Hall Effect Sensors for Electric Power Steering
Sensors for rotational orientation of a shaft are often Hall Effect sensors. Hall Effect sensors are
magnetically biased transducers that vary output voltage or current in response to changes in a magnetic
field. Hall Effect sensors can be designed to sense rotary movement or torque action of a steering-wheel
shaft. The rotation of the shaft changes the IC's position with respect to the magnets and thus detects the
change in flux density. Rotary sensors are designed to measure up to 360 degrees, or full circle. The Hall
Effect sensor gets its name from Edwin Hall, who, in 1879 discovered that a voltage difference can be
produced across an electrical conductor where the magnetic field is perpendicular to the direction of
current flow.
CAN Transceivers for Electric Power Steering
CAN is an acronym for Controller Area Network and refers to a fault-tolerant communications protocol that is
flexible for system design, supports multiple network topologies, and has become a de facto standard for
high integrity serial communications in industrial and automotive embedded applications. In a CAN network,
several short pieces of data like a motor???s run status, temperature, or RPM is broadcast over the entire
network at up to 1 megabit per second (Mbps.)
Watchdog Timers for Electric Power Steering
The function of a Watchdog Timer (WDT) is to trigger a system reset or some corrective action when the main
processor stops regularly sending a signal to the watchdog timer. Embedded systems rarely have a
"ctrl-alt-delete" such that a human can reset them if they suddenly stop working, and a power cycle may not
be feasible. Therefore, embedded systems with critical functions may have a WDT to force a reboot of the
processor in case it is unable to execute instructions or simply does not send the WDT a signal in time.
Low Drop Out Regulators for Electric Power Steering
A Low Drop Out (voltage) Regulator is a voltage regulator that automatically maintains a constant voltage
level and features a low potential at below which it can no longer reliably regulate. LDOs stabilize input
or supply voltages. LDOs are instrumental in enabling the power-efficient portables in use today because
they enable very low minimum operating voltages.
Processors for Electric Power Steering
The term "processor" refers to an electronic device that performs computational functions and carries out
the instructions of a stored program. Other terms for processor are microprocessor, central processing unit,
and digital signal processor. Essentially, the processor refers to "the brains of a computer."
DC/DC Converters for Electric Power Steering
DC/DC Converters are circuits that convert DC voltage from one level to another and maintain that voltage at
a constant level. Electronic systems often have several sub-circuits, each with its own voltage level
requirement that may be higher or lower than the main power supply. Step-up (boost) converters raise a
voltage to a higher level, while step-down (buck) converters lower it.
Charge Pumps for Electric Power Steering
A charge pump is a type of DC/DC converter that uses multiple capacitors and switching devices to produce an
output voltage either higher or lower than the input. Battery-powered and handheld devices will often employ
charge pumps as an alternative to low-dropout regulators (LDOs) because they have higher efficiencies, lower
noise levels, and better thermal management properties. Furthermore, charge pumps can lower costs and board
space requirements because they do not require inductors. Switched-mode regulators offer even higher
efficiencies than charge pumps, but they are more complex and generate higher noise levels.
3-Phase Pre-Drivers for Electric Power Steering
A three-phase predriver is essentially three gate drivers integrated on a single IC ??? one for each phase
of a three-phase electric motor. It is a common misconception that most power MOSFETs or IGBTs can be driven
directly from a logic circuit or microcontroller. The reality is that most of these high-power transistors
require current and voltage levels that far exceed the capacity of control electronics. A gate driver is, in
essence, a power amplifier which provides an interface between a low-power PWM signal and the gate of an
IGBT/MOSFET transistor.
Signal Conditioners for Electric Power Steering
The term "signal conditioning" refers to the preservation of a signal through circuit protection, buffering,
isolating, or boosting a signal. Analog signal conditioners are also used to preserve the accuracy and
legibility of measurements. In a control system, measurements such as temperature, pressure, level, flow,
weight, or speed, for example, are used to determine if more or less control should be applied. This
measurement, or feedback, typically has a long way to travel before it is used by the processor, displayed,
or recorded. Signal conditioners boost and ???clean??? the signal to help maintain signal integrity and/or
isolate it from other circuitry.
Power Switches for Electric Power Steering
A MOSFET can be used as a switch for a power source, turning the current on and off by applying a voltage
bias on the gate of the MOSFET. Important characteristics for a MOSFET used as a power switch are a low
ON-resistance (R
DS(ON)
), the reverse current protection of the MOSFET, the amount of power it can dissipate, and a high maximum
continuous current. A low R
DS(ON)
is important when switching high current loads. When operating as a pass-through switch, power dissipation
of the MOSFET depends upon the ON resistance as well as the current load that is being switched. A high
power dissipation will increase operating temperature, affecting performance and can cause failure.
Power MOSFETs for Electric Power Steering
MOSFETs are also for power switching circuits. Unlike bipolar junction transistors (BJTs), the competing
type of power transistor, MOSFETs do not require a continuous flow of drive current to remain in the ON
state. Additionally, MOSFETs can offer higher switching speeds, lower switching power losses, lower
on-resistances, and reduced susceptibility to thermal runaway. In switched-mode power supplies (SMPSs),
MOSFETS are often used as the switching elements for regulation as well as for power factor correction
(PFC).
Current Monitoring for Electric Power Steering
Current monitors, or current sense amplifiers, are special purpose amplifiers that measure electrical
current. These amplifiers output a voltage that is proportional to the current flowing in the power rail, or
the supply/return to the load relative to ground. There are two references to current-shunt placement:
low-side refers to the return path from the load and is usually at a low voltage to ground. High-side is
with respect to the supply path to the load and is usually at a high voltage to ground. The decision to
place a current shunt in either position needs to be assessed based on the particular application.
Amplifiers should introduce as little noise as possible so that the signal transfers an accurate measure of
what it is sensing. Amplifiers can be identified by the device they are intended to drive (e.g., audio
amplifier), the input that they are to amplify (e.g. sensing amplifier), the frequency range of the signal
(e.g., RF, audio), and by the function that they perform (e.g. buffer or current-shunt amplifier) .
Position Sensors for Electric Power Steering
A position sensor is any device that permits position measurement. It can either be an absolute position
sensor or a relative one. Position sensors can be either linear or angular. Poisitioning Sensors are finding
their way into more handheld, medical and industrial devices every day. Knowing the position and orientaion
of a device or tool is critical for any modern control system to work accurately. Examples are as varied as
a smart phone, a drilling platform, or the attitude control of a Boeing 777.
