JPS60171827A - Pulse width modulation circuit - Google Patents

Abstract

PURPOSE:To reduce its cost and to miniaturize a pulse width modulation circuit by integrating an input pulse by an integration device, amplifying it at an amplifier and applying waveform shaping at a waveform shaping circuit. CONSTITUTION:The input pulse from a phase comparator is integrated by the integration device comprising a resistor 38 and a capacitor 40 through buffers 36, 37, amplified by an amplifier comprising an inverter 42 and a resistor 39, and waveform-shaped into a pulse waveform by a waveform shaping circuit comprising an inverter 43. An output pulse of the inverter 43 and the input pulse from the phase comparator 22 are added and inverted by an NOR circuit 44 and the result is fed to an AND circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a pulse width modulation circuit that pulse width modulates an input pulse.

(Prior art) Conventionally, as shown in FIG. 1, a pulse width modulation circuit integrates an input pulse using a first integrator consisting of a resistor 1 and a capacitor 2, converts it into a binary value using a reference voltage using a comparator 3, and outputs the resulting pulse. is integrated by a second integrator consisting of a resistor 4 and a capacitor 5 and applied as a reference voltage to a comparator 3, and the output signal of the first integrator is binarized by the output voltage of the second integrator by a comparator 6. There is.

However, in this pulse width modulation circuit, comparator 3
, 6 is a linear ICL or a logic IC that cannot be used.
cannot be used, resulting in high costs. Furthermore, since two integrators are used, the size becomes large.

(Objective) It is an object of the present invention to provide a pulse width modulation circuit that can improve the above-mentioned drawbacks and achieve cost reduction and miniaturization.

(Structure) The present invention will be described below based on examples with reference to the drawings.

FIG. 2 shows an example of a graph/less motor phase control system to which the present invention is applied.

A brushless motor has a rotor 11 made of two-pole permanent magnets.
is rotated by the rotating magnetic field generated by the four-phase coils 12 to 15, and the rotational position of the rotor 11 is detected by a position detector consisting of two Hall elements 16 and 17. The speed detector 18 includes a multipolar permanent magnet 19 connected to the rotor 11 and a detection coil 2.
0, the detection coil 20 detects the rotation of the permanent magnet 19 and generates a speed signal.

This speed signal is shaped into a rectangular wave by a waveform shaping circuit 21, and a crystal oscillator 23 and a frequency divider 2 are passed through a phase comparator 22.
The phase of the clock pulse is compared with a reference signal (clock pulse) from a reference signal generator consisting of four clock pulses. The output pulse of this phase comparator 22 is pulse width modulated by a pulse width modulator 25 to widen the pulse width, and the output pulse of the phase comparator 22 is added to the output pulse of the pulse width modulator 25 in an OR circuit 26. The phase delay caused by the pulse width modulator 25 is corrected. Further, the two-phase signals shifted by 7r/2 from the Hall elements 16 and 17 are shaped into rectangular waves by waveform shaping circuits 27 and 28, and inverted by inverters 29 and 30. The distribution circuit 31 encodes the output signals of the waveform shaping circuits 27 and 28 and the inverters 29 and 30 with an encoder to sequentially generate excitation signals for each phase coil 12 to 15, and outputs them from an OR circuit 26 to an AND circuit 32.
By ANDing the control signal inputted through the control signal and the excitation signal, the excitation signal is turned on and off with the control signal and outputted to the l-phase unipolar drive circuit 33. Drive circuit 3
3, the coil 1 is activated by the excitation signal of each phase from the distribution circuit 31.
2 to 15 are sequentially excited to rotate the rotor 11. Therefore, the rotation of rotor 11 is phase controlled based on the reference signal from frequency divider 24. When the brushless motor is started, the output pulse width of the OR circuit 26 is large and the coil 1
A large current flows through circuits 2 to 15, and this current is detected by a current detection resistor 34, and a detection signal thereof is turned on and off by a starter circuit 35 and applied to a distribution circuit 31 via an AND circuit 32. Therefore, the distribution circuit 31 controls the coil excitation signal on and off based on the output signal of the starting circuit 35 to limit the coil current.

FIG. 3 shows an embodiment of the present invention, in which the pulse width modulator 25 and the OR circuit 26 are configured. The pulse width modulator 25 includes a buffer 36.17 and a resistor 38.3.
9, capacitors 40 and 41, and inverters 42 and 43, and a NOR circuit 44 is used as the OR circuit 26. The input pulse from the phase comparator 22 is sent to the buffer 36.
．． 37, is integrated by an integrator made up of a resistor 38 and a capacitor 40, amplified by an amplifier made up of an inverter 42 and a resistor 39, and shaped into a pulse waveform by a waveform shaping circuit made up of an inverter 43. The output pulse of the inverter 43 and the input pulse from the phase comparator 22 are added and inverted by a NOR circuit 44 and then applied to an AND circuit 32. Buffers 36, 37 and inverters 42.
43 is a logic IC, and buffers 36 and 37 are used as necessary.

(Effects) As described above, according to the present invention, the input pulse is integrated by the integrator, amplified by the amplifier, and waveform-shaped by the waveform shaping circuit.
It can be constructed at low cost using a logic IC, and it can be made smaller because it only uses one integrator and there is no need to use two.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional pulse width modulation circuit, FIG. 2 is a block diagram showing an example of a blurless morph phase control method, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 38, 39...Resistor, 40...Capacitor, 42,
43. Inverter.

Claims (1)

[Claims] A pulse width modulation circuit comprising an integrator that integrates an input pulse, an amplifier to which the output signal of the integrator is input, and a waveform shaping circuit that shapes the output signal of the amplifier into a pulse waveform.