System for sharing power and signal pins on a motor controller

Details System for sharing power and signal pins on a motor controller System for sharing power and signal pins on a motor controller

2002-09-19

2004-06-08

Masih, Karen (Department: 2837)

Electricity: motive power systems

Switched reluctance motor commutation control

C318S569000, C318S560000, C318S650000, C318S567000

Reexamination Certificate

active

06747425

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to motor controllers, and more specifically, to the sharing of signal and power pins on a motor controller.
2. Background Art
The direct current (DC) motor was one of the earliest machines used to convert electrical power into mechanical power. A permanent magnet (PM) converts electrical energy into mechanical energy through the interaction of two magnetic fields. One field is produced by a permanent magnet assembly and the other field is produced by an electrical current flowing in the motor windings. The two fields result in a torque that tends to rotate a rotor of the DC motor. As the rotor turns, the current in the windings is commutated to produce a continuous torque output. The permanent magnet (PM) motor is likely the most commonly used DC motor, but there are also other type of DC motors such as shunt that act in a similar fashion wherein the shunt wound field is permanently energized, and behaves like a permanent magnet.
In a permanent magnet motor, a coil of wire called the armature is arranged in the magnetic field of the magnet so that it rotates when a current is passed through it. A coil of wire moving in a magnetic field induces a voltage in the coil, and the current caused by applying a voltage to the coil therefore causes the armature to rotate and generate a voltage.
There is a back electromotive force (EMF) in the induced voltage caused by the armature's movement that tends to cancel out the applied voltage so that the actual voltage across the armature is the difference between the applied voltage and the back EMF. The value of the back EMF is determined by factors such as the speed of rotation and the strength of the magnet. It should also be apparent that if you apply more voltage the motor will speed up, apply less and it will slow, which is the basic function of a speed controller does, which varies the voltage applied to the motor.
DC motors typically operate from a direct current (DC) power source, wherein the movement of the magnetic field is achieved by switching current between coils within the motor in a process called “commutation”. Many DC motors are brush-type, and have built-in commutation, so that as the motor rotates, mechanical brushes automatically commutate coils on the rotor. There are various forms of motor speed control of DC motors in the prior art. One method to control the rotation speed of a DC motor is to control the motor driving voltage. For example, the higher the voltage—the higher the speed of the motor. In many applications a simple voltage regulation causes a significant power loss on the control circuit, requiring a pulse width modulation (PWM) scheme for more efficient DC motor control. The PWM technique operates by alternating the operating power to the motors, by turning the motor “on” and “off” to modulate the current to the motor. It is the ratio of “on” time to the “off” time that determines the speed of the motor. For certain applications it is necessary to change the direction of rotation for the motor. Normal permanent magnet motors change the rotation by changing the polarity of the operating power, such as switching from negative power supply to positive. The change in direction is typically implemented using a relay or an H bridge circuit.
A brushless DC motor relies on an external power drive to perform the commutation of stationary winding, generally copper, on the stator. The changing stator field causes the permanent magnet rotor to rotate. A brushless permanent magnet motor is the normally the optimal choice with respect to torque versus weight, but are also more expensive.
Electronically commutated brushless DC motor systems are used as drives for blowers and fans used in electronics, telecommunications and industrial equipment applications. There is a wide variety of different brushless motors for various applications. Some are designed to rotate at a constant speed, such as in disk drives, while others control the speed by varying the applied voltage, such as the motors used in fans. Some brushless DC motors even have a built-in tachometer that generates pulses as the motor rotates. In the commercial environment, users select brush type DC motors when low system cost is a priority, and use brushless motors to satisfy higher end requirements.
There are numerous high volume commercial applications for DC motors and motor controllers. For example, the market for cellular phone vibrating motor systems, used to provide a silent “ringing” system is a 300 to 400 million units per year. In addition, the market for other simple motors is an additional 400 million/year. Therefore, even a small incremental cost saving is very significant.
It is reported by a major cell phone maker that this motor is one of the top failure mechanisms in cellular phones. These failures are caused by brush contact problems in brush type motors. These motors operate at a high speed, which is stressful on the brushes, making a brushless motor more attractive, though more costly.
There are many examples of pin sharing in the prior art. A concept of sharing a voltage supply and input pins is described in U.S. Pat. No. 3,735,378 relating to lighting systems and U.S. Pat. No. 5,247,239 discloses a voltage converter. U.S. Pat. No. 3,753,378 relates to a lamp failure indicating apparatus, wherein control signals generated from two detector networks detecting the operation of two lamp arrays are provided to an output amplifier through two diodes.
Pin sharing is also commercially available from companies such as National Semiconductor, Allegro Microsystems, and Melexis. Their datasheets generally show a method of sharing voltage supply with the output, in what is commonly called a two wire current loop. This configuration is well known in the art and illustrated in FIG.
1
. The supply voltage
5
connects to the pin sharing circuit
10
and there is a current sensor
15
coupled to the supply line to sense the current into the device
10
. A more common example of pin sharing it the common telephone that shares supply voltage with both input and output wires, with a switching system disposed between the phone company system and the residential phones.
Another example of pin sharing is described in U.S. Pat. No. 6,300,736 ('736), where there are no power supply pins. The power supply voltage for the Hall plate and Hall amplifier are taken from the “Off” output pin, through a switch. A complex digital controller synchronizes the Vdd switch and the gate drive of the power FETs to insure an uninterrupted Vdd. The block diagram of '736 illustrates this complex approach to sharing, requiring two voltage regulators, complex switching and timing circuitry, high voltage (40V) transmission gates, etc. The higher complexity of '736 is only a useful advantage in low voltage applications such as 2V or 3V, which are a very small portion of the total market for two phase brushless DC motors.
The Japanese Patent Application Laid-Open No. 4-317598 ('598) discloses a motor driving circuit and a fan driving circuit, wherein the fan driving circuit can be driven without providing a power supply by counter electromotive force generated in each coil while a motor is driven. The switching transistors are individually switched ‘On’ and ‘Off’ to rotate, and current caused by counter electromotive force, which is generated in each coil, enters into a fan driving circuit transistor capable of operating as a regulator. Thus, each terminal of each of the switching transistor switchably connects to the fan driving circuit transistor. The '598 patent does not disclose that the magnet sensor detects the rotor magnet, and that the regulator supplies power to the magnet sensor.
What is needed is a cost-effective and simplistic scheme for pin sharing. The pin sharing scheme should be flexible to allow incorporation in different designs. Such a scheme should also be practical for manufacturing concerns so as to be simple to incorporate into present manufactured des

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