JP2014225841A - Load drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably prevent a driving transistor from being erroneously turned on at power input even if, in a connection line for feeding a nonconducting potential to a conduction control terminal of the driving transistor while controlling transistors are off, a transistor capable of switching the connection line between conductive and nonconductive states is disposed.SOLUTION: A potential fixing transistor 30 is disposed in a connection line 28 connecting a gate terminal 10A of a driving transistor 10 and a high potential power line 26 having a nonconducting potential of the driving transistor 10. A base terminal 30A of the potential fixing transistor 30 is connected to the high potential power line 26 having a conducting potential of the potential fixing transistor 30. At power input, the potential fixing transistor 30 immediately becomes conductive to fix a potential of the gate terminal 10A of the driving transistor 10 at a supply potential that is the nonconducting potential.

Description

  The present invention relates to a load driving circuit for driving a load such as a motor.

  For example, Patent Document 1 discloses a semiconductor element control device that controls conduction of a driving semiconductor element connected in series to a load. The semiconductor element control device includes two control transistors that control the potential of the gate terminal of the driving semiconductor element. A resistance element is connected between the power source and the gate terminal of the driving transistor in order to prevent the driving semiconductor element from being turned on accidentally when both of these two control transistors are turned off. ing. As a result, while the two control transistors are both turned off, the potential of the gate terminal of the driving semiconductor element becomes the power supply potential (non-conducting potential), and the driving semiconductor element maintains the off state.

  A series circuit of a capacitor and an open circuit transistor is connected between the gate terminal of the driving transistor and the ground line. When the drive control circuit uses two control transistors to control the conduction state of the drive semiconductor element, the open-circuit transistor is turned on to suppress the generation of switching noise by the capacitor. . On the other hand, when both of the two control transistors are turned off at the time of starting the power supply or in the standby state, the open circuit transistor connected in series with the capacitor is turned off. As a result, even when the power supply voltage fluctuates, the gate potential of the driving semiconductor element is prevented from being increased by the CR circuit formed by the resistance element and the capacitor. The increase in the potential between the sources is suppressed.

JP 2013-9244 A

  In the semiconductor element control device described above, a resistance is applied in order to apply a predetermined voltage between the source terminal and the gate terminal of the driving semiconductor element and to measure the leakage current flowing between the terminals. An open circuit transistor may be provided separately in series with the element. In this case, the resistance element is separated from the gate terminal of the driving semiconductor element by turning off the open circuit transistor during the measurement of the leakage current.

  However, the conduction state of the open circuit transistor is controlled by a drive signal from the drive control circuit. Therefore, at the time of starting the power supply, the open circuit transistor connected in series with the resistance element is in a non-conducting state after the supply of the power supply voltage is started until the drive control circuit can operate normally. Or the state may become unstable (undefined). In this case, immediately after the power is turned on, the power supply potential is not applied to the gate terminal of the driving semiconductor element, the source potential of the driving semiconductor element becomes higher than the gate potential, and the driving semiconductor element may be erroneously turned on. Occurs.

  The present invention has been made in view of the above-described points, and when the control transistor is stopped, the connection line for applying a non-conduction potential to the conduction control terminal of the driving transistor is connected to the connection line. An object of the present invention is to provide a load driving circuit capable of reliably preventing a driving transistor from being turned on accidentally when a power source is started even when a transistor capable of switching non-conduction is provided. To do.

In order to achieve the above object, a load driving circuit according to the present invention comprises:
Connected between the power supply and the ground, and conducts when a conduction potential is applied to the conduction control terminals (10A, 112A), causes a drive current to flow through the load (1), and conducts when a non-conduction potential is applied. Driving transistors (10, 112),
A control transistor (22, 24, 122, 124) capable of switching a potential applied to the conduction control terminal of the driving transistor to either a conduction potential or a non-conduction potential;
Provided on connection lines (28, 128) for connecting the conduction control terminal of the driving transistor and the signal lines (26, 126) having the non-conduction potential of the driving transistor, and their own conduction control terminals (30A, 130A). ) Are connected to signal lines (26, 126) having a conduction potential, and when conducting, a potential fixing transistor (30, 130) that fixes the potential of the conduction control terminal of the driving transistor to a non-conduction potential. With
When the power is turned on and the control transistor is stopped, a conduction potential is applied to the conduction control terminal of the potential fixing transistor so that the potential fixing transistor is turned on.

  Thus, according to the load driving circuit of the present invention, the potential fixing transistor is provided on the connection line connecting the conduction control terminal of the driving transistor and the signal line having the non-conduction potential of the driving transistor. It is done. The conduction control terminal of the potential fixing transistor is connected to a signal line having a conduction potential. For this reason, when the power is turned on, the potential fixing transistor immediately conducts, and the potential of the conduction control terminal of the driving transistor is fixed to the non-conduction potential. Therefore, it is possible to reliably prevent the driving transistor from being turned on by mistake when the power is turned on.

  The load driving circuit described above preferably includes an off transistor (36) that switches the potential applied to the conduction control terminal of the potential fixing transistor from the conduction potential to the non-conduction potential. By providing this off transistor, the potential fixing transistor can be turned off as necessary. For example, the potential fixing transistor is preferably in a non-conducting state when a leakage current inspection is performed on the control transistor or the driving transistor. This is because the connection line can be electrically disconnected from the conduction control terminal of the driving transistor, and the leakage current inspection can be performed correctly. The potential fixing transistor may be in a non-conductive state when the potential is switched by the control transistor. In this case, for example, excess current can be prevented from flowing from the connection line through the control transistor, and current consumption can be reduced.

  Note that the reference numerals in the parentheses merely show an example of a correspondence relationship with a specific configuration in an embodiment described later in order to facilitate understanding of the present invention, and limit the scope of the present invention. It is not intended.

  Further, the features of the present invention other than the features described above will be apparent from the description of embodiments and the accompanying drawings described later.

It is a block diagram which shows roughly the structure of the load drive circuit in 1st Embodiment. 5 is a table summarizing on / off states of transistors in various states of the load driving circuit. (a)-(c) is the figure which showed the signal waveform of each part of the load drive circuit at the time of power activation. It is a block diagram which shows schematically the structure of the load drive circuit in 2nd Embodiment.

(First embodiment)
Hereinafter, a load driving circuit according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram schematically showing a configuration of a load driving circuit in the present embodiment.

  In FIG. 1, reference numeral 1 denotes a motor as a load. The motor 1 is, for example, a blower motor for blowing used in an air conditioner mounted on a vehicle or a direct current motor used as a fan motor for a radiator. However, the load applied to the load driving circuit of the present embodiment is not limited to a DC motor, and for example, a three-phase motor may be used as a load, or an electric device other than the motor may be used as a load.

  A driving transistor 10 and the motor 1 are connected in series between an in-vehicle battery as a power source and the ground. As a result, when the driving transistor 10 becomes conductive, a driving current flows through the motor 1, and when the driving transistor 10 becomes non-conductive, the driving current stops. In the example shown in FIG. 1, a P-channel power MOSFET is used as the driving transistor 10.

  An N-channel power MOSFET 12 is connected in parallel to the motor 1. The N-channel power MOSFET 12 is used to circulate a surge current caused by a counter electromotive force generated when the drive current to the motor 1 is stopped. Therefore, the N-channel power MOSFET 12 is turned on / off in the opposite phase to the driving transistor 10.

  A power MOS control circuit 20 is provided to turn on and off the P-channel power MOSFET and the N-channel power MOSFET 12 as the driving transistor 10. In the power MOS control circuit 20, a first control transistor 22 and a second control transistor 24 are connected in series between a high potential power line 26 and a low potential power line 27. The first control transistor 22 is a P-channel MOSFET, and the second control transistor 24 is an N-channel MOSFET. A connection line 23 that connects the first control transistor 22 and the second control transistor 24 to each other is connected to the gate terminal of the drive transistor 10. In the example shown in FIG. 1, the high potential power line 26 is connected to the on-vehicle battery, and the low potential power line 27 is connected to the ground. However, the low potential power supply line 27 in the power MOS control circuit 20 may be set to a predetermined potential higher than the ground potential in order to protect the source-gate breakdown voltage of the driving transistor 10.

  When one of the first control transistor 22 and the second control transistor 24 is turned on by the drive signal from the control unit 38, the other is turned off. That is, when the first control transistor 22 is turned on, the second control transistor 24 is turned off. In this case, the power supply potential is applied to the gate terminal 10 </ b> A of the driving transistor 10. Then, since the gate-source voltage VGS of the driving transistor 10 becomes substantially zero, the driving transistor 10 is turned off (off). Thus, the power supply potential provided by the high potential power supply line 26 corresponds to a non-conduction potential.

  On the other hand, when the first control transistor 22 is turned off, the second control transistor 24 is turned on. In this case, a low potential is applied to the gate terminal 10 </ b> A of the driving transistor 10. Then, since the gate-source voltage VGS of the driving transistor 10 exceeds the threshold voltage Vth, the driving transistor 10 becomes conductive (ON). Thus, the low potential provided by the low potential power supply line 27 corresponds to the conduction potential.

  The control unit 38 drives the first control transistor 22 and the second control transistor 24 in a duty manner in accordance with a drive command (target duty ratio) given from an external host control device (not shown). Is output. For this reason, the on and off states of the first and second control transistors 22 and 24 are alternately switched in opposite phases at each on time and off time in a predetermined duty control cycle. As a result, the potential applied to the gate terminal 10A of the driving transistor 10 is also alternately switched between a high potential and a low potential, and the driving transistor 10 repeats an on state and an off state according to the target duty ratio. . In this way, the magnitude of the drive current supplied to the motor 1 by the drive transistor 10 is PWM controlled.

  The control unit 38 stops outputting the drive signal to the control transistors 22 and 24 when instructed to stop the operation from the host controller. In this case, the first and second control transistors 22 and 24 are both in a non-conductive state, and are in a standby state in which a new drive command is awaited from the host controller.

  In the power MOS control circuit 20, there is further provided a connection line 28 for connecting the gate terminal 10A of the driving transistor 10 and a high potential power line 26 having a power supply potential which is a non-conduction potential of the driving transistor 10. Is provided. A series circuit of a potential fixing transistor 30 and a resistance element 32 is inserted into the connection line 28. The potential fixing transistor 30 is an NPN-type bipolar transistor. A base terminal 30A that is a conduction control terminal of the potential fixing transistor 30 is connected to a high potential power supply line 26 having a power supply potential via a resistance element 34. Accordingly, when the supply of power from the in-vehicle battery is started and the potential of the high potential power supply line 26 rises to the power supply potential, the potential of the base terminal 30A of the potential fixing transistor 30 immediately rises toward the power supply potential. When the potential of the base terminal 30A exceeds the threshold voltage (about 0.7V), the potential fixing transistor 30 is turned on. Then, the gate terminal 10A of the driving transistor 10 is connected to the high potential power supply line 26 having the power supply potential via the resistance element 32. Therefore, the potential of the gate terminal 10A of the driving transistor 10 is fixed to the power supply potential, and the driving transistor 10 is maintained in a non-conductive state.

  An off transistor 36 is connected between the base terminal 30A of the potential fixing transistor 30 and the ground. The off transistor 36 is an N-channel MOSFET. The off transistor 36 is controlled to be in a conductive state or a non-conductive state by a drive signal supplied from the control unit 38. When the off transistor 36 becomes conductive, the ground potential is applied to the base terminal 30A of the potential fixing transistor 30. In this case, the potential fixing transistor 30 is turned off. On the other hand, when the off transistor 36 is turned off, the power supply potential is applied to the base terminal 30A of the potential fixing transistor 30. In this case, the potential fixing transistor 30 is turned on.

  Next, operations and effects of the load driving circuit according to the present embodiment will be described with reference to FIGS. FIG. 2 is a table summarizing the on / off states of the transistors in various states of the load driving circuit. FIGS. 3A to 3C are diagrams showing signal waveforms of respective parts of the load driving circuit when the power is turned on.

  Before the power supply to the load driving circuit is turned on, the driving transistor 10, the control transistors 22, 24, the potential fixing transistor 30, and the off transistor 36 are all in an off state. In this state, when power is supplied to the load driving circuit, the source potential of the driving transistor 10 rises with a steep slope, as shown in FIG.

  Here, as shown in FIG. 2, when the power is turned on, the off-transistor 36 remains off. For this reason, the potential of the base terminal 30 A of the potential fixing transistor 30 rises with a steep slope, like the source potential of the driving transistor 10. And then. When the potential of the base terminal 30A exceeds the threshold voltage, the potential fixing transistor 30 is turned on.

  Here, in the case of a bipolar transistor, the threshold voltage is sufficiently lower than that of a power MOSFET. For example, the threshold voltage Vth between the gate and the source of the power MOSFET is 2.0 V or higher, whereas the threshold voltage between the base and the emitter of the bipolar transistor is about 0.7 V. For this reason, the voltage fixing transistor 30 made of a bipolar transistor is turned on sufficiently earlier than the driving transistor 10 is turned on.

  Then, the gate terminal 10A of the driving transistor 10 is connected to the high potential power supply line 26 having the power supply potential via the connection line 28 in which the resistance element 32 is inserted. For this reason, the potential of the gate terminal 10A of the driving transistor 10 rises with the same slope as the source potential of the driving transistor 10 as shown in FIG. Therefore, the gate-source voltage VGS of the driving transistor 10 is limited to a very small value as shown in FIG. As a result, when the power is turned on, the driving transistor 10 is not intentionally turned on but is kept off. Therefore, as shown in FIG. 3A, the current IPMos does not flow between the source and drain of the driving transistor 10 when the power is turned on. The state in which the driving transistor 10 is turned on unintentionally includes a so-called half-on state in which the gate-source voltage VGS is relatively low and the on-state has a relatively high on-resistance.

  In addition, as shown in FIG. 2, in standby mode, that is, with the power on, output of the drive signal to the control transistors 22 and 24 is stopped, and both the control transistors 22 and 24 are turned off. Even when the driving transistor 10 is also in the off state, the off transistor 36 is set in the off state as in the case of power-on. Therefore, the potential fixing transistor 30 is turned on, and the potential of the gate terminal 10A of the driving transistor 10 is fixed to the power supply potential that is a non-conductive potential. Accordingly, the driving transistor 10 is prevented from being unintentionally turned on even during standby.

  Further, as shown in FIG. 2, in the normal control in which the first and second control transistors 22 and 24 are duty-driven by the drive signal from the control unit 38, and thereby the drive transistor 10 is PWM-controlled. The off transistor 36 is switched to the on state. Therefore, the ground potential is applied to the base terminal 30A of the potential fixing transistor 30, and the potential fixing transistor 30 is turned off.

  Here, if the potential fixing transistor 30 remains in the on state during the above-described normal control, the potential fixing transistor 30 → the resistance element 32 → the second element when the second control transistor 24 is turned on. A current flows through the path of the two control transistors 24. Therefore, an increase in power consumption in the load driving circuit is caused. On the other hand, in this embodiment, the potential fixing transistor 30 is turned off during normal control. As a result, even if the first and second control transistors are alternately turned on and off alternately, it is possible to prevent unnecessary current from flowing in the load driving circuit.

  Finally, also when the leakage current of the first control transistor 22 or the driving transistor 10 is inspected, the off transistor 36 is switched to the on state, whereby the potential fixing transistor 30 is turned off.

  Here, in the leakage current inspection of the first control transistor 22 or the driving transistor 10, a predetermined voltage is applied between the gate and the source of the transistor to be inspected, and the current flowing between them is measured. . At the time of this leakage current inspection, by turning off the potential fixing transistor 30, the gate terminal of the transistor to be inspected can be electrically disconnected from the connection line 28, and the impedance can be made high. Therefore, the leak current inspection can be executed with high accuracy.

  In the case where the first control transistor 22 is to be subjected to a leakage current inspection, the driving transistor 10 may be removed from the power MOS control circuit 20. In this way, the leakage current inspection of the first control transistor 22 can be performed without being affected by the driving transistor 10 at all.

  As described above, in the load driving circuit of the present embodiment, the connection line 28 that connects the gate terminal 10A of the driving transistor 10 and the high-potential power line 26 having the non-conductive potential of the driving transistor 10 is connected. In addition, a potential fixing transistor 30 is provided. The base terminal 30 A of the potential fixing transistor 30 is connected to a high potential power supply line 26 having the conduction potential of the potential fixing transistor 30. For this reason, the potential fixing transistor 30 is immediately turned on when the power is turned on and on standby, and the potential of the gate terminal 10A of the driving transistor 10 is fixed to the power supply potential which is a non-conductive potential. Therefore, it is possible to reliably prevent the driving transistor 10 from being turned on erroneously at the time of power activation and standby.

  Furthermore, the load driving circuit of the present embodiment includes an off transistor 36 that switches the potential applied to the base terminal 30A of the potential fixing transistor 30 from the power supply potential that is the conduction potential to the ground potential that is the non-conduction potential. ing. By providing the off transistor 36, the potential fixing transistor 30 can be turned off as necessary.

  Specifically, the potential fixing transistor 30 is turned off when a leakage current inspection of the first control transistor 22 or the driving transistor 10 is performed. As a result, the leak current inspection can be correctly executed. The potential fixing transistor 30 is turned off when the first and second control transistors 22 and 24 are driven by duty. Thereby, it is possible to prevent an excessive current from flowing in the load driving circuit, and to reduce the current consumption.

(Second Embodiment)
Next, a load driving circuit according to a second embodiment of the present invention will be described with reference to FIG. In the first embodiment described above, an example in which the driving transistor 10 is connected to the upstream side of the motor 1 and the motor 1 is driven by so-called high-side driving has been described. However, it is also possible to drive the motor 1 by so-called low side driving. Hereinafter, a load driving circuit when the motor 1 is driven on the low side will be described as a second embodiment.

  As shown in FIG. 4, a series circuit is connected between the power source and the ground, with the motor 1 being the upstream side and the driving transistor 112 being the downstream side. The driving transistor 112 is an N-channel power MOSFET. A P-channel power MOSFET 110 for circulating a surge current is connected to the upstream side of the driving transistor 112 and in parallel with the motor 1.

  In order to cope with such low-side driving, in the power MOS control circuit 120, the gate terminal 112A of the driving transistor 112 and the ground (correctly, the low-potential power line 126 having a low potential such as the ground potential) are connected. A connection line 128 is provided to connect them, and a series circuit of a potential fixing transistor 130 and a resistance element 132 is inserted into the connection line 128. The potential fixing transistor 130 is a PNP-type bipolar transistor. The base terminal 130A of the potential fixing transistor 130 is connected to a low potential power supply line 126 that provides a conduction potential of the potential fixing transistor 130 via a resistance element 134.

  Therefore, even when the potential of the gate terminal 112A of the driving transistor 112 is going to rise at the time of power-on or standby, the potential fixing transistor 130 is immediately turned on. Thereby, the potential increase of the gate terminal 112A of the driving transistor 112 can be suppressed. That is, the potential fixing transistor 130 can maintain the potential of the gate terminal 112A of the driving transistor 112 at a low potential that is substantially a non-conduction potential.

  The drain terminal of the off transistor 136 is connected to the base terminal 130 </ b> A of the potential fixing transistor 130. The off transistor 136 is a P-channel MOSFET, the source terminal of which is connected to the power supply, and the gate terminal of which is connected to the control unit 138. For this reason, when the off transistor 136 is turned on by the drive signal from the control unit 138, the power supply potential which is a non-conduction potential is applied to the base terminal 130A of the potential fixing transistor 130. In this case, the potential fixing transistor 130 is turned off.

  As in the first embodiment, the control unit 138 maintains the off transistor 136 in the off state at power-on and standby, and switches the off transistor 136 in the on state during normal control and leakage current inspection. Therefore, the driving transistor 112 is maintained in the off state at the time of power-on and standby. Further, during normal control and leakage current inspection, the potential fixing transistor 130 is turned off.

  As described above, the load driving circuit according to the second embodiment can obtain the same operations and effects as those of the load driving circuit according to the first embodiment.

(Modification)
The preferred embodiments according to the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. .

  For example, in each of the above-described embodiments, the power MOSFETs 12 and 110 are used to return the surge current caused by the counter electromotive force of the motor 1. However, instead of the power MOSFETs 12 and 110, a diode may be connected in parallel to the motor 1.

  In each of the above-described embodiments, the first control transistors 22 and 122 and the second control transistors 24 and 124 are used as the control transistors. However, only the first control transistors 22 and 122 may be used as the control transistors, and a resistance element may be connected instead of the second control transistors 24 and 124.

  Further, in each of the above-described embodiments, bipolar transistors are used as the potential fixing transistors 30 and 130. As described above, in the case of a bipolar transistor, the threshold voltage is sufficiently lower than that of a power MOSFET. Therefore, before the driving transistors 10 and 112 are turned on, the gate terminals 10A and 112A of the driving transistors 10 and 112 can be fixed to a non-conductive potential, and the driving transistors 10 and 112 are unintentionally turned on. There is a merit that it can be surely prevented from becoming a state.

  However, some MOSFETs have a threshold voltage of 1.2 V or less. Any MOSFET having a threshold voltage sufficiently lower than that of such a power MOSFET can also be used as a potential fixing transistor.

DESCRIPTION OF SYMBOLS 1 Motor 10, 112 Drive transistor 22, 122 1st control transistor 24, 124 2nd control transistor 30, 130 Potential fixing transistor 36, 136 Off transistor 38, 138 Control part

Claims (6)

Connected between the power supply and the ground, and conducts when a conduction potential is applied to the conduction control terminals (10A, 112A), causes a drive current to flow through the load (1), and conducts when a non-conduction potential is applied. Driving transistors (10, 112),
A control transistor (22, 24, 122, 124) capable of switching a potential applied to a conduction control terminal of the driving transistor between the conduction potential and the non-conduction potential;
Provided on a connection line (28, 128) connecting the conduction control terminal of the driving transistor and a signal line (26, 126) having a non-conduction potential of the driving transistor, and its own conduction control terminal (30A). , 130A) are connected to signal lines (26, 126) having a conduction potential, and when conducting, potential fixing transistors (30, 30) that fix the potential of the conduction control terminal of the driving transistor to a non-conduction potential. 130), and
When the power is turned on and the control transistor is stopped, a conduction potential is applied to the conduction control terminal of the potential fixing transistor, and the potential fixing transistor is turned on. Load control circuit.   2. The load drive circuit according to claim 1, further comprising an off transistor that switches a potential applied to a conduction control terminal of the potential fixing transistor from a conduction potential to a non-conduction potential.   The off transistor switches a potential applied to a conduction control terminal of the potential fixing transistor to a non-conduction potential when a leakage current inspection of the control transistor or the driving transistor is performed. The load driving circuit according to claim 2.   3. The off transistor switches the potential applied to the conduction control terminal of the potential fixing transistor to a non-conduction potential when the potential is switched by the control transistor. Load drive circuit.   The control transistor includes two transistors connected in series between a high potential power supply line (26, 127) having a power supply potential and a low potential power supply line (27, 126) having a lower potential. (22, 24, 122, 124), and the connection lines (23, 123) that connect each other are connected to the conduction control terminal of the driving transistor, and either one of the transistors is selectively turned on. Thus, the potential applied to the conduction control terminal of the driving transistor is a power supply potential, the conduction potential that is one of the lower potentials, and the non-conduction potential that is the other of the power supply potential and the lower potential. The load drive circuit according to claim 1, wherein the load drive circuit is switched between.   The control transistor is duty-driven according to a target duty ratio, whereby the potential applied to the conduction control terminal of the driving transistor is alternately switched between the conduction potential and the non-conduction potential. A load driving circuit according to any one of claims 1 to 5.

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