Electricity: motive power systems – Positional servo systems – Pulse-width modulated power input to motor
Reexamination Certificate
2000-02-22
2002-03-19
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
Pulse-width modulated power input to motor
C318S432000, C318S434000, C318S807000, C318S808000, C318S811000, C318S812000
Reexamination Certificate
active
06359410
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to an apparatus and method for improved current protection for an electrical controller. More particularly, the invention is directed for use in pulse width modulation controllers that use a power-limiting signal as a comparative base for determining power overload conditions for the device being controlled. These circuits are used to control various types of motors, including fan blower motors and fuel pumps in automobiles.
As shown in
FIG. 1
of the drawings, a typical application diagram for a pulse-width modulation motor controller is generally shown by the reference numeral
10
. The pulse-width modulation motor controller integrated circuit chip
12
shown in the drawing is the heart of the pulse width modulation motor controller circuit
10
. This integrated circuit chip
12
is sold by DELCO ELECTRONICS CORPORATION of Kocomo, Indiana, United States of America as Part No. 16214712, IC-Bi-Polar: PMDH—Pulse-Width Modulation High Side Motor Control IC and is sold in a standard
16
pin package.
The pins of this integrated circuit
12
allow for power inputs and control signals to enter and leave the circuit
12
and supply the controlling signals for powering the MOSFET
14
that adjusts the power flow to the motor or device being controlled. The first pin is a drive output power pin
16
that provides a pulse-width modulation signal to a resistor network
18
. The resistor network
18
drives the gate of the N-channel logic level power MOSFET
14
to control the motor. The second pin is a boost pin
20
that provides an increased positive voltage supply for the integrated circuit chip's
12
output drive circuitry. This increased voltage supply is generated by an external voltage boosting circuit that includes an inductor
22
and capacitor
24
circuit that is connected to the battery or power supply
26
.
The third pin is the default retry capacitor pin
28
that acts as an input and output pin for charging and discharging a capacitor
30
. If the capacitor charging occurs faster than the discharging, an internal comparator to the chip
12
trips which disables the drive signal on the drive output power pin
16
. This continues until the capacitor
30
discharges. This discharge time gives the MOSFET
14
time to cool down.
The resistor isolation pin
32
and capacitor isolation pin
34
allow for the connection of a resistor
36
and capacitor
38
to control the frequency at which the pulse-width modulation integrated chip
12
will operate.
The control input signal pin
40
inputs a voltage signal between 0 and 5 volts that is generated by a voltage control circuit
42
to directly control the motor speed. If the voltage at the control input signal pin
40
is less than 10% of the value of the regulated voltage at output pin
30
, then the integrated circuit
12
will enter a quiescent mode. This quiescent mode helps to limit the ignition-off current draw in automobile applications. The positive ground pin
44
allows for a high current ground to discharge current from the integrated circuit chip
12
.
The input voltage pin
46
is also known as the VCC power pin
46
. This is the input pin for the positive voltage supply for the integrated circuit chip
12
. The normal operating range for integrated circuit chip
12
input voltage is between 7 and 18 volts, however, voltages from −0.3 volts to 30 volts are acceptable. The voltage regulator pin
48
uses a standard band-gap regulator to provide a stable 5 volt output that is used internally for the chip
12
and is also made available externally through the voltage regulation pin
48
.
The inductor sense pin
50
is used to monitor the current through the external boost inductor
22
in order to limit the current for each pulse of the pulse width modulation signal. The charge pump capacitor pin
52
uses the external capacitor
24
to create a boost voltage above the normal supply voltage.
The sensor negative pin
54
and sensor positive pin
56
are used to monitor the voltage across a device or motor power-sensing resistor
58
. These pins read a voltage corresponding to the current flow through the motor or other device being driven by the circuit
10
. The current adjustment signal pin
60
is used to read in a voltage from a voltage divider
62
. This voltage divider
62
is formed from a first resistor
64
and second resistor
66
. The voltage divider
62
provides a voltage signal to the current adjustment signal pin
60
that is used as basis for comparison against the input of the sensor input negative pin
36
and sensor input positive pin
38
. This comparison is used to control the power flow through the MOSFET
14
. If the voltage of the current adjustment pin
60
is greater than the voltage across the sensor negative pin
54
and sensor positive pin
56
, then the power to the MOSFET
14
is allowed to flow in an unrestricted manner from the drive pin
16
. However, when the voltage across the sensor negative pin
54
and sensor positive pin
56
exceeds the voltage on the current adjustment pin
60
, the power to the MOSFET
14
is restricted or turned off. This controls the power flow to the motor or other driven device and limits the current flow to the device or motor.
The inhibit sensor pin
68
allows for either a temperature or resistor-type configuration to provide a control signal to shut down of the MOSFET
14
. The inhibit sensor pin
68
may be used as a general purpose inhibit pin. Finally, the ground signal pin
70
is used as a return ground. The ground signal pin
70
is connected to the original power source ground
72
.
The primary function of this integrated circuit chip
12
and circuit
10
is to control the speed of a DC brush motor by driving the gate of an N-channel enhancement mode power MOSFET
14
with a pulse-width modulation signal through resistor network
18
in a hi-side drive configuration.
FIG. 2
of the drawings is a subset schematic of the application diagram of FIG.
1
. As shown in
FIG. 2
of the drawings, the prior art design teaches the connection of the current adjustment signal pin
60
through a voltage divider
62
that is powered by the voltage regulator pin
48
. The voltage diver
62
is formed from first resistor
64
and a second resistor
66
joined a connection point
68
. Because the voltage regulator pin
48
supplies a constant voltage power supply to the voltage divider
62
, the current adjustment signal pin
60
is maintained at a constant voltage level that is a percentage of the voltage supplied by the voltage regulation pin
48
output.
This prior art system suffers from several disadvantages including the inefficient use of a voltage protection circuit, the inefficient use of available voltage information, and a reduction of the available power for the motor circuitry. The inefficiencies of the operation of this circuitry are easily understood by reviewing the operating characteristics of this circuit.
FIG. 4
of the drawing showns the relationship between an input voltage VCC and an output voltage of the regulator VREG. As shown by
FIG. 4
of the drawings, for different VCC the VREG remains a consistent voltage level. Because the prior art teaches a circuit for deriving the voltage limiting signal, as shown by line VLIM, from the constant voltage signal VREG, the voltage limiting signal will also remain at a constant voltage level that is independent of the input voltage VCC.
FIG. 5
of the drawings shows the voltage limiting signal VLIM of
FIG. 4
, and adds the maximum power signal VMAX that shows the relationship of the maximum available power output for the motor circuitry. As the maximum power signal VMAX available to the motor increases, the output approaches the protection level VLIM. As noted by the voltage limiting signal VLIM shown in this chart, the voltage limiting signal VLIM is constant and independent of the maximum available power output VMAX for the operation of the motor. Thus by maintaining the voltage limiting signal VLIM at a consistent level,
CEI Co., Ltd.
Masih Karen
Pieper David B.
Waddey & Patterson
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