Drive circuit device for inductive load

A drive circuit device for an inductive load, comprising:

• (a) a current supply circuit having a power source and drive transistor means, said inductive load that is to be a subject of control being incorporated in said current supply circuit in series relation to said drive transistor means;
• (b) detecting resistor means incorporated in said current supply circuit in series relation to said drive transistor means, wherein when said drive transistor means is turned on, a voltage drop occurs at said detecting resistor means in proportion to supply current flowing through said inductive load, said voltage drop serving as detecting voltage;
• (c) operational amplifier having an output terminal, a noninverting input terminal and an inverting input terminal, reference voltage being applied to said noninverting input terminal, said detecting voltage at said detecting resistor means being applied to said inverting input terminal, and said output terminal being connected to a control terminal of said drive transistor means, wherein said operational amplifier controls said drive transistor means in such a manner that said detecting voltage at said detecting resistor means is made substantially equal to said reference voltage, thereby controlling said supply current flowing through said inductive load to a predetermined value;
• (d) switching means operative in response to a control signal for connecting said control terminal of said drive transistor means to a ground side and for disconnecting said control terminal of said drive transistor means from said ground side, wherein when said control terminal of said drive transistor means is disconnected from said ground side so that said drive transistor means is turned on, supply current is supplied to said inductive load, and wherein when said control terminal of said drive transistor means is grounded so that the latter is turned off, supply of the supply current to said inductive load is stopped;
• and
• (e) a feed-back circuit having response means and feed-back resistor means, wherein said response means is operative in response to the turning-off of said drive transistor means for supplying feed-back current to said feed-back resistor means to generate voltage at the same, said voltage generated at said feed-back resistor means being supplied, as feed-back voltage, to said inverting input terminal of said operational amplifier, wherein said operational amplifier controls said feedback current flowing through said feed-back resistor means in such a manner that said feed-back voltage is made substantially equal to said reference voltage, and wherein said response means is operative in response to the turning-on of said drive transistor means for stopping supply of the feed-back current to said feedback resistor means.