Control circuit and ideal diode circuit

A control circuit includes: a transistor controller that controls a voltage at a gate terminal of a field effect transistor in accordance with a difference in voltage between a source terminal and a drain terminal of the field effect transistor connected so that a body diode is in a forward direction; and a current controller that reduces an operating current for operating the transistor controller when a load connected via the source terminal of the field effect transistor is light, and increases the operating current when the load is heavy.

This application is the U.S. national phase of International Application No. PCT/JP2017/024167 filed Jun. 30, 2017 which designated the U.S., and the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a control circuit and an ideal diode circuit.

BACKGROUND ART

In recent years, a technique of using a field effect transistor as an ideal diode is known (see, for example, Patent Document 1). In such an ideal transistor, a control circuit includes a comparator that compares a source voltage and a drain voltage of the field effect transistor, and controls a gate voltage in accordance with a comparison result of the comparator, thereby controlling the field effect transistor to operate as a diode.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, in the above-described conventional control circuit, for example, when it is necessary to flow a large current through the ideal diode, it has been necessary to increase the drive capability for controlling the gate voltage in order to prevent backflow when blocking backflow. For this reason, the conventional control circuit has a problem that, for example, current consumption increases in a standby state in which a light load is connected to the ideal diode.

The present invention has been made to solve the above problem, and an object thereof is to provide a control circuit and an ideal diode circuit capable of reducing current consumption in the standby state while maintaining the function of the ideal diode.

Means for Solving the Problems

To solve the above problem, a control circuit according to one aspect of the present invention includes: a transistor controller that controls a voltage at a gate terminal of a field effect transistor in accordance with a difference in voltage between a source terminal and a drain terminal of the field effect transistor connected so that a body diode is in a forward direction; and a current controller that reduces an operating current for operating the transistor controller when a load connected via the source terminal of the field effect transistor is light, and increases the operating current when the load is heavy.

Additionally, in the above control circuit according to one aspect of the present invention, the current controller may reduce the operating current for operating the transistor controller when the voltage at the gate terminal becomes a voltage at which a transistor current flowing through the field effect transistor becomes equal to or lower than a predetermined current value, and increase the operating current when the voltage at the gate terminal becomes a voltage at which the transistor current exceeds the predetermined current value.

Additionally, in the above control circuit according to one aspect of the present invention, the current controller may include: a first current source that supplies a constant current serving as a reference for the operating current at the time of startup; and a second current source that adds and supplies an additional constant current to the first current source when the voltage at the gate terminal becomes the voltage at which the transistor current flowing through the field effect transistor exceeds the predetermined current value.

Additionally, in the above control circuit according to one aspect of the present invention, the current controller may include a plurality of current sources each of which supplies a constant current serving as a reference for the operating current, switch the plurality of current sources in accordance with the voltage at the gate terminal, and supply the constant current serving as the reference for the operating current.

Additionally, in the above control circuit according to one aspect of the present invention, the current controller may select any one or a combination of the plurality of current sources in accordance with the voltage at the gate terminal, and supply the constant current serving as the reference for the operating current.

Additionally, in the above control circuit according to one aspect of the present invention, the transistor controller may include a differential amplifier circuit that controls the voltage at the gate terminal in accordance with the difference in voltage between the drain terminal and the source terminal.

Additionally, an ideal diode circuit according to one aspect of the present invention includes: the above-described control circuit; and the field effect transistor.

Effects of the Invention

According to the present invention, the transistor controller controls the voltage at the gate terminal of the field effect transistor in accordance with the difference in voltage between the source terminal and the drain terminal of the field effect transistor connected so that the body diode is in the forward direction. Then, the current controller reduces the operating current for operating the transistor controller when the load connected via the source terminal of the field effect transistor is light. Additionally, the current controller increases the operating current when the load is heavy. As a result, the control circuit reduces the operating current for operating the transistor controller in a standby state, such as during a light load, so that the current consumption can be reduced in the standby state while maintaining the function of the ideal diode.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a control circuit and an ideal diode circuit according to an embodiment of the present invention will be described with reference to the drawings.

First Embodiment

FIG. 1is a block diagram showing an example of a configuration of an ideal diode circuit1according to the present embodiment.

As shown inFIG. 1, the ideal diode circuit1includes a MOS transistor2and a control circuit10.

It is assumed that the ideal diode circuit1is connected between a DC power source (not shown) such as a battery and a load (not shown). That is, it is assumed that, for example, a battery is connected to a VIN terminal (input terminal) and a GND terminal of the ideal diode circuit1, and a load is connected between a VOUT terminal (output terminal) and a GND signal line.

The ideal diode circuit1conducts between the VIN terminal and the VOUT terminal when a voltage at the VIN terminal (node N1) is equal to or higher than a voltage at the VOUT terminal (node N2) (in a forward direction). In addition, when the voltage at the VOUT terminal becomes higher than the voltage at the VIN terminal (in a reverse direction), the ideal diode circuit1blocks the conduction between the VIN terminal and the VOUT terminal and prevents current backflow.

The MOS transistor2(an example of a field effect transistor) is, for example, a P-channel MOSFET (Metal Oxide Semiconductor field effect transistor) and includes a body diode21. The MOS transistor2has a source terminal connected to the node N2, a drain terminal connected to the node N1, and a gate terminal connected to a node N3. Here, the MOS transistor2is connected so that the body diode21is in the forward direction. A voltage at the gate terminal is controlled by a transistor controller11described later, so that the MOS transistor2functions as a diode element in the ideal diode circuit1.

Here, since the MOS transistor2has the body diode21, current flows from the drain terminal (node N1) to the source terminal (node N2) when the voltage at the drain terminal (node N1) becomes higher than the voltage at the source terminal (node N2) by the forward voltage or more.

The control circuit10includes the transistor controller11and a current controller12.

The transistor controller11controls the voltage at the gate terminal (node N3) of the MOS transistor2in accordance with a difference in voltage between the source terminal (node N2) and the drain terminal (node N1) of the MOS transistor2.

For example, when the voltage at the drain terminal (node N1) is equal to or higher than the voltage at the source terminal (node N2), the transistor controller11controls the voltage at the gate terminal (node N3) so that a current according to the load flows through the MOS transistor2, and turns on the MOS transistor2(on state). In addition, for example, when the voltage at the source terminal (node N2) is higher than the voltage at the drain terminal (node N1), the transistor controller11controls the voltage at the gate terminal (node N3) so as to prevent a reverse bias current from flowing into the MOS transistor2, and turns off the MOS transistor2(off state).

Further, the transistor controller11includes a differential amplifier111.

The differential amplifier111(an example of a differential amplifier circuit) is, for example, an operational amplifier and controls the voltage at the gate terminal (node N3) in accordance with the difference in voltage between the drain terminal (node N1) and the source terminal (node N2). Here, a Vds voltage (=drain voltage−source voltage) changes in accordance with the load. When the Vds voltage is a positive value, the differential amplifier111controls the voltage at the gate terminal (node N3) so that a larger current flows through the MOS transistor2as the value of the Vds voltage is larger, and controls the voltage at the gate terminal (node N3) so that a smaller current flows through the MOS transistor2as the value of the Vds voltage is smaller. Additionally, the differential amplifier111controls the voltage at the gate terminal (node N3) so that the MOS transistor2is turned off when the Vds voltage is a negative value. Here, when the Vds voltage is a positive value, the Vds voltage is larger as the load is larger.

Specifically, when the MOS transistor2is made conductive, the differential amplifier111outputs to the gate terminal (node N3), a voltage lower than the voltage at the source terminal (node N2). Additionally, when the conduction of the MOS transistor2is cut off, the differential amplifier111outputs to the gate terminal (node N3), a voltage equal to or higher than the voltage at the source terminal (node N2).

The differential amplifier111has a + terminal (non-inverting input terminal) connected to the node N2, a − terminal (inverting input terminal) connected to the node N1, and an output terminal connected to the gate terminal (node N3) of the MOS transistor2. Here, the differential amplifier111may include, for example, a differential (comparator) and an output amplifier. Additionally, the differential amplifier111may have a predetermined offset value when comparing the + terminal (non-inverting input terminal) and the − terminal (inverting input terminal).

Further, the differential amplifier111operates with a current source supplied from the current controller12.

The current controller12controls, in accordance with the load, operating current for operating the transistor controller11. For example, the current controller12reduces the operating current for operating the transistor controller11when the voltage at the gate terminal (node N3) becomes a voltage at which a transistor current flowing through the MOS transistor2becomes equal to or lower than a predetermined current value. That is, the current controller12reduces the current of the current source supplied to the transistor controller11when the load is equal to or less than a predetermined threshold value. Thereby, the current controller12reduces the operating current of the transistor controller11.

Additionally, the current controller12increases the operating current when the voltage at the gate terminal (node N3) becomes a voltage at which the transistor current exceeds the predetermined current value. That is, the current controller12increases the current of the current source supplied to the transistor controller11when the load exceeds the predetermined threshold value. Thereby, the current controller12increases the operating current of the transistor controller11.

Further, the current controller12includes a startup current source121, a VGS detection voltage current conversion circuit122, and a current adder123.

The startup current source121(an example of a first current source) supplies a constant current serving as a reference for the operating current at the time of startup in the control circuit10. For example, the startup current source121generates a constant current source based on a constant voltage source, such as a band gap reference circuit. The startup current source121always operates as a constant current source in a state where the control circuit10is activated, and supplies the operating current to the transistor controller11via the current adder123.

The VGS detection voltage current conversion circuit122(an example of a second current source) generates a current source in accordance with the voltage at the gate terminal (node N3), and supplies the current source to the transistor controller11via the current adder123. The VGS detection voltage current conversion circuit122increases the current source supplied to the transistor controller11, in accordance with a decrease in voltage at the gate terminal (node N3) (increase in load). In other words, the VGS detection voltage current conversion circuit122adds and supplies an additional constant current to the startup current source121when, for example, the voltage becomes a voltage at which the transistor current flowing through the MOS transistor2exceeds a predetermined current value.

Additionally, the VGS detection voltage current conversion circuit122decreases the current source supplied to the transistor controller11, in accordance with an increase in voltage at the gate terminal (node N3) (decrease in load).

Here, a specific example of the VGS detection voltage current conversion circuit122will be described later with reference toFIG. 2.

The current adder123adds a current from the startup current source121and a current from the VGS detection voltage current conversion circuit122, and supplies the resultant current to the transistor controller11as the current source.

Next, a specific example of the VGS detection voltage current conversion circuit122will be described with reference toFIG. 2.

FIG. 2is a diagram illustrating a configuration example of the VGS detection voltage current conversion circuit122according to the present embodiment.

As shown inFIG. 2, the VGS detection voltage current conversion circuit122includes a resistor124and a MOS transistor125. The resistor124and the MOS transistor125are connected in series, so that the VGS detection voltage current conversion circuit122forms the current source.

The resistor124has a first terminal connected to the node N2and a second terminal connected to a source terminal of the MOS transistor125.

The MOS transistor125is a P-channel MOSFET similar to the MOS transistor2. The MOS transistor125has a source terminal connected to the node N2, a drain terminal connected to the node N4, and a gate terminal connected to the node N3. In accordance with the voltage at the gate terminal (node N3), the MOS transistor125outputs from the node N2via the resistor124, a current from the drain terminal, as the current source.

Here, inFIG. 2, the output line of the startup current source and the output line of the VGS detection voltage current conversion circuit122are connected at the node N4, and the node N4corresponds to the above-described current adder123. Thus, at the node N4, the output line of the startup current source and the output line of the VGS detection voltage current conversion circuit122are connected, so that the current from the startup current source121and the current from the VGS detection voltage current conversion circuit122are added and supplied to the transistor controller11as the current source.

In addition, when the voltage at the gate terminal (node N3) becomes equal to or greater than a predetermined voltage (for example, a negative value of the Vgs voltage (difference in voltage between the gate terminal and the source terminal) becomes equal to or lower than a threshold value Vth), the MOS transistor125turns off (off state), and the VGS detection voltage current conversion circuit122stops the supply of the current source.

Next, operations of the control circuit10and the ideal diode circuit1according to the present embodiment will be described with reference to the drawings.

FIG. 3is a flowchart showing an example of the operation of the transistor controller11in the present embodiment.

As shown inFIG. 3, the transistor controller11of the control circuit10determines whether or not the voltage at the node N1is equal to or higher than the voltage at the node N2((the voltage at the node N1−the voltage at the node N2)≥0) (step S101). For example, the differential amplifier111of the transistor controller11compares the voltage at the node N1with the voltage at the node N2, and determines whether or not the voltage at the node N1is equal to or higher than the voltage at the node N2. When the voltage at the node N1is equal to or higher than the voltage at the node N2(step S101: YES), the transistor controller11proceeds to step S103. In addition, when the voltage at the node N1is lower than the voltage at the node N2((the voltage at the node N1−the voltage at the node N2)<0) (step S101: NO), the transistor controller11proceeds to step S102.

In step S102, the transistor controller11controls the voltage at the gate terminal (node N3) so that the MOS transistor2is turned off. That is, the differential amplifier111supplies to the gate terminal (node N3) of the MOS transistor2, a voltage for turning off the MOS transistor2. The transistor controller11returns to step S101after the process in step S102.

Additionally, in step S103, the transistor controller11applies to the gate terminal (node N3), a voltage in accordance with the difference in voltage between the node N1and the node N2(the voltage at the node N1−the voltage at the node N2), thus turning on the MOS transistor2. That is, the differential amplifier111changes and supplies the voltage at the gate terminal (node N3) so that the current of the MOS transistor2(transistor current) increases as the value of (the voltage at the node N1−the voltage at the node N2) increases, and the transistor current decreases as the value of (the voltage at the node N1−the voltage at the node N2) decreases. The transistor controller11returns to step S101after the process in step S103.

Next, the operation of the current controller12according to the present embodiment will be described with reference toFIG. 4.

FIG. 4is a flowchart showing an example of the operation of the current controller12in the present embodiment.

As shown inFIG. 4, the current controller12of the control circuit10first determines whether or not the voltage at the gate terminal (node N3) is equal to or higher than the predetermined voltage (step S201). That is, based on whether or not the MOS transistor125is in the on-state, the VGS detection voltage current conversion circuit122of the current controller12determines whether or not the voltage at the gate terminal (node N3) is equal to or higher than the predetermined voltage. When the voltage at the gate terminal (node N3) is equal to or higher than the predetermined voltage (step S201: YES), the current controller12proceeds to step S202. Additionally, if the voltage at the gate terminal (node N3) is lower than the predetermined voltage (step S201: NO), the current controller12proceeds to step S203.

In step S202, the current controller12stops the VGS detection voltage current conversion circuit122. That is, when the MOS transistor125is turned off, the current source from the VGS detection voltage current conversion circuit122is stopped, and the current controller12reduces the operating current of the transistor controller11. The current controller12returns to step S201after the process in step S202.

Additionally, in step S203, the current controller12adds the current from the VGS detection voltage current conversion circuit122to the startup current of the startup current source121and supplies the resultant current to the transistor controller11. That is, when the MOS transistor125is turned on, the VGS detection voltage current conversion circuit122functions as the current source, and the current flowing through the resistor124and the MOS transistor125(additional constant current) is added to the startup current of the startup current source121, and the resultant current is supplied to the transistor controller11. Thereby, the current controller12increases the operating current of the transistor controller11. The current controller12returns to step S201after the process in step S203.

Next, operations of the control circuit10and the ideal diode circuit1according to the present embodiment will be described with reference toFIGS. 5 to 7

FIG. 5is a first timing chart showing an example of the operation of the control circuit10in the present embodiment. In this figure, a vertical axis of each graph indicates, in order from the top, the voltages at the node N1and the node N2, the input current from the battery, the current passing through the MOS transistor2, the load current, and the current at the GND terminal. In addition, a horizontal axis of each graph indicates time.

Additionally, inFIG. 5, waveforms W1to W6indicate a voltage waveform at the node N1, a voltage waveform at the node N2, a waveform of the input current from the battery, a waveform of the current passing through the MOS transistor2, a waveform of the load current, and a current waveform of the control circuit10including the operating current of the transistor controller11, in this order. Here, the voltage at the node N1is an output voltage of the battery. In addition, each current is shown assuming that a current in the input direction is a positive current, while an output current is a negative current.

When the load current increases at time T1inFIG. 5(see waveform W5), the voltage at the node N2decreases below the voltage at the node N1, in accordance with the load current. As a result, the differential amplifier111of the transistor controller11decreases the voltage at the gate terminal (node N3) so that the current flowing through the MOS transistor2increases in accordance with the difference in voltage between the node N1and the node N2. When the voltage at the gate terminal (node N3) decreases, the input current from the battery and the current passing through the MOS transistor2increase (see waveforms W3and W4). Further, when the voltage at the gate terminal (node N3) decreases, the VGS detection voltage current conversion circuit122starts operating, and the operating current of the transistor controller11increases (see waveform W6).

Additionally, at time T2, when the load current decreases and the node N2becomes at a high voltage so that a reverse bias occurs (see waveform W2), the differential amplifier111of the transistor controller11supplies to the gate terminal (node N3), the voltage for turning off the MOS transistor2so as to prevent current backflow due to the reverse bias. Thereby, the MOS transistor2functions as a diode, thereby preventing the high voltage at node N2from flowing back to the battery.

Further, at time T3, when the high voltage at the node N2is resolved (see waveform W2) and, for example, the state shifts to a standby state or the like where the load current is small, the current controller12causes the VGS detection voltage current conversion circuit122to stop operating so that the operating current of the transistor controller11is reduced. In this case, as indicated by the waveform W6, the current of the control circuit10including the operating current of the transistor controller11can be kept low.

Additionally,FIG. 6is a second timing chart showing an example of the operation of the control circuit10in the present embodiment. In this figure, a vertical axis of each graph indicates, in order from the top, the voltage at the gate terminal (node N3), the voltage at the source terminal (node N2), the Vgs voltage, and the load current. In addition, a horizontal axis of each graph indicates time.

Further, inFIG. 6, waveforms W11to W14indicate a voltage waveform at the gate terminal (node N3), a voltage waveform at the source terminal (node N2), a Vgs voltage, and a waveform of the load current, in this order. Here, the Vgs voltage indicates a voltage (the voltage at the gate terminal−the voltage at the source terminal) obtained by subtracting the voltage at the source terminal (node N2) from the voltage at the gate terminal (node N3).

At time T1, when the load current increases (see waveform W14), the voltage at the source terminal (node N2) decreases. In response to this, the differential amplifier111of the transistor controller11reduces the voltage at the gate terminal (node N3) in accordance with the difference in voltage between the node N1and the node N2, so that the current flowing through the MOS transistor2increases (see waveform W11). Then, as a result, the Vgs voltage of the MOS transistor2comes to have a waveform as indicated by the waveform W13, and the MOS transistor2is turned on. In this case, the MOS transistor2functions as a diode through which a current flows in the forward direction.

Further, at time T2, when the load current decreases and the node N2becomes at a high voltage so that a reverse bias occurs, the differential amplifier111of the transistor controller11supplies to the gate terminal (node N3), a voltage for turning off the MOS transistor2, as indicated by the waveform W11. In this case, the MOS transistor2functions as a diode to which the reverse bias is applied, and prevents current backflow due to the reverse bias.

Further, at time T3, when the high voltage at the node N2is resolved (see waveform W12) and, for example, the state shifts to the standby state or the like where the load current is small, the differential amplifier111of the transistor controller11supplies to the gate terminal (node N3), the voltage in accordance with the load current (see waveform W11). That is, the differential amplifier111supplies to the gate terminal (node N3), a voltage in accordance with the difference in voltage between the node N1and the node N2.

Additionally,FIG. 7is a diagram showing an example of the operation of the current controller12in the present embodiment. In this figure, a vertical axis of each graph indicates, in order from the top, the Vds voltage and the current consumption of the control circuit10. Further, a horizontal axis of each graph shows a log plot (logarithmic plot) of the load current (load current Iout).

Further, inFIG. 7, a waveform W21and a waveform W22indicate a waveform of the Vds voltage and a waveform of the current consumption of the control circuit10, in this order. Here, the Vds voltage indicates a voltage (the voltage at the drain terminal−the voltage at the source terminal) obtained by subtracting the voltage at the source terminal (node N2) from the voltage at the drain terminal (node N1) of the MOS transistor.

As indicated by the waveform W21inFIG. 7, the Vds voltage of the MOS transistor2increases as the load current Iout increases. Further, the current controller12increases the operating current of the transistor controller11in accordance with the increase in load current Iout. Thereby, as indicated by the waveform W22, the current consumption of the control circuit10increases as the load current Iout increases. Here, in this case, since the operating current of the transistor controller11increases, the MOS transistor2can be quickly turned off.

Further, the current controller12decreases the operating current of the transistor controller11when the operating current of the transistor controller11decreases. Thereby, the current consumption of the control circuit10is reduced during a light load, such as in the standby state.

As described above, the control circuit10according to the present embodiment includes the transistor controller11and the current controller12. The transistor controller11controls the voltage at the gate terminal (node N3) of the MOS transistor2in accordance with the difference in voltage between the source terminal (node N2) and the drain terminal (node N1) of the MOS transistor2(field effect transistor) connected so that the body diode21is in the forward direction. The current controller12reduces the operating current for operating the transistor controller11when the load connected via the source terminal (node N2) of the MOS transistor2is light, and increases the operating current when the load is heavy.

Thereby, the transistor controller11controls the MOS transistor2as an ideal diode, and the current controller12appropriately controls the operating current for operating the transistor controller11, in accordance with the load. Therefore, the control circuit10according to the present embodiment reduces the operating current for operating the transistor controller11in the standby state, such as during a light load, so that the current consumption can be reduced in the standby state while maintaining the function of the ideal diode.

Further, in the present embodiment, the current controller12reduces the operating current for operating the transistor controller11when the voltage at the gate terminal (node N3) becomes the voltage at which the transistor current flowing through the MOS transistor2becomes equal to or lower than the predetermined current value; and increases the operating current for operating the transistor controller11when the voltage at the gate terminal (node N3) becomes the voltage at which the transistor current exceeds the predetermined current value.

As a result, the current controller12reduces the operating current for operating the transistor controller11when the voltage at the gate terminal (node N3) is a voltage corresponding to a light load; and increases the operating current for operating the transistor controller11when the voltage is a voltage corresponding to a heavy load. Therefore, the control circuit10according to the present embodiment can reduce the current consumption in the standby state while maintaining the function of the ideal diode by the simple method of increasing or decreasing the operating current by the voltage of the gate terminal (node N3).

Additionally, in the present embodiment, the current controller12includes: the startup current source121(first current source) that supplies a constant current serving as the reference for the operating current at the time of startup; and the VGS detection voltage current conversion circuit122(second current source) that adds and supplies an additional constant current to the startup current source121when the voltage at the gate terminal becomes the voltage at which the transistor current flowing through the MOS transistor2exceeds the predetermined current value.

Accordingly, the control circuit10according to the present embodiment can appropriately control the operating current for operating the transistor controller11with the simple configuration in which the additional current source (the VGS detection voltage current conversion circuit122) is added to the startup current source121.

Additionally, in this embodiment, the transistor controller11includes the differential amplifier111(differential amplifier circuit) that controls the voltage at the gate terminal in accordance with the difference in voltage between the drain terminal and the source terminal.

Thereby, the control circuit10according to the present embodiment can appropriately control the MOS transistor2as an ideal diode with the simple circuit configuration.

Further, the ideal diode circuit1according to the present embodiment includes the control circuit10and the MOS transistor2.

Thereby, like the control circuit10, the ideal diode circuit1according to the present embodiment can reduce the current consumption in the standby state while maintaining the function of the ideal diode.

Second Embodiment

Next, a control circuit10aand an ideal diode circuit1aaccording to a second embodiment will be described with reference to the drawings.

FIG. 8is a block diagram showing an example of a configuration of the ideal diode circuit1aaccording to the present embodiment.

As shown inFIG. 8, the ideal diode circuit1aincludes the MOS transistor2and a control circuit10a.

Here, in this figure, the same components as those inFIG. 1described above are denoted by the same reference numerals, and description thereof is omitted.

The ideal diode circuit1aconducts between the VIN terminal and the VOUT terminal when the voltage at the VIN terminal (node N1) is equal to or higher than the voltage at the VOUT terminal (node N2) (in the forward direction). In addition, when the voltage at the VOUT terminal becomes higher than the voltage at the VIN terminal (in the reverse direction), the ideal diode circuit1blocks the conduction between the VIN terminal and the VOUT terminal and prevents current backflow.

The control circuit10aincludes the transistor controller11and a current controller12a.

This embodiment differs from the first embodiment in that a configuration of the current controller12adiffers.

The current controller12controls, in accordance with the load, the operating current for operating the transistor controller11. For example, the current controller12reduces the operating current for operating the transistor controller11when the voltage at the gate terminal (node N3) becomes a voltage at which the transistor current flowing through the MOS transistor2becomes equal to or lower than a predetermined current value. That is, the current controller12reduces the current of the current source supplied to the transistor controller11when the load is equal to or less than a predetermined threshold value. Thereby, the current controller12reduces the operating current of the transistor controller11.

The current controller12aincreases the operating current when the voltage at the gate terminal (node N3) becomes a voltage at which the transistor current exceeds the predetermined current value. That is, the current controller12aincreases the current of the current source supplied to the transistor controller11when the load exceeds the predetermined threshold value. Thus, the current controller12aincreases the operating current of the transistor controller11.

Additionally, the current controller12aincludes a plurality of current sources120(first current source120-1, second current source120-2, . . . ), a VGS detector126, a current source selector127, and a switch128.

Here, in the present embodiment, the first current source120-1, the second current source120-2, . . . are current sources having different current values, and will be described as the current source120when each indicates an arbitrary current source included in the control circuit10a, and unless otherwise distinguished from one another.

Additionally, the current controller12aswitches the plurality of current sources120in accordance with the voltage at the gate terminal (node N3), and supplies a constant current serving as a reference for the operating current of the transistor controller11. Here, the current controller12amay select any one or a combination of the plurality of current sources120in accordance with the voltage at the gate terminal (node N3), and supply a constant current serving as a reference for the operating current.

The current source120generates the constant current serving as the reference for the operating current, and supplies the generated constant current to the transistor controller11. Here, for example, the second current source120-2supplies a constant current larger than that of the first current source120-1, and the plurality of current sources120each supply constant currents having different sizes.

The VGS detector126detects a voltage (Vgs voltage) at the gate terminal (node N3).

For example, the switch128is a changeover switch such as a transistor, and supplies to the transistor controller11, the constant current that is an output of the current source120selected by the current source selector127.

In accordance with the voltage (Vgs voltage) at the gate terminal (node N3) detected by the VGS detector126, the current source selector127selects from the plurality of current sources120, a current source120that supplies the constant current to the transistor controller11. The current source selector127outputs a control signal to the switch128so that the constant current is supplied from the selected current source120to the transistor controller11.

For example, when the voltage at the gate terminal (node N3) becomes a voltage at which the transistor current becomes equal to or lower than a predetermined current value (equal to or higher than a first threshold value), the current source selector127selects the first current source120-1and reduces the operating current for operating the transistor controller11. In addition, for example, when the voltage at the gate terminal (node N3) becomes a voltage at which the transistor current exceeds the predetermined current value (less than the first threshold value), the current source selector127selects the second current source120-2and increases the operating current for operating the transistor controller11.

Next, operations of the control circuit10aand the ideal diode circuit1aaccording to the present embodiment will be described with reference to the drawings.

FIG. 9is a flowchart showing an example of the operation of the current controller12ain the present embodiment.

InFIG. 9, the current controller12afirst detects the Vgs voltage (step S301). That is, the VGS detector126of the current controller12adetects the voltage (Vgs voltage) at the gate terminal (node N3).

Next, the current controller12aselects a current source120in accordance with the Vgs voltage (step S302). In other words, in accordance with the voltage (Vgs voltage) at the gate terminal (node N3) detected by the VGS detector126, the current source selector127of the current controller12aselects from the plurality of current sources120, a current source120that supplies the constant current to the transistor controller11. For example, when the Vgs voltage is equal to or higher than the first threshold value, the current source selector127selects the first current source120-1. In addition, for example, when the Vgs voltage is less than the first threshold value, the current source selector127selects the second current source120-2having a larger current than that of the first current source120-1. The current source selector127outputs a control signal to the switch128so that the constant current is supplied from the selected current source120to the transistor controller11. The current controller12areturns to step S301after the process in step S302.

Here, since operations other than that of the above-described current controller12aare the same as those in the first embodiment, description thereof is omitted here.

As described above, the control circuit10aaccording to the present embodiment includes the transistor controller11and the current controller12a. The transistor controller11controls the voltage at the gate terminal (node N3) of the MOS transistor2in accordance with the difference in voltage between the source terminal (node N2) and the drain terminal (node N1) of the MOS transistor2(field effect transistor) connected so that the body diode21is in the forward direction. The current controller12areduces the operating current for operating the transistor controller11when the load connected via the source terminal (node N2) of the MOS transistor2is light, and increases the operating current when the load is heavy.

Thereby, the control circuit10aaccording to the present embodiment has the same effect as that of the first embodiment, and can reduce the current consumption in the standby state while maintaining the function of the ideal diode.

Additionally, in the present embodiment, the current controller12aincludes the plurality of current sources120each of which supplies the constant current serving as the reference for the operating current for operating the transistor controller11, switches the plurality of current sources120in accordance with the voltage (Vgs voltage) at the gate terminal (node N3), and supplies to the transistor controller11, the constant current serving as the reference for the operating current.

Thereby, the control circuit10aaccording to the present embodiment can appropriately control the operating current for operating the transistor controller11with the simple configuration in which the plurality of current sources120are switched and used.

Further, in the present embodiment, the current controller12amay select any one or a combination of the plurality of current sources120in accordance with the voltage at the gate terminal, thus supplying the constant current serving as the reference for the operating current. In other words, in accordance with the voltage (Vgs voltage) at the gate terminal (node N3), the current controller12aselects any one or a combination of the plurality of current sources120so that the constant current to be supplied increases as the transistor current increases, and supplies to the transistor controller11, the constant current serving as the reference for the operating current.

As a result, the control circuit10aaccording to the present embodiment can finely control the operating current for operating the transistor controller11by selecting or combining the plurality of current sources120, thereby reducing current consumption.

Here, the present invention is not limited to the above-described embodiments, and can be modified without departing from the spirit of the present invention.

For example, although the case where the P-channel MOSFET is used as an example of the field effect transistor has been described in each of the above-described embodiments, the present invention is not limited thereto. For example, the ideal diode circuit1(1a) may use another type of field effect transistor, such as an N-channel MOSFET, as the field effect transistor.

Additionally, although the example in which the current controller12aswitches between the two current sources120, which are the first current source120-1and the second current source120-2, has been described in the above second embodiment, three or more current sources120may be switched and used. In addition, the current controller12amay add and supply the second current source120-2as an additional constant current to the first current source120-1, as in the first embodiment.

Further, some or all of the functions of the control circuit10(10a) and the ideal diode circuit1(1a) described above may be realized as an integrated circuit, such as an LSI (Large Scale Integration).

DESCRIPTION OF REFERENCE NUMERALS