Load driving and diagnosis system and control method

A load driving and diagnosis system that includes a switching circuit which feeds a current to a connected load, a voltage holding means which holds the output terminal voltage of the switching circuit at a predetermined value, and a current detection means which detects a current flowing into the load, wherein:

• a plurality of predetermined values is set as values of voltages at which the voltage holding means holds the output terminal voltage;
• a switching means is included for switching the plurality of predetermined values, at which the voltage holding means holds the output terminal voltage, according to the output of the current detection means;
• and
• the plurality of predetermined values at which the output terminal voltage is held includes a first predetermined value which is larger than the value of a supply voltage and at which a load current that flows when the load is energized or de-energized is quickly blocked, and a second predetermined value that is smaller than the first predetermined value and is slightly larger than the value of the supply voltage;
• and
• the load driving and diagnosis system further comprises,
• a diagnostic detection means that detects whether the current detected by the current detection means is identical with the predetermined value, a holding means that sustains the output signal of the diagnostic detection means for a predetermined time, and a control circuit that controls the on and off states of the switching circuit according to the output of the holding means, and outputs the output of the holding means to outside;
• and
• a state transition means that changes states thereof according to the output of the diagnostic detection means and the output of the holding means, and a diagnostic output means that outputs the output of the state transition means to outside.