JPH01268326A - Power control circuit for lowering generation of electromagnetic noise - Google Patents

Abstract

PURPOSE:To lower the generation of an electromagnetic noise by constituting the title circuit so that an intermediate voltage of voltages of both ends of a load becomes constant. CONSTITUTION:Signals having a PWM waveform which have been generated by a logic circuit A are inputted to bases of an NPN type transistor Q1 and a PNP type transistor Q2, respectively by allowing one of them to pass through an inverter B. The transistors Q1, Q2 constitute an emitter follower circuit, a response waveform of an output against an input waveform is quick enough, and the transistors Q1, Q2 become ON or OFF roughly simultaneously. Resistances R3, R4 use an equal resistance so that when the transistors Q1, Q2 are both OFF, an intermediate voltage of voltages of both ends of a motor M becomes 1/2 of a pull-up voltage Vcc. In such a way, a pulse voltage applied to electric wires D1, D2 which have been connected to both ends of a load is negated and it does not occur that an electromagnetic noise is generated in the periphery.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is for controlling the power of loads that use relatively large currents, such as DC motors used in automobiles or other industrial applications, or electric lights. be.

[Conventional technology]

Power semiconductors are used to control the power of loads that use relatively large currents, such as DC motors used in automobiles or other general applications, or electric lights. However, in simple analog control of power semiconductors, the heat loss of the power semiconductors becomes extremely large depending on the control state of a load such as a motor. Therefore, in actual equipment, expensive power semiconductors with high power loss, large heat sinks, fan motors, etc. are required, resulting in large equipment in terms of space and weight.For this reason, it is more difficult to use power semiconductors for control than before. A method of controlling the power supplied to the load while reducing heat generation is the PWM control method, which finely controls the ratio of ON and OFF times. However, with this method, a sudden voltage is applied to the load, causing damage to the surrounding area. It may generate electromagnetic noise in wireless equipment, etc. Especially when in a car, there is always an AM nearby.
This is a serious problem since FM radio exists, and conventional countermeasures include using shielded wires for the wires that transmit power to the load, and methods that blunt the pulse waveform itself.

[Problem to be solved by the invention]

However, the method of using shielded wires is expensive;
When the motor is a load, it is difficult to reverse its polarity, and if the method of dulling the pulse waveform itself is done beyond a certain level, it actually defeats the purpose of preventing power semiconductors from generating heat, which is the original purpose of the PWM control method. There was a problem in that the amount of heat generated by the power semiconductor increased due to the fluctuation. An object of the present invention is to provide a power control circuit that reduces electromagnetic noise generated during PWM control of a load.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and it controls the power supplied to a load such as a motor or a light bulb based on the ON/OFF time ratio of a switch element. This circuit is characterized in that the intermediate voltage between the voltages at both ends of the load is constant.

[Effect]

The electric wire D1 connected to both ends of the load is
, D2 are canceled and no electromagnetic noise is generated in the surrounding area.

[Example] The first example is an example of a power control circuit using PWM control method 2 to which the present invention is applied. A is a logic circuit that generates a PWM waveform, and the signal with the PWM waveform generated here is passed through an inverter B, which inverts the logic, and passes through resistors R1 and R2, respectively, to an NPN transistor Q1,
The two transistors Q1 and Q2 that enter the base of the PNP transistor Q2 constitute an emitter follower circuit.
The response waveform of the output to the input waveform is sufficiently fast, and both transistors Q1 and Q2 turn on or off almost simultaneously.
The reason why a capacitor ClC2 is inserted between the hearth of both transistors Ql and Q2 and the ground to form an integrating circuit is to further improve the simultaneity of turning on or off both transistors Q1 and Q2. Resistors R3 and R4 are equal in resistance, and both transistors QI and Q2 are both O
At the time of FF, the intermediate voltage between the voltages at both ends of the motor M is made to be 1/2 of the pull-up voltage Vcc.

In this way, the intermediate voltage between the voltages across the motor M becomes Vcc/2 regardless of whether the transistors Q1 and Q2 are on or off. Actually both transistors Q
1. Due to a slight switching error in Q2, the voltage VLV2 across the load as shown in Fig. 4(a) is synthesized, resulting in the intermediate voltage (V1+V2) shown in Φ) in the same figure.
A whisker-like waveform ■1 appears in the /2 waveform, but there is no problem as long as the voltage of the high frequency component of the waveform H is sufficiently small.It is preferable that the electric wires D1 and D2 be twisted pair wires, but parallel wires close to that. Even so, it is quite effective. It is important to place the two wires D1 and D2 at the same position as much as possible.The power control circuit of the present invention not only uses an emitter follower circuit, but also uses a switch circuit that can be turned on and off at the same time. There are several possible configuration examples. FIG. 2 shows an example in which a Schottky diode is used in the switch portion to prevent saturation of the transistor. In addition to this, a similar circuit can be constructed using MOS and FET. FIG. 3 shows how the reverse rotation and rotational speed of the motor M are controlled simultaneously. NPN transistors Ql and Q3 and PNP transistors Q2 and Q4 constitute an emitter follower circuit similar to that shown in FIG. When the motor M rotates forward, if the TL flow is to flow in the direction of the arrow, PWM control is performed by turning off the PNP transistor Q2 and NPN transistor Q3, and turning on and off the NPN transistor Q1 and PNP transistor Q4. It is controlled by a logic circuit A such as a microcomputer so as to do so. Turn off NPN type transistor Q1 and PNP type transistor Q4,
PNP type transistor Q2, NPN type transistor Q3
If the logic circuit A such as a microcomputer is used to perform PWM control by turning ON and OFF, PWM control during reverse rotation is possible. Resistors R1, R2, R3, and R4 are transistors Q
1. Even when Q2, Q3, and Q4 are all OFF, the intermediate voltage between the voltages across the motor M is the pull amplifier voltage Vcc.
This is to make it 1/2 of that. FIG. 5 shows another embodiment for keeping the intermediate voltage between the voltages across the load constant. The switch circuit is connected only to one end of the load, and the other end is connected to a current control circuit E that is controlled by the difference in the intermediate voltage between the voltages at both ends of the load coming from the intermediate voltage detection circuit P and comparison circuit F. is input. Although this method is more complicated than the embodiment shown in FIG. 1, it responds well to the slight transient voltage of the motor M, and can further reduce the generation of electromagnetic noise.

〔Effect of the invention〕

As explained above, the power control circuit of the present invention that reduces the generation of electromagnetic noise is configured so that the intermediate voltage between the voltages at both ends of the load is constant, so the heat generation of the transistor is reduced, so the circuit itself is It is possible to make it compact and reduce the generation of electric M1 noise, making it suitable for home and automobile PWM with strict EMI regulations.
It has the advantage of being applicable to power control circuits using control methods.

[Brief explanation of the drawing]

Figures 1 to 3 are circuit diagrams showing embodiments of the present invention, Figure 4 is a line diagram showing the voltage at both ends of the load and the intermediate voltage, and Figure 5 is a circuit diagram showing the voltage across the load and the intermediate voltage. FIG. 2 is a block diagram illustrating a method. A~Logic circuit, B~Inverter, CI, C2~
Capacitor, M~motor, R1, R2゜R3,
R4~resistance, Ql, Q3~NPN type transistor,
Q2. Q4~PNP type transistor, DI, 02~Electric wire.

Claims (1)

[Claims] A circuit that controls the power supplied to a load such as a motor or a light bulb based on the ON/OFF time ratio of a switch element, characterized in that the intermediate voltage between the voltages at both ends of the load is constant. A power control circuit that reduces the generation of electromagnetic noise.