Driving circuit of stepping motor

Details Driving circuit of stepping motor Driving circuit of stepping motor

2000-05-02

2001-06-26

Dang, Khanh (Department: 2837)

Electricity: motive power systems

Open-loop stepping motor control systems

C318S254100

Reexamination Certificate

active

06252371

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a driving circuit of a stepping motor and, more particularly, relates to an improvement of a driving circuit of a stepping motor for driving the stepping motor at a high speed.
DESCRIPTION OF THE PRIOR ART
Referring to
FIG. 2
, a conventional driving circuit of a stepping motor will be described. In
FIG. 2
, a reference symbol Vm denotes a direct current electric power source. U
1
denotes a driver circuit connected to the direct current electric power source Vm. Tr
1
to Tr
3
denote power switching transistors at the positive terminal side of the direct current electric power source Vm. Tr
4
to Tr
6
denote power switching transistors at the negative terminal side of the direct current electric power source Vm. R
1
denotes a current detection circuit. M denote windings of the stepping motor. According to the conventional driving circuit, six power switching transistors Tr
1
to Tr
6
form an excitation control circuit, which is driven by an output current from the driver circuit U
1
, so that three windings M of the stepping motor are excited in order and that the stepping motor is driven.
As shown in
FIG. 3
, the driver circuit U
1
comprises six output switching transistors Pd
1
to Pd
6
, a commutation logic signal generation circuit C for forming a three-phase exciting sequence of an exciting current signal to be applied to input terminals of the switching transistors Pd
1
to Pd
6
in order, a PWM (pulse width) control circuit P for controlling the excitation control circuit, resistances Ru connected between output terminals of the output switching transistors Pd
1
to Pd
3
and a power input terminal Vcc of the driver circuit U
1
, and resistors Rd connected between the output terminals of the output switching transistors Pd
4
to Pd
6
and a ground, an output of the PWM control circuit P being applied to control input terminals of the output switching transistors Pd
1
to Pd
3
. In case that either one of the power switching transistors Tr
1
to Tr
3
is to be turned ON, a constant output current is supplied from one of output terminals U, V, W to corresponding one of the output switching transistors Pd
1
to Pd
3
.
In case that either one of the power switching transistors Tr
1
to Tr
3
is to be turned OFF, a constant output SINK current is supplied from one of the output switching transistors Pd
1
to Pd
3
to corresponding one of the output terminals U, V, W. In these cases, the voltages at the output terminals of the output switching transistors Pd
1
to Pd
3
are substantially the same with the voltage at the power input terminal Vcc of the driver circuit U
1
.
In general, there is such a problem that if the driving frequency of the stepping motor is increased, the build up of the current is delayed due to the effect of the inductance of the windings M, the effective current is reduced, the torque is reduced, and the synchronism is lost. In order to solve the problem, it is generally adopted that the number of turn of the windings M is reduced so as to reduce the inductance. However, it is unfavorable, because there is such a problem that the holding torque which is determined by the ampere-turn of the stepping motor is decreased.
An another measure to solve the problem is to increase the voltage of the electric power source. According to the measure, it is possible to operate the stepping motor with a large torque in the range from the lower frequency to the higher frequency. However, if the voltage of the electric power source is increased, the voltage of the driver circuit U
1
might over the maximum rated voltage of the driver circuit U
1
so that the driver circuit U
1
becomes inoperative or damaged.
In order to prevent such accident from being occurred, it may be considered that an exclusive electric power source for the driver circuit U
1
is used, or a driver circuit of the stepping motor corresponding to a higher voltage is used. However, such exclusive electric power source or the driver circuit is not a general purpose goods, so that it is expensive.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems in the conventional driving circuit of the stepping motor, it is an object of the present invention to provide a driving circuit of a stepping motor using a common electric power source and a general purpose driver circuit, which is operable in a wide frequency range.
It is another object of the present invention to provide a driving circuit of a stepping motor comprising an excitation control circuit connected to windings of a stepping motor, a driver circuit consisting of power switching transistors at a positive terminal side of a power source and of power switching transistors at a negative terminal side of the power source for controlling the excitation control circuit, a Zener diode inserted between the power source and a power input terminal of the driver circuit, and Zener diodes inserted between output terminals of the driver circuit and control signal input terminals of the power switching transistors at the positive terminal side of the power source, respectively, wherein the Zener voltage of the Zener diode for the power switching transistor is determined to a value not less than a voltage difference between the voltage of the power source and the maximum rated voltage of the driver circuit.
It is a further object of the present invention to provide a driving circuit of a stepping motor, wherein the number of the power switching transistors at the positive side of power source is selected to be three, and the number of the power switching transistors at the negative side of power source is selected to be three.
It is yet another object of the present invention to provide a driving circuit of a stepping motor, wherein the number of the windings of the stepping motor is selected to be three.
These and other objects and features of the present invention will become apparent from the following description in conjunction with the attached drawings.


REFERENCES:
patent: 4673856 (1987-06-01), Takaishi
patent: 4760320 (1988-07-01), Tsugita
patent: 5075610 (1991-12-01), Harris
patent: 5541487 (1996-07-01), Yorozu
patent: 6046560 (2000-04-01), Lu et al.

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