JP2012044850A - Power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power circuit capable of suppressing an adverse effect upon MOSFET for rectification in a booster circuit even when the MOSFET for rectification is impossible to turn on due to a broken drive circuit.SOLUTION: When a voltage of a battery 2 temporarily drops, MOSFET 7 for boosting and MOSFET 9 for rectification are alternately turned on and off and, when a voltage of the battery 2 that has dropped temporarily returns to an original voltage, the MOSFET 7 for boosting is always turned off and the MOSFET 9 for rectification is always turned on. When a detection circuit 13 determines that a drive circuit 11 is broken after the voltage of the battery 2 returns to the original voltage, the operation of a MOSFET 14 for current interruption is controlled to interrupt a current flowing through a load 6 from the battery 2.

Description

  The present invention relates to a power supply circuit that keeps a battery voltage constant and outputs it to a load.

  In recent years, idle stop vehicles have been put into practical use for the purpose of reducing fuel consumption and reducing exhaust gas. An idle stop vehicle is a vehicle that automatically stops the engine when it detects a stop operation of the vehicle, such as waiting for a signal, and then automatically restarts the engine when it detects a start operation of the vehicle.

  In such a vehicle, when the engine is restarted, a large current flows through the starter motor for starting the engine, so that the battery voltage temporarily decreases. Along with this, the voltage supplied to a load such as an electrical component other than the starter motor connected to the battery also temporarily decreases. Therefore, depending on the load, the supplied voltage may be out of the range of the voltage necessary for the operation, and may not operate normally temporarily. For example, reset may be performed in car navigation or audio, sound skipping may occur in audio, or an operation unintended by the driver may be performed. Therefore, in such a vehicle, an auxiliary power supply circuit is provided so that the supply of a necessary voltage to the load can be maintained even when the voltage of the battery temporarily decreases.

  As an auxiliary power supply circuit, for example, there is a circuit that includes a booster circuit and controls the output voltage to the load by boosting the voltage of the battery by turning on and off switching elements in the booster circuit ( For example, see Patent Document 1).

  However, in such a power supply circuit, a current always flows through the rectifying diode in the booster circuit at the normal time after the voltage of the battery that has been temporarily reduced returns to the original voltage. A decrease in efficiency due to a loss in the diode and a rise in temperature of the diode are problems.

  Therefore, as a power supply circuit, there is one in which a MOSFET is provided instead of a rectifying diode and the rectifying MOSFET is normally turned on to suppress a decrease in efficiency and an increase in element temperature. In this power supply circuit, even if the drive circuit that drives the rectifying MOSFET fails and the rectifying MOSFET cannot be turned on, the current flows through the body diode of the rectifying MOSFET, so the power supply to the load continues. Can be made.

JP 2005-237149 A

  However, as described above, when the drive circuit that drives the rectifying MOSFET fails and the rectifying MOSFET cannot be turned on, a current always flows through the body diode of the rectifying MOSFET, and the rectifying MOSFET The temperature of the MOSFET rises. In this case, since the current flowing through the body diode cannot be stopped by the control circuit in the booster circuit, the temperature rise of the rectifying MOSFET cannot be suppressed and self-protection cannot be performed. Therefore, there is a possibility that the rectifying MOSFET may be adversely affected such as element breakage due to the temperature rise.

  Accordingly, the present invention provides a power supply circuit capable of suppressing adverse effects on the rectifying MOSFET even when the drive circuit fails and the rectifying MOSFET in the booster circuit cannot be turned on. The purpose is to do.

  The power supply circuit of the present invention includes a booster circuit including a battery, a switch, a coil provided between the battery and the switch, and a rectifying MOSFET provided between the coil and a load, and the battery. A current cut-off switch provided in a path of a current flowing to the load via the coil and the rectifying MOSFET, an abnormality detecting means for determining whether or not a drive circuit for driving the rectifying MOSFET has failed, and When the voltage of the battery is temporarily lowered, the output voltage to the load is kept constant by alternately turning on and off the switch and the rectifying MOSFET and always turning on the current cutoff switch. When the voltage of the battery that has been temporarily reduced returns to the original voltage, the switch is always turned on. The rectifying MOSFET and the current cut-off switch are always turned on to supply power from the battery to the load, and after the battery voltage returns to the original voltage, the abnormality detection means causes the drive circuit to If it is determined that a fault has occurred, a control means is provided for controlling an operation of the current cutoff switch to cut off a current flowing from the battery to the load via the coil and the rectifying MOSFET.

  As a result, when the drive circuit fails, current does not flow to the rectifying MOSFET, so even if the drive circuit fails and the rectifying MOSFET cannot be turned on, the rectifying MOSFET is adversely affected. Can be suppressed.

  Further, the power supply circuit of the present invention is connected in series to each other, a plurality of resistors connected to a path of current flowing from the battery to the load via the coil and the rectifying MOSFET, and the plurality of resistors. A transistor that turns on the current cut-off switch, which is a P-channel MOSFET, and flows current from the battery to the load via the coil and the rectifying MOSFET by applying a current to a voltage generated at a connection point of the plurality of resistors. And when the abnormality detecting means determines that the drive circuit has failed, the control means turns off the transistor and stops the current flowing through the plurality of resistors, thereby stopping the current cutoff switch. From the battery to the load via the coil and the rectifying MOSFET. It may be configured to interrupt the current that.

As a result, it is not necessary to prepare a new power source for generating a voltage for controlling on / off of the current interrupting switch, so that an increase in cost and circuit scale can be suppressed.
The power supply circuit of the present invention is connected in series with each other, and a plurality of resistors connected to a path of current flowing from the battery to the load via the coil and the rectifying MOSFET, and current flowing from the battery When the switch is turned on, the current cut-off switch, which is a P-channel MOSFET, is turned on by applying a current to the plurality of resistors and generating a voltage at the connection point of the plurality of resistors, thereby turning the coil and the rectifier from the battery. When the first transistor that supplies current to the load via the MOSFET is turned on, the current that has flowed from the battery to the first transistor is supplied to the ground to turn off the first transistor, and By preventing the current from flowing through a plurality of resistors, the current cutoff switch is turned off before A second transistor that cuts off a current flowing from the battery to the load via the coil and the rectifying MOSFET, and when the control means determines that the drive circuit has failed by the abnormality detection means, The second transistor may be turned on.

  Thereby, even when power is not supplied to the control circuit, power can be supplied from the battery to the load via the current cutoff switch.

  The present invention provides a power supply circuit that keeps the battery voltage constant and outputs it to a load even if the drive circuit fails and the rectifying MOSFET in the booster circuit cannot be turned on. An adverse effect can be suppressed.

It is a figure which shows the power supply circuit of embodiment of this invention. It is a flowchart which shows operation | movement of a control circuit. It is a figure which shows the power supply circuit of other embodiment of this invention.

FIG. 1 is a diagram showing a power supply circuit according to an embodiment of the present invention.
A power supply circuit 1 shown in FIG. 1 includes a battery 2 and a booster circuit 3. The step-up circuit 3 is connected to the battery 2 through the capacitor 4 and is connected to the load 6 through the capacitor 5, and supplies power obtained from the battery 2 to the load 6.

  The power supply circuit 1 according to the present embodiment includes, for example, an electric component (input, such as car navigation or audio as a load 6 while keeping the voltage of a battery 2 that supplies power to an engine starter motor for starting an idle stop vehicle constant. It is used as an output to an electrical component that temporarily does not normally operate with a temporary drop in voltage.

  The booster circuit 3 includes an N-channel booster MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 7 (switch), a coil 8 provided between the battery 2 and the booster MOSFET 7, and a coil 8 and a load 6. Detected by an N-channel rectifying MOSFET 9 provided therebetween, a drive circuit 10 for driving the boosting MOSFET 7, a drive circuit 11 for driving the rectifying MOSFET 9, a thermistor 12 provided in the vicinity of the rectifying MOSFET 9, and the thermistor 12 And a detection circuit 13 that determines that the drive circuit 11 has failed when the temperature obtained based on the applied voltage is equal to or higher than a predetermined temperature. In addition, the abnormality detection means of a claim is comprised by the thermistor 12 and the detection circuit 13, for example.

  The power supply circuit 1 includes a P-channel current cutoff MOSFET (current cutoff switch) 14, resistors 15 and 16, an npn bipolar transistor 17 (transistor), a host ECU (Electronic Control Unit) 18, and a display unit. 19.

  The current cutoff MOSFET 14 is provided in a path of current flowing from the battery 2 to the load 6 via the coil 8 and the rectifying MOSFET 9. That is, the drain of the current interrupting MOSFET 14 (terminal on the battery 2 side) is connected to the source of the rectifying MOSFET 9 (terminal on the load 6 side), and the source of the current interrupting MOSFET 14 (terminal on the load 6 side) is connected to the capacitor 5. Has been.

  The resistors 15 and 16 are connected in series with each other and are connected to a path of current flowing from the battery 2 to the load 6 through the coil 8 and the rectifying MOSFET 9. The connection point of the resistors 15 and 16 is connected to the gate of the current interrupting MOSFET 14.

  The npn bipolar transistor 17 has a collector connected to the resistor 16 and an emitter connected to the ground (the negative terminal of the battery 2). When the npn bipolar transistor 17 is turned on, a current flows through the resistors 15 and 16 and a voltage is generated at the connection point of the resistors 15 and 16. Then, this voltage (a negative bias voltage generated between the gate and the source of the current blocking MOSFET 14) turns on the current blocking MOSFET 14, and the load 6 from the battery 2 through the coil 8, the rectifying MOSFET 9, and the current blocking MOSFET 14 is turned on. Current flows to

  The booster circuit 3 includes a control circuit 20 (control means) and a control circuit power supply 21 that supplies power to the control circuit 20. The control circuit power supply 21 controls whether or not to supply power to the control circuit 20 based on a power supply instruction (such as a LIN signal or a CAN signal) given from the host ECU 18. The control circuit 20 is realized by software or hardware. When realized by software, the control circuit 20 includes a CPU and a memory, and is realized by the CPU reading and executing a control program stored in the memory.

FIG. 2 is a flowchart showing the operation of the control circuit 20.
First, when the ignition key or the like is pressed by the user or when the engine is started from the idle stop state, the control circuit 20 drives the starter motor for starting the engine, so that the voltage ( For example, when 12V) is temporarily reduced (boosting mode), the boosting MOSFET 7 and the rectifying MOSFET 9 are alternately turned on and off, and the npn bipolar transistor 17 is always turned on so that the current blocking MOSFET 14 is always turned on. By turning on, the voltage of the battery 2 (voltage applied to the capacitor 4) is boosted, and the voltage applied to the load 6 (voltage applied to the capacitor 5) is kept constant (S1). Note that the control circuit 20 alternately turns on and off the boosting MOSFET 7 and the rectifying MOSFET 9 so that the boosting MOSFET 7 and the rectifying MOSFET 9 do not turn on at the same time.

  Next, after the voltage of the battery 2 that has been temporarily reduced returns to the original voltage (bypass mode), the control circuit 20 always turns off the boosting MOSFET 7 and also turns on the rectifying MOSFET 9 and the current cutoff MOSFET 14. Always on (S2). At this time, current flows from the battery 2 to the load 6 via the coil 8, the rectifying MOSFET 9, and the current cutoff MOSFET 14, and power is supplied to the load 6.

Next, the control circuit 20 checks whether or not the drive circuit 11 is determined to have failed by the detection circuit 13 (S3).
If it is determined by the detection circuit 13 that the drive circuit 11 has failed (S3 is Yes), the control circuit 20 notifies the host ECU 18 that the drive circuit 11 has failed (S4). When notified that the drive circuit 11 has failed, the host ECU 18 causes the display unit 19 to display a message indicating that fact.

  Next, the control circuit 20 turns off the npn bipolar transistor 17 and stops the current flowing through the resistors 15 and 16, thereby turning off the current interrupting MOSFET 14 to load from the battery 2 via the coil 8 and the rectifying MOSFET 9. The current flowing to 6 is cut off. As a result, no current flows through the rectifying MOSFET 9.

  As described above, in the power supply circuit 1 shown in FIG. 1, when the detection circuit 13 determines that the drive circuit 11 is out of order, no current flows through the rectification MOSFET 9, so that the drive circuit 11 is out of order and Even when the MOSFET 9 cannot be turned on, it is possible to prevent the rectifying MOSFET 9 from being adversely affected.

  Further, in the power supply circuit 1 shown in FIG. 1, since a P-channel MOSFET is used as the current cutoff MOSFET 14, the voltage generated at the connection point of the resistors 15 and 16 using the current flowing from the battery 2 to the load 6 Thus, the current interrupting MOSFET 14 can be driven. Therefore, it is not necessary to prepare a new power source for driving the current interrupting MOSFET 14, and an increase in cost and circuit scale can be suppressed.

  In addition, since the power supply circuit 1 shown in FIG. 1 employs a MOSFET as a rectifying element, it is possible to suppress a decrease in efficiency and an increase in element temperature as compared with the case where a diode is employed as a rectifying element. And miniaturization can be achieved.

FIG. 3 is a diagram showing a power supply circuit according to another embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same structure as the structure shown in FIG.
The power supply circuit 22 shown in FIG. 3 is different from the power supply circuit 1 shown in FIG. 1 in that even when power is not supplied from the control circuit power supply 21 to the control circuit 20, the current interrupting MOSFET 14 is turned on to The point is that power is supplied to the load 6.

  That is, in the power supply circuit 22 shown in FIG. 3, the npn bipolar transistor 17 is configured such that the voltage of the battery 2 is temporarily reduced when the voltage of the battery 2 is temporarily lowered (step-up mode) or the voltage of the battery 2 that has been temporarily lowered is the original voltage. After returning to (bypass mode), the battery 2 is always turned on by the current flowing from the battery 2 through the resistors 23 and 24. At this time, current flows through the resistors 15 and 16, and the current interrupting MOSFET 14 is turned on by the voltage generated at the connection point of the resistors 15 and 16, and from the battery 2 through the coil 8, the rectifying MOSFET 9, and the current interrupting MOSFET 14. A current flows to the load 6.

The sum of the resistance values of the resistors 23 and 24 is set to a large value of, for example, 100 kΩ or more so that the current flowing from the battery 2 to the npn bipolar transistor 17 becomes small.
The power supply circuit 22 includes an npn bipolar transistor 26 whose collector is connected to the connection point of the resistors 23 and 24, whose emitter is connected to the ground, and which is turned on / off by a current flowing from the control circuit 20 through the resistor 25. I have. The resistance values of the resistor 27 provided at the base-emitter of the npn bipolar transistor 17 and the resistor 28 provided between the base-emitter of the npn bipolar transistor 26 are also large, for example, 100 kΩ or more so that the current flowing through them becomes small. Set to value.

  Then, when the control circuit 20 in the power supply circuit 22 shown in FIG. 3 determines that the drive circuit 11 has failed by the detection circuit 13, the control circuit 20 notifies the host ECU 18 and turns on the npn bipolar transistor 26. Then, the current flowing from the battery 2 to the npn bipolar transistor 17 flows to the ground, the npn bipolar transistor 17 is turned off, and no current flows through the resistors 15 and 16. Thereby, the current interrupting MOSFET 14 is turned off, and the current flowing from the battery 2 to the load 6 through the coil 8 and the rectifying MOSFET 9 is interrupted.

  Thus, as in the power supply circuit 1 shown in FIG. 1, when the detection circuit 13 determines that the drive circuit 11 has failed, no current flows through the rectifying MOSFET 9, so that the drive circuit 11 fails and rectifies. Even if the MOSFET 9 cannot be turned on, the rectifying MOSFET 9 can be prevented from being adversely affected.

  In the power supply circuit 22 shown in FIG. 3, the npn bipolar transistor 17 is always turned on by the current from the battery 2 even when power is not supplied from the control circuit power supply 21 to the control circuit 20. Therefore, even when no power is supplied to the control circuit 20, the current interrupting MOSFET 14 is always turned on, so that power can be supplied from the battery 2 to the load 6. Thereby, for example, even when power is not supplied to the control circuit 20, information can be continuously held in the memory provided in the load 6.

  The power supply circuit 1 shown in FIG. 1 and the power supply circuit 22 shown in FIG. 3 are configured to include the control circuit 20 in the booster circuit 3, but may be configured to include the control circuit 20 outside the booster circuit 3. Good.

  Further, the detection circuit 13 in the power supply circuit 1 shown in FIG. 1 or the power supply circuit 22 shown in FIG. 3 drives the rectifying MOSFET 9 after the voltage of the battery 2 that has temporarily decreased returns to the original voltage. When the drive signal 11 is no longer output from the drive circuit 11, it may be determined that the drive circuit 11 has failed. In the case of such a configuration, the thermistor 12 may be omitted.

  Further, in the power supply circuit 1 shown in FIG. 1 or the power supply circuit 22 shown in FIG. 3, a plurality of booster circuits 3 may be connected in parallel to each other. In the case of such a configuration, a current blocking MOSFET 14, an npn bipolar transistor 17, and the like are provided for each booster circuit 3.

  Further, in the power supply circuit 1 shown in FIG. 1 and the power supply circuit 22 shown in FIG. 3, the current blocking MOSFET 14, the npn bipolar transistor 17, and the like are provided at the output stage of the power supply circuit 1 and the power supply circuit 22. It may be provided at the input stage of the power supply circuit 1 or the power supply circuit 22. In the case of such a configuration, it is desirable to apply to a power supply circuit with little voltage fluctuation of the battery 2 in order to prevent malfunction of the current interrupting MOSFET 14.

  Further, in the power supply circuit 1 shown in FIG. 1 and the power supply circuit 22 shown in FIG. 3, a P-channel MOSFET is employed as the current cutoff MOSFET 14, but an N-channel MOSFET or a pnp bipolar transistor may be employed. .

DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 Battery 3 Boosting circuit 4, 5 Capacitor 6 Load 7 Boosting MOSFET
8 Coil 9 Rectification MOSFET
DESCRIPTION OF SYMBOLS 10, 11 Drive circuit 12 Thermistor 13 Detection circuit 14 Current interruption MOSFET
15, 16 Resistor 17 npn bipolar transistor 18 Upper ECU
19 Display Unit 20 Control Circuit 21 Control Circuit Power Supply 22 Power Supply Circuits 23 to 25 Resistance 26 npn Bipolar Transistors 27 and 28 Resistance

Claims (3)

Battery,
A booster circuit comprising: a switch; a coil provided between the battery and the switch; and a rectifying MOSFET provided between the coil and a load;
A current cutoff switch provided in a path of current flowing from the battery to the load via the coil and the rectifying MOSFET;
An abnormality detection means for determining whether or not a drive circuit for driving the rectifying MOSFET has failed;
When the voltage of the battery is temporarily reduced, the output voltage to the load is kept constant by alternately turning on and off the switch and the rectifying MOSFET and always turning on the current cutoff switch. When the voltage of the battery, which has been temporarily reduced, returns to the original voltage, the switch is always turned off, and the rectifying MOSFET and the current cut-off switch are always turned on. After power is supplied to the load and the voltage of the battery returns to the original voltage, when the abnormality detection means determines that the drive circuit has failed, the operation of the current cutoff switch is controlled to Control means for cutting off current flowing from the battery to the load via the coil and the rectifying MOSFET;
A power supply circuit comprising: The power supply circuit according to claim 1,
A plurality of resistors connected in series to each other and connected to a path of a current flowing from the battery to the load via the coil and the rectifying MOSFET;
A current flowing through the plurality of resistors and a voltage generated at a connection point of the plurality of resistors turn on the current cutoff switch, which is a P-channel MOSFET, and the load from the battery through the coil and the rectifying MOSFET A transistor for passing current to
With
When the abnormality detecting means determines that the drive circuit has failed, the control means turns off the current cutoff switch by turning off the transistor and stopping the current flowing through the plurality of resistors. A power circuit that cuts off a current flowing from the battery to the load via the coil and the rectifying MOSFET. The power supply circuit according to claim 1,
A plurality of resistors connected in series to each other and connected to a path of a current flowing from the battery to the load via the coil and the rectifying MOSFET;
When the current is turned on by the current flowing from the battery, the current cutoff switch, which is a P-channel MOSFET, is turned on by the voltage generated at the connection point of the plurality of resistors by flowing the current through the plurality of resistors. A first transistor for passing a current to the load via the coil and the rectifying MOSFET;
When the device is turned on, the current interrupted by flowing current from the battery to the first transistor to ground and turning off the first transistor so that no current flows through the plurality of resistors. A second transistor that shuts off a current flowing from the battery to the load via the coil and the rectifying MOSFET by turning off the switch;
With
The power supply circuit, wherein the control means turns on the second transistor when it is determined by the abnormality detection means that the drive circuit has failed.

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