Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2001-07-17
2003-02-11
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S799000, C318S800000, C318S802000, C318S803000, C318S700000, C388S905000, C388S907000, C388S907200, C388S907500
Reexamination Certificate
active
06518723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an H-bridge motor driving circuit for controlling a DC motor using pulse width modulation (PWM).
2. Description of the Related Art
One general motor driving circuit for controlling a DC motor to rotate selectively in normal and reverse directions is an H-bridge motor driving circuit which has an H-shaped bridge circuit comprising four transistors and a DC motor. The four transistors are turned on and off to energize, de-energize, and rotate the DC motor selectively in the normal and reverse directions.
FIG. 1
of the accompanying drawings shows a typical conventional H-bridge motor driving circuit.
As shown in
FIG. 1
, the conventional H-bridge motor driving circuit comprises H-bridge output circuit
10
, triangular wave oscillator
11
, PWM comparator
12
, inverter
13
, and control circuit
14
.
H-bridge output circuit
10
has MOS transistors Q
1
, Q
2
each having a drain connected to the positive terminal of a DC power supply E, a source connected to the circuit board, and a gate supplied with control signals S
11
, S
12
, respectively, for turning on and off MOS transistors Q
1
, Q
2
, and MOS transistors Q
3
, Q
4
, each having a drain connected to the sources of MOS transistors Q
1
, Q
2
, respectively, a source connected to the circuit boards and a ground potential point to which the negative terminal of the DC power supply E is connected, and a gate supplied with control signals S
13
, S
14
, respectively, for turning on and off MOS transistors Q
3
, Q
4
. Motor M is connected between the junction between MOS transistors Q
1
, Q
3
and the junction between MOS transistors Q
2
, Q
4
. Parasitic diodes D
1
through D
4
exist at the junctions between the sources of MOS transistors Q
1
through Q
4
, the circuit board, and the drains of MOS transistors Q
1
through Q
4
.
Triangular wave oscillator
11
generates triangular wave signal S
21
.
PWM comparator
12
compares triangular wave signal S
21
from triangular wave oscillator
11
with constant-level signal S
22
, and outputs PWM pulse signal S
23
.
Inverter
13
inverts pulse signal S
23
from PWM comparator
12
into pulse signal S
24
.
Control circuit
14
is supplied with pulse signals S
23
, S
24
, power-supply-level signals S
25
, S
26
, and rotation control signal S
0
, and outputs signals S
25
, S
24
, S
26
, S
23
as control signals S
11
through S
14
for MOS transistors Q
1
through Q
4
.
Operation of the conventional H-bridge motor driving circuit shown in
FIG. 1
will be described below with reference to a timing chart of
FIG. 4
of the accompanying drawings.
Triangular wave signal S
21
generated by triangular wave oscillator
11
and constant-level signal S
22
are supplied to comparator
12
, which generates PWM pulse signal S
23
. PWM pulse signal S
23
is inverted into signal S
24
by inverter
13
. Signals S
23
, S
24
, power-supply-level signal S
25
. and ground-level signal S
26
are supplied to control circuit
14
, and then applied as respective control signals S
14
, S
12
, S
11
, S
13
to the gates of MOS transistors Q
4
, Q
2
, Q
1
, Q
3
, respectively. It is assumed that MOS transistors Q
1
, Q
4
are energized , and MOS transistor Q
4
is PWM-controlled. During period T
1
, signals S
23
, S
25
are high and MOS transistors Q
1
, Q
4
are turned on, causing a current to flow through motor M. During period T
2
, signals S
24
, S
25
are high and MOS transistors Q
1
, Q
2
are turned on, entering a regenerative mode to produce a regenerative current flowing through a loop from motor M to MOS transistor Q
2
to MOS transistor Q
1
to motor M (in case of an inductive load). In case of a resistive load, the MOS transistors are not conducted.
The conventional H-bridge motor driving circuit described above is disadvantageous in that since MOS transistor Q
1
is energized at all times and hence a current flows through MOS transistor Q
1
at all times, a large amount of electric power needs to be supplied to the H-bridge motor driving circuit, which generates a large amount of heat and hence suffers poor reliability. The H-bridge motor driving circuit is necessarily of increased cost as it needs a high-performance device such as a low-on-resistance MOSFET or a low-saturation-voltage transistor for reducing the amount of generated heat.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an H-bridge motor driving circuit which includes a circuit arrangement for distributing an amount of applied electric power among a plurality of transistors to equalize the amounts of heat generated by the transistors.
To achieve the above object, an H-bridge motor driving circuit according to the present invention comprises, connected between a PWM comparator and a control circuit, first and second frequency dividers for frequency-dividing, by 2, an output signal from the PWM comparator with positive-going edges and negative-going edges, respectively, thereof, an AND gate for ANDing an output signal from the first frequency divider, an OR gate for ORing the output signal from the first frequency divider and the output signal from the second frequency divider, and first and second inverters for inverting an output signal from the AND gate and an output signal from the OR gate, respectively.
The control circuit applies an output signal from the first inverter, an output signal from the second inverter, the output signal from the AND gate, and the output signal from the OR gate to the gates of first, second, third, and fourth MOS transistors, respectively.
During a first period, the first and second transistors are turned on, and the second and third transistors are turned off, causing a current to flow through a motor. During a next second period, the third and fourth transistors are turned on, and the first and second transistors are turned off, causing a regenerative current to flow through the motor. During a next third period, the MOS transistors are turned on and off in the same manner as during the first period, causing a current to flow through the motor. During a final fourth period, the first and second transistors are turned on, and the third and fourth transistors are turned off, causing a regenerative current to flow through the motor.
In a regenerative mode, the first and second MOS transistors, and the third and fourth MOS transistors are alternately turned on. Therefore, the amount of applied electric power is distributed among the MOS transistors, thus equalizing the amounts of heat generated by the MOS transistors.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference t the accompanying drawing s which illustrate an example of the present invention.
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Nappi Robert E.
Smith Tyrone
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