JP2003333828A - Semiconductor device and power supply using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve low power consumption, an improvement in detection voltage accuracy (detection at a constant and low-ripple voltage), reduction in the number of parts with regard to a semiconductor device for controlling the voltage of a terminal to which power is supplied at a desired voltage. <P>SOLUTION: The semiconductor device largely reduces a current into a detection signal transmission means (photocoupler 17) and reduces the circuit current of a voltage detection semiconductor device 12 by replacing a portion equivalent to a conventional-type shunt regulator with the voltage detection semiconductor device 12. A ripple voltage is controlled at a value determined by a current 14 which is always supplied from a constant-current supply 4 of the voltage detection semiconductor device 12 and resistors 15, 16. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detecting semiconductor device. In particular, it relates to an output voltage detecting semiconductor device used in an output voltage detecting circuit unit of a power supply device (switching power supply or the like).

[0002]

2. Description of the Related Art FIG. 10 is a block diagram of a voltage detection circuit used for a secondary side output of a conventional power supply device. 11 is shown in FIG.
0 is an operation waveform diagram for explaining the circuit operation of the conventional voltage detection circuit shown in FIG. 0, and FIG. 12 is a circuit configuration diagram of a power supply device using the conventional voltage detection circuit.

As shown in FIG. 10, the conventional voltage detection circuit is one in which the voltage of the VOUT terminal 13 is resistance-divided by the resistors 35 and 36 and detected by the shunt regulator 33. A capacitor 14 is connected to the VOUT terminal 13, and charges are supplied to the capacitor 14 from the outside, so that the voltage of the VOUT terminal 13 rises. Further, the detection voltage level VO of the VOUT terminal 13 is
Threshold voltage Vth of shunt regulator 33, resistance 35
The resistance value R35 and the resistance value R36 of the resistor 36 are determined by the following equation.

VO = Vth. (R35 + R36) / R3
5 In order to stably control the detection voltage level VO, the following measures are necessary. (1) The resistor 37 and the capacitor 38 are connected in series as shown in FIG. (2) In order to stabilize the detection voltage level, FIG.
By additionally connecting the resistor 34 as shown in, the detection current value to the shunt regulator is increased.

FIG. 11 shows VOUT of the voltage detection circuit of FIG.
The waveform of the current I33 flowing through the terminal 13, VO, and the shunt regulator 33 is shown. The ripple voltage of the VOUT terminal 13 is determined by the time constant of the resistor 37 and the capacitor 38 (because it is necessary to have a hysteresis characteristic).

FIG. 12 is a diagram showing a circuit configuration of a power supply device using the conventional voltage detection circuit shown in FIG. 10 as a secondary side voltage detection circuit. A photo coupler 17 is used as the detection signal transmission means. When the voltage is detected by the conventional voltage detection circuit of FIG. 10, the shunt regulator 3
Since 3 becomes conductive, the light emitting unit 1 of the photocoupler 17
An electric current flows through 7a to emit light (output of a detection signal). The output of the detection signal by this light emission is detected by the light receiving portion 17b of the photocoupler 17, and the on / off control of the switching element 27 by the control circuit 26 on the primary side is stopped (or stopped). As a result, the energy supply from the primary side to the secondary side is stopped (or stopped), so that the VOUT terminal 13
Voltage gradually decreases. When the voltage becomes lower than the detection voltage level, the output of the detection signal by the photocoupler 17 and the shunt regulator 33 disappears, so that the on / off control of the switching element 27 by the control circuit 26 is restarted.
Energy is supplied from the primary side to the secondary side. As a result, the voltage of the VOUT terminal 13 rises. VOUT terminal 1
The ripple voltage of No. 3 depends on the time constant of the resistor 37 and the capacitor 38, and therefore varies depending on the load state of the VOUT terminal 13.

[0007]

The conventional voltage detection circuit has the following problems. (1) In order to improve the detection voltage accuracy, it is necessary to increase the current value of the current I33 flowing through the shunt regulator 33. The current flowing at the time of this detection is generally on the order of several mA. Therefore, it is an obstacle to high efficiency (that is, energy saving), which is currently a global effort. (2) When the current value of the current I33 flowing through the shunt regulator 33 is insufficient, the detection voltage accuracy deteriorates. Therefore, it is necessary to add the resistor 34. (3) Since the voltage control of the VOUT terminal 13 depends on the time constant of the resistor 37 and the capacitor 38, the ripple voltage width of the VOUT terminal 13 varies greatly depending on the load condition. (4) Since the number of components forming the voltage detection circuit is large,
As shown in, at least 8 points are required.

[0008]

A first semiconductor device according to the present invention is a regulator having one end connected to a connection terminal for connecting to a voltage detection terminal and the other end connected to a reference voltage terminal, and the reference. A first constant current source connected to the voltage terminal,
A second constant current source, a start / stop circuit, a NAND circuit in which the other end of the start / stop circuit is connected to a first input terminal, the first constant current source, and a first switch element. And a second switch element, and a detection signal output terminal for transmitting a detection signal to the output terminal of the first switch element is connected to the current mirror circuit, and the first constant circuit of the current mirror circuit. A third switch element having a control terminal connected between a current source and the second switch element and having an output terminal of the NAND circuit connected thereto;
A fourth switch element having one end connected to the second constant current source, the other end connected to a voltage detection terminal, and a control terminal connected to the output terminal of the NAND circuit; and the voltage detection terminal. Is connected to a detection terminal, a reference voltage source to a reference terminal, and an output terminal to a second input terminal of the NAND circuit.

The second semiconductor device of the present invention is connected to a regulator having one end connected to a connection terminal for connecting to a voltage detection terminal and the other end connected to a reference voltage terminal, and the reference voltage terminal. The first constant current source, the second constant current source, the third constant current source, and the start / stop circuit, and the NA having the other end of the start / stop circuit connected to the first input terminal
An ND circuit, the third constant current source, a first switch element and a second switch element, and a detection signal output terminal for transmitting a detection signal to the output terminal of the first switch element. A connected current mirror circuit, a third switch element connected between the first constant current source and the second switch element, and having a control terminal connected to the output terminal of the NAND circuit, A fourth switch element having one end connected to the second constant current source, the other end connected to a voltage detection terminal, and a control terminal connected to the output terminal of the NAND circuit; and the voltage detection terminal. Is connected to a detection terminal, a reference voltage source to a reference terminal, and an output terminal to a second input terminal of the NAND circuit.

In the first and second semiconductor devices, it is preferable that at least five terminals of a ground terminal, a connection terminal, a reference voltage terminal, a voltage detection terminal, and a detection signal output terminal are provided. To do.

The first voltage detection circuit of the present invention includes a first resistor connected between the connection terminal and the voltage detection terminal of the first and second semiconductor devices of the present invention, and the voltage detection terminal. A second resistor connected between the ground terminals, a first capacitor connected between the reference voltage terminal and the ground terminal, a second capacitor connected between the connection terminal and the ground terminal, and a detection signal It is characterized by having a voltage detection signal transmission means connected to the output terminal.

As described above, the voltage detecting circuit is constructed by using the first and second semiconductor devices of the present invention,
The number of constituent parts can be reduced (8 points in the above-mentioned conventional example, but 6 points in the embodiment described later, which is a reduction of 2 points).

Further, when the voltage is detected by the first resistor and the second resistor, the current is supplied from the second constant current source to the resistor 2, so that the voltage at the voltage-detected terminal is slightly raised. It has a hysteresis characteristic. Since this lifted voltage width becomes the ripple voltage width, this ripple voltage width is always constant regardless of the load state of the voltage-detected terminal.

Further, the detection current flowing through the first switch element connected to the detection signal output terminal in the first and second semiconductor devices of the present invention is the same as that of the first switch element and the second switch element.
Since it can be adjusted by the mirror ratio of the current mirror circuit configured with the switch element of, the current can be reduced.

The first power supply device of the present invention is the first power supply device of the present invention.
The voltage detecting circuit is used for the output voltage detecting section.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 shows a semiconductor device according to a first embodiment of the present invention. 2 is a voltage detection circuit using the semiconductor device of FIG. 1, and FIG. 3 is a VO1 terminal voltage waveform, a VCC terminal voltage waveform, a VO2 terminal voltage waveform, and I of this voltage detection circuit.
The PC current waveform is shown.

The semiconductor device of FIG. 1 has a connection terminal VO1 for connecting to a detection terminal, a reference voltage terminal VCC, a voltage detection terminal VO2, a detection signal output terminal VPC for transmitting a detection signal, and a ground terminal. Is GND / S
It consists of a total of five terminals. VO1 and V
There is a regulator 1 between CC and keeps the reference voltage VCC constant during operation. A start / stop circuit 2, a constant current source 3, and a constant current source 4 are connected to VCC.
A switch element 5 is connected between the constant current source 4 and VO2, and VO2 is connected to a detection terminal of a comparator 7 having a reference voltage source 6 (hereinafter, this reference voltage is VBG). The output terminal of the comparator 7 and the output terminal of the start / stop circuit 2 are both connected to the input terminal of the NAND circuit 8, and the output signal of the NAND circuit 8 is connected to the gate terminals of the switch elements 5 and 9. The constant current source 3 constitutes a current mirror circuit with the switch element 10 and the switch element 11, but the constant current source 3 and the switch element 1
A switch element 9 is connected between 1 and 1. The switch element 10 is connected to the detection signal output terminal VPC.

The voltage detection circuit shown in FIG. 2 has a VOUT terminal 13 for detecting the voltage of VO1 of the semiconductor device 12 of FIG.
, VO2 terminal to VOUT terminal 13 and GND / SOUR
A resistor 15 (resistance value is R1
5) and a resistor 16 (whose resistance value is R16). A light emitting portion of the photocoupler 17 is connected to the VPC terminal as a detection signal output means, and a capacitor 18 is connected to VCC. When the light emitting portion 17a of the photocoupler is not emitting light, power is supplied to the capacitor 14 connected to the VOUT terminal 13, and when the light emitting portion 17a of the photocoupler is emitting light, the power is supplied to the capacitor 14. The power supply is stopped.

The operation of the first semiconductor device of the present invention and the voltage detection circuit using the same will be described with reference to FIG.

When power is supplied to the capacitor 14 connected to the VOUT terminal 13, the voltage across the capacitor 14 rises. Therefore, current is supplied from VO1 of the voltage detection semiconductor device 12 connected to the VOUT terminal 13 to the capacitor 18 connected to VCC via the regulator 1, and the voltage of VCC also rises. When the voltage of VCC becomes equal to or higher than the starting voltage VCC0 set by the starting / stopping circuit 2, the semiconductor device 12 for voltage detection starts, and
The output signal from the stop circuit 2 changes from the "L (low)" signal to the "H (high)" signal. As a result, the output signal of the NAND circuit 8 depends on the output signal of the comparator 7, and V
The voltage detection of the OUT terminal 13 is started. Where VCC
As for the voltage of the terminal, a current is supplied from the VOUT terminal 13 to the capacitor 18 connected to the VCC terminal via the regulator 1, and the regulator 1 supplies the constant voltage VCC1 (>
It is controlled to become VCC0). Power is supplied to the voltage detecting semiconductor device 12 from the capacitor 18, and the power consumption of each component circuit is reduced.

The voltage at the VOUT terminal 13 rises, that is, VO
2 terminal voltage rises, the reference voltage VBG of the comparator 7
(If the detection voltage of the VOUT terminal 13 is Vo, VBG
= Vo · R16 / (R15 + R16)) or more,
The output signal of the comparator 7 changes from the "L (low)" signal to the "H (high)" signal. Since the output signal of the start / stop circuit 2 and the output signal of the comparator 7 are both “H (high)” signals, the output signal of the NAND circuit 8 becomes “L (low)”. As a result, the switch element 9 is turned on, so that a current flows from the constant current source 3 to the switch element 11 via the switch element 9. As a result, the switch element 10 is also turned on. When the switch element 10 is turned on, a current flows through the light emitting element 17a of the photocoupler, and the light emitting element 17a of the photocoupler emits light.
The output signal is transmitted to the power supply source for the external capacitor 14, and the power supply to the capacitor 14 is stopped. At this time, since the switch element 5 is also turned on by the output signal of the NAND circuit 8 at the same time, the constant current sources 4 to I4 are connected to the VO2 terminal via the switch element 5 and the resistor 16 is connected.
And the voltage of the VOUT terminal 13 is I4. (R15 + R
16), and the voltage of VOUT terminal 13 is Vo
+ I4 · (R15 + R16) Since the power supply to the capacitor 14 is stopped by the transmission signal of the light emitting element 17a of the photocoupler, the voltage of the VOUT terminal 13 gradually decreases from Vo + I4. (R15 + R16) (the VO2 terminal voltage also decreases).

When the VO2 terminal voltage becomes equal to or lower than the reference voltage VBG of the comparator 7, the output signal of the comparator 7 becomes "L (low)" and the output signal of the NAND circuit 8 becomes "H (high)", and the switch element 5 and The switch element 9 is turned off. Therefore, since the switch element 10 is turned off, no current flows in the light emitting portion 17a of the photocoupler, and the output signal to the power supply source to the capacitor 14 is stopped, so that power is supplied to the capacitor 14 again. . As a result, the voltage of VOUT13 rises again (VO2 terminal voltage also rises).

After that, by repeating this operation, the VOU
The voltage of the T terminal 13 is controlled to be a desired voltage Vo.

Here, as described above, the ripple voltage width of the VOUT terminal 13 is constant as I4 · (R15 + R16) regardless of the state of the load connected to the VOUT terminal 13.

From the above, the following effects are obtained. (1) Current IPC flowing through the light emitting portion 17a of the photocoupler
(= Α · I3, where α represents a mirror ratio) is defined as the constant current source 3 of the voltage detection semiconductor device 12 and the switch elements 10, 1.
Since it can be adjusted by the current mirror circuit configured by 1, the power consumption at the time of detection can be reduced by narrowing down the IPC. And as mentioned above,
Since the circuit current of the voltage detection semiconductor device 12 is reduced, the power consumed during normal operation can be reduced. Specifically, the voltage detecting semiconductor device 12 and the resistor 1
The total value of the currents consumed by the photo couplers 5, 16 and the photo coupler 17 can be about 1/10 or less of that of the conventional example. (2) The ripple voltage of the VOUT terminal 13 is I4 · (R
15 + R16) and is constant regardless of the state of the load connected to the VOUT terminal 13, I4, R1
By adjusting 5 and R16, the ripple voltage can be made lower. (3) The number of parts of the output voltage detection circuit is 6, and the number of parts is reduced.

Further, FIG. 4 shows a semiconductor device representing a second embodiment of the present invention. 5 shows a voltage detection circuit using the semiconductor device of FIG. 4, and FIG. 6 shows a VO1 terminal voltage waveform, a VCC terminal voltage waveform, a VO2 terminal voltage waveform, and an IPC current waveform of this voltage detection circuit.

The semiconductor device shown in FIG. 4 has the constant current source 1 shown in FIG.
Since 9 is added, when the voltage of the VOUT terminal 13 is equal to or lower than the desired voltage Vo, a certain current α · I
3 is flowing (however, the light emitting portion 17a of the photocoupler does not emit light due to this current), and other configurations, operations, and characteristics are the same as those in FIG. Since the constant current source 19 is connected, the gate voltages of the switch elements 10 and 11 are constantly set to "H" while the voltage detecting semiconductor device 12 is detecting the voltage of the VOUT terminal 13.
Since it is fixed in the (high) state, the operation as a semiconductor device is ensured.

FIG. 7 shows a switching power supply device using a transformer, which is the first embodiment of the present invention using the voltage detection circuit of FIG.
Power supply device. The input voltage power supply 21 is the filter circuit 2
2 is rectified by the rectifier circuit 23 and smoothed by the input-side smoothing capacitor 24. The voltage smoothed by the input-side smoothing capacitor 24 is connected to the primary winding 20a of the transformer 20, and energy is transmitted to the secondary winding 20b of the transformer by the switching of the switching element 27 by the control circuit 26. Here, as indicated by 28 in FIG. 7, if the control circuit 26 and the switching element 27 are integrated on the same substrate, there is an advantage that the number of parts can be reduced and the cost can be reduced.

The energy transferred to the secondary winding 20b is supplied to the output smoothing capacitor 14. The voltage across the output-side smoothing capacitor 14 is divided by the resistors 15 and 16, and is controlled to a desired voltage by the voltage detection semiconductor device 12. The control operation contents are the same as in FIG.
The power supply is characterized by low power consumption and highly accurate output voltage with low ripple voltage. The output signal from the light emitting portion 17a of the photo coupler is the light receiving portion 1 of the photo coupler.
When it is transmitted to 7b, the light receiving unit 17b is turned on,
The on / off control of the switching element 27 by the control circuit 26 is stopped. Here, the operation is similar when the voltage detection circuit shown in FIG. 5 is used.

FIG. 8 shows a step-down chopper type switching power supply device using a coil, which is a second power supply device of the present invention using the voltage detection circuit of FIG. VIN in Figure 8
When the input voltage power supply 21 is input from the terminal and rectified by the rectifier circuit 30 composed of a diode, it is smoothed by the input-side smoothing capacitor 24. The voltage smoothed by the input-side smoothing capacitor 24 is regenerated by the switching of the switching element 27 by the control circuit 26 from the coil 32 to the output-side smoothing capacitor 14 when the switching element 27 is on, and when the switching element 27 is off. Power is supplied to the output-side smoothing capacitor 14 from the diode for use 31 via the coil 32. Here, as in 28 in FIG. 8, if the control circuit 26 and the switching element 27 are integrated on the same substrate as in the case of FIG. 7, there is an advantage that the number of parts can be reduced and the cost can be reduced. .

The voltage across the output-side smoothing capacitor 14 is
The voltage is divided by the resistors 15 and 16 and is controlled to a desired voltage by the voltage detection semiconductor device 12. The content of the control operation is the same as that of FIG. 3, and the power supply is characterized by low power consumption and highly accurate output voltage with low ripple voltage. When the output signal is transmitted from the light emitting portion 17a of the photo coupler to the light receiving portion 17b of the photo coupler, the light receiving portion 1
7b is turned on, and the on / off control of the switching element 27 by the control circuit 26 is stopped. As a result, the power supply to the output side smoothing capacitor 14 is stopped. Here, the operation is similar when the voltage detection circuit shown in FIG. 5 is used.

FIG. 9 shows a step-down chopper type switching power supply device using a coil, which is a third power supply device of the present invention using the voltage detection circuit of FIG. In the step-down chopper type switching power supply device shown in FIG. 8, the photocoupler 17 is used as the voltage detection signal transmitting means, but in FIG. 9, the control circuit 26 stops the on / off control of the switching element 27. The VPC terminal of the voltage detection semiconductor device 12 is directly connected to the FB terminal of the switch element 10 and the switch element 10 is turned on when the desired voltage Vo of the VOUT terminal 13 is detected. Stop the on-off control. Here, the switch element 10 has an input voltage VIN
Is high voltage, it is necessary to use a high breakdown voltage element. The content of the control operation is the same as that of FIG. 8, and is characterized in that the power supply can obtain an accurate output voltage with low power consumption and low ripple voltage.

Even when the voltage detection circuit shown in FIG. 5 is used in the step-down chopper type switching power supply device of FIG. 9, the control operation contents are the same as those of FIG. 8, and the power supply is low in power consumption and of ripple voltage. It is characterized in that a high output voltage with low accuracy can be obtained. Here, the current value IFB flowing from the FB terminal to stop the on / off control of the switching element 27 by the control circuit 26 and α · I in FIG.
The magnitude relationship of 3 is IFB> α · I3.

[0035]

According to the present invention, the power consumption can be reduced in the voltage detection circuit. In particular, in a power supply device using the semiconductor device for voltage detection of the present invention,
The efficiency of the power supply can be improved.

Further, since the ripple voltage can be constantly controlled and the ripple voltage can be suppressed, highly accurate control as a power source is possible.

Further, since the number of components constituting the voltage detection circuit can be reduced, the size and cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram inside a semiconductor device for voltage detection according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a voltage detection circuit according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the circuit operation of the voltage detection circuit according to the first embodiment.

FIG. 4 is a circuit configuration diagram inside a voltage detection semiconductor device according to a second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a voltage detection circuit according to a second embodiment of the present invention.

FIG. 6 is a diagram for explaining the circuit operation of the voltage detection circuit according to the second embodiment.

FIG. 7 is a circuit configuration diagram of a power supply device according to a third embodiment of the present invention.

FIG. 8 is a circuit configuration diagram of a power supply device according to a fourth embodiment of the present invention.

FIG. 9 is a circuit configuration diagram of a power supply device according to a fifth embodiment of the present invention.

FIG. 10 is a circuit configuration diagram showing a conventional voltage detection circuit.

FIG. 11 is a diagram for explaining the circuit operation of a conventional voltage detection circuit.

FIG. 12 is a configuration diagram of an entire power supply device using a conventional voltage detection circuit.

[Explanation of symbols]

1 regulator 2 Start / stop circuit 3 constant current source 4 constant current source 5 switch elements 6 Reference voltage source 7 comparator 8 NAND circuit 9 switch elements 10 switch elements 11 Switch element 12 Semiconductor device for voltage detection 13 Output voltage terminal 14 Output side smoothing capacitor 15,16 resistance 17 Photocoupler 17a Light emitting part of photocoupler 17b Photodetector of photocoupler 18 capacitors 19 constant current source 20 transformers 20a transformer primary winding 20b transformer secondary winding 21 Input voltage source 22 Filter circuit 23 Rectifier circuit 24 Input side smoothing capacitor 25 snubber circuit 26 Control circuit 27 switching elements 28 Range integrated on the same semiconductor substrate 29 capacitors 30 rectifier circuit 31 Regeneration diode 32 coils

Claims (5)

[Claims] 1. A regulator having one end connected to a connection terminal for connecting to a voltage detection terminal and the other end connected to a reference voltage terminal; a first constant current source connected to the reference voltage terminal; 2. A constant current source and a start / stop circuit, a NAND circuit in which the other end of the start / stop circuit is connected to a first input terminal, the first constant current source, and a first switch element. A current mirror circuit comprising a second switch element and having a detection signal output terminal for transmitting a detection signal connected to the output terminal of the first switch element; and the first constant current of the current mirror circuit. A third switch element having a control terminal connected between a power source and the second switch element and having an output terminal of the NAND circuit connected; one end connected to the second constant current source; Terminal for voltage detection A fourth switch element connected to the NAND circuit and having a control terminal connected to the output terminal of the NAND circuit, the voltage detection terminal connected to the detection terminal, and the reference terminal connected to the reference voltage source, and the output terminal connected to the NAND. A semiconductor device having a comparator connected to a second input terminal of a circuit. 2. A regulator having one end connected to a connection terminal for connecting to a voltage detection terminal and the other end connected to a reference voltage terminal; a first constant current source connected to the reference voltage terminal; A second constant current source, a third constant current source, and a start / stop circuit, a NAND circuit in which the other end of the start / stop circuit is connected to a first input terminal, and the third constant current source A current mirror circuit comprising a first switch element and a second switch element, and a detection signal output terminal for transmitting a detection signal connected to an output terminal of the first switch element; A third switch element connected between a constant current source and the second switch element and having a control terminal to which an output terminal of the NAND circuit is connected; and one end connected to the second constant current source , The other end is connected to the voltage detection terminal. A fourth switch element having a control terminal connected to the output terminal of the NAND circuit, the voltage detection terminal connected to the detection terminal, and the reference terminal connected to the reference voltage source, and the output terminal connected to the NAND circuit. A semiconductor device having a comparator connected to a second input terminal. 3. A ground terminal, a connection terminal, a reference voltage terminal, a voltage detection terminal, and at least five terminals of a detection signal output terminal.
The semiconductor device described. 4. A first resistor connected between a connection terminal and a voltage detection terminal of the semiconductor device according to claim 1, and a connection between the voltage detection terminal and a ground terminal. A second resistor, a first capacitor connected between the reference voltage terminal and the ground terminal, a second capacitor connected between the connection terminal and the ground terminal, and a voltage connected to the detection signal output terminal. A voltage detection circuit using the semiconductor device according to any one of claims 1, 2, and 3, further comprising a detection signal transmission means. 5. A power supply device using the voltage detection circuit according to claim 4 in an output voltage detection unit.