JP2011244534A - Power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power circuit capable of suppressing having an adverse effect upon a MOSFET for rectification in a booster circuit even when it is impossible to turn on the MOSFET due to failure in a drive circuit.SOLUTION: When a voltage of a battery 5 is temporarily low, MOSFETs 8, 10 of a booster circuit 2 are alternately turned on and off and MOSFETs 8, 10 of a booster circuit 3 are alternately turned on and off. When a current running through each of the booster circuits 2, 3 is unbalanced after the voltage of the battery 5 has restored to an original voltage, it is determined that a drive circuit 12 of the booster circuit 2 or the booster circuit 3 has some failure and power supply to a predetermined load of a plurality of loads 7-1, 7-2 connected with the booster circuits 2, 3 is stopped.

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 when the drive circuit that drives the rectifying MOSFET fails and the rectifying MOSFET cannot be turned on, current flows through the body diode (parasitic diode) of the rectifying MOSFET. The power supply to the load can be continued.

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. As a result, the temperature of the rectifying 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.

  The present invention provides a power supply circuit capable of suppressing adverse effects on a 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.

  A power supply circuit according to the present invention includes a battery, first and second booster circuits that are connected in parallel to each other and boost the voltage of the battery, and control means that controls the operations of the first and second booster circuits. The first and second booster circuits each include a switching element, an inductor provided between the battery and the switching element, a rectifying MOSFET provided between the inductor and a plurality of loads, A drive circuit for driving the rectifying MOSFET, and the control means alternately turns on and off the switching element and the rectifying MOSFET of the first booster circuit when the voltage of the battery is temporarily reduced. And alternately turning on and off the switching element and the rectifying MOSFET of the second booster circuit to When the output voltage to the battery is controlled to be constant and the voltage of the battery, which has been temporarily reduced, returns to the original voltage, the currents flowing in the first and second booster circuits become unbalanced, respectively. When the drive signal for driving the rectifying MOSFET is not output from the drive circuit of the first or second booster circuit, or when the temperature of the rectifying MOSFET exceeds a predetermined temperature, the first or second It is determined that the drive circuit of the two booster circuit has failed, and power supply to a predetermined load among the plurality of loads is stopped.

  As a result, the currents flowing through the first and second booster circuits can be reduced, so that the temperature rise of the rectifying MOSFET of the booster circuit in which the drive circuit has failed can be suppressed. Therefore, even if the drive circuit fails and the rectifying MOSFET cannot be turned on, it is possible to suppress the adverse effect on the rectifying MOSFET.

  The control means determines that the drive circuit of the first or second booster circuit has failed, and then maintains the temperature of each rectifying MOSFET of the first and second booster circuits at a predetermined temperature. In addition, the booster circuit in which the drive circuit has failed may be configured to intermittently perform a boost operation.

  As a result, even if the drive circuit fails and the rectifying MOSFET cannot be turned on, power is transferred from the battery to the load while the rectifying MOSFET is not adversely affected until the power supply circuit is replaced. Can be continuously supplied.

  In the power supply circuit that outputs the battery voltage to the load while keeping the battery voltage constant, the rectifying MOSFET can be turned on even when the drive circuit fails and the rectifying MOSFET in the booster circuit cannot be turned on. An adverse effect on the MOSFET 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.

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 boosting circuits 2 and 3 connected in parallel to each other. Each of the booster circuits 2 and 3 is connected to the battery 5 via the capacitor 4 and is connected to a plurality of loads 7-1 and 7-2 via the capacitor 6 so that the electric power obtained from the battery 5 is 1 / 2 is divided and supplied to a plurality of loads 7-1 and 7-2. The power supply circuit 1 of the present embodiment, for example, keeps the voltage of the battery 5 that supplies power to the starter motor for starting the engine of an idle stop vehicle constant, and performs car navigation and audio as loads 7-1 and 7-2. It is used as an output to an electrical component such as an electrical component that temporarily stops normal operation as the input voltage temporarily decreases. In addition, the load 7-1 is a load that cannot stop power supply while the idle stop vehicle is traveling (for example, a load related to running, turning, or stopping in the idle stop vehicle), and the load 7-2 is: A load (for example, car navigation, audio, etc.) that may stop power supply while the idle stop vehicle is running is set.

  The booster circuits 2 and 3 include a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 8 (switching element), an inductor 9 provided between the battery 5 and the MOSFET 8, and an inductor 9 and loads 7-1 and 7-2, respectively. A rectifying MOSFET 10 (rectifying MOSFET), a drive circuit 11 for driving the MOSFET 8, a drive circuit 12 for driving the MOSFET 10, and a thermistor 13 (temperature detecting means) provided in the vicinity of the MOSFET 10, Provided between the battery 5 and the inductor 9, a detection circuit 14 that detects that the drive circuit 12 has failed when the temperature obtained based on the voltage detected by the thermistor 13 is equal to or higher than a predetermined temperature. Fuse 15 and a shunt resistor 16 (current detection means) provided between the fuse 15 and the inductor 9.

The power supply circuit 1 also includes a relay 17 provided between the booster circuits 2 and 3 and the load 7-2, a host ECU 18 that controls on / off of the relay 17, and a display unit 19.
The booster circuit 2 includes a control circuit 20. 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. Further, the control means in the claims is constituted by, for example, the relay 17, the host ECU 18, and the control circuit 20.

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 starts from the idle stop state, the control circuit 20 drives the starter motor for starting the engine, so that the voltage of the battery 5 (for example, 12V) is temporarily lowered, the voltage of the battery 5 (voltage applied to the capacitor 4) is boosted by turning on and off the MOSFETs 8 of the booster circuits 2 and 3 via the drive circuit 11. The voltage applied to the load 7 (voltage applied to the capacitor 6) is kept constant (S1). At this time, for example, the control circuit 20 turns on and off the MOSFET 8 of the booster circuit 2 and the MOSFET 8 of the booster circuit 3 by shifting the phase by 180 degrees (shifting the timing by 1/2 of the period). Thereby, the ripple currents generated by the switching of the MOSFETs 8 of the booster circuits 2 and 3 cancel each other, and the ripple current of the entire power supply circuit 1 can be reduced. Note that the control circuit 20 turns on and off the MOSFET 10 via the drive circuit 12 so that the MOSFET 8 and the MOSFET 10 do not turn on at the same time.

  Next, the control circuit 20 always turns off the MOSFETs 8 of the booster circuits 2 and 3 at the normal time after the voltage of the battery 5 that has been temporarily reduced returns to the original voltage, 3 are always turned on (S2). Then, current flows from the battery 5 to the loads 7-1 and 7-2 through the fuse 15, the shunt resistor 16, the inductor 9, and the MOSFET 10, and power is supplied to the loads 7-1 and 7-2.

  Next, the control circuit 20 determines whether or not the booster circuit 2 or the drive circuit 12 of the booster circuit 3 has failed (S3). For example, the control circuit 20 determines that the currents flowing through the booster circuits 2 and 3 are unbalanced based on the current obtained based on the voltage applied to the shunt resistor 16, thereby increasing the booster circuit 2 or the booster circuit 3. It can be determined that the drive circuit 12 has failed. Further, for example, the control circuit 20 determines that the booster circuit 2 or the drive circuit 12 of the booster circuit 3 has failed based on the detection result of the detection circuit 14.

  When determining that the drive circuit 12 of the booster circuit 2 or the booster circuit 3 has failed (S3 is Yes), the control circuit 20 notifies the host ECU 18 by communication that the drive circuit 12 has failed (S4). When notified that the drive circuit 12 has failed, the host ECU 18 turns off the relay 17 and stops the power supply to the load 7-2. Further, when notified that the drive circuit 12 has failed, the host ECU 18 may cause the display unit 19 to display a message indicating that the power supply circuit 1 needs to be replaced.

  Next, the control circuit 20 obtains the temperature based on the voltage detected by the thermistor 13 of the booster circuit in which the drive circuit 12 has not failed (S5). When the drive circuit 12 fails and the MOSFET 10 cannot always be turned on, current concentrates on the booster circuit where the drive circuit 12 does not fail, and the temperature of the MOSFET 10 rises.

  Next, the control circuit 20 determines whether or not the temperature obtained based on the voltage detected by the thermistor 13 of the booster circuit in which the drive circuit 12 has not failed exceeds a predetermined temperature (S6).

  When it is determined that the temperature obtained based on the voltage detected by the thermistor 13 of the booster circuit in which the drive circuit 12 has not failed has exceeded a predetermined temperature (Yes in S6), the control circuit 20 causes the drive circuit 12 to fail. The MOSFET 8 of the boosting circuit being turned on is turned on / off by a control signal with a small duty (S7). As a result, a voltage slightly higher than the voltage of the battery 5 is output from the booster circuit in which the drive circuit 12 is faulty, so that the current flowing in the booster circuit in which the drive circuit 12 is faulty increases, The current flowing through the booster circuit that has not failed is reduced. For this reason, the temperature of the MOSFET 10 of the booster circuit in which the drive circuit 12 has not failed decreases, and the temperature of the MOSFET 10 of the booster circuit in which the drive circuit 12 has failed increases.

  Next, the control circuit 20 obtains the temperature based on the voltage detected by the thermistor 13 of the booster circuit in which the drive circuit 12 has failed (S8), and determines whether or not the temperature is equal to or higher than the predetermined temperature. (S9). Each predetermined temperature in S6 and S9 is set to a temperature lower than the temperature of the MOSFET 10 when there is a possibility that the MOSFET 10 is adversely affected, such as the MOSFET 10 being damaged.

  When it is determined that the temperature obtained based on the voltage detected by the thermistor 13 of the booster circuit in which the drive circuit 12 is faulty has become equal to or higher than the predetermined temperature (Yes in S9), the control circuit 20 causes the drive circuit 12 to fail. After the MOSFET 8 of the boosting circuit being operated is always turned off (S10), the process returns to S5. As a result, the current concentrates again on the booster circuit in which the drive circuit 12 has not failed, and the temperature of the MOSFET 10 rises.

  The control circuit 20 starts the boosting operation of the booster circuit in which the drive circuit 12 has failed instead of performing the processes of S8 and S9 (S7), and then the control circuit 20 has failed for a predetermined time (the drive circuit 12 has failed). If it is determined that the time taken until the temperature of the MOSFET 10 reaches the predetermined temperature after the booster circuit starts the booster operation), the booster operation of the booster circuit in which the drive circuit 12 has failed is stopped (S10). The process may return to S5.

  As described above, in the power supply circuit 1 of the present embodiment, when the booster circuit 2 or the drive circuit 12 of the booster circuit 3 fails during normal operation, the host ECU 18 is notified that the drive circuit 12 has failed, and the relay 17 is turned off. Thus, power supply to the load 7-2 without any problem is stopped. As a result, the load is reduced and the currents flowing through the booster circuits 2 and 3 can be reduced, so that the temperature rise of the MOSFET 10 of the booster circuit in which the drive circuit has failed can be suppressed. For this reason, even when the drive circuit fails and the MOSFET 10 of the booster circuit cannot be turned on, it is possible to prevent the MOSFET 10 from being adversely affected.

  Further, in the power supply circuit 1 of the present embodiment, after the drive circuit 12 of the booster circuit 2 or the booster circuit 3 breaks down and the currents flowing through the booster circuits 2 and 3 are reduced, The booster circuit in which the drive circuit 12 is broken is intermittently boosted so that the temperature of the MOSFET 10 is maintained at a predetermined temperature at which the MOSFET 10 is not adversely affected. As a result, even if the drive circuit fails and the MOSFET 10 of the booster circuit cannot be turned on, until the power supply circuit 1 is replaced, the MOSFET 10 does not adversely affect the load 7. -1 can be continuously supplied with electric power.

In the above embodiment, the control circuit 20 is provided in the booster circuit 2. However, the control circuit 20 may be provided in the booster circuit 3 or outside the booster circuits 2 and 3.
In the above-described embodiment, the detection circuit 14 is configured to detect that the drive circuit 12 is out of order when a drive signal that always turns on the MOSFET 10 is not output from the drive circuit 12 during normal operation. Also good. In the case of such a configuration, the control circuit 20 can determine that the booster circuit 2 or the drive circuit 12 of the booster circuit 3 has failed based on the detection result of the detection circuit 14. In the case of such a configuration, the thermistor 13 can be omitted.

  Further, in the above embodiment, the control circuit 20 notifies the host ECU 18 that the drive circuit 12 has failed (S4), and then the current flowing through the booster circuit in which the drive circuit 12 has not failed causes the drive circuit 12 to fail. If not, it is determined that the current is equal to or greater than 1/2 of the current for two phases flowing through the booster circuits 2 and 3 (the maximum value of the current for one phase flowing through the booster circuit when the drive circuit 12 is not faulty). In this case, the processing after S5 may be performed. In the case of such a configuration, the control circuit 20 causes the current flowing in the booster circuit in which the drive circuit 12 has not failed to be equivalent to the two phases flowing in the booster circuits 2 and 3 when the drive circuit 12 has not failed. When it is determined that the current is smaller than ½ of the current, the power is continuously supplied to the undisconnected load 7-1 by using the booster circuit in which the drive circuit 12 is not broken without performing the processing after S5. May be configured to be supplied.

1 Power supply circuit 2, 3 Booster circuit 4, 6 Capacitor 5 Battery 7-1, 7-2 Load 8, 10 MOSFET
9 Inductors 11 and 12 Drive circuit 13 Thermistor 14 Detection circuit 15 Fuse 16 Shunt resistor 17 Relay 18 Host ECU
19 Display 20 Control circuit

Claims (2)

Battery,
First and second booster circuits connected in parallel to each other and boosting the voltage of the battery;
Control means for controlling the respective operations of the first and second booster circuits;
With
The first and second booster circuits are respectively
A switching element;
An inductor provided between the battery and the switching element;
A rectifying MOSFET provided between the inductor and a plurality of loads;
A drive circuit for driving the rectifying MOSFET;
With
The control means includes
When the voltage of the battery is temporarily reduced, the switching element and the rectifying MOSFET of the first booster circuit are alternately turned on and off, and the switching element and the rectifying MOSFET of the second booster circuit are alternately turned on and off. By turning on and off, control to keep the output voltage to the plurality of loads constant,
After the voltage of the battery, which has been temporarily reduced, returns to the original voltage, when the currents flowing through the first and second booster circuits become unbalanced, the drive circuit of the first or second booster circuit When a drive signal for driving the rectifying MOSFET is not output, or when the temperature of the rectifying MOSFET exceeds a predetermined temperature, it is determined that the drive circuit of the first or second booster circuit has failed. A power supply circuit that stops power supply to a predetermined load among the plurality of loads. The power supply circuit according to claim 1,
After the control means determines that the drive circuit of the first or second booster circuit has failed, the temperature of each rectifying MOSFET of the first and second booster circuits is maintained at a predetermined temperature. A power supply circuit characterized by intermittently boosting a booster circuit in which the drive circuit has failed.

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