PULSE WIDTH MODULATED CONSTANT CURRENT SERVO DRIVER

摘要

A method and apparatus for controlling a coil (40) operated hydraulic valve (48) employs a constant current source (36) to consistently control valve response (Pu) irrespective of variations in power supply voltage and coil resistance (Ru). A switching circuit (58) controls the delivery of constant current pulses from the current source (36) to the coil (40) in accordance with a series of pulse width modulated control signals whose duty factors (tu/tu) are proportionate to preselected values of hydraulic output pressures (Pu) developed by the valve (48). A voltage regulator circuit (38) provides regulated supply voltage to the constant current source (36) in order to reduce variations in the coil current (Iu) at small pulse widths.