JPH0241208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable reference voltage comparator having hysteresis characteristics used in load current control devices and the like.

In a load current control device, for example, when the load current increases and exceeds a certain value, a comparator detects a drop in voltage across a resistor connected in series with the load, and controls the load current to be decreased. However, if the voltage drop across the resistor decreases due to a decrease in the load current, and the load current is immediately increased again,
A so-called hunting phenomenon occurs. In order to prevent this, as shown in FIG. 1, the reference voltage of the comparator is given a hysteresis characteristic to make the control start voltage different when the voltage rises and when the voltage falls.

An example of a conventional variable reference voltage comparator is shown in FIG. In FIG. 2, resistors R ₁ and R ₂ constitute a voltage divider, and the first reference voltage Vt ₁ is generated by this voltage division ratio. The emitter of the transistor TR ₁ and the emitter of the transistor TR ₂ are connected to each other and grounded via a constant current circuit I, and the input voltage E is input to the base of the transistor TR ₁ .
The base of the transistor _TR2 is connected to a voltage dividing point of the voltage divider, and a reference voltage is input thereto. Also, the collector of the transistor _TR2 is a transistor
The transistor TR ₅ is connected to the power supply Vcc via its base and emitter, and the collector and base of the transistor TR ₅ are connected to each other. On the other hand, the collector of the transistor TR ₂ is also connected to the base of the transistor TR _{6 .}
is turned on when the transistor _TR2 is turned on, turning on the transistor _TR4 . When the above transistor TR ₄ turns on, the transistor TR ₃
is turned on, and the resistor _R3 is connected in parallel to the resistor _R1 . This changes the voltage division ratio of the voltage divider and generates the second reference voltage _Vt2 . The first or second reference voltage maintains the emitters of the transistors TR1 and _TR2 at the reference voltage via the base-to-emitter of _the transistor _TR2 . The transistor _TR1 constitutes a first switch that is in an off state when the input voltage E is lower than the reference voltage, and is in an on state when the input voltage E is higher than the reference voltage. Said transistor TR ₂
is in an off state because when the transistor _TR1 is in an on state, the entire current of the constant current I is passed through the transistor _TR1 , and the transistor _TR1 is in an off state.
constitutes a second switch that is turned on when the switch is turned off. When the transistor TR ₂ is turned on, the transistors TR ₅ and TR ₆ are turned on, turning on the transistor TR ₄ . This turns on the transistor TR ₃ and inserts the resistor R ₃ in parallel with the resistor R ₁ to generate the second reference voltage Vt ₂ . That is, the above transistor TR ₆ ,
TR ₄ , TR ₃ and resistors R ₃ , R ₄ and the voltage divider together constitute means for generating the second reference voltage. When the input voltage increases, when the input voltage exceeds the second reference voltage, the first
Turn on the switch and turn off the second switch to generate the first reference voltage Vt _1. When the input voltage decreases thereafter, the first reference voltage Vt1 is generated.
When Vt is lower than ₁ , the first switch is turned off;
Turn on the second switch to set the second reference voltage again. When the second switch is turned on, the transistor _TR7 is turned on and an output signal is output, thereby controlling the load current, for example, in the direction of increasing it.

The conventional comparator described above has the following drawbacks because there is a delay in switching the reference voltage. That is, as shown in FIG. 3, a controlled system is controlled by the output of the comparator, and the voltage E generated as a result of the control is compared by the comparator.
When a so-called loop control circuit is configured, the response of the controlled system is fast and the reference voltage of the above comparator can be switched (from Vt ₁ to Vt ₂ or from Vt ₂ to Vt ₁ ).
When the delay occurs, the loop circuit has the disadvantage of causing an oscillation phenomenon.

For example, as shown in FIG. 4, resistors R ₈ , R ₉ ,
A load current control circuit consisting of R ₁₀ and transistors TR ₈ and TR ₉ and a resistor R load RL are connected in series, and the voltage drop of the resistor R is inputted to the comparator through a buffer amplifier, so that the load current becomes excessive. When the input voltage E of the comparator becomes higher than the second reference voltage, the load current is reduced by turning on the transistor TR ₈ and turning off the transistor TR ₉ to disconnect the resistor R ₁₀ from the resistor R ₉ . When such a control loop is configured, immediately after the input voltage E of the comparator exceeds the second reference voltage and the load current is reduced, the final reference voltage is in the state of the second reference voltage. Since the input voltage of the comparator, which has decreased due to the decrease in the load current, is lower than the second reference voltage, the load current is controlled to be increased again, and the above operation is repeated any number of times. That is, it has the disadvantage that it causes oscillation and cannot be smoothly controlled. This drawback is due to the transistor shown in Fig.
Delay in switching the reference voltage by passing through the steps of turning off the transistor TR ₆ → turning off the transistor TR ₄ → turning off the transistor TR ₃ → setting the first reference voltage after TR ₃ turns off. It is caused by. A similar oscillation phenomenon may occur even when control is performed to increase the load current as the load current decreases.

The purpose of the present invention is to rectify the above-mentioned conventional drawbacks and
An object of the present invention is to provide a variable reference voltage comparator that is free from oscillation when the comparator is used in a control circuit loop.

In order to achieve this object, the present invention includes a voltage divider that generates a first reference voltage by resistive voltage division, a first switch that is turned on when the input voltage is higher than the reference voltage, and a first switch that is in the on state. a comparator circuit consisting of a second switch that is turned off when means for generating a reference voltage, the first switch is turned on when the input voltage exceeds the second reference voltage when the input voltage increases, and when the input voltage falls below the first reference voltage. In a variable reference voltage comparator having a hysteresis characteristic such that the first switch is turned off when It consists of an equivalent PNPN switch circuit which is connected to the base, and a resistor is connected between the anode of the equivalent PNPN switch circuit and the power supply, and the above equivalent PNPN
The resistor is configured to be connected to the voltage divider when the switch circuit is on, and an output stage transistor is connected in parallel with a transistor equivalent to the means for generating the second reference voltage in the equivalent switch circuit. It is characterized by being connected.

As a result, in the present invention, depending on whether the second switch (transistor) of the comparison circuit is turned on or off,
Since the means (transistor) for generating the second reference voltage and the output stage transistor are turned on and off immediately, there is no delay in the reference voltage switching time, and the output voltage can be changed at the same time as the reference voltage is switched. Can be done. a second switch that is turned off when the first switch is in the on state; and means for changing the voltage division ratio of the voltage divider to generate a second reference voltage when the second switch is in the on state. When the input voltage increases, the first switch is turned on when it exceeds the second reference voltage, and when the input voltage decreases, the first switch is turned off when it falls below the first reference voltage. In the variable reference voltage comparator with hysteresis characteristics, the second switch is constituted by an equivalent PNPN switch circuit in which the collectors and bases of a pair of complementary transistors are connected to each other, and the equivalent PNPN switch circuit is A resistor is connected between the anode of the PNPN switch circuit and the power source, and the resistor is connected to the voltage divider when the PNPN switch circuit is in an on state, thereby generating the second reference voltage. It is characterized by This eliminates the delay in the switching time of the reference voltage, and
It was possible to reduce the number of components such as transistors.

Next, one embodiment of the present invention will be described in detail based on the drawings. FIG. 5 is a circuit diagram showing one embodiment of the present invention, in which transistors TR ₁₁ and TR ₁₂
The emitters of the transistors are connected to each other and grounded through a constant current circuit I, an input voltage E is applied to the base of the transistor _TR11 , and a reference voltage _V1 or _Vt2 is applied to the base of the transistor _TR12 . The collector and base of the transistor TR ₁₂ are connected to the base and collector of the transistor TR ₁₃ ,
The emitter of the transistor _TR13 is connected to the power supply through a resistor _R13 . Said transistor TR ₁₁
constitutes a first switch, and the transistor
The equivalent PNPN switch constituted by TR ₁₂ and TR ₁₃ constitutes a second switch and means for generating a second reference voltage. Note that there is a gap between transistors TR ₁₁ and TR ₁₂ constituting the equivalent PNPN switch.
The elements controlling the operation of the PNPN switch are not coupled and the operation of the PNPN switch is saturated operation. Further, resistors R ₁₁ and R ₁₂ are connected in series to constitute a voltage divider that divides the power supply voltage Vcc, and the divided voltage is set as the first reference voltage Vt ₁ . This voltage dividing point is connected to the collector of the transistor TR ₁₃ , and when the second switch is on, that is, when the transistor TR ₁₃ is on, the resistor R ₁₃ is connected in parallel to the resistor R ₁₁ . is connected to generate a second reference voltage _Vt2 . On the other hand, the collector of the transistor _TR12 is also connected to the base of the transistor _TR17 , and the collector is used as an output terminal.

Next, the operation of this embodiment will be explained. When the input voltage E is higher than the reference voltage, the transistor
TR ₁₁ is turned on and TR ₁₂ is turned off. Transistor TR ₁₃ is therefore also off and resistors R ₁₁ and R ₁₂
A first reference voltage Vt1 divided by _Vt1 is input to the base of the transistor _TR12 . In this state, no voltage is output to the output terminal. When the input voltage E decreases from this state and becomes less than the first reference voltage _Vt1 , the first transistor _TR11 is turned off and the first transistor _TR12 is turned on. This inversion is quickly accomplished by the cooperation of the transistor _TR13 . That is, the second switch is rapidly turned on. As a result, the resistor _R13 is connected in parallel to the resistor _R11 via the transistor _TR13 , and the base of the transistor _TR12 has a second
A reference voltage Vt ₂ is applied. Meanwhile, in this state, the transistor _TR17 is turned on, and the power supply voltage Vcc is outputted to the output terminal through the resistor _R20 .
The rise of this output change is steep. When the input voltage E increases from this state and exceeds the second reference voltage _Vt2 , the transistor _TR11 is turned on, _TR12 is turned off, and the transistor _TR13 is turned on.
is also turned off, and resistor R ₁₃ is isolated from the voltage divider,
As a result, said voltage divider generates a first reference voltage Vt ₁ . Then, the transistor _TR17 is also turned off, and the output voltage disappears. To switch the reference voltage above,
There is no delay in switching time since the switching is performed simultaneously with the turning on and off of the transistor _TR12 . Therefore,
This has the effect that it is possible to prevent oscillation in the control loop due to the delay in switching time, unlike in the conventional case. Furthermore, in this embodiment, as described above, the second reference voltage generating means is achieved by the transistor ₁₃ , so there is no need for a separate transistor as in the conventional configuration. That is, there is an advantage that the number of transistors can be reduced.

Next, another embodiment of the present invention is shown in FIG. In this case, as the equivalent PNPN switch,
A PNPN junction element (thyristor) is used whose gate terminal is connected to the voltage dividing point of the voltage divider and whose anode terminal is connected to the base of the transistor TR ₁₇ . This has the advantage of reducing the number of elements and further reduces the on-state voltage. Furthermore, a more accurate reference voltage can be generated than in the embodiments described above.

Next, another embodiment of the present invention is shown in FIG. In this case, the transistors TR ₂₁ , TR ₂₂ ,
The configuration of TR ₂₃ and resistors R ₂₁ , R ₂₂ , R _{23 is} as _shown in Figure 5 _.
The structure is similar to that of R ₁₁ , R ₁₂ , and R ₁₃ , but resistors R ₂₄ and R ₂₅ are connected to the base of the transistor TR ₂₁ .
The charged voltage is input to capacitor C ₂₁ through. The resistor _R25 is connected to the collector of the transistor _TR24 , and when an input voltage is input to the base of the transistor _TR24 , the transistor
TR ₂₄ is turned on, and the charge stored in the capacitor C ₂₁ is transferred to the resistor R ₂₅ and the transistor TR _24.
is discharged through. That is, after a certain time _t1 after the input becomes high, the transistor _TR21
is turned off, so transistors TR ₂₂ , TR ₂₃
is turned on to switch to the second reference voltage. Then, transistors TR ₂₇ and TR ₂₅ are turned on to make the output voltage low. That is, it is configured to perform a delay operation in which the input voltage becomes high and the output voltage becomes low after a certain period of time. If the input voltage becomes 0 within this delay time, the above-mentioned change in output voltage will not occur, so a delay characteristic can be provided to prevent malfunctions due to noise, for example. The same applies when the input voltage changes from high to low. Such delay characteristics can also be achieved by a conventional fixed reference voltage comparator, but in this case it is constructed as shown in FIG. The configuration is the same as that shown in FIG. 7 except for the means for changing the reference voltage, but the reference voltage Vt in this case is different from the first reference voltage Vt ₁ and the second reference voltage as shown in FIG. 9b. Voltage intermediate between voltage Vt ₂
It is considered to be Vt. Therefore, if the output voltage is to be made low with the same delay time as the delay time _t1 described above, the discharge voltage characteristic must be as shown by curve C in FIG. 9B. That is, the time constant must be made larger than the discharge characteristic shown by curve A in FIG. 9a (the discharge characteristic of the embodiment in FIG. 7). In other words, the embodiment shown in FIG. 7 has a lower resistance than the conventional example shown in FIG.
There is an advantage that R ₂₅ and capacitor C ₂₁ can be made small. Similarly to the above, if the output voltage becomes high after a delay of t ₂ when the input voltage changes from high to low, the resistor
R ₂₄ , R ₂₅ and capacitor C ₂₁ can be made smaller.

As described above, since the variable reference voltage comparator of the present invention is configured to change the output voltage at the same time as the reference voltage is switched, there is an effect that oscillation does not occur in the control loop. That is, it becomes possible to perform stable control. Furthermore, the comparator has the advantage that it requires fewer transistors and the like as compared to conventional comparators.

[Brief explanation of the drawing]

Fig. 1 shows the hysteresis relationship between the input voltage of the comparator and the reference voltage, Fig. 2 shows an example of a conventional variable reference voltage comparator, and Fig. 3 shows the hysteresis relationship between the input voltage of the comparator and the reference voltage.
The figure shows a state in which a variable reference voltage comparator is used in a loop circuit of a control system, FIG. 4 shows a state in which a comparator is used in an overload current prevention circuit, and FIG. 5 shows an embodiment of the present invention. A circuit diagram showing,
FIG. 6 is a circuit diagram showing another embodiment of the present invention;
The figure is a circuit diagram showing another embodiment of the present invention,
FIG. 8 is a circuit diagram showing an example of a fixed reference voltage comparator, and FIG. 9 is a time chart showing charging/discharging characteristics and input/output voltages of the comparator with delay characteristics. TR ₁ ~ TR ₉ , TR ₁₁ ~ TR ₁₃ , TR ₁₇ , TR ₂₁ ~
TR ₂₅ , TR ₂₇ , TR ₃₁ ~ TR ₃₂ , TR ₃₄ , TR ₃₅ ,
TR ₃₇ ...transistor, R, _R1 to _R4 , _R8 to _R10 ,
R ₁₁ ~ R ₁₃ , R ₂₀ , R ₂₁ ~ R ₂₆ , R ₃₀ ~ R ₃₂ , R ₃₄ ~
R ₃₆ , R ₄₀ , R _L ... Resistor, C ₂₁ , C ₃₁ ... Capacitor, V, Vcc ... DC power supply, I ... Constant current circuit,
E...Input voltage, Vt ₁ ...First reference voltage, Vt ₂
...Second reference voltage.

Claims (1)

[Claims] 1. A voltage divider that connects two or more resistors in series with a power supply voltage and generates a divided voltage by those resistors as a first reference voltage; The reference voltage generated by the voltage divider is connected to the base of the second switch, and when the input voltage becomes higher than the reference voltage, the first switch is turned on, and when the first switch is turned on, the second switch is turned on. a comparator circuit configured such that the second switch is turned off, and another resistor connected in parallel to one of the resistors forming the voltage divider when the second switch is in the on state, so that the voltage divider is turned off. and means for generating a second reference voltage by changing the voltage ratio, the first switch is turned on when the input voltage exceeds the second reference voltage when the input voltage increases, and the first switch is turned on when the input voltage decreases. In a variable reference voltage comparator having a hysteresis characteristic such that the first switch is turned off when the voltage drops below a first reference voltage, the second switch and means for generating the second reference voltage are provided. It consists of a saturation operation equivalent PNPN switch circuit in which the collectors and bases of a pair of complementary transistors are connected together, and a resistor is connected between the anode of the saturation operation equivalent PNPN switch circuit and the power supply, Operational equivalent PNPN
The resistor is configured to be connected to the voltage divider when the switch circuit is in the on state, and is connected in parallel with a transistor equivalent to means for generating a second reference voltage in the saturation operation equivalent PNPN switch circuit. A variable reference voltage comparator characterized by connecting stage transistors. 2. The reference voltage generator according to claim 1, wherein the saturation operation equivalent PNPN switch circuit constituting the second switch and the means for generating the second reference voltage is a PNPN junction element. Deformation comparator.