which it is desired to analyze whether the wiring is broken or the like and to deal with it. The voltage limiter circuit 1 of the present embodiment accurately limits the output voltage with a small number of elements. In particular, when the output voltage of the control target circuit 2 exceeds the limit voltage VLim, the voltage at the output terminal is reduced to the limit voltage VL.
Fix to im. Therefore, if the voltage limiter circuit of the present embodiment is used in such a system, the excessive output voltage value and the fact that the obtained output voltage value is larger than the Is easy to determine as correct, and the reason for the voltage excess etc. can be easily determined.

[0036]

As described above, the voltage limiter circuit of the present invention operates so that the base voltage of the second transistor (or the anode voltage of the diode) becomes equal to the limit voltage applied to the base of the first transistor. To do
When the output voltage of the control target circuit becomes higher than the limit voltage, the second transistor (or diode) operates,
Fix the output voltage to the limit voltage. Further, since the first transistor and the second transistor (or diode) cancel variations in characteristics due to temperature changes and variations in device manufacturing conditions, the limit voltage is
It is not affected by temperature changes and variations during device manufacture. Therefore, in the present invention, a voltage limiter capable of limiting the output voltage with high accuracy can be realized by a simple circuit with a small number of elements. Therefore, when the voltage limit circuit of the present invention is integrated, for example, when integrated on the same chip as the control target circuit, the number of elements is small. An integrated circuit with a small area can be provided.

In the present invention, by reducing the emitter current of the first transistor, the current consumption of the circuit can be reduced when the first transistor is constantly operating.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a configuration of a voltage limiter circuit according to an embodiment.

FIG. 2 is a diagram illustrating a configuration example of an output stage of a control target circuit controlled by a voltage limiter circuit according to the present embodiment.

FIG. 3 is a diagram illustrating a configuration of a control target circuit controlled by a voltage limiter circuit of the present embodiment and a control characteristic of an output voltage.

FIG. 4 is a diagram illustrating a specific configuration example of a voltage limiter circuit according to the present embodiment.

FIG. 5 is a diagram illustrating a specific configuration example of the voltage limiter circuit according to the present embodiment, which is different from FIG. 4;

FIG. 6 is a diagram illustrating a configuration of a conventional voltage limiter circuit.

FIG. 7 is a diagram showing another configuration of a conventional voltage limiter circuit.

[Explanation of symbols]

1 voltage limiter circuit, 2 controlled circuit, 4, 22,
24 current mirror circuit, 10 first constant current source, 20
Second constant current source.

Claims (2)

[Claims] 1. A voltage limiter circuit for limiting an output voltage from a control target circuit to be higher than a limit voltage, comprising: a first transistor to which the limit voltage is applied to a base; and a differential between the first transistor and the first transistor. A second transistor having a diode connection configuration or a diode connected in a forward direction, which is connected in a forward direction to an output terminal of the controlled circuit, and an emitter current of the first transistor. The density and the second
A voltage limiter circuit, wherein an emitter current density of a transistor or a forward current density of the diode is set substantially equal. 2. The voltage limiter circuit according to claim 1, wherein an emitter current of said first transistor is set smaller than an emitter current of said second transistor or a forward current of said diode. Voltage limiter circuit.