JPH0711560B2 - Voltage control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A voltage control circuit having a function of varying an output voltage by a control signal, wherein a variable resistor is omitted and a higher output voltage is obtained by a control signal. Between an amplifier that operates so that the voltages at the input terminals are equal, a reference voltage that is connected to one of the input terminals of the amplifier, and the other of the input terminals of the amplifier and the output terminal of the voltage control circuit. A first resistor connected to the second resistor, a second resistor connected between the other of the input terminals of the amplifier and a reference voltage, a fourth resistor connected in parallel with the first resistor, and A first switch means, a fifth resistor and a second switch means connected in parallel with the second resistor, and a third resistor and a third switch means. The switch means of each is the first
And when the second control signal is applied, it is turned on,
The third switch means is configured to be turned on when the first and second control signals are applied.

[Industrial application field]

The present invention relates to a voltage control circuit, and more particularly to a voltage control circuit having a function of varying an output voltage with a control signal.

In a power source or the like incorporated in an electronic device, a function of changing the output voltage of the power source by, for example, ± 10% is often added by a control signal for a voltage margin test of an element or the like.

[Conventional technology]

FIG. 3 is an explanatory view of a conventional technique and shows a conventional voltage control circuit.

In FIG. 3, R1, R4, R5, R11 and R12 are resistors, R2 'is a variable resistor, PI1 and PI2 are photocouplers, AMP is an amplifier, and V _R is a reference voltage.

The amplifier AMP is a voltage-stabilized error amplifier and operates so that the voltages at its two input terminals become equal. Therefore,
The voltage V _{a at} the connection point between the resistor R1 and the variable resistor R2 ′ is the reference voltage.
To be equal to V _R.

Normally, the control signals * _VL and * _VH are both set to "H" (high level). As a result, the photocouplers PI1 and PI2 are turned off, and the voltage V _a depends on the ratio between the resistance R1 and the variable resistance R2 ′. If V _R = 2.5V and R1 = 2 ', the output voltage V _o = 5.0V.

When the control signal * _{VL is set} to "L" (low level), the photo coupler PI1 is turned on. Therefore, the voltage V _a depends on the ratio between the resistances R1 and R4 connected in parallel and the variable resistance R2 ′. As a result, if R1 = 2 ', V _a > V _o −V
the _a. On the other hand, V _a = V _R is maintained by the function of the amplifier AMP. From the above, by setting V _R = 2.5V and appropriately setting the values of the resistors R1 and R4, the output voltage V _o = 4.5V (-10% output) is obtained.

Conversely, when the control signal * _{VH is set} to "L", the photocoupler PI2 is turned on. Then, by setting R1 = R2 ', V _R = 2.5V and appropriately setting the values of the resistors R1 and R5, the output voltage V _o
= 5.5V (+ 10% output) is obtained.

According to such a voltage control circuit, ICs such as TTL
In addition to enabling normal operation at V, it is possible to perform voltage margin tests by operating at 4.5V and 5.5V.

[Problems to be Solved by the Invention]

In general, a power supply incorporated in an electronic device is provided with an overvoltage protection circuit so that an overvoltage is not applied to an IC such as TTL. Therefore, as one of the tests, it is necessary to confirm whether or not the overvoltage protection circuit also operates normally.

By the way, according to the above voltage control circuit, R2 '(or R2
If 1) is used as a fixed resistance, only a maximum voltage of 5.5 V can be obtained (it is not suitable for the voltage margin test widely performed at other than 5.5 V). With this, the overvoltage protection circuit cannot be tested, so the variable resistor R2 'to obtain a high voltage was indispensable.

The need for the variable resistor R2 'has been a cause of various problems in the past.

For example, the value of the variable resistor R2 'needs to be adjusted manually, which is an obstacle to automation of the test. Further, since the variable resistor R2 'is usually realized as an external component (volume), there is a defect that an overvoltage occurs due to the defect.

It is an object of the present invention to provide a voltage control circuit which can omit a variable resistor and can obtain a higher output voltage by a control signal.

[Means for Solving the Problems]

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

In FIG. 1, 1 voltage control circuit, 2 power supply, 3 electronic device, 4
Is an overvoltage protection circuit, R1 to R5 are resistors, SW1 to S3 are switch means, AMP is an amplifier, and V _R is a reference voltage.

The amplifier AMP is a voltage-stabilized error amplifier and operates so that the voltages at its two input terminals become equal.

The reference voltage V _R is connected to one of the input terminals of the amplifier AMP (between the reference voltage). The reference voltage V _R is a voltage supply means for applying a predetermined voltage (V _R ).

The dividing resistors R1 and R2 for dividing the voltage from the power supply 2 are connected in series and are connected between the output terminal (power supply voltage line) of the voltage control circuit 1 and the reference (ground) voltage (reference voltage line).
That is, the first resistor R1 is connected between the other input terminal of the amplifier AMP and the output terminal of the voltage control circuit 1, and the second resistor R2 is connected between the other input terminal of the amplifier AMP and the reference voltage. Connected in between.

Resistor R4 is connected in parallel with resistor R1 and resistor is connected in parallel with resistor R2.
R5 and R3 are connected. Resistors R4, R5 and R3 are respectively
The switch means SW1, SW2 and SW3 are connected in series. That is,
The fourth resistor R4 and the first switch means SW1 are connected in parallel with the resistor R1. Further, the fifth resistor R5 and the second switch means RSW2, and the third resistor R3 and the third switch means RSW3 are connected in parallel to the resistor R2.

The voltage control circuit 1, from the outside, first and second control signals * V _L and * V _H is supplied. Four kinds of output voltages V _o can be obtained by combining the two control signals. The control signals * _VL and * _VH are mainly a signal for obtaining an output voltage lower than the normal output voltage and a signal for obtaining an output voltage higher than the normal output voltage, respectively. The first and second switch means RSW1 and SW2 respectively have a first control signal * _VL
And the second control signal * V _H is turned on, and the third switch means SW3 is turned on when both the first and second control signals * V _L and * V _H are applied. Becomes

[Action]

By the action of the amplifier AMP, the voltage V _a of the connection point between the fixed resistor R1 and the fixed resistor R2 is made equal to the reference voltage V _R.

Normally, the control signals * _VL and * _VH are both set to "H" (high level). As a result, the switching means SW1 and SW2 are turned off, so that the voltage V _a depends on the ratio of the resistors R1 and R2. If V _R = 2.5V and R1 = R2, then the output voltage V _o
= 5.0V.

When the control signal * _{VL is set} to "L" (low level), the switch means SW1 is turned on. Therefore, the voltage V _a is
And R4 connected in parallel and the resistance of R2. As a result, if R1 = R2, then V _a > V _o −V _a . On the other hand, V _a = V _R is maintained by the function of the amplifier AMP. From the above, by setting V _R = 2.5V and appropriately setting the values of the resistors R1 and R4, the output voltage V _o = 4.5V (-10% output) is obtained. At this time, the control signal * _VH is "H", and the switch means SW2 and SW3 are in the off state.

On the contrary, when the control signal * V _{H is set} to “L” and the control signal * V _{L is set} to “H”, only the switch means SW2 is turned on. And
And _{R1 = R2, V R = 2.5V} , obtained by determining the value of the resistor R1, R5 properly, the output voltage V _o = 5.5V (the + 10% of the output).

On the other hand, when the control signals * _VL and * _VH are both set to "L", the switch means SW1 to SW3 are turned on. Therefore, the voltage
V _o depends on the ratio of the resistors R1 and R4 connected in parallel and the resistors R2, R3 and R5 connected in parallel.

As described above, assuming that the normal voltage of 5.0 V is changed to the + side and the-side by the same ratio (± 10%), R1 = R2 and R4 = R5. Then, with V _R = 2.5V, the output voltage V _o = 7.0V is obtained by appropriately setting the value of the resistor R3.

Therefore, according to the voltage control circuit 1 as described above, it is possible to obtain the normal operating voltage for normally operating the electronic element 3 such as TTL, and the normal operating voltage for performing the voltage margin test of the electronic element 3. It is possible to obtain a voltage (higher and lower) by changing the voltage to + and-sides by a predetermined ratio,
Further, it is possible to obtain a higher voltage than the voltage obtained by raising the normal operation voltage by a predetermined ratio for testing whether the overvoltage protection circuit 4 of the power supply device operates normally. Selection of these voltages can be set by the control signal * V _L and * V _H.

〔Example〕

FIG. 2 is a configuration diagram of the embodiment and shows the configuration of the voltage control circuit 1.

In FIG. 2, Q1 and Q2 are transistors and R7 to R12.
Is a resistor, D is a Zener diode, and PI1 and PI2 are photocouplers.

The first switch means AW1 is composed of a photocoupler PI1 and a resistor R11. When the control signal * _VL is set to "L", a voltage is applied to the light emitting diode to emit light, and the phototransistor that receives the light is turned on. In addition, instead of such a configuration,
A transistor that is turned on by the “L” of the control signal * V _L may be used.

The second switch means SW2 has the same structure as the first switch means, and is composed of a photocoupler PI2 and a resistor R12, and the phototransistor is turned on by the control signal * _VH "L".

The third switch means SW3 comprises resistors R7 to R10, transistors Q1 and Q2, and a zener diode D. As illustrated, the switch means SW3 via the photocoupler PI1 and PI2 (the switch means SW1 and SW2), respectively, receiving the control signal * V _L and * V _H. That is, the Zener diode D (and the resistors R9 and R10) is connected between the connection point b between the photocoupler PI1 and the resistor R4 and the connection point c between the photocoupler PI2 and the resistor R5. Then, the (npn) transistor Q1 which is substantially the switch means SW3 is driven by the Zener diode D which receives the control signals * _VL and * _VH at its both terminals.

When control signals * _VL and * _VH are both "L", connection points b and c
The voltage V _bc during is approximately equal to the voltage V _o . By this,
Zener diode D breaks down, and resistor R9 and
Current flows through R10. As a result, (pnp) transistor Q2
Turns on and current flows through resistors R7 and R8. Therefore, the transistor Q1 turns on.

In order to enable such operation, the Zener diode D is connected between the connection points bc in the direction shown in the figure, and its breakdown voltage V _z is V _o −V _R <V _z + V _BEQ2 and V _R <. V _z + V
_BEQ2 and V _z + V _BEQ2 <V _o are satisfied. Also, since the voltage V _bc is obtained when both the control signals * V _L and * V _H are “L”, the photocoupler PI1 is connected from the resistor R4 to the output terminal side.
The photocoupler PI2 is connected to the reference voltage side of the resistor R5.

When at least one of "H" of the control signal * V _L and * V _H, the voltage V _bc is zero. Therefore, the Zener diode does not turn on and the transistor Q1 does not turn on.

Now, V _R = 2.5V, the resistance ratio is R1: R2: R3: R4: R5 = 1: 1: 1: 3.9:
Assuming 3.9, the combination of control signals * V _L and * V _H
The output voltage V _o is calculated as follows.

When * V _H = “H” and * V _L = “H”, this combination is used when a normal operating voltage for normally operating the electronic element 3, for example +5.0 V, is obtained as the output voltage V _o .

Due to * _VH = * _VL = "H", both photocouplers PI1 and PI2 are turned off. The voltage at the connection points b and c becomes equal to the voltage V _a , and the Zener diode D does not turn on. As a result, the voltage V _a depends on the ratio of the resistors R1 and R2.

Therefore, the output voltage V _o is Becomes

As a result, the electronic device 3 such as TTL can be operated at + 5.0V.

* V _H = “H”, * V _L = “L” When obtaining a low voltage for operating low voltage, such as +4.5 V, when performing a voltage margin test on the electronic device 3 as the output voltage V _o This combination is used.

By * _VH = "H" and * _VL = "L", the photocoupler PI2 is turned off and the photocoupler PI1 is turned on. Connection point b
The voltages of c and c become approximately equal to the voltage V _o , and the Zener diode D does not turn on. As a result, the voltage V _a is
It depends on the ratio of the resistor R2 connected in parallel.

Therefore, the output voltage V _o is Becomes

As a result, the voltage margin test can be performed by operating the electronic element 3 at a low voltage of + 4.5V.

* V _H = “L”, * V _L = “H” When obtaining a high voltage for operating a high voltage, such as +5.5 V, when performing a voltage margin test on the electronic element 3 as the output voltage V _o This combination is used.

By * V _H = “L” and * V _L = “H”, photocoupler PI2 is turned on and photocoupler PI1 is turned off. Connection point b
The voltages of c and c become approximately equal to the voltage V _o , and the Zener diode D does not turn on. As a result, the voltage V _a is
And R5 in parallel.

Therefore, the output voltage V _o is Becomes

As a result, the electronic element 3 can be operated at a high voltage of +5.5 V to perform a voltage margin test.

When * V _H = “L” and * V _L = “L”, this combination is used when a voltage for confirming the operation of the overvoltage protection circuit 4 is obtained as the output voltage V _o .

By * _VH = * _VL = "L", both photocouplers PI1 and PI2 are turned on. The voltage V _bc between the connection points b and c is the voltage V
_It becomes equal to _o , and the Zener diode D turns on (breakdown). As a result, the voltage V _a depends on the ratio of the resistors R1 and R4 connected in parallel and the resistors R2, R3 and R5 connected in parallel.

Therefore, the output voltage V _o is Becomes

Thus, the operation can be confirmed by applying the voltage to the overvoltage protection circuit 4 of about 7V.

This overvoltage is a control signal * V _L for the voltage margin test.
And * V _H can be used, so that the number of signal lines does not increase. Moreover, since this overvoltage value is constant, damage to the load can be prevented. For example, like a standard logic IC such as TTL, normally used voltage is 5V and maximum rating is
The overvoltage can be set to 7V or less for the 7V electronic element 3. As a result, even if the overvoltage protection circuit 4 is defective, the electronic element 3 can be prevented from being destroyed.

〔The invention's effect〕

As described above, according to the present invention, in the voltage control circuit, the variable resistor for generating the overvoltage can be omitted by generating the overvoltage by the specific combination of the control signals. Can be automated, and stable overvoltage and output voltage can be obtained to improve reliability. Further, by omitting the variable resistance, it is possible to improve the environmental resistance against gas and the like.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment, and FIG. 1 is a voltage control circuit, 2 is a power supply, 3 is an electronic element, 4 is an overvoltage protection circuit, R1 to R5 are resistors, SW1 to SW3 are switch means, A
MP amplifiers, V _R is the reference voltage.

Claims (1)

[Claims] And 1. A amplifier operates as a voltage of the two input terminals are equal (AMP), one connected to the reference voltage of said input terminal of said amplifier (AMP) and (V _R), the amplifier A first resistor (R1) connected between the other of the input terminals of (AMP) and the output terminal of the voltage control circuit.
A second resistor (R2) connected between the other input terminal of the amplifier (AMP) and a reference voltage, and a second resistor (R2) connected in series with each other and in parallel with the first resistor (R1). A fourth resistor (R4) and a first switch means (SW1), and a fifth resistor (R5) and a second resistor (R5) connected in series with each other and in parallel with the second resistor (R2). Switch means (SW2), a third resistor (R3) and a third switch means (SW3) connected in series with each other and connected in parallel with the second resistor (R2), The first and second switch means (SW1, SW2) are turned on when the first and second control signals are applied, respectively, and the third switch means (SW3) is connected to the first and second switch means (SW3). Second
The voltage control circuit is turned on when the control signal of is applied.