JPH03253286A - Pulse width modulation drive circuit of dc motor - Google Patents

Abstract

PURPOSE:To reduce noise of a motor to be small by making the frequency of a PWM signal larger sufficiently than that in an audible band by a simple circuit construction without using a high-speed microcomputer. CONSTITUTION:A PWM signal outputted by a microcomputer(MC) 11 is integrated by a circuit constructed of a resistor 25 and a capacitor 26 and enters an inversion input terminal of a comparator 27. A clock of several megahertz outputted by an oscillator 20 is subjected, together with the signal of the MC 11, to frequency division in a frequency divider 28 and made to be a rectangular wave of a frequency fh being larger sufficiently than the one in an audible band. This rectangular wave is turned into a triangular wave by an integrating circuit and enters a non-inversion input terminal of the comparator 27. The comparator 27 compares the triangular wave with the integral wave, generates a high frequency PWM signal having the frequency fh and supplies it to a control circuit 12. The pulse width of the high-frequency PWM signal enables execution of a control of rotation of a motor 10 as usual, when a switching signal is generated in accordance with the PWM signal generated by the MC 11 and outputs of Hall elements.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a pulse width modulation drive circuit for a DC motor, and a pulse width modulation drive circuit for a DC motor that performs pulse width modulation of the drive current of the DC motor to control rotation. Regarding.

Conventionally, a single-chip microcomputer has been used to vary the pulse width of the drive current of a DC brushless motor as a method of generating and driving a pulse width variable II (PWM) signal using digital signal processing to perform advanced rotation control. There are some that perform II (PWM) to control the rotation of the motor.

[Conventional technology]

FIG. 4 shows a block diagram of an example of a conventional PWM drive circuit.

In the same figure, the output of one of the three Hall element outputs attached to the three-phase DC motor 10 is supplied to the microcomputer 11, where it is used to set the rotational speed of the motor 10 to the set rotational speed. Pulse width modulation (PWM)
) signal is generated and supplied to the control circuit 12. The control circuit 12 generates switching signals for controlling the drive current of each phase according to this PWM signal and the outputs of the three Hall elements. The power amplifier circuit 13 causes the drive current of each phase to flow through the motor 10 based on this switching signal.

[Problem to be solved by the invention]

In the conventional circuit, the frequency of the PWM signal is limited to about several hundred Hz, for example, depending on the processing speed of the microcomputer 11.

However, if the PWM signal frequency is in the audible band of about several hundred Hz, there is a problem in that the frequency component of the drive current affects the driving of the motor, resulting in a loud drive sound in the audible band, which becomes intense. Further, even if a high-speed microcomputer is used, there is a problem in that a high-speed microcomputer is required to keep the PWM signal frequency out of the audible band, resulting in an increase in cost.

The present invention has been made in view of the above points, and is pulse width modulation of a DC motor that suppresses motor noise by increasing the frequency of the PWM signal sufficiently above the audible band using a simple circuit configuration without using a high-speed microcomputer. The purpose is to provide a drive circuit.

[Means for Solving the Problems] A pulse width modulation drive circuit for a DC motor according to the present invention includes: an arithmetic circuit that calculates a rotation error for setting the rotation speed of the DC motor to a set speed from a rotation detection signal of the DC motor; A level signal generation circuit that generates a level signal with a level corresponding to the rotation error, a slope wave generation circuit that generates a slope wave with a first frequency that is sufficiently higher than the audible band, and a comparison between the level signal and the slope wave. and a comparison circuit that obtains a pulse width modulation signal of a first frequency, and switches the driving current of the DC motor according to the pulse width modulation signal of the first frequency and the rotation detection signal.

(Function) In the present invention, since a pulse width modulation signal is obtained by comparing a level signal corresponding to a rotational error with a slope wave, this pulse width modulation signal has a frequency sufficiently higher than the same audible band as that of the slope wave. The frequency of the drive current that is switched according to this pulse width modulation signal is outside the audible band, and the drive sound in the audible band is small and noise is reduced.

[Embodiment] FIG. 1 shows a block diagram of an embodiment of the circuit of the present invention. In this figure, the same parts as in FIG. 4 are given the same reference numerals, and their explanations will be omitted.

In FIG. 1, a microcomputer 11 operates by being supplied with a clock from a clock oscillator 20 and generates a PWM signal. As shown in FIG. 2, the microcomputer 11 calculates the rotational speed of the motor 10 from the output of one Hall element in step 21, and then compares this rotational speed with a predetermined set rotational speed. A speed error is determined (step 22), and a PWM signal with a pulse width and a frequency of, for example, several hundred bits 2 is generated according to the speed error (step 23).

A PWM signal as shown in FIG. 3(B) outputted from the microcomputer 11 is integrated by an integrating circuit consisting of a resistor 25 and a capacitor 26, and is converted into an integral wave shown by the solid line in FIG. Supplied to the inverting input terminal.

The clock of several M days 2 outputted by the clock oscillator 20 is divided by the frequency divider 28 together with the microcomputer 11 to produce a frequency fh sufficiently larger than the audible band (for example, several tens of KHz) as shown in FIG. 3 (A). This rectangular wave is integrated by an integrating circuit consisting of a resistor 29 and a capacitor 30, and is converted into a triangular wave shown by the solid line H in FIG. .

The comparator 27 compares the triangular wave and the integral wave to generate a high frequency PWM signal having a frequency fh shown in FIG. 3(D) and supplies it to the control circuit 12.

This high frequency PWM signal has the same frequency fh as the rectangular wave, and its pulse width is proportional to the pulse width of the PWM signal output from the microcomputer 11.
Even if the switching signal is generated according to the high frequency PWM signal and the outputs of the three Hall elements, the rotation of the motor 10 can be controlled as in the conventional case.

Further, in this case, since the switching frequency of the drive current of the motor 10 is also outside the audible band, the generation of drive sound in the audible band is extremely small and noise is reduced.

Note that instead of outputting a PWM signal from the microcomputer 11, the speed error is expressed as an n-bit digital value (n is a positive integer), and this digital value is converted into an analog staircase wave by a built-in D/A converter and then outputted to the comparator 2.
It may also be supplied to the inverting input terminal of No. 7. In this case, the microcomputer 11 generates a PWM signal in step 23.
There is no need to execute this, and the operation of the microcomputer 11 becomes even faster.

Note that instead of the triangular wave, other slope waves such as a sawtooth wave or a trapezoidal wave may be generated and supplied to the non-inverting input terminal of the comparator 27, and the present invention is not limited to the above embodiment.

〔Effect of the invention〕

As described above, according to the pulse width modulation drive circuit for a DC motor of the present invention, motor noise can be reduced by making the frequency of the PWM signal sufficiently higher than the audible band with a simple circuit configuration without using a high-speed microcomputer. In addition, the circuit can be constructed at low cost, and is extremely useful in practice.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the circuit of the present invention, Fig. 2 is a flowchart of processing executed by a microcomputer, Fig. 3 is a signal waveform diagram of each part of the circuit of Fig. 1, and Fig. 4 is a diagram of the conventional circuit. It is a block diagram of an example. 11 is a microcomputer, 12 is a control circuit, 13 is a power amplification circuit, 20 is a clock oscillator, 25.29 is a resistor, 26.30 is a capacitor, 27 is a ] comparator, and 28 is a frequency divider.

Claims (1)

[Claims] Based on the rotation detection signal of the DC motor (10),
an arithmetic circuit (11) that calculates a rotational error to set the rotational speed of 10) to a set speed; and a level signal generation circuit (25, 2) that generates a level signal corresponding to the rotational error.
6), a gradient wave generation circuit (28 to 30) that generates a gradient wave of a first frequency that is sufficiently larger than the audible band, and a pulse width of the first frequency that is determined by comparing the level signal and the gradient wave. a comparison circuit (27) that obtains a modulation signal, and switches the drive current of the DC motor (10) according to the pulse width modulation signal of the first frequency and the rotation detection signal. Motor pulse width modulation drive circuit.