US Patent 7430102 Pulse width modulated servo clutch driver

Disclosed is a system and method for controlling a clutch associated with a solenoid using a pulse width modulated (PWM) signal, which keeps the current through the coil constant over a wide temperature range and fluctuations in line voltage. The system may include a voltage source, a switch (such as a FET), a current sensor, and a processor. The system controls the clutch by sampling the voltage source, sampling the current measured by the current sensor, and computing a duty cycle, which is then used to generate a PWM control signal.