JP2003244943A - Booster for power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a booster for a power unit, which is fit for the supply of power to an electric power steering device or the like of a passenger car and lessens power consumption at a one-way current pass circuit which lets a current flow, based on a high voltage generated by boosting action, and reduces heat generation. <P>SOLUTION: This booster is equipped with an FET 12 which is turned on or turned off by a drive signal S, a coil 1 which accumulates energy when the FET is on and releases the energy the instant it is turned off, an FET 13 which is connected downstream of the coil and lets a current supplied from the coil flow, being turned on by a drive signal S' when the FET is off, a capacitor 15 which is connected downstream of the FET, and a drive control means 14 which supplies the drive signal S and the drive signal S'. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a booster device for a power supply device, and more particularly to a booster device for a power supply device that supplies electric power to an electric power steering device of a passenger car.

[0002]

2. Description of the Related Art An electric circuit portion of a booster (hereinafter referred to as a "boost circuit") usually includes a coil as an inductance circuit element and a field effect transistor (FET) as a switch element.
ct Transistor), a diode, and a capacitor as a storage element. The booster is a device that boosts a predetermined voltage applied to an input terminal to generate a high voltage at an output terminal, and is included in, for example, a power supply device of an electric power steering device. FIG. 6 is a circuit configuration diagram of a conventional well-known booster circuit. The booster circuit 101 is disclosed in, for example, Japanese Patent Publication No. 8-539 and Japanese Patent Laid-Open No. 8-127351. In the booster circuit 101, the diode 102
The coil 103 and the FET 104 are connected to the anode side of, and the capacitor 1 is connected to the cathode side of the diode 102.
05 is connected. Output terminal V of booster circuit 101
_A battery and a load are further connected to the _out side.

When a predetermined voltage is applied to the input terminal V _in and the FET 104 is on and in the energized state, the coil 103 stores energy as a current. F
When the ET 104 is off and in a non-energized state, the energy stored in the coil 103 is released. At this time, the current does not flow to the FET 104 but to the diode 102. The high voltage due to the boosting action is smoothed by the capacitor 105 and is given to the output terminal V _out . As described above, a relatively low voltage applied to the input terminal V _in is boosted, at the output terminal V _out of _the cathode side of the diode 102 as a high voltage.

The diode 102 has an output terminal V_outSide
It is provided to prevent current from flowing in from
It This is the output terminal V in the booster circuit 101._outOn the side
The boosted voltage becomes higher than the input voltage and flows backward.
This is because there is a possibility to prevent it. here
Is usually a Schottky diode with a low forward voltage
used. The power consumption of this diode 102 is
The forward voltage of the ion 102 is Vf, and the current is I
_outAnd the off duty of FET 104 is FET
_offdutyThen, it is calculated by the following formula.

Vf × I _out × FET _offduty ... (1)

The power consumption by the above equation (1) is FET1
The power consumption is when 04 is off, that is, when the forward voltage is applied to the diode 102. This power consumption increases as the current supplied from the output terminal V _out to the load or the like increases, and thus the amount of heat generation also increases.

Next, a power supply device used in an electric power steering device will be described as an example of a power supply device including a booster device. The electric power steering device is
When the driver operates a steering wheel (steering wheel) while the vehicle is driving, the motor is interlocked to assist the steering force. The electric power steering apparatus uses a steering torque signal from a steering torque detection unit that detects a steering torque generated on a steering shaft by a driver's steering of a steering wheel, a vehicle speed signal from a vehicle speed detection unit that detects a vehicle speed, and the like. Based on the control operation of the control unit, the assisting motor that outputs the auxiliary steering force is drive-controlled to reduce the steering force of the driver. For example, when the steering wheel is stationary, a large amount of auxiliary steering force is required instantaneously, so it is necessary to supply a large current to the motor.

Conventionally, a large current has been supplied to a motor directly from a battery. Therefore, the voltage of the battery fluctuated. Therefore, for example, in the electric power steering power supply device of Japanese Patent Publication No. 8-539, the capacity of the booster circuit for boosting the low voltage is larger than the average power used by the battery connected to the output side of the booster circuit and used. By making the electric power smaller than the maximum electric power, a large current required when the steering wheel is installed is supplied while the voltage fluctuation of the battery on the input side is small.

[0009]

In the step-up circuit disclosed in the above publication, a diode is used in a one-way energizing circuit section that causes a current to flow based on a high voltage due to the step-up action.
Even if a Schottky diode having a low forward voltage is used in such a booster circuit, the power calculated by the equation (1) is consumed. As a result, power is consumed by the diode and the diode heats up. In a vehicle device such as an electric power steering device that requires a relatively large current in a very short period of time such as when stationary, it is particularly desirable to reduce the power consumption and heat generation as described above.

An object of the present invention is to solve the above problems, and to reduce the power consumption in the one-way energizing circuit section for flowing a current based on the high voltage due to the boosting action and to reduce the heat generation. To provide a device.

[0011]

In order to achieve the above object, a booster device for a power supply device according to the present invention is constructed as follows.

The step-up device (corresponding to claim 1) of the first power supply device outputs energy when the first switch element (FET 12) is turned on / off by the first drive signal and the first switch element is on. The inductance circuit element (coil) that stores and releases energy at the moment of turning off and the inductance circuit element connected to the downstream side of the inductance circuit element and turned on by the second drive signal when the first switch element is off A second switch element (FET 13) for supplying the supplied current, a storage element such as a capacitor connected to the downstream side of the second switch element, and a drive control section for supplying the first drive signal and the second drive signal are provided. It is characterized by comprising.

According to the above structure, the energy stored in the inductance circuit element when the first switch element is on causes a current to flow based on the high voltage due to the boosting action at the moment when the first switch element is turned off. It is released to the output side through the directional energizing circuit section. In this one-way energizing circuit section,
Since the second switch element, which is an FET that satisfies a predetermined condition, is provided instead of the diode that consumes the power calculated by the above formula (1), it is possible to suppress the power consumption and thereby reduce heat generation. Can be achieved. This is due to the following reasons.

For example, when the first and second FETs are used as the first switch element and the second switch element, the drive control section supplies a drive signal having a predetermined off duty to each. The current flowing based on the boosted high voltage is I _out, and the resistance of the second FET is R _on .
If the off duty of the FET is FET _offduty , the power consumption of the second FET can be calculated by the following equation.

I _out ² × R _on × FET _offduty ... (2)

Since it is possible to make the on-state voltage smaller than that of the diode by selecting the second FET having a small on-state resistance, based on the condition of the following equation (3). It is possible to reduce the power consumed in the one-way energization circuit section of the booster circuit to be smaller than the power consumption in the booster device using the conventional diode. Note that I _out and FET in the equations (1) and (2)
_{The offduty} is the same.

Vf> I _out × R _on (3)

By using the second FET satisfying the expression (3), it is possible to reduce the power consumption and the heat generation of the power supply device.

The step-up device (corresponding to claim 2) of the second power supply device preferably has the above-mentioned first device configuration.
It is characterized in that the first switch element is turned off by the first drive signal, and then the second switch element is turned on by the second drive signal so that the simultaneous on state does not occur. According to the above configuration, after the first switch element is turned off, the second switch element is turned on so that the simultaneous on state does not occur.
Without overlapping the transition state of the switch element from ON to OFF and the transition state of the second switch element from OFF to ON,
It is possible to prevent current from flowing from the output side to the input side of the booster circuit.

The step-up device (corresponding to claim 3) of the third power supply device is preferably the one having the above-mentioned second device configuration.
The second switch element is a FET, and the source of the FET is connected to the inductance circuit element.

According to the above construction, the second switch element is also connected in the direction opposite to the direction in which the normal FET current flows. After turning off the first switch element,
Since the second switch element is turned on so that the simultaneous on state does not occur, there is a timing when both the first switch element and the second switch element are turned off, but the parasitic diode of the second switch element is the diode of the conventional booster circuit. Since it functions in the same manner as above, no surge voltage is generated by the coil storing energy, and no current flows from the output side to the input side of the booster circuit.

[0022]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a typical embodiment of a booster device for a power supply device according to the present invention. The electric circuit portion is a booster circuit. The booster 10 includes a coil 11, a first FET 12 that is a first switch element, a second FET 13 that is a second switch element, and a drive controller that supplies drive signals S and S ′ to the FET 12 and FET 13, respectively. 14 and a capacitor 15. In FIG. 1, the FET 13 is depicted as being composed of two elements, a switch energizing portion 13a and a diode 13b. This diode 13
b is a parasitic diode of the FET 13. Capacitor 1
5 has a power storage function and a smoothing function. In addition, capacitor 1
A battery (rechargeable battery) may be used in place of 5.

The upstream side of the coil 11 (left end in the drawing) is a input terminal _{V in,} the downstream side (right end in the drawing) is FET1
2 is connected to the drain and the source of the FET 13. The drain of the FET 12 is connected to the downstream side of the coil 11, and the source is grounded. The drive signal S from the drive control unit 14 is input to the gate of the FET 12. FE
T13 is configured to include the parasitic diode 13b, the source is connected to the downstream side of the coil 11, and the drain is connected to the output terminal V _out . The drive signal S ′ from the drive control unit 14 is input to the gate of the FET 13. FET1
The drive control unit 14 that supplies the drive signals S and S ′ to the FET 2 and the FET 13 is composed of a circuit for boosting drive and a dedicated IC.

When the FET 12 is on, the coil 11
A current flows through the device, and energy is stored due to its inductance effect. At this time, the FET 13 is off, and no current flows to the output terminal V _out side. Next, when the FET 12 is turned on by the drive signal S,
The current flowing through the coil 11 is cut off. An electromotive force is generated in the coil 11 so as to prevent the change in the magnetic flux due to this interruption. As a result, a voltage is generated across the coil 11.
At this time, when the FET 13 is turned on by the drive signal S ′, a current is supplied from the coil 11 side to the output terminal V _out via the switch energization portion 13a of the FET 13.
Voltage generated in the downstream side of the coil 11 has a sum of voltage generated across the voltage and the coil 11 which is applied to the input terminal V _in. FET13 by the drive signal S '
Immediately before turning on, the parasitic diode 13b of the FET 13
Via the current flows to the output terminal _{V out} side, a voltage is supplied to the output terminal _{V o ut.}

As described above, the FET is connected to the output terminal V _out .
13 switch energizing portion 13a and parasitic diode 13
The high voltage generated by the boosting action is applied via b. The capacitor 15 stores electricity by the applied high voltage and smoothes fluctuations of the high voltage generated by repeating ON / OFF of the FET 12 and the FET 13. Even when a battery is used instead of the capacitor 15, electricity is stored based on the high voltage generated by repeating the on / off operation of the FET 12 and the FET 13.

FIG. 2 shows the input state of the drive signals S and S'applied to the gates of the FET 12 and the FET 13. In order to turn off the FET 12 by the drive signal S and then turn on the FET 13 by the drive signal S ′ so that the simultaneous on state does not occur, the time of the on state of the drive signal S to the gate of the FET 12 is set to the gate of the FET 13. The drive signal S ′ is set to be shorter than the off-state time. In FIG. 2, the drive signals S and S ′ are separately input, but the drive signals S and S ′ are supplied from the same drive control unit 14.

FIG. 3 shows the waveforms of the drive signals S and S ',
The operation states of the FET 12 and the FET 13 are shown. Sd represents the operating state of the FET 12, and S′d represents the operating state of the FET 13. The FET 12 is turned off by the drive signal S, and then the FE is turned by the drive signal S ′ so that the simultaneous ON state does not occur.
In order to turn on T13, the ON time of the drive signal S to the gate of the FET 12 is set shorter than the OFF time of the drive signal S ′ to the gate of the FET 13. Here, the difference between the time T1 when the FET 12 switches from on to off and the time T2 when the FET 13 switches from off to on is the dead time DT. With this dead time DT, a simultaneous off state is created between two drive signals.

Dead time DT in this simultaneous off state
Drive signals S and S ′ having
When the FET 12 switches from on to off and from off to on even in the operating state,
Simultaneous off section W in which 12 and FET 13 are simultaneously off
Occurs. Therefore, even in the transient state of each operation of the FET 12 and the FET 13, the ON states of the two FETs do not overlap, and the current based on the high voltage on the output side does not flow backward.

In the booster circuit having the above structure,
Driving with dead time DT so that they are simultaneously turned off
Input motion signals S and S'to FET12 and FET13, respectively.
When the power is applied, the power consumption of the FET 13 is calculated by the equation (2).
It is calculated by. In equation (2), I_outIs FET1
Current flowing through 3, R_onIs the on-resistance of the FET, the FET
_offdutyIs the off duty of the FET 12.
Here, the conventional diode calculated by the above equation (1)
Power consumption is less than that when using
In order to do so, it is necessary to satisfy the condition of the above expression (3).

If the FET 13 satisfying the expression (3) is used, the power consumption can be reduced as compared with the case where the diode as in the conventional case is used, and thereby the heat generation amount can be reduced. In addition, the parasitic diode 13 is used to prevent the backflow of the current.
Since b works, it is possible to completely prevent backflow of current.

FIG. 4 shows a first application example to which the booster device of the power supply device according to the present invention is applied. In FIG. 4, elements that are substantially the same as the elements described in the above embodiment are assigned the same reference numerals. In FIG. 4, reference numeral 15 is the capacitor, 16 is a vehicle battery, and 17 is a motor unit. The motor unit 17 is a drive source used for supplying an auxiliary steering force in the electric power steering device. Drive control unit 14
Drive signal S, to FET 12 and FET 13, respectively.
S'is supplied to control the on / off operation of the FETs 12 and 13. When the FET 12 is on, energy is stored in the coil 11 by application of a predetermined low voltage by the vehicle-mounted battery 16. FET12 is turned off, FET13
When is turned on, the energy stored in the coil 11 is released, and a current flows to the downstream side through the FET 13 that is turned on. The capacitor 15 stores electricity, smoothes current, and supplies a large current of high voltage to the motor 17 unit. As described above, in the electric power steering device that requires a large current when stationary, an appropriate current is supplied by the booster device. In this case, the power consumption of the FET 13 is small and heat generation is reduced.

FIG. 5 is a diagram showing a second application example to which the booster device of the power supply device according to the present invention is applied. In FIG. 5, elements that are substantially the same as the elements described in the above embodiment are assigned the same reference numerals. Reference numeral 18 is a low-voltage power supply battery, and 19 is a charging battery. The low voltage applied by the battery 18 releases the energy stored in the coil 11 when the FET 12 is turned on and when the FET 12 is turned off and the FET 13 is turned on. The voltage due to the back electromotive force generated in the coil 11 and the battery 18
The voltage boosted by the voltage is applied to the battery 19 and stored. Since the FET 13 is used in the portion where the conventional diode is used, the power consumption is low, and the voltage applied from the battery 18 can be boosted to efficiently charge the battery 19.

[0034]

As is apparent from the above description, the present invention has the following effects.

According to the first aspect of the present invention, a switch element such as an FET is used in place of the diode, so that the power consumption can be suppressed and a booster device of a power supply device having a heat generation reducing effect can be provided. Can be realized.

According to the second aspect of the present invention, in addition to the above effects, since the drive signal having the simultaneous OFF state is input, it is possible to prevent the backflow of the current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a typical embodiment of a booster device of a power supply device according to the present invention.

FIG. 2 is a diagram showing an input state of a drive signal to each gate of two FETs.

FIG. 3 is a diagram showing waveforms of drive signals input to respective gates of two FETs and respective operating states of the two FETs.

FIG. 4 is a circuit diagram showing a first application example to which the booster device of the power supply device according to the present invention is applied.

FIG. 5 is a circuit diagram showing a second application example to which the booster device of the power supply device according to the present invention is applied.

FIG. 6 is a circuit configuration diagram of a conventional booster circuit.

[Explanation of symbols]

10 Booster 11 coils 12 FET 13 FET 13a Switch energizing part 13b diode 14 Drive controller 15 capacitors 16 Car battery 17 Motor unit 18 Battery for power supply 19 Charging battery DT dead time S, S'drive signal W simultaneous off section

Claims (3)

[Claims] 1. A first switch element that is turned on / off by a first drive signal, and stores energy when the first switch element is on,
An inductance circuit element that releases the energy at the moment of turning off, and an inductance circuit element that is connected downstream of the inductance circuit element and that is turned on by a second drive signal when the first switch element is off and is supplied from the inductance circuit element. A second switch element that allows a current to flow therethrough, a power storage element that is connected to the downstream side of the second switch element, and drive control means that supplies the first drive signal and the second drive signal. A booster for a power supply device characterized by the above. 2. The first drive signal turns off the first switch element, and then the second drive signal turns on the second switch element so that a simultaneous on-state does not occur. 1. A booster device for the power supply device according to 1. 3. The second switch element is a FET,
3. The booster device for a power supply device according to claim 2, wherein the source of the FET is connected to the inductance circuit element.