Load-drive controller

1. A load-drive controller for controlling a drive of a load by setting a load current to be a desired current to be applied to the load, said load-drive controller comprising:

a voltage source for obtaining a reference voltage which is equivalent to a setting current of the desired current;

an H bridge circuit comprised of output transistors for controlling the drive of the load;

a first comparing unit for comparing a value of a load current supplied from the H bridge circuit and the desired current value of the setting current;

a PWM control unit for generating a control signal to control the load current;

an output drive unit for driving and controlling the output transistors of said H bridge circuit based on the control signal; and

a load current monitoring unit for determining which is larger: a level shifted value of the setting current or a peak hold value of the load current,

wherein said PWM control unit controls increase or decrease of the load current based on a comparison result of the first comparing unit and a determination result of the load current monitoring unit.

2. The load-drive controller according to claim 1 , wherein said PWM control unit includes control mode selection means for selecting at constant intervals a first mode in which the load current is increased or a second mode in which the load current is decayed based on the comparison result of the first comparing unit, and for selectively performing the second mode or a third mode in which the load current is decayed faster than in the second mode,

wherein, in a predetermined duration of a predetermined period, in the case where the load current monitoring unit determines that the level shift equivalent value of the setting current is smaller than the peak hold equivalent value of the load current, the control mode selection means performs the third mode in the predetermined duration according to the determination result.

3. The load-drive controller according to claim 1 , further comprising a current detecting resistor which is connected to a load current output terminal of the H bridge circuit to convert the load current into a voltage equivalent to the load current value,

wherein said load current monitoring unit includes:

a peak hold circuit for holding a peak value of a detection voltage equivalent to the value of the load current generated in the current detecting resistance;

a level shift circuit for level-shifting the reference voltage by a predetermined value, the reference voltage being equivalent to the desired setting current obtained from the current setting voltage source; and

a second comparing unit for comparing an output value of the peak hold circuit and an output value of the level shift circuit.

4. The load-drive controller according to claim 3 , wherein said control mode selection means includes a decay selection command unit for selecting the second mode or the third mode based on a comparison result of the second comparing unit.

5. The load-drive controller according to claim 4 , wherein said PWM control unit includes first and second switching elements for switching a control signal of upper side transistors of the H bridge circuit in accordance with a selection command outputted of said decay selection command unit.

6. The load-drive controller according to claim 1 , having an integrated circuit formed on a semiconductor chip construction.

7. A load driving apparatus having a load-drive controller as defined in claim 1 .