JPH10326117A - Power switch and voltage control method using the switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the change of output voltage even in the case of the increase of output current of a power switch, and also to prevent occurrence of malfunctions even when the current consumption of a device increases to lower the power voltage level. SOLUTION: The output voltage level of a current detection circuit 2 rises in response to increase of the current value flowing to a power switch. Accordingly, the frequency of the output rectangular clock signal of a VCO 9 increases and also the output voltage level of a charge pump rises. Under such conditions, the gate voltage level of an N-channel MOSFET 4 rises and therefore the ON resistance of the MOSFET 4 reduces. As a result, the voltage drop caused between the input/output terminals 1 and 6 is suppressed as a whole for the power switch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an N-channel MOSFET as a switching element in a power supply control circuit or the like.
More particularly, the present invention relates to a power switch incorporating a charge pump and a voltage control method using the same.

[0002]

2. Description of the Related Art Conventionally, this kind of power with built-in charge pump
A common structure, known as a switch, is an N-channel M
Gate voltage V applied to the gate electrode of the OSFET_G of
Values are gate voltage and source voltage of N-channel MOSFET.
On-resistance between rain (V _G -R_ONCharacteristic)
The value is set to a value sufficiently larger than the saturation point, and the N-channel MO
SFET source-drain on-resistance is fixed
I have.

Therefore, when the current flowing between the source and the drain of the N-channel MOSFET increases, there is a problem that the voltage drop between the source and the drain increases and the output voltage of the power switch decreases.

FIG. 12 shows a conventional example of such a power switch with a built-in charge pump. N-channel MOSF
In order to use ET in a region where the on-resistance is very small, an N-channel M channel must be connected between both terminals of the gate electrode and the source electrode.
It is necessary to apply a voltage higher than the threshold voltage of the OSFET. When the gate voltage cannot be supplied from the outside such as when the reference voltage is higher than the power supply voltage, the signal boosted by the charge pump is connected to the gate terminal, and the N-channel MOSF
A method of operating the ET is employed.

That is, as shown in FIG. 12, an N-channel MOSFET inserted between an input terminal 1 and an output terminal 6 is provided.
T4 is a switching element, and the input / output terminals 1,
It plays the role of a switch between six. N-channel MO
SFET4 when performs ON operation, the gate terminal 7, it is necessary to apply a gate voltage V _G higher than the power supply voltage the voltage from the charge pump 8.

In order to perform such a switching operation, a control terminal 10 is connected to a charge pump 8. Therefore, when the signal input to control terminal 10 is at the active level, charge pump 8 operates and N-channel M
The gate voltage V _G of the above clique value voltage OSFET4 applied to the gate terminal 7. As a result, the resistance between the drain terminal 3 and the source terminal 5 decreases, and the N-channel MO
The SFET 4 operates as a switch and becomes conductive.

The OSC 19 supplies the charge pump 8 with a clock signal for boosting operation at a constant frequency. The charge pump 8 applies a constant gate voltage to the N-channel MOSFET 4 based on the constant frequency clock signal.
To supply.

The current limiter 13 detects the current value from the voltage across the fixed resistor 11 for current detection, stops the operation of the charge pump 8 when an overcurrent flows, and sets a circuit when an excessive current flows. It works to cut off.

[0009]

However, the conventional power switch with a built-in charge pump has the following problems to be solved.

[0010] As shown in FIG.
The source-drain on-resistance of SFET4 is
It is set to a constant value irrespective of the amount of current between drains. Therefore, when the source-drain current increases,
The voltage drop between the source and the drain increases, and the output voltage of the power switch decreases.

When a conventional power switch having such characteristics is used for a power supply control circuit or the like of a device, if the current consumption of each device in the device increases, the power supply voltage supplied to each device decreases. There are inconveniences.

Note that the source of the N-channel MOSFET is
The reason why the on-resistance between drains is set to a constant value is as follows.

[0013] When for N-channel MOSFET ON operation, the value of the gate voltage V _G applied to the gate terminal, a constant value corresponding to the "ON state" of V _G -R _ON characteristics of N-channel MOSFET (e.g. FIG. 5 V _G1 ).

[0014] Therefore, an object of the present invention is to suppress a change in the output voltage even when the output current of the power switch is increased, and to prevent a malfunction even when the power consumption voltage is reduced due to an increase in the current consumption of the device. In particular, it is an object of the present invention to provide a power switch with a built-in charge pump, which has a required switching element function capable of preventing generation of a voltage, and a voltage control method using the power switch.

[0015]

SUMMARY OF THE INVENTION A power switch of the present invention is an N-channel type or the like having an extremely small on-resistance, which performs a switch-on operation when a gate voltage higher than a power supply voltage is applied to a gate electrode. Detects the value of the circuit current flowing between the transistor and the input and output terminals,
A current detection circuit for converting and amplifying the circuit current value to a voltage value proportional to both ends of the field effect transistor, outputting the voltage, and a voltage supplied from the current detection circuit and having a frequency having a positive correlation with the voltage. A voltage-controlled oscillation circuit that generates and outputs a square-wave clock signal, and a clock signal from the voltage-controlled oscillation circuit, and a voltage range in which the source-drain resistance of the field-effect transistor decreases due to an increase in gate voltage. A charge pump circuit for applying the gate voltage to the field effect transistor.

In this case, the current detection circuit is configured to detect a voltage between an input terminal and an output terminal, that is, a voltage between both ends of the field effect transistor, and amplify and output the voltage between the input terminal and the output terminal instead of the voltage detection means. Is also possible.

According to the voltage control method of the present invention using such a power switch, a field effect transistor having an extremely small on-resistance value that switches on when a gate voltage higher than a power supply voltage is applied to a gate electrode is used as a switching element. And a circuit current value flowing between the input terminal and the output terminal of the switch circuit is detected, and the circuit current value is converted to a voltage value proportional to both ends of the field-effect transistor and amplified. Receiving a square wave clock signal having a frequency having a positive correlation, and applying the gate voltage of the voltage range in which the source-drain resistance of the field-effect transistor decreases due to an increase in the gate voltage to the field-effect transistor, The voltage drop between the source and the drain is suppressed.

Therefore, from the above, the current flowing through the power switch of the present invention is detected by the current detection circuit. In this current detection circuit, a current flowing from an input terminal and flowing out of an output terminal is converted into a voltage. At this time, the leakage current to the terminals other than the output terminal can be ignored because it is extremely small.

Further, in this current detection circuit, a voltage value proportional to the detected current value is amplified to an appropriate magnitude, and the current between the input and output of the power switch, that is, between the source and drain of the N-channel MOSFET of the switching element is amplified. Generates a voltage proportional to the current. This generated voltage is output from a voltage output terminal in the current detection circuit and is supplied to a voltage controlled oscillation circuit. This voltage controlled oscillation circuit generates a rectangular wave signal having a frequency having a positive correlation with the output voltage from the voltage output terminal, and supplies it to the charge pump circuit.

The charge pump circuit has an output voltage characteristic corresponding to the frequency of the input rectangular wave. As the source-drain current increases and the output frequency from the voltage controlled oscillation circuit increases, The charge pump output voltage, that is, the gate voltage of the N-channel MOSFET increases.

As the N-channel MOSFET has an on-resistance characteristic, the on-resistance of the N-channel MOSFET decreases with an increase in the current between the source and the drain, and the voltage drop between the source and the drain, that is, the output voltage of the power switch. Can be suppressed from decreasing.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a power switch and a power supply voltage control method using the same according to the present invention will be described in detail with reference to the drawings.

As shown in the block diagram of FIG. 1, the preferred embodiment of the power switch according to the present invention comprises the following units.

A current detection circuit 2 is provided, which converts a current value flowing between the input / output terminals 1 and 6 as a power switch into a voltage value. It also has an N-channel MOSFET 4 which is a power transistor serving as a switching element, which has an extremely small on-resistance value for performing a switching operation in the power switch, and has terminals 3 and 5 of source / drain electrodes and a gate electrode. It consists of terminal 7.
It also has a voltage-controlled oscillation circuit (hereinafter, referred to as VCO) 9 which outputs a rectangular wave signal whose frequency increases with an increase in input voltage. Furthermore, VC
A charge pump 8 having a characteristic that the output voltage increases with an increase in the frequency of the rectangular wave signal supplied from O9 is provided.

The input terminal 1 is an input terminal l of the current detection circuit 2.
Connected to _IN, an output terminal l _O and N-channel MOSFET
4 are connected to the drain terminal 3. N-channel MO
The source terminal 5 of the SFET 4 is connected to the output terminal 6 of the power switch. Voltage output terminal V of current detection circuit 2
_O is connected to the control terminal of the VCO 9. The output terminal of the VCO 9 is connected to the clock input terminal for boosting operation of the charge pump 8, and the voltage output terminal of the charge pump 8 is N
It is connected to the gate terminal 7 of the channel MOSFET 4. The control terminal 10 of the power switch is a charge pump 8
Is connected to the control input terminal of The overcurrent detection signal output from the overcurrent detection signal terminal Limit of the current detection circuit 2 is connected to the overcurrent detection signal input terminal of the charge pump 8.

With the above configuration, the operation and operation are performed as follows. In each of FIGS. 1 to 6, the power switch has a control signal input to the control terminal 10 in an “off state”.
If so, the charge pump 8 does not perform the boosting operation. Therefore, the gate voltage of the N-channel MOSFET 4 (the voltage of the gate terminal 7) becomes lower than the threshold voltage of the MOSFET, and the source / drain resistance of the N-channel MOSFET 4 becomes large ("OFF state"). As a result, the switch is also in the “off state”.

When the control signal input to the control signal 10 is turned on, the charge pump 8 performs a boosting operation, and is higher than the power supply voltage. Supply. Thereby, the source of the N-channel MOSFET 4 is
The drain resistance drops to about 100 mOhm, and the power switch performs an "ON operation".

The current flowing between the input / output terminals 1 and 6 of the power switch is detected by a current detection circuit 2. In the current detection circuit 2, the current flows from the input terminal I _IN and the output terminal I _IN
Converts the current flowing out of _O to voltage. At this time, since the leakage current to portions other than the output terminal _IO is extremely small, it can be ignored.

In the current detection circuit 2, a voltage proportional to the detected current amount is amplified to an appropriate magnitude, and a current between the input and output of the power switch, that is, an N-channel MOSFET is amplified.
A voltage proportional to the source and drain of ET4 is generated. This voltage is a voltage output terminal V _O of the current detection circuit 2.
And is supplied to the VCO 9.

In FIG. 3, as indicated by the characteristic indicated by reference numeral 14, V
The CO 9 generates a rectangular wave signal having a frequency having a positive correlation with the voltage and supplies the signal to the charge pump circuit 8.

As shown by reference numeral 15 in FIG. 4, the charge pump circuit 8 has an output voltage characteristic with respect to the frequency of the input rectangular wave. Therefore, as the source-drain current increases and the output frequency of the VCO 9 increases, the output voltage of the charge pump circuit 8, that is, N
Gate voltage V _G of the channel MOSFET4 increases.

As indicated by reference numeral 16 in FIG. 5, the N-channel MOSFET 4 has an on-resistance characteristic.
The on-resistance of the OSFET 4 decreases. Therefore, a voltage drop between the source and the drain, that is, a decrease in the output voltage of the power switch can be suppressed.

As a result, as shown in FIG. 6, the current-voltage characteristic 18 of the power switch of the present embodiment is different from the current-voltage characteristic 17 of the prior art in that the output voltage is higher even if the source-drain current increases. Is less reduced.

When the current detection circuit 2 detects an overcurrent, the operation of the charge pump circuit 8 is stopped by activating the output signal Limit to prevent the overcurrent from flowing to the power switch.

[0035]

Referring to FIG. 2, this embodiment has an on-resistance of about 50 mOhm when the gate cut-off voltage is 5 V and the source-gate voltage is 8 V, and about 30 mOhm when the source-gate voltage is 12 V. N-channel MOS acting as switch in power switch having value
It has an FET 4 and a fixed resistor 11 having a resistance of about 10 milliohms for converting a current flowing between the input and output terminals 1 and 6 of the power switch into a voltage. An input terminal having an amplification factor of about 100 has a high impedance. Operational amplifier 12,
It has a voltage controlled oscillator (VCO) 9 for outputting a rectangular wave signal whose frequency increases as the input voltage increases, and a charge pump circuit 8 having a characteristic that the output voltage increases as the frequency of the input rectangular wave signal increases. doing.

The input terminal 1 is a fixed resistor 11 for detecting current.
, And the other terminal is an N-channel M
It is connected to the drain terminal 3 of the OSFET 4. The source terminal 5 of the N-channel MOSFET 4 is connected to the output terminal 6 of the power switch. Both ends of the fixed resistor 11 are connected to two input terminals of the operational amplifier 12, respectively. An output terminal of the operational amplifier 12 is connected to a control terminal of the VCO 9. The output terminal of the VCO 9 is connected to the clock input terminal for boost operation of the charge pump 8, and the voltage output terminal of the charge pump 8 is an N-channel MOSFET.
It is connected to the gate terminal 7 of T4. The control terminal 10 of the power switch is connected to the control input terminal of the charge pump 8. Both ends of the fixed resistor 11 are connected to two input terminals of the current limiter 13, and the overcurrent detection signal output from the overcurrent detection signal terminal of the current limiter 13 Connected to signal input terminal.

With the above configuration, the present embodiment operates and operates as follows. The power switch shown in FIG.
When the control signal input to the control terminal 10 is in the “L” state (“off state”) of the TTL level, the charge pump 8 does not perform the boosting operation, so that the N-channel MOSFET
4 becomes almost zero volts and is equal to or lower than the cut-off voltage (5 V) of the N-channel MOSFET 4, so that the N-channel MOSFET
The source / drain resistance of No. 4 is 100 kΩ or more, and the power switch is in the “off state”.

The control signal input to the control signal 10 is TT
When the L level goes to the “H” state (“ON state”), the charge pump 8 performs a step-up operation, and the gate voltage is increased to approximately 10 V, which is higher than the stagnant voltage of 5 V, and the gate voltage is reduced to N channel MOSF.
In order to supply to the gate terminal 7 of ET4, an N-channel MO
The source / drain resistance value of the SFET 4 decreases to about 50 mOhm, and the power switch performs "ON operation".

The current flowing between the input / output terminals 1 and 6 of the power switch is detected as a voltage drop across the fixed resistor 11 connected in series with the N-channel M08 FET4. Since the resistance value in this embodiment is 10 milliohms, a voltage drop of 10 millivolts occurs when a current of 1 amp flows.

In this case, since the input terminals of the current limiter 13 and the operational amplifier 12 have high impedance,
The current flowing through them is negligible.

Next, the voltage proportional to the source drain current of the N-channel MOSFET 4 detected as the voltage drop of the fixed resistor 11 is amplified by the operational amplifier 12 about 100 times. When a current of 1 amp flows through the power switch of the present invention, a voltage of about 1 V is supplied to the VCO 9.

In the characteristic diagram of FIG. 8, the VCO of this embodiment
Numeral 9 oscillates a rectangular wave signal having a frequency f that increases exponentially with respect to the input voltage as indicated by reference numeral 20. For example, when a current of 1 A flows through the power switch, the VCO output frequency is about 40 KHz. Next, the rectangular wave signal oscillated from the VCO 9 is supplied to a clock input terminal for boost operation of the charge pump 8. The charge pump 8 has an output voltage characteristic as indicated by 21 in FIG. 10 with respect to the frequency f of the input rectangular wave. Therefore, when the current flowing through the power switch is 0.1 A, the input voltage of the VCO 9 is 0.1 V.
The output frequency of the VCO 9 is about 10 KHz, and the output voltage of the charge pump 8 is about 8 V. When the current flowing through the power switch is 2 A, the input voltage of the VCO 9 is 2 V, the output frequency of the VCO 9 is about 100 KHz, and the output voltage of the charge pump 8 is about 12 V. Thus, in the power switch of this embodiment, when the current flowing through the power switch increases from 0.1 A to 2 A, the N-channel MOS
The gate voltage VG of the FET 4 increases from 8V to 12V.

Here, the N-channel MOSFET 4 has an on-resistance characteristic as indicated by reference numeral 22 in FIG.
As the current flowing in the power switch as described above is increased to 2A from 0.1 A, the gate voltage V _G rises to 12V 8V, the on-resistance of N-channel MOSFET4 is reduced from 50 milliohms to 30 milliohms.
Due to the decrease in the on-resistance of the N-channel MOSFET 4, the voltage drop between the source and the drain of the N-channel MOSFET 4 is suppressed, and the voltage drop in the entire power switch is also suppressed.

As a result, the output current-output voltage characteristic of the power switch according to the present embodiment is as indicated by reference numeral 23 in FIG. Compared to the current-voltage characteristic 24 in the case where the on-resistance value of the N-channel MOSFET 4 is constant, the current-voltage characteristic 23 of the present embodiment indicates that the output voltage does not decrease much even if the current flowing through the power switch increases. ing.

The current limiter 13 shown in FIG.
Monitors the potential difference between both ends of the fixed resistor 11, and activates the output signal when the amount of current flowing through the power switch exceeds a specified value (2.5 A in this embodiment) and becomes an overcurrent. To stop the operation of the charge pump 8,
This prevents overcurrent from flowing through the power switch.

FIG. 7 shows a second embodiment.

In this case, an N-channel MOSF having an extremely small on-resistance for performing a switching operation in the power switch is provided.
ET4, an operational amplifier 12 for detecting a voltage between both ends of the N-channel MOSFET 4, a voltage controlled oscillator (VCO) 9 for outputting a square wave signal whose frequency increases with an increase in the input voltage, and a frequency of the input square wave signal It comprises a charge pump 8 having the characteristic that the output voltage increases with the increase.

The input terminal 1 is connected to the current input terminal of the current limiter 13, and the current output terminal of the current limiter 13 is N
It is connected to the drain terminal 3 of the channel MOSFET 4. The source terminal 5 of the N-channel MOSFET 4 is connected to the output terminal 6 of the power switch. One of the input terminals of the operational amplifier 12 is connected to the input terminal 1, and the other is connected to the output terminal 6. The output terminal of the operational amplifier 12 is connected to the control voltage input terminal of VC09. An output terminal of the VCO 9 is connected to a clock input terminal for boost operation of the charge pump 8. The voltage output terminal of the charge pump 8 is connected to the gate terminal 7 of the N-channel MOSFET 4. Power switch control terminal 1
0 is connected to the control input terminal of the charge pump 8. Also, an overcurrent detection signal terminal Limi of the current limiter 13
The overcurrent detection signal output from the t
Is connected to the overcurrent detection signal input terminal.

With the above-described configuration, the second embodiment operates and operates as follows.

In the power switch shown in FIG. 2, when the control signal input to the control terminal 10 is in the "OFF state", the charge pump 8 does not perform the boosting operation.
The gate voltage of FET4 (the voltage of gate terminal 7) is MOS
N-channel MOSFET below the threshold voltage of FET
Since the source / drain resistance of No. 4 is large ("off state"), the switch is also "off state".

When the control signal input to the control signal 10 is turned on, the charge pump 8 performs a boosting operation and is higher than the power supply voltage.
In order to supply the gate voltage at which the channel MOSFET 4 is almost turned on, the source / drain resistance of the N-channel MOSFET 4 drops to about 100 mOhm,
Perform "ON operation" as a power switch.

The operational amplifier 12 connected to the input terminal 1 and the output terminal 6 detects a potential difference between the input terminal 1 and the output terminal 6. The output terminal voltage V _I -V _O is predominantly a voltage drop due to the on resistance of the N-channel MOSFET 4, current Rimitsuta 13 is negligible since the internal resistance is made very small. The voltage between the input and output terminals detected by the operational amplifier 13 is amplified to an appropriate magnitude in the operational amplifier and supplied to the VCO 9. VCO 9
As shown by reference numeral 14 in FIG. 3, a rectangular wave signal having a frequency having a positive correlation with the voltage is generated, and the rectangular wave signal is supplied to the charge pump circuit 8. The charge pump circuit 8 has an output voltage characteristic as indicated by reference numeral 15 in FIG. 4 with respect to the frequency of the input rectangular wave.

Therefore, as the input / output voltage V _I -V _{O of} the power switch increases, the voltage input to the VCO 9 increases, and the frequency of the rectangular wave signal input to the charge pump 8 also increases. Then, the output voltage of the charge pump 8, i.e., so that also increases the gate voltage V _G of the N-channel MOSFET 4.

Since the N-channel MOSFET 4 has an on-resistance characteristic as indicated by reference numeral 16 in FIG. 5, the current between the input and output of the power switch increases, and the input / output voltage V _I -V _O is reduced. N channel MOSFE as it increases
The ON resistance of T is reduced, and the voltage drop between the source and the drain of the N-channel MOSFET 4 is suppressed accordingly.

As a result, as shown in FIG. 6, the current-voltage characteristic 18 of the power switch of the present invention is different from the current-voltage characteristic 17 of the prior art in that the output voltage of the power switch increases even if the source-drain current increases. The drop is less.

When an overcurrent is detected, the current limiter 13 activates the output signal Limit to stop the operation of the charge pump circuit 8, thereby preventing the overcurrent from flowing to the power switch.

[0057]

As described above, the power switch with a built-in charge pump according to the present invention can suppress a voltage drop when the amount of current flowing through the power switch increases. As a result, in a device using the power switch of the present invention, even when the current consumption fluctuates greatly, the fluctuation of the power supply voltage supplied to the devices in the device can be reduced, and malfunction due to the power supply voltage fluctuation can be prevented. Can be prevented.

The reason is that the power switch of the present invention
Internal N-channel MOSFE causing voltage drop
This is because the ON resistance of T can be reduced as the current flowing through the power switch increases.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a power switch with a built-in charge pump according to the present invention.

FIG. 2 is a block diagram showing a first embodiment.

FIG. 3 is a graph showing VCO oscillation frequency characteristics of the VCO according to the first embodiment.

FIG. 4 is a graph showing a charge pump output voltage characteristic of the charge pump according to the first embodiment.

FIG. 5 is a graph showing on-resistance characteristics of the N-channel MOSFET according to the first embodiment.

FIG. 6 is a graph showing current-voltage characteristics of the power switch with a built-in charge pump according to the first embodiment;

FIG. 7 is a block diagram showing a second embodiment according to the present invention.

FIG. 8 is a graph showing VCO oscillation frequency characteristics of the VCO of the first embodiment.

FIG. 9 is a graph showing a charge pump output voltage characteristic of the charge pump of the first embodiment.

FIG. 10 is a graph showing on-resistance characteristics of the N-channel MOSFET of the first embodiment.

FIG. 11 is a graph showing current-voltage characteristics of the power switch with a built-in charge pump according to the first embodiment.

FIG. 12 is a block diagram showing a conventional power switch with a built-in charge pump.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 input terminal 2 current detection circuit 3 drain terminal 4 N-channel MOSFET 5 source terminal 6 output terminal 7 gate terminal 8 charge pump circuit 9 VCO 10 control terminal 11 fixed resistor 12 operational amplifier 13 current limiter 14 VCO oscillation frequency characteristic 15 charge pump Output voltage characteristic 16 N-channel MOSFET on-resistance characteristic 17 Current-voltage characteristic of conventional example 18 Current-voltage characteristic 19 0SC 20 VCO oscillation frequency characteristic of first example 21 Charge pump output voltage characteristic of first example 22 First N-channel MOSFET on-resistance characteristics of the embodiment 23 Current-voltage characteristics of the first embodiment 24 Current-voltage characteristics of the conventional example

Claims (11)

[Claims] 1. A field effect transistor having an extremely low on-resistance value that is turned on when a gate voltage higher than a power supply voltage is applied to a gate electrode, and a circuit current value flowing between an input terminal and an output terminal is detected. A current detection circuit for converting and amplifying the circuit current value to a voltage value proportional to both ends of the field-effect transistor and outputting the voltage; and a voltage supplied from the current detection circuit, and having a positive correlation with the voltage. A voltage-controlled oscillation circuit that generates and outputs a square-wave clock signal having a frequency; and a clock signal from the voltage-controlled oscillation circuit,
A charge pump circuit for applying the gate voltage to the field effect transistor in a voltage range in which the source-drain resistance of the field effect transistor decreases as the gate voltage increases. 2. The method according to claim 1, wherein the current detection circuit comprises a fixed resistor for converting the circuit current value to a voltage value, and an operational amplifier having a high impedance characteristic for amplifying the voltage value at a required amplification factor. The power switch according to claim 1, wherein: 3. The charge pump is connected in parallel with the fixed resistor and monitors a potential difference between input and output terminals of the fixed resistor. When the circuit current value exceeds a specified value and becomes overcurrent, the charge pump 3. The power switch according to claim 2, further comprising a current limiter for preventing an overcurrent that outputs an off signal for turning off the operation of the circuit. 4. The power switch according to claim 1, wherein said field effect transistor is an N-channel MOS type. 5. A field-effect transistor having an extremely small on-resistance value that is turned on when a gate voltage higher than a power supply voltage is applied to a gate electrode, and a voltage between the input terminal and the output terminal, that is, the field effect. Voltage detecting means for detecting, amplifying and outputting a voltage between both ends of the transistor; and a voltage supplied from the voltage detecting means, and generating and outputting a square wave clock signal having a frequency having a positive correlation with the voltage. A voltage-controlled oscillation circuit, and a clock signal from the voltage-controlled oscillation circuit,
A charge pump circuit for applying the gate voltage to the field effect transistor in a voltage range in which the source-drain resistance of the field effect transistor decreases as the gate voltage increases. 6. The power switch according to claim 5, wherein said voltage detection means is an operational amplifier having a required amplification factor and an input terminal having a high impedance characteristic. 7. The power switch according to claim 5, wherein said field effect transistor is an N-channel MOS type. 8. A switching circuit comprising: a field effect transistor having an extremely small on-resistance value which is turned on when a gate voltage higher than a power supply voltage is applied to a gate electrode; And amplifies the circuit current value by converting the circuit current value into a voltage value proportional to both ends of the field effect transistor, and a square wave clock signal having a frequency having a positive correlation with the voltage value. Receiving the source of the field effect transistor
By applying a gate voltage in a voltage range in which a drain-to-drain resistance value decreases with an increase in a gate voltage to the field-effect transistor to suppress a voltage drop between the source and the drain, a power switch is used. Voltage control method. 9. The voltage control method using a power switch according to claim 8, wherein the circuit current value is converted into a voltage value by a fixed resistor, and the voltage value is amplified by an operational amplifier. 10. A decrease in output voltage of the field-effect transistor is minimized even when the circuit current value increases in correlation with an output current, as compared with a current-voltage characteristic when an on-resistance value is constant. A voltage control method using a power switch according to claim 8 or 9, 11. The voltage control method using a power switch according to claim 8, wherein said field effect transistor is an N-channel MOS type.