JPH09204231A - Power control circuit for automobile - Google Patents

Abstract

(57) Abstract: A low-cost and compact configuration suppresses noise while performing good power control by PWM control. An FET 12 is provided between a power source and a load 10, and a gate signal creating means 14 is provided for creating a pulse signal having a predetermined duty ratio and outputting the pulse signal to the gate of the FET 12. Further, the capacitor 1 is provided in the circuit from the gate signal creating means 14 to the gate.
8 is connected, the time rate of change of the gate voltage is reduced by the action of this capacitor 18, and the increase / decrease in the current flowing between the source and drain of the FET 12 is moderated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse width modulation (Pulse Widt) provided between a power source and a load in an automobile.
h Modulation; hereinafter referred to as PWM. ) Relates to an electric power control circuit for an automobile, which controls the electric power supplied from the power source to the load.

[0002]

2. Description of the Related Art Conventionally, a variable resistor is provided between a lamp and a motor, that is, a load and its power source, as a means for adjusting the dimming of a lamp mounted on an automobile and the adjustment of the motor rotation speed. Means of changing the number are generally known. However, with this means, the energy loss of the resistor is large, which greatly hinders the reduction of power consumption, and there is a possibility that the heat generated from the resistor may adversely affect other circuit elements and the like.

Therefore, PWM control is in the limelight as an alternative to such resistance value control. This PW
FIG. 5 shows an example of a circuit for performing M control. In the figure, a field effect transistor (Field Effect Transistor; hereinafter) is provided between a power source (+ BV battery) and a load 10.
It is called a FET. ) 12 are provided. In the example shown,
A p-channel MOSFET is used as the FET 12, the battery is connected to the source and the gate, the load 10 is connected to the drain, and the gate signal generating means 14 is provided between the gate and the battery. . The gate signal generating means 14 is composed of an oscillator or the like, and periodically changes the voltage applied from the battery to the gate of the FET in a pulse form between + B and a voltage lower than + B (that is, has a set frequency). The pulse signal is input to the gate).

In this circuit, current flows between the source and drain of the FET 12 and power is supplied to the load 10 only when the gate voltage is lower than the source voltage by a predetermined value or more. Therefore, by adjusting the duty ratio of the pulse signal created by the gate signal creating means 14, the load 1
The total energization time of 0 can be controlled (in other words, the amount of electric power supplied from the battery to the load 10 can be controlled).

By using such PWM control, vehicle-mounted lamp dimming and motor rotation speed adjustment can be performed without causing significant energy loss and heat generation as in the case of using a variable resistor.

[0006]

It has been confirmed that when an electric device such as a radio is provided near the circuit shown in FIG. 5, noise is generated in this device. A factor for this is a rapid increase / decrease in current generated in the circuit.

That is, in the above circuit, since a pulse signal having a substantially rectangular waveform is input to the gate, the current flowing into the load 10 between the source and the drain sharply increases or decreases corresponding to this, and this circuit Pulse-like noise will be caused by electromagnetic induction in a device arranged near the.

Conventionally, the following measures have been taken as measures against such noise generation.

A ground layer is provided on the back surface of the printed circuit board on which the circuit is assembled.

Noise from the electric wire is suppressed by providing a shielding layer formed of a metal mesh, a semiconductive resin layer, or the like around the electric wire, or by using an electric wire coming from a load as a twisted pair.

However, although the means can suppress the noise excited by the circuit assembled on the board, when an electric wire is connected to the board, the electric current flowing through the electric wire causes a sharp increase or decrease. It is not possible to suppress the generation of noise.

On the other hand, the means (1) can suppress the noise from the electric wire, but has the drawback that the structure becomes complicated and large due to the addition of the shielding layer or the twisted pair electric wire. It is extremely difficult to apply it to a part where a wide variety of electric wires are combined and wired in a narrow space. In addition, the cost of the entire system is inevitable.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and is provided between a power supply and a load in an automobile to control the power supplied from the power supply to the load. In the automobile power control circuit, one of a source and a drain is connected to the power source,
The other is provided with an FET connected to the load, and a gate signal creating means for creating a pulse signal having a set duty ratio and outputting the pulse signal to the gate of the FET,
A capacitor for reducing the time change rate of the gate voltage is connected in the middle of the circuit from the gate signal generating means to the gate.

According to this circuit, even if a pulse signal having a sharp voltage change is created by the gate signal creating means,
Due to the action of the capacitor provided between the gate signal generating means and the gate of the FET, the time change rate of the gate voltage is reduced, and the gate voltage rises and falls relatively slowly. Therefore, the source of this FET
The current flowing between the drains also gently increases and decreases, effectively suppressing the generation of noise due to the sharp increase and decrease of the current.

The rate of change of the gate voltage with time is the product R of the resistance R (Ω) of the circuit from the gate signal generating means to the gate and the electrostatic capacitance C (F) of the capacitor.
It depends on the time constant determined by C. Therefore, this product RC
By setting, the change characteristics of the gate voltage can be adjusted freely. Specifically, it is preferable to set the product RC to 1 × 10 ⁻⁷ or more in order to sufficiently obtain the noise reducing effect. However, if this product RC is too large,
It is preferable to set the product RC to 1 × 10 ⁻⁵ or less because the change of the gate voltage becomes extremely slow and good PWM control cannot be performed.

The frequency of the pulse signal may be set as appropriate, but if the frequency is too low, the operating state of the load will not be smooth. Therefore, it is more preferable that the frequency be 50 Hz or higher.

Various types of FETs can be used as the above-mentioned FET, but an inexpensive MOSFET having a relatively high withstand voltage performance is preferable. In order to make the MOSFET follow ON / OFF of the gate signal and realize good PWM control, the frequency of the pulse signal may be set to 5000 Hz or less.

[0018]

FIG. 1 shows a first embodiment of the present invention.
It will be described based on.

In the figure, the FET 1 is connected between the power supply (+ BV battery) and the grounded load 10.
2 are provided. In the illustrated example, as in the circuit shown in FIG. 5, a p-channel MOSFET is used as the FET 12, and the battery is connected to the source and the gate of the FET 12 and the load 10 is connected to the drain thereof, and the gate and the battery are connected. A gate signal generating means 14 is provided between and. This gate signal creating means 14
Also, like the one shown in FIG.
The battery is configured to periodically change the voltage applied to the gate of the FET 12 from + B to a voltage lower than + B (that is, input a pulse signal having a set frequency to the gate). The duty ratio of the pulse signal can be adjusted manually or by a control signal input from a controller (not shown).

The resistor 16 shown in FIG. 1 symbolizes the resistance component from the gate signal generating means 14 to the gate of the FET 12, and is not necessarily between the gate signal generating means 14 and the gate. It does not suggest that a special resistor be installed. However, it is free to install a special resistor in this part.

The features of this circuit are the battery and the FE.
Between the gate of T12 and the gate signal generating means 14
A capacitor 18 is arranged in parallel with the. That is, the capacitor 18 is connected in the middle of the circuit from the gate signal generating means 14 to the gate.

Next, the operation of this circuit will be described. The gate signal generating means 14 is a substantially rectangular pulse signal which is supplied with a voltage from a battery and periodically changes between the battery voltage (+ BV) and a voltage lower than that, and is set. A pulse signal having a duty ratio is created and output to the gate of the FET 12. Meanwhile, FE
At T12, current flows between the source and drain of the FET 12 and power is supplied to the load 10 only when the gate voltage is lower than the source voltage by a predetermined value or more. Therefore, the total energization time of the load 10 is determined by the duty ratio of the pulse signal, and the amount of power supplied from the battery to the load 10 is controlled.

Here, in the conventional circuit shown in FIG.
The pulse signal having the substantially rectangular waveform created by the gate signal creating means 14 is directly input to the gate.
In the circuit of the present invention shown in FIG. 3, the time rate of change of the gate voltage is reduced by the action of the capacitor 18, and the gate voltage rises gently and falls gently. Between the source and the drain, a current starts to flow when the gate voltage exceeds a predetermined threshold voltage, but when the gate voltage is close to the threshold voltage, the conduction resistance between the source and the drain is high, and the gate voltage and the threshold voltage are high. Since the conduction resistance becomes lower as the difference between the current and the source becomes larger, the increase / decrease in the current between the source and the drain also becomes gentle as the change in the gate voltage becomes gentle as described above, and the steep Noise resulting from the increase / decrease is effectively suppressed.

Specifically, when the maximum voltage of the pulse signal created by the gate signal creating means 14 is Vo, F is actually
The voltage V at the beginning of rising and the voltage V at the beginning of falling of the signal input to the gate of the ET 12 are as shown in (a) and (b) below.
Each is represented by a formula.

[0025]

[Equation 1]

Here, t represents the elapsed time from the rising start time in the equation (a) and the elapsed time from the falling start time in the equation (b). τ is a time constant, and the greater the time constant τ, the more marked the effect of reducing the time change rate. Since this time constant τ is determined by the product RC of the resistance value R of the resistor 16 and the electrostatic capacitance C of the capacitor 18 shown in FIG. 1, the desired voltage change characteristic can be obtained freely by setting this product RC. it can. Specifically, the unit of the resistance value R is Ω (ohm), and the unit of the electrostatic capacitance C is F.
When (Farad) is set, the value of the product RC is 1 × C.
It has been confirmed that a sufficient noise suppressing effect can be obtained by setting it to 10 ^-7 or more. However, the product R
If C is excessively large, the rise and fall of the gate voltage will be significantly delayed, and good PWM control will not be possible. Therefore, the value of the product RC is preferably suppressed to 1 × 10 ⁻⁵ or less.

The frequency of the pulse signal generated by the gate signal generating means 14 can be freely set. However, when the load 10 is a vehicle lamp or a motor, if the pulse frequency is too low, the lamp light flickers. However, since the movement of an object (window glass or the like) driven by a motor becomes awkward, the above frequency may be set to 50 Hz (more preferably 80 Hz) or more in the automobile power control circuit according to the present invention. preferable.

On the contrary, if the frequency is excessively high, the FET 12 may not be able to follow the change in the gate signal, and good PWM control may not be possible.
If it is set to 0 Hz or less (more preferably 1000 Hz or less), even if a relatively inexpensive MOSFET is used as the FET 12, it is possible to sufficiently follow the change of the gate signal and to obtain a good P
WM control can be realized.

Note that FIG. 1 shows an enhancement type MO.
SFET is shown, but depletion type MOS
It goes without saying that the same effect can be obtained by using the FET.

The second embodiment is shown in FIG. Here, an n-channel MOSFET is used as the FET 12, the battery is connected to the drain, and the load 10 is connected to the source. The gate signal generating means 14 is connected between the load 10 and the ground via the charge pump 20, and the charge pump 20 causes the FE to operate.
A stable voltage difference is secured between the source of T12 and the input terminal of the gate signal generating means 14. A capacitor 18 is arranged in parallel with the charge pump 20 and the gate signal generating means 14.

In such a circuit as well, the gate signal producing means 14 produces a pulse signal having a predetermined duty ratio and outputs it to the gate of the FET 12,
The current flowing from the battery to the load 10 between the drain and the source is controlled, and the capacitor 18
By the action, the time rate of change of the pulse signal is lowered and the increase / decrease in the current flowing between the drain and the source is moderated, so that the noise caused by the increase / decrease in the current is effectively suppressed.

In the present invention, the charge pump 20 can be omitted as appropriate. In addition to the above-described forms, the present invention can take various forms according to the specifications.

[0033]

EXAMPLES The present inventors conducted experiments using the circuit shown in FIG. The basic configuration of this circuit is the same as that shown in FIG. 1, and a 12V lead-acid battery 22 is used as a power source. The FET 1 is connected to the positive electrode of the lead storage battery 22.
2 is connected to the source, the gate signal generating means 14, and the capacitor 18, and the load 10 is connected to the negative electrode. A loop is formed.

In this circuit, the capacitance of the capacitor 18 is 1.0 μF and the resistance value R of the resistor 16 is 0.2 Ω (that is, the value of the product RC is 2 × 10 ^-7 ).
And the capacitance of the capacitor 18 is 1.0 μ.
F, the resistance value R of the resistor 16 is 10Ω (that is, the value of the product RC is 1 × 10 ⁻⁵ ) is taken as an example,
Omitting the capacitor 18 and setting the resistance value R of the resistor 16 to 0.2
Ω is used as a comparative example, the waveforms of the input signal to the gate and the output signal from the drain in each example are examined, and the radio 24 is connected to the conductor portion connecting the load 10 and the negative electrode of the lead storage battery 22. It was approached and it was confirmed whether or not the noise was generated. The signal waveform in the comparative example is shown in FIG.
FIG. 4A shows the signal waveform in the embodiment in FIG.
Table 1 below shows the results of checking whether or not noise was generated.

[0035]

[Table 1]

As shown in Table 1 above, noise was confirmed in both bands in the comparative example. This is shown in FIG.
Since the substantially rectangular pulse signal shown in the lower part of (a) is directly input to the gate, the drain voltage also sharply increases and decreases as shown in the upper part of FIG. It can be considered that a pulse is generated.), Which causes a sudden change in the current flowing between the source and the drain, causing the noise.

On the other hand, in the embodiments, noise is eliminated in both the FM band and the AM band.
This is because the rise and fall of the gate voltage is moderated by the action of the capacitor 18 as shown in the lower part of FIG. 4B, and the drain voltage and the drain voltage shown in the upper part of FIG. It can be considered that this is because the current between the source and the drain also gradually increases and decreases, and the generation of noise due to the steep increase and decrease of the current is avoided.

[0038]

As described above, according to the present invention, the capacitor for reducing the time change rate of the gate voltage is connected in the middle of the circuit from the gate signal generating means for generating the gate signal for PWM control to the gate of the FET. Therefore, it is possible to suppress the noise caused by the sharp increase / decrease in the current between the source and drain of the FET while performing good PWM control with an inexpensive and compact configuration that does not use a shielding layer or a special electric wire. effective.

Here, the product RC of the resistance R (Ω) of the circuit from the gate signal generating means to the gate and the electrostatic capacitance C (F) of the capacitor is 1 × 10 ⁻⁷ or more and 1 ×.
If it is set to 10 ⁻⁵ or less, it is possible to effectively suppress noise while realizing good PWM control.

If the frequency of the pulse signal produced by the gate signal producing means is set to 50 Hz or higher, a smooth operating state of the load can be secured.

Further, if the frequency is set to 5000 Hz or less, M which is inexpensive and has relatively high withstand voltage performance.
An effect that good PWM control can be realized while using the OSFET is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4A is a diagram showing waveforms of a gate input signal and a drain output signal in a power control circuit according to a comparative example,
(B) is a diagram showing waveforms of a gate input signal and a drain output signal in the power control circuit according to the embodiment of the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional power control circuit.

[Explanation of symbols]

 10 Load 12 FET (Field Effect Transistor) 14 Gate Signal Creating Means 18 Capacitor 22 Lead Acid Battery (Power Supply)

Claims (4)

[Claims] 1. A power control circuit for an automobile, which is provided between a power source and a load in an automobile and controls electric power supplied from the power source to the load, wherein one of a source and a drain is connected to the power source. And a gate signal generating means for generating a pulse signal having a set duty ratio and outputting the pulse signal to the gate of the electric field transistor. A power control circuit for an automobile, wherein a capacitor for reducing a time change rate of a gate voltage is connected in the middle of a circuit from the gate to the gate. 2. A vehicle power control circuit according to claim 1, wherein a resistance R (Ω) of a circuit from the gate signal generating means to the gate and a capacitance C (F) of the capacitor. A power control circuit for an automobile, wherein RC is set to 1 × 10 ⁻⁷ or more and 1 × 10 ⁻⁵ or less. 3. The automobile power control circuit according to claim 1, wherein the frequency of the pulse signal produced by the gate signal producing means is 50 Hz or higher. 4. The automobile power control circuit according to claim 1, wherein a MOS field effect transistor is provided as the field effect transistor, and a frequency of a pulse signal created by the gate signal creating means is set. An electric power control circuit for an automobile, which has a frequency of 5000 Hz or less.