| 摘要 |
PURPOSE:To reduce a loss of a collector of a transistor which drives a proportional valve and to restrain a rise in interior temperature of the device by adopting a switching system for a drive circuit wherein intermittent electric current is directly supplied to a solenoid coil. CONSTITUTION:A comparator 21 which is composed of an arithmetic amplifier receives a control voltage VA at the noninverted input terminal and a terminal voltage VB of a resistance 23 which detects a valve current flowing through a solenoid coil 22 at the inverted input terminal, while inverting its output dependently on the relationship between the intensities of both the voltages VA and VB to turn on or off a transistor 24. A transistor 26 is turned on and off in company with the on and off actions of the transistor 24 and directly supplies the solenoid coil 22 with an intermittent current. The switching frequency of the transistor 26 depends on a delay of the input or output response of the arithmetic amplifier and the time constant. |
