JP2011239631A - Power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power circuit capable of suppressing loss and increases in circuit scale and cost.SOLUTION: When a voltage of a battery 21 is temporarily low, MOSFETs 23, 33 are alternately turned on to keep an output voltage to a load 25 constant. After the temporarily lowered voltage of the battery 21 is restored to an original voltage, the MOSFET 23 is turned off and the MOSFET 33 is turned on. Moreover, regularly the MOSFET 23 is turned on and the MOSFET 33 is turned off to run a current through a current path from an internal power supply 30 to a boost trap capacitor 2 for charging the boost trap capacitor 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.

FIG. 2 is a diagram showing an existing power supply circuit.
The power supply circuit 20 illustrated in FIG. 2 includes a battery 21 and a booster circuit 22.
The booster circuit 22 includes a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 23, an inductor 24 provided between the battery 21 and the MOSFET 23, a rectifying diode 26 provided between the inductor 24 and the load 25, and the MOSFET 23. A control circuit 27 for outputting a control signal S1 for controlling on / off of the power supply, an internal power supply 28 for supplying power to the control circuit 27, and a drive circuit 29 (first drive circuit) for driving the MOSFET 23 based on the control signal S1. And an internal power supply 30 for supplying power for driving the MOSFET 23 to the drive circuit 29, a capacitor 31 provided in the input stage, and a capacitor 32 provided in the output stage. The internal power supply 30 supplies power to the internal power supply 28 based on the power obtained from the output stage of the booster circuit 22, and the internal power supply 28 supplies power to the control circuit 27 based on the power obtained from the internal power supply 30. Supply.

  Thus, as an existing power supply circuit, for example, the booster circuit 22 is provided, and the voltage of the battery 21 is boosted by turning on and off the MOSFET 23 in the booster circuit 22 to control the output voltage to the load 25. There is something like that (see, for example, Patent Document 1). When the voltage of the battery 21 is about 12V, the output power of the booster circuit 22 can be used as it is as power for driving the MOSFET 23.

However, since the power supply circuit 20 shown in FIG. 2 uses the diode 26 as a rectifying element, the voltage drop in the diode 26 is large and the loss is large.
Therefore, as shown in FIG. 3, instead of the diode 26, the MOSFET 33 is provided, and when the battery 21 is temporarily lowered, the MOSFET 23 and the MOSFET 33 are alternately turned on and the battery 21 that has been temporarily lowered is provided. It is conceivable that the MOSFET 23 is always turned off and the MOSFET 33 is always turned on at a normal time after the first voltage returns to the original voltage. Thereby, the voltage drop in a rectifier can be made small and a loss can be reduced. The control circuit 27 outputs a control signal S2 for controlling on / off of the MOSFET 33, and the drive circuit 34 drives the MOSFET 33 based on the control signal S2.

JP 2005-237149 A

  However, in the power supply circuit 20 shown in FIG. 3, when the power of the output stage of the booster circuit 22 is used to generate not only the control circuit 27 and the MOSFET 23 but also power for driving the MOSFET 33, the MOSFET 33 is The reference potential of the internal power source 35 that supplies power for driving to the drive circuit 34 needs to be the same as the potential at the connection point between the MOSFET 23 and the MOSFET 33, and the internal power source 35 is configured by using a transformer. There is a problem that 35 has a complicated configuration and the circuit scale and cost increase.

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

  The power supply circuit according to the present invention includes a battery, a booster circuit that boosts the voltage of the battery, and a control unit that controls the operation of the booster circuit, and the booster circuit drives the main MOSFET and the main MOSFET. A first drive circuit; an internal power supply for supplying power for driving the main MOSFET to the first drive circuit based on power obtained from an output stage of the booster circuit; and the battery and the main MOSFET. An inductor provided therebetween, a rectifying MOSFET provided between the inductor and a load, a second drive circuit for driving the rectifying MOSFET, a connection point between the main MOSFET and the rectifying MOSFET, A bootstrap capacitor provided between the second drive circuit and the internal power supply; A diode provided in a current path to the bootstrap capacitor, and the control means alternately turns on the main MOSFET and the rectifying MOSFET when the voltage of the battery is temporarily reduced. The output voltage to the load is controlled to be constant, and after the battery voltage that has been temporarily reduced returns to the original voltage, the main MOSFET is turned off and the rectifying MOSFET is turned on. By periodically turning on the main MOSFET and turning off the rectifying MOSFET, a current is passed through the current path to charge the bootstrap capacitor.

  As a result, the power for driving the rectifying MOSFET can be charged to the bootstrap capacitor having the potential at the connection point between the main MOSFET and the rectifying MOSFET as a reference potential in the normal state. Electric power for driving the rectifying MOSFET can be generated without using a transformer or the like by using the obtained electric power, and an increase in circuit scale and cost can be suppressed. Further, since the rectifying MOSFET is used instead of the rectifying diode, loss can be reduced.

  In addition, the control means may be configured to switch the main MOSFET and the rectifying MOSFET when the battery voltage temporarily decreases after the battery voltage that has been temporarily decreased returns to the original voltage. Control signal duty that is lower than the frequency of the control signal that is alternately turned on, and that alternately turns on the main MOSFET and the rectifying MOSFET when the battery voltage is temporarily reduced The main MOSFET and the rectifying MOSFET may be alternately turned on by a control signal having a smaller duty.

  The control means turns off the main MOSFET and turns on the rectifying MOSFET after the voltage of the battery, which has been temporarily reduced, returns to the original voltage, and the voltage of the bootstrap capacitor is predetermined. When the voltage is lower than the voltage, the main MOSFET and the rectifying MOSFET may be alternately turned on.

  The present invention can reduce loss and 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 figure which shows the existing power supply circuit. It is a figure which shows the other existing power supply circuit.

FIG. 1 is a diagram showing a power supply circuit according to an embodiment of the present invention. The same components as those shown in FIGS. 2 and 3 are denoted by the same reference numerals.
A feature of the power supply circuit 1 shown in FIG. 1 is that an MOSFET 23 (main MOSFET) and a MOSFET 33 are used as internal power supplies for supplying power for driving the MOSFET 33 (rectifying MOSFET) to the drive circuit 34 (second drive circuit). The bootstrap capacitor 2 having the potential at the connection point with the reference potential as a reference potential is provided, and the resistor 3 and the diode 4 are provided in the current path from the internal power supply 30 to the bootstrap capacitor 2. That is, the bootstrap capacitor 2 is provided between the connection point of the MOSFETs 23 and 33 and the drive circuit 34. The anode of the diode 4 is connected to the internal power supply 30 via the resistor 3, and the cathode of the diode 4 is connected to a connection point between the drive circuit 34 and the bootstrap capacitor 2. The power supply circuit 1 may be configured by omitting the resistor 3.

  Further, another characteristic feature of the power supply circuit 1 shown in FIG. 1 is that in the control circuit 5 (control means), when the battery 21 is temporarily lowered, the load is obtained by alternately turning on the MOSFETs 23 and 33. In the normal time after the voltage of the battery 21 that has been temporarily reduced returns to the original voltage, the MOSFET 23 is turned off, the MOSFET 33 is turned on, and the MOSFET 23 is turned on periodically. The point that the MOSFET 33 is turned off is that the current is passed through the current path from the internal power supply 30 to the bootstrap capacitor 2 to charge the bootstrap capacitor 2. The control circuit 5 is realized by software or hardware. When realized by software, the control circuit 5 includes a CPU and a memory, and is realized by the CPU reading and executing a control program stored in the memory.

  For example, the control circuit 5 normally controls the control signal S1 having a frequency (several kHz or less) lower than the frequency (several tens to several hundreds kHz) of the control signals S1 and S2 when the battery 21 is temporarily lowered. , S2, and MOSFETs 23, 33 are alternately turned on by control signals S1, S2 having a duty smaller than that of control signals S1, S2 when battery 21 is temporarily lowered. When the MOSFET 23 is turned on and the MOSFET 33 is turned off, a current flows through the path of the internal power supply 30, the resistor 3, the diode 4, the bootstrap capacitor 2, and the MOSFET 23, and the bootstrap capacitor 2 is charged. At this time, the bootstrap capacitor 2 needs to be charged with electric power necessary to turn on the MOSFET 33 next time. Therefore, the capacitance value of the bootstrap capacitor 2, the resistance value of the resistor 3, the frequencies of the control signals S1 and S2 at the normal time, and the duties of the control signals S1 and S2 at the normal time are the outputs of the booster circuit 22 at the normal time. While the voltage is not as high as possible with respect to the input voltage, the power required to turn on the MOSFET 33 next is charged to the bootstrap capacitor 2 in one on period of the MOSFET 23 at normal time. It is assumed that it is set.

  As described above, the power supply circuit 1 according to the present embodiment is provided with the bootstrap capacitor 2 that uses the potential at the connection point of the MOSFETs 23 and 33 as the reference potential as an internal power supply that supplies power for driving the MOSFET 33 to the drive circuit 34. In normal times, the MOSFETs 23 are periodically turned on and the MOSFETs 33 are turned off by the control signals S1 and S2. As a result, power for driving the MOSFET 33 can be charged to the bootstrap capacitor 2 having the potential at the connection point between the MOSFET 23 and the MOSFET 33 as a reference potential at normal times, and thus the power obtained from the output stage of the booster circuit 22 Can be used to generate power for driving the MOSFET 33 without using a transformer or the like, and an increase in circuit scale and cost can be suppressed. Further, since the MOSFET 33 is used instead of the rectifying diode, the loss can be reduced.

  The control circuit 5 keeps the voltage output to the load 25 constant by alternately turning on the MOSFETs 23 and 33 when the battery 21 is temporarily lowered, and normally turns off the MOSFET 23 and turns off the MOSFET 33. Further, the MOSFETs 23 and 33 may be alternately turned on when the voltage of the bootstrap capacitor 2 becomes equal to or lower than a predetermined voltage. In such a configuration, the control circuit 5 always detects the voltage of the bootstrap capacitor 2 at normal times. The predetermined voltage, the capacitance value of the bootstrap capacitor 2, the resistance value of the resistor 3, the frequencies of the normal control signals S1 and S2, and the duties of the normal control signals S1 and S2 are boosted during normal operation. The bootstrap capacitor 2 is charged with the power required to turn on the MOSFET 33 in the normal on-time period of the MOSFET 23 while keeping the output voltage of the circuit 22 as high as possible with respect to the input voltage. It shall be set to such a value.

  In the above embodiment, the control circuit 5 is provided in the booster circuit 22, but the control circuit 5 may be provided outside the booster circuit 22.

DESCRIPTION OF SYMBOLS 1,20 Power supply circuit 2 Bootstrap capacitor | condenser 3 Resistance 4,26 Diode 5,27 Control circuit 21 Battery 22 Booster circuit 23, 33 MOSFET
24 Inductor 25 Load 28, 30, 35 Internal power supply 29, 34 Drive circuit 31, 32 Capacitor

Claims (3)

Battery,
A booster circuit for boosting the voltage of the battery;
Control means for controlling the operation of the booster circuit;
With
The booster circuit includes:
A main MOSFET,
A first drive circuit for driving the main MOSFET;
An internal power supply for supplying power for driving the main MOSFET to the first drive circuit based on power obtained from the output stage of the booster circuit;
An inductor provided between the battery and the main MOSFET;
A rectifying MOSFET provided between the inductor and a load;
A second drive circuit for driving the rectifying MOSFET;
A bootstrap capacitor provided between a connection point between the main MOSFET and the rectifying MOSFET and the second drive circuit;
A diode provided in a current path from the internal power supply to the bootstrap capacitor;
With
The control means includes
When the voltage of the battery is temporarily reduced, the main MOSFET and the rectifying MOSFET are alternately turned on to control the output voltage to the load to be kept constant,
After the voltage of the battery, which has been temporarily reduced, returns to the original voltage, the main MOSFET is turned off, the rectifying MOSFET is turned on, the main MOSFET is turned on periodically, and the rectifying MOSFET is turned off. To cause the current to flow in the current path to charge the bootstrap capacitor. The power supply circuit according to claim 1,
The control means alternates between the main MOSFET and the rectifying MOSFET when the voltage of the battery temporarily decreases after the voltage of the battery that has been temporarily decreased returns to the original voltage. A control signal having a frequency lower than the frequency of the control signal to be turned on, and the duty of the control signal for alternately turning on the main MOSFET and the rectifying MOSFET when the battery voltage is temporarily reduced A power supply circuit, wherein the main MOSFET and the rectifying MOSFET are alternately turned on by a control signal having a small duty. The power supply circuit according to claim 1,
The control means turns off the main MOSFET and turns on the rectifying MOSFET after the voltage of the battery that has been temporarily reduced returns to the original voltage, and the voltage of the bootstrap capacitor is equal to or lower than a predetermined voltage. Then, the main MOSFET and the rectifying MOSFET are alternately turned on.

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