Non-feedback type load current controller

A load current controller comprising:

• a power supply driving circuit portion constructed by an in-series circuit comprising a driving power source, an inductive electrical load and an opening/closing element;
• and
• a power supply control circuit portion for controlling a pulse duty factor corresponding to a ratio between an ON pulse width and an ON/OFF period of the opening/closing element in response to the values of a predetermined supply target current and a driving power source voltage to be applied to the electrical load, wherein the power supply driving circuit portion comprises a current detecting resistor connected between the opening/closing element and a ground circuit of the driving power source, a current detecting amplifying circuit portion provided with an operational amplifier for amplifying the voltage between both the terminals of the current detecting resistor and a smoothening capacitor that is provided to at least one of an input circuit and an output circuit of the operational amplifier and achieves a measurement voltage substantially proportional to the average value of the voltage between both the terminals of the current detecting resistor, and a commutating circuit that is connected to the electrical load in parallel and subjects the load current supplied when the opening/closing element is under the close circuit condition to flow-back and attenuation when the opening/closing element is opened, and the power supply control circuit portion is equipped with a microprocessor supplied with power from a control power source unit that is supplied with power from the driving power source and generates a stabilized control power source voltage lower than the driving power source voltage, a multi-channel AD converter to which plural analog signals are input, and a non-volatile program memory that stores a load current control program in cooperation with the microprocessor and contains a program as an abnormality sign detecting unit, and wherein the output of the operational amplifier is input to the microprocessor through the multi-channel AD converter as a monitor voltage which is limited to a value not more than the control power source voltage, the abnormality sign detecting unit generates an abnormality notification instructing output when the relative error between the comparison target voltage corresponding to the predetermined supply target current and the monitor voltage is out of a band of a first permissible error width in which the relative error is slightly deviated from a normal value range, and the measurement voltage when the abnormality sign detecting unit carries out abnormality detection is set to a value less than the control power source voltage,
• wherein the pulse duty factor is determined based on the value of the predetermined supply target current, the value of the driving power source voltage, and an estimate value of electrical resistance of the electrical load, irrespective of an increase or decrease of the monitor voltage.