Current regulating circuit for EM proportional valve - provides current sensing in both supply and feedback paths with summing of both components

摘要

The coil is regulated by a pulsed voltage fed from a modulator (10,17) receiving the actual and desired voltage, the actual voltage being derived from a first measuring resistor (3). The measurement device has two measuring resistors (3,31) one being in the feedline from the positive potential (4) to the power transistor (1). A second resistor (31) is coupled via a freewheeling diode (30), parallel to the coil (7). Parallel to the second resistor (31) is an operational amplifier (34) with feedback (32,36) and the output of this, together with the output of a buffer (21,41) across the first resistor, is summed via a resistor (40) to the modulator. ADVANTAGE - Connection errors cannot destroy measuring resistor.