JPH05167400A - Hysteresis circuit - Google Patents

Abstract

PURPOSE:To obtain the hysteresis circuit whose threshold level is externally set by changing an output voltage of a changeover circuit with an input voltage at other input terminal of a voltage comparator circuit. CONSTITUTION:When an input voltage Vin applied to an input terminal 202 of a voltage comparator circuit 20 is sufficiently low, a threshold level is a 2nd reference voltage Vref2. However, when the input voltage Vin is increased and larger than the 2nd reference voltage Vref2, the threshold level is decreased to a 1st reference voltage Vref1. When the input voltage Vin is decreased from a sufficiently high voltage conversely and the input voltage Vin is decreased from the 1st reference voltage Vref1, the threshold level increased from the 1st reference voltage Vref1 to the 2nd reference voltage Vref2. That is, the threshold level is optionally set by the input voltage Vin given externally. Furthermore, a hysteresis width (Rref1-Vref2) is optionally set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hysteresis circuit.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional hysteresis circuit. In the figure, Q21 is a transistor, Q22 is a transistor, Q23 is a transistor, and Q is a transistor.
24 is a transistor, Q25 is a transistor, Q26 is a transistor, R11, R12 and R3 are resistors, 41 is an input power supply, 42 is a reference current source, 43 is a drive power supply, and 44 is a reference voltage output terminal.

[0003] In the hysteresis circuit thus configured, when the input voltage V _in of the input power source 41 is changed slowly, the input voltage V _in is in the vicinity of the threshold voltage comparator circuit, noise due, its output is abnormal It is known to shake (chatter). In order to avoid this, the threshold value has been changed according to the input voltage V _in .

This will be described with reference to FIG. Input voltage V
_{When in} is sufficiently lower than the reference voltage V _ref that determines the threshold value, the transistor Q21 is off and the transistor Q22 is on, so the transistors Q25 and Q26 are also off, and the value of the reference voltage V _ref (V ₁ ) Indicates the power supply voltage V _cc of the drive power supply 43 as resistors R11, R12, R
It is a value obtained by resistance division by 13. _{V 1 = V cc × (R12} + R13) / (R11 + R12 + R13) ·· (1)

[0005] exceeds the value of formula (1) the input voltage V _in this state is increased, the transistor Q21 is turned on, the transistor Q22 is turned off, the transistor Q2
5. The transistor Q26 is also turned on and the voltage across the resistor R13 becomes approximately 0V. At this time, the value (V ₂ ) of the reference voltage V _ref is V ₂ = V _cc × R12 / (R11 + R12), assuming that the collector-emitter voltage of the transistor Q26 is 0V.・ It becomes (2).

Here, the reference voltage value V ₂ is smaller than the reference voltage value V ₁ and the reference voltage value V _2, and the threshold value becomes smaller when the input voltage V _in increases. ing. This prevents the output from chattering even when the input voltage V _in changes slowly.
The same applies when the input voltage V _in decreases conversely.

[0007]

However, in the hysteresis circuit configured as described above, the threshold value is determined by the ratio of the resistance R11, the resistance 12, and the resistance R13. To change this value, the resistance is changed. The value must be changed, and when configuring such a circuit inside the IC,
The threshold could not be changed. Also, the transistor Q26
Since the value of the current flowing through the resistor R11 changes depending on whether the switch is turned on or off, there is a problem that it also becomes a noise source.

Therefore, the present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a hysteresis circuit capable of setting a threshold value from the outside.

[0009]

In order to achieve such an object, a hysteresis circuit according to the present invention has a voltage comparison circuit for comparing two input voltages, two input terminals and one output terminal. And a switching circuit that outputs one of the input voltages input to the two input terminals to the output terminal, one input terminal of the voltage comparison circuit being connected to the output terminal of the switching circuit, and the output of the voltage comparison circuit. The signal is connected to the switching circuit, and the output voltage of the switching circuit is changed by the input voltage input to the other input terminal of the voltage comparison circuit.

[0010]

In the present invention, by changing the output voltage of the switching circuit by the input voltage of the other input terminal of the voltage comparison circuit, the threshold value of the voltage comparison circuit and its hysteresis width can be freely set from the outside.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of a hysteresis circuit according to the present invention. In the figure, a switching circuit 10 includes a reference voltage input terminal 10 _{1 for} inputting a first reference voltage V _ref1 and a second reference voltage V _{ref2 supplied} from the outside, a reference voltage input terminal 10 ₂ and a first of these. Reference voltage V _ref1 of the second reference voltage V
Reference voltage output terminal 10 ₃ that outputs either _ref2
have.

Further, the voltage comparison circuit 20 receives from the outside an input terminal 20 ₁ for inputting either one of the first reference voltage V _ref1 and the second reference voltage V _{ref2 which} have been switched by the switching circuit 10. It has an input terminal 20 ₂ and an output terminal 20 ₃ for inputting the input voltage V _in to be applied, and the output signal of this output terminal 20 ₃ is given from the outside by inputting it as the control signal of the switching circuit 10 described above. In addition, either the first reference voltage V _ref1 or the second reference voltage V _ref2 is output to the reference voltage output terminal 10 ₃ .

FIG. 2 is a diagram for explaining the operation of this voltage comparison circuit. As can be seen from the figure, when the input voltage V _in input to the input terminal 20 ₂ of the voltage comparison circuit 20 is sufficiently low, the threshold is the second reference voltage V _ref2 , but the input voltage V _in Increases and becomes larger than the second reference voltage V _ref2 , the threshold decreases to the first reference voltage V _ref1 . When the input voltage V _in the reverse decreases from when sufficiently high, the input voltage V _in is less than the first reference voltage V _ref1,
The threshold value is from the first reference voltage V _ref1 to the second reference voltage V _ref2.
Increase to.

That is, the threshold value can be arbitrarily set and the hysteresis width (V _ref2- V _ref1 ) can be arbitrarily set by the input voltage V _in supplied from the outside.

FIG. 3 is a specific circuit diagram showing the configuration of the above voltage comparison circuit. In the figure, the switching circuit 1
0 is composed of transistors Q9 to Q18 and a constant current source 11a, constant current source 11b and resistors R1 and R2, and the voltage comparison circuit 20 is composed of transistors Q1 to Q8 and a constant current source 21.

In such a configuration, the voltage comparison circuit 2
For 0, the magnitudes of the base voltages of the transistor Q1 and the transistor Q2 are compared, and the output is changed accordingly. In the voltage comparison circuit 20, the transistors Q6 to Q8 are output circuits, and a predetermined voltage _Vb1 is applied to the base voltage of the transistor Q6 so that the output stage operates.

In the switching circuit 10, the transistors Q9 to Q14 and the constant current source 11a and the constant current source 11b constitute a circuit for outputting one of the first reference voltage V _ref1 and the second reference voltage V _ref2. The output voltage becomes the emitter voltage of the transistors Q11 and Q12. This switching is done by transistor Q15
And turning on and off the transistor 17,
The transistors Q15 to 18 form signals in phase and in phase from the output voltage of the voltage comparison circuit 20,
The voltage is applied to the bases of the transistors 15 and 17.

Here, the transistors Q16 and the transistor 18 form signals of opposite phases, and a predetermined voltage is applied to the base voltage of the transistor 18 so that the inverting circuit thereof operates.

[0019] (1) when the input voltage V _in is sufficiently low (transistor Q1: on, transistor Q2: off)
→ (transistor Q5: on, output terminal 20 ₃ : output signal "1") → (transistor Q15: on, transistor Q17: off) → (transistor 9: off, transistor 11: off, transistor Q10: on, transistor Q12: ON).

Since the collector currents of the transistors Q10 and 12 are made substantially equal by the current mirror circuit of the transistors 13 and 14, the base-emitter voltage V _{BE of} the transistor Q10 and the base of the transistor Q12 are set. -It can be considered that the emitter-to-emitter voltage V _BE is equal. Therefore, the base voltage of the transistor Q1 (= the emitter voltage of the transistors 11 and 12) is the second reference voltage V
_{It has the same} value as _ref2 .

[0021] (2) when the input voltage V _in is sufficiently high (transistor Q1: off, transistor Q2: On)
→ (Transistor Q5: Off) → (Output signal "0") →
(Transistor Q15: Off, Transistor Q17: On) → (Transistor 9: On, Transistor 11: On, Transistor Q10: Off, Transistor Q12:
Off).

Considering in the same manner as the above-mentioned (1),
Since the base-emitter voltage V _BE of the base-emitter voltage V _BE of the transistor Q11 of the transistor Q9 becomes equal, the base voltage of the transistor Q1 becomes equal to the first reference voltage V _ref1.

Therefore, by setting the first reference voltage V _ref1 to be smaller than the second reference voltage V _ref2 , the input voltage V _ref
the second reference voltage V gradually increase from _in a small state
When it becomes almost equal to _ref2 , the output is inverted and the base voltage of the transistor Q1 is set to the first reference voltage V
_It will be lowered to _ref1 and will have a hysteresis characteristic. Conversely, when the input voltage V _in decreases, the output is inverted when the input voltage V _in becomes substantially equal to the first reference voltage V _ref1, and the base voltage of the transistor Q1 becomes the second reference voltage V _ref1. It increases to _ref2 (see Figure 2).

According to such a configuration, the switching circuit 1
Since two input voltages of 0 become two thresholds, the threshold can be freely set by the voltage from the outside. Further, since there is no change in current consumption, noise is extremely small.

[0025]

As described above, according to the present invention,
The threshold value, which is the criterion for the voltage, can be set arbitrarily by the voltage from the outside, so the degree of freedom is extremely large. Also, since there is no change in the current consumption due to the switching of the reference voltage, very little noise is generated. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of a hysteresis circuit according to the present invention.

FIG. 2 is a diagram for explaining the operation of the hysteresis circuit of FIG.

FIG. 3 is a circuit diagram showing a configuration according to an embodiment of a hysteresis circuit according to the present invention.

FIG. 4 is a diagram showing a configuration of a conventional hysteresis circuit.

[Explanation of symbols]

10 Switching circuit 10 ₁ Reference voltage input terminal 10 ₂ Reference voltage input terminal 10 ₃ Reference voltage output terminal 11a Constant current source 11b Constant current source 20 Voltage comparison circuit 20 ₁ Input terminal 20 ₂ Input terminal 20 ₃ Output terminal 21 Constant current source Q1 Transistor Q2 Transistor Q3 Transistor Q4 Transistor Q5 Transistor Q6 Transistor Q7 Transistor Q8 Transistor Q9 Transistor Q10 Transistor Q12 Transistor Q13 Transistor Q14 Transistor Q15 Transistor Q16 Transistor Q17 Transistor Q18 Transistor R1 Resistor R2 Resistor

Claims (1)

[Claims] 1. A voltage comparator circuit for comparing two input voltages, two input terminals and one output terminal, and any one of the input voltages input to the two input terminals is output to the output terminal. A switching circuit that is connected to an output terminal of the switching circuit and an output signal of the voltage comparison circuit is connected to the switching circuit, and the other input terminal of the voltage comparison circuit is A hysteresis circuit characterized in that an output voltage of the switching circuit is changed by an input voltage input to an input terminal.