Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-01-30
2004-03-30
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C310S06800R, C318S254100
Reexamination Certificate
active
06713906
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pre-drive circuit for a brushless DC single-phase motor appropriately for use as a fan motor to outwardly discharge heat generated within the casing of electronic equipment and, more particularly, to a pre-drive circuit for supplying a control signal to a switching element in a drive circuit of the motor.
2. Description of the Related Art
In office automation apparatuses such as personal computers and photocopying apparatuses, a number of electronic components is mounted in a limited space available within the casing thereof, and heat generated from the electronic components builds up in the casing, possibly damaging the electronic components.
Ventilation holes are opened in the side wall and top wall of the casing of the electronic equipment, and a fan motor is installed in the ventilation hole to discharge heat from within the casing.
Brushless DC single-phase motors are typically employed as a fan motor. A conventional pre-drive circuit for such a brushless DC single-phase motor is discussed below with reference to FIG.
3
.
Referring to
FIG. 3
, a pre-drive circuit is a circuit portion other than a coil (motor coil) L
1
for a brushless DC single-phase motor and a drive circuit
31
thereof. There are shown a DC power supply +B for motor driving, and a DC power supply +Vcc for driving the circuit.
As shown, the drive circuit
31
includes four switching elements N-channel MOS type power FETs (Field-Effect Transistors) PF
1
-PF
4
, a diode D
31
, and a capacitor C
31
.
The coil L
1
is mounted on a motor stator (not shown), and is driven by a current from four power FETs PF
1
through PF
4
in the drive circuit
31
in a predetermined ON/OFF timing. The coil L
1
thus generates a dynamic magnetic field (a rotating magnetic field).
The rotor (not shown) of the motor is provided with a permanent magnet, and is rotated as the permanent magnet rotates in step with the rotation of the rotating magnetic field.
The pre-drive circuit includes dedicated integrated circuits IC
1
and IC
2
, resistors R
31
through R
35
, capacitors C
32
through C
35
, and diodes D
32
through D
35
. Each of the power FETs PF
1
-PF
4
contains a parasitic diode, as shown.
In the discussion that follows, the dedicated integrated circuits IC
1
and IC
2
are simply referred to as dedicated IC
1
and IC
2
, respectively, and power FETs PF
1
through PF
4
are simply referred to as PF
1
through PF
4
, respectively.
The dedicated IC
1
receives a rotary position signal x of the motor (of the rotor, namely, the permanent magnet) detected by an unshown Hall effect device, a high-intensity signal y for shutdown, and a duty factor setting signal z for controlling the motor rotational speed. The dedicated IC
1
receives a stepped up voltage VB1 discussed later, and turns on and off PF
1
and PF
3
in the timing determined by the signals x, y, and z.
The dedicated IC
2
also receives signals x, y, and z. The dedicated IC
2
receives a stepped up voltage VB2 discussed later, and turns on and off PF
2
and PF
4
in the timing determined by the signals x, y, and z.
Since PF
3
and PF
4
, from among PF
1
through PF
4
, are grounded at the sources thereof, PF
3
and PF
4
are turned on as long as the gates thereof (control input terminals) are slightly higher in voltage than the ground. PF
1
and PF
2
are arranged on the side of the power supply +B with respect to the coil L
1
. In the normal operating conditions under which a drive voltage of the coil L
1
is approximately equal to a power supply voltage (VB), the gates of PF
1
and PF
2
need to be supplied with a voltage equal to or higher than-the power supply voltage (namely, a sum of the power supply voltage and a gate-source voltage to turn on PF
1
and PF
2
).
To receive a voltage other than the power supply voltage, a power supply circuit becomes complicated in design and large in size, and costly. For this reason, any voltage is preferably prepared within the power supply circuit itself.
A voltage stepup circuit such as a charge pump circuit is thus added. A circuit of the diode
32
, the capacitor
34
, and the resistor R
31
, and a circuit of the diode D
33
, the capacitor C
35
, and the resistor R
31
respectively form such a charge pump circuit.
The stepped up voltage VB1 from the node of the diode
32
and the capacitor C
34
is fed to the dedicated IC
1
as a stepped up voltage VB for turning on PF
1
. The stepped up voltage VB2 from the node of the diode D
33
and the capacitor C
35
is fed to the dedicated IC
2
as a stepped up voltage VB for turning on PF
2
.
The dedicated IC
1
feeds, at the gate of PF
1
, a high-voltage pulse signal HO responsive to the voltage VB at a predetermined ON/OFF timing, and the dedicated IC
2
feeds, at the gate of PF
2
, a high-voltage pulse signal HO responsive to the voltage VB at a predetermined ON/OFF timing. The gates of PF
3
and PF
4
receive low-voltage pulse signals LO responsive to the power supply voltage (Vcc) from the dedicated IC
1
and IC
2
at predetermined ON/OFF timings.
The ON/OFF timings are set within the dedicated IC
1
and IC
2
in response to the signals x, y, and z. Signals from the dedicated IC
1
and IC
2
respectively turn on and off PF
1
through PF
4
at a predetermined duty factor at the predetermined timing, thereby feeding a current to the coil L.
The motor (the rotor) is thus rotated in a predetermined direction in accordance with the signals x, y, and z. The motor has a fan, and is mounted at a ventilation hole of a casing of electronic equipment. The motor is then rotated as a fan motor to outwardly discharge heat from within the casing of the electronic equipment.
Such a conventional circuit is costly because of its dedicated IC
1
and IC
2
.
IC
1
and IC
2
are both bulky. With the bulky IC
1
and IC
2
and other individual electronic components, the circuit requires a large mounting space. When the circuit is applied to a small motor, it is difficult to mount the large two IC
1
and IC
2
and other electronic components on an associated small circuit board.
SUMMARY OF THE INVENTION
The present invention has been developed in view of this problem, and it is an object of the present invention to provide a pre-drive circuit for a brushless DC single-phase motor, which is low-cost, requires no large mounting space, and is easy to mount on a small printed wiring board.
To achieve the above object, a pre-drive circuit of the present invention for a brushless DC single-phase motor controls a motor rotational speed by changing a duty factor of an ON/OFF control voltage to switching elements. The pre-drive circuit drives a brushless DC single-phase motor drive circuit including a pair of series connections of switching elements being connected between a power supply and ground, each series connection formed of two switching elements, and a motor coil connected between the two nodes, each node of the two switching elements in each series connection, wherein the motor coil is controlled with a current fed therethrough at any timing in any direction in an ON/OFF manner by turning on and off the switching elements, and a control voltage exceeding the voltage of the power supply is needed to turn on two power-supply-side switching elements. The pre-drive circuit includes a voltage stepup circuit for stepping up the power supply voltage to a predetermined voltage, a logic circuit for generating and then outputting pulse signals for controlling the switching elements, based on a motor rotary position signal and a duty factor setting signal for controlling the motor rotational speed, a pair of operational amplifiers which are respectively connected to output terminals of the logic circuit for the pulse signals for controlling the two power supply side switching elements, are supplied with the stepped up voltage from the voltage stepup circuit as a power source, amplify the pulse signal for controlling the two power-supply-side switching elements to a predetermined voltage level above the
Lam Thanh
Minebea Co., LTD
LandOfFree
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