An operation coil drive device includes a drive control unit to perform control to set, for a semiconductor switching element to switch on and off the source voltage applied to an operation coil of a magnetic contactor, a larger ON/OFF time ratio for a circuit-closing control and a smaller ON/OFF time ratio for a holding control, wherein the drive control unit includes: a circuit-closing-control inductance calculation unit to calculate an inductance of the operation coil immediately after a start of the circuit-closing control; a circuit-closing-control resistance value calculation unit to calculate a direct current resistance value of the operation coil based on the calculation result; and a circuit-closing-control switching correction unit to correct the ON/OFF time ratio of the semiconductor switching element for the circuit-closing control based on the calculation result.

A load drive device that drives and controls an inductive load based on a PWM signal from a microcomputer is provided, and the load drive device has excellent reliability and responsiveness capable of quickly detecting disconnection of the inductive load. The load drive device includes a microcomputer and a driver circuit that drives an inductive load by a pulse width modulation signal of a constant cycle based on a control command from the microcomputer, in which the driver circuit includes a current monitoring circuit that monitors a current flowing through the inductive load, and a disconnection diagnosis circuit that detects disconnection of the inductive load based on a current value detected by the current monitoring circuit, and the disconnection diagnosis circuit obtains a change amount of a current value detected by the current monitoring circuit, and when the change amount is equal to or less than a predetermined threshold, determines that the inductive load is disconnected and notifies the microcomputer of the disconnection.

A drive circuit for controlling a solenoid valve having a solenoid coil and a poppet that translates therein is provided. The drive circuit includes a supply bus, a return bus, a flyback circuit, and a switch. The supply bus is configured to couple the solenoid coil to a power supply and supply a coil current. The return bus is configured to provide a ground path for the coil current. The flyback circuit is coupled in parallel to only the solenoid coil. The flyback circuit includes only a bipolar diode. The switch is coupled in series with the solenoid coil and configured to couple and decouple the solenoid coil to the return bus.

A solenoid system and method can include: providing an energizing voltage to a coil of a solenoid; providing an AC signal superimposed onto the energizing voltage; detecting current through the coil including an AC current amplitude induced by the AC signal and including a DC offset current amplitude; determining the AC current amplitude is a low AC current amplitude based on an armature within the solenoid being in a retracted position or determining the AC current amplitude is a high AC current amplitude based on the armature being in an extended position with the control logic, and where the AC current amplitude is determined utilizing the AC signal for synchronous demodulation; and determining a temperature fault based on the DC offset current amplitude falling below a DC offset current amplitude threshold.

A constant-current controller that supplies a constant current to an inductive load. This controller comprises an electric control circuit module. The electric control circuit module comprises a primary switch and a secondary switch. During a time interval in which the primary switch is closed (t.sub.on), the secondary switch is open and the voltage across the inductive load is equal to the source voltage (V.sub.s). At time t.sub.on until the end of a time interval (T), zero volts appears across the inductive load. During this interval, current continues to flow as supplied by the energy stored in the inductance. The periodic current in the inductive load becomes constant with a sufficiently large PWM switching frequency and is dependent upon the parameters of the control circuit and the duration of t.sub.on.

A solenoid drive device includes a first solenoid drive circuit, a second solenoid drive circuit, a selection circuit, and circuitry. The circuitry controls the first switching element and the second switching element with a duty control in a control cycle according to acquired values of the first drive current and the second drive current so that a first on/off switching direction of the first switching element at a start timing of the control cycle is opposite to a second on/off switching direction of the second switching element at the start timing. The circuitry determines whether a failure in at least one of the selector, the first solenoid drive circuit, and the second solenoid drive circuit occurs based on a change in the selection detection signal in a period during which an on/off state of the first switching element is different form an on/off state of the second switching element.

A current control circuit controls a linear solenoid valve provided in an oil pressure circuit to feed back an output oil pressure. The current control circuit includes a PWM signal generation part, a target setting part, a duty ratio setting part and a vibration detection circuit. The target setting part sets a target current value, which is a target value of an excitation current of the linear solenoid valve and periodically varies with a predetermined dither amplitude and a dither period longer than a pulse period of the PWM signal. The self-excited vibration detection part calculates a phase difference between the target current value and an actual current value and detects a presence of self-excited vibration because of a resonance of a feedback of the output oil pressure and driving of the linear solenoid valve in the dither period when the phase difference decreases relative to an increase in the target current value or the phase difference increases relative to a decrease in the dither period.

The magnetic coil driving circuit of the magnetic contactor according to the present invention comprises a semiconductor switch configured to open or close a circuit for magnetizing or demagnetizing a magnetic coil; a pulse width modulation unit configured to output a pulse signal as a control signal for turning on or off the semiconductor switch; a control unit configured to output a control signal for changing a pulse width of the pulse signal to the pulse width modulation unit; and a temperature detection and protection unit configured to detect a temperature inside the magnetic contactor, output an output signal for turning off the semiconductor switch when the temperature exceeds an allowable temperature, and control the semiconductor switch by the pulse signal from the pulse width modulation unit when the temperature is within the allowable temperature.

A solenoid system and method can include: providing an energizing voltage to a coil of a solenoid; providing an AC signal superimposed onto the energizing voltage; detecting current through the coil including an AC current amplitude induced by the AC signal and including a DC offset current amplitude; determining the AC current amplitude is a low AC current amplitude based on an armature within the solenoid being in a retracted position or determining the AC current amplitude is a high AC current amplitude based on the armature being in an extended position with the control logic, and where the AC current amplitude is determined utilizing the AC signal for synchronous demodulation; and determining a temperature fault based on the DC offset current amplitude falling below a DC offset current amplitude threshold.

A semiconductor device includes an output driving circuit configured to output an output current to an output terminal; a detection resistor connected between the output terminal and the output driving circuit; an amplification unit configured to output an analog detection signal generated by amplifying a voltage between both ends of the detection resistor; a current generation circuit configured to output a reference current; a reference resistor connected between the current generation circuit and a ground and configured to output a reference voltage according to the reference current; an A/D converter configured to convert the analog detection signal into a digital detection signal using the reference voltage as a reference; and a control circuit configured to control the output current output from the output driving circuit according to the digital detection signal. The detection resistor has a same temperature characteristics as the reference resistor.