JP5510048B2 - Power circuit - Google Patents

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, a power supply circuit including a booster circuit generates a ripple current due to switching of a switching element in the booster circuit, and it is necessary to configure the booster circuit using an element with a large rated power in consideration of the ripple current. There is a problem that the circuit scale and cost increase.

  Thus, as a power supply circuit, for example, it is conceivable to connect a plurality of booster circuits in parallel to each other and shift the phases of the drive signals of the respective switching elements in the booster circuits. As a result, the ripple currents generated in the respective booster circuits are canceled each other, and the ripple current of the entire power supply circuit can be reduced.

JP 2005-237149 A

  However, as described above, in a power supply circuit in which a plurality of booster circuits are connected in parallel to each other, the switching element is always turned off at normal times after the voltage of the battery, which has been temporarily reduced, returns to the original voltage. The current that flows in the booster circuit is the current that corresponds to the impedance in each booster circuit, but the difference in the current that flows in each booster circuit is due to variations in the elements in each booster circuit and imbalances in the wiring in each booster circuit. May occur. Therefore, it is necessary to configure each booster circuit using an element with a large rated current in consideration of the difference in current, and there is a problem that the circuit scale and cost increase.

  Therefore, an object of the present invention is to provide a power supply circuit capable of suppressing an increase in circuit scale and cost.

  The power supply circuit of the present invention includes a battery, a plurality of booster circuits that are connected in parallel to each other and boost the voltage of the battery, and a control circuit that controls the operation of each of the plurality of booster circuits. The circuit includes a current detecting means for detecting a current flowing through the booster circuit, a switching element, an inductor provided between the battery and the switching element, and a rectifier provided between the inductor and a load. And the control circuit keeps the output voltage to the load constant by turning on and off each switching element of the plurality of booster circuits when the voltage of the battery is temporarily reduced. Control is performed so that the voltage of the battery, which has been temporarily reduced, returns to the original voltage, and then detected by each current detection means of the plurality of booster circuits When current is unbalanced, it turns on the switching element of the step-up circuit a small current flows, by turning off, to increase the current flowing through the boost circuit.

  As a result, a balance can be maintained so that the currents flowing through the plurality of booster circuits are substantially the same, and therefore it is necessary to use an element with a large rated current in consideration of the difference between the currents flowing through the plurality of booster circuits. Therefore, an increase in circuit scale and cost can be suppressed.

  The control circuit may be configured such that when the voltage of the battery, which has been temporarily reduced, returns to the original voltage, the difference between the currents detected by the current detection units of the plurality of booster circuits is equal to or greater than a predetermined value. The current detected by each of the current detection means may be determined to be unbalanced.

  In addition, when the difference between the currents detected by the current detection units of the plurality of booster circuits is not zero after the voltage of the battery that has been temporarily reduced returns to the original voltage, You may comprise so that it may judge that the electric current detected by each electric current detection means is unbalanced.

  The present invention can suppress an increase in circuit scale and cost in a power supply circuit that outputs a load while keeping the battery voltage constant.

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 the load 7 via the capacitor 6, and shares the electric power obtained from the battery 5 by ½ each time. To supply. 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 7 while keeping the voltage of a battery 5 that supplies power to a starter motor for starting an engine of 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 circuits 2 and 3 are provided between 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 a load 7, respectively. A rectifying MOSFET 10, a drive circuit 11 for driving the MOSFET 8, a drive circuit 12 for driving the MOSFET 10, a thermistor 13 (temperature detecting means) provided in the vicinity of the MOSFET 10, and a temperature obtained based on a voltage applied to the thermistor 13. Is a predetermined temperature or higher, a detection circuit 14 for detecting that the drive circuit 12 has failed, a fuse 15 provided between the battery 5 and the inductor 9, and a fuse 15 and an inductor And a shunt resistor 16 (current detection means) provided between the Kuta 9 and the Kuta 9. The MOSFET 10 may be replaced with a diode as a rectifying element. In this case, the drive circuit 12, the thermistor 13, and the detection circuit 14 can be omitted. Since the power supply circuit 1 according to the present embodiment employs the MOSFET 10 as the rectifying element, the voltage drop in the rectifying element can be reduced and the loss can be suppressed as compared with the case where the diode is employed.

  Further, the power supply circuit 1 includes a control circuit 17. The control circuit 17 is realized by software or hardware. When realized by software, the control circuit 17 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 17.
First, for example, the control circuit 17 starts the engine by pressing an ignition key or the like by the user, or restarts the engine from the idle stop state, and drives the starter motor for starting the engine. Of the battery 5 (for example, 12V) is temporarily reduced 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 17 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 17 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 17 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 load 7 via the fuse 15, the shunt resistor 16, the inductor 9, and the MOSFET 10, and power is supplied to the load 7.

  Next, the control circuit 17 detects the current I1 flowing through the booster circuit 2 based on the voltage applied to the shunt resistor 16 of the booster circuit 2, and the booster circuit based on the voltage applied to the shunt resistor 16 of the booster circuit 3. 3 is detected (S3).

  Next, the control circuit 17 obtains a difference between the current I1 and the current I2 (S4), and determines whether or not the difference is a predetermined value or more (S5). Note that the predetermined value is set in advance based on the rated current of the elements constituting the booster circuits 2 and 3.

  When it is determined that the difference is equal to or greater than the predetermined value (that is, when the currents I1 and I2 are determined to be unbalanced) (S5 is Yes), the control circuit 17 determines the duty of the drive signal of the MOSFET 8 according to the difference. (For example, 10% or less) is determined, and on the basis of the duty driving signal, the MOSFET 8 of the booster circuit through which a small current flows is turned on and off, so that the output voltage of the booster circuit is slightly lower than the voltage of the battery 5 After increasing the current flowing through the booster circuit (S6), the process returns to S3 to detect the currents I1 and I2 again. For example, the control circuit 17 increases the duty as the difference increases, and decreases the duty as the difference decreases.

  On the other hand, when it is determined that the difference is not equal to or greater than the predetermined value (that is, when it is determined that the currents I1 and I2 are not unbalanced) (S5 is No), the control circuit 17 is one of the booster circuits 2 and 3. It is determined whether or not the booster circuit is boosted (S7).

  When it is determined that one of the booster circuits is being boosted (S7 is Yes), the control circuit 17 always turns off the MOSFET 8 and keeps the MOSFET 10 on in order to stop the booster circuit during the boosting operation. (S8), the process returns to S3, and the currents I1 and I2 are detected again.

On the other hand, if it is determined that neither booster circuit is boosted (S7 is No), the control circuit 17 returns to S3 and detects the currents I1 and I2 again.
In S5, the control circuit 17 determines whether or not the difference between the currents I1 and I2 is zero, and determines that the difference is zero (that is, determines that the currents I1 and I2 are unbalanced). If it is determined that the difference is not zero (that is, if it is determined that the currents I1 and I2 are not unbalanced), the process may proceed to S7.

  As described above, in the power supply circuit 1 of the present embodiment, when the currents I1 and I2 are unbalanced during normal operation, the booster MOSFET 8 of the booster circuit in which a small current flows is boosted by a drive signal with a small duty, thereby boosting the voltage. The balance is maintained by increasing the current flowing through the circuit so that the currents I1 and I2 are substantially the same. This eliminates the need to use an element with a large rated current in consideration of the difference between the currents I1 and I2, thereby suppressing an increase in circuit scale and cost.

  In the above-described embodiment, the control circuit 17 increases the temperature of the fuse 15 when the detection circuit 14 detects that the temperature obtained based on the voltage applied to the thermistor 13 exceeds a predetermined temperature and the drive circuit 12 has failed. The MOSFET 8 is always turned on so that a current flows and the fuse 15 is cut. As a result, even if the MOSFET 8 is turned on / off in a state where the drive circuit 12 fails and the MOSFET 10 cannot be turned on / off, it is possible to prevent an overcurrent from flowing through the MOSFET 10. Damage to the MOSFET 10 due to the rise can be prevented.

  In the above embodiment, two booster circuits are connected in parallel to each other, but three or more booster circuits may be connected in parallel to each other. Even in such a configuration, the control circuit 17 determines whether each current is unbalanced based on the current of each booster circuit obtained from the voltage of the shunt resistor 16.

  In the above embodiment, the control circuit 17 is provided in the booster circuit 2. However, the control circuit 17 may be provided in the booster circuit 3 or outside the booster circuits 2 and 3.

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

Claims (3)

Battery,
A plurality of booster circuits connected in parallel with each other to boost the voltage of the battery;
A control circuit for controlling the operation of each of the plurality of booster circuits;
With
Each of the plurality of booster circuits is
Current detecting means for detecting a current flowing in the booster circuit;
A switching element;
An inductor provided between the battery and the switching element;
A rectifying element provided between the inductor and a load;
With
The control circuit controls the output voltage to the load to be constant by turning on and off each switching element of the plurality of booster circuits when the battery voltage is temporarily reduced. In a normal state after the voltage of the battery, which has been temporarily reduced, returns to the original voltage, each switching element of the plurality of booster circuits is always turned off, and each current of the plurality of booster circuits is A power supply circuit characterized in that when the current detected by the detection means is unbalanced, the current flowing through the booster circuit is increased by turning on and off the switching element of the booster circuit through which a small current flows. The power supply circuit according to claim 1,
The control circuit always turns off each switching element of the plurality of booster circuits at a normal time after the voltage of the battery that has been temporarily reduced returns to the original voltage, and at this time, the plurality of boosters A power supply circuit characterized by determining that the current detected by each current detection means is unbalanced when the difference between the currents detected by each current detection means of the circuit is a predetermined value or more. The power supply circuit according to claim 1,
The control circuit always turns off each switching element of the plurality of booster circuits at a normal time after the voltage of the battery that has been temporarily reduced returns to the original voltage, and at this time, the plurality of boosters A power supply circuit, characterized in that when the difference between currents detected by each current detection means of the circuit is not zero, the current detected by each current detection means is determined to be unbalanced.

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