Motor control unit
A motor control unit includes an H-bridge circuit, a current detection part and a control part. The current detection part includes current detection resistors provided at both sides of a DC motor. The control part feedback-controls high-side arm switches and low-side arm switches of the H-bridge circuit so that a detection value of the current detection part follows a target value. In the feedback control, normal control and current circulation control are performed alternately. In the current circulation control, either the high-side arm switches or the low-side arm switches are turned on for both of normal rotation time and reverse rotation time. The control part performs the feedback control based on a detection value of the current detection resistor, which has the same potential reference between the normal control and the current circulation control under the same rotation direction.
1. A motor control unit for controlling a current flowing in a DC motor, which has a first terminal and a second terminal, the motor control unit comprising:
an H-bridge circuit including a high-side arm circuit including two high-side arm switches connected in parallel to a power supply, a low-side arm circuit including two low-side arm switches connected in parallel to a ground, one of the two high-side arm switches and one of the two low-side arm switches being connected in series at a first connection node electrically connected to the first terminal of the DC motor, the other of the two high-side arm switches and the other of the two low-side arm switches being connected in series at a second connection node electrically connected to the second terminal of the DC motor;
a current detection part including, as current detection resistors for detecting the current flowing in the DC motor, a first resistor provided between the first connection node and the first terminal and a second resistor provided between the second connection node and the second terminal; and
a control part for feedback-controlling the high-side arm switches and the low-side arm switches of the H-bridge circuit so that a detection value of the current detection part follows a target value, the control part alternately performing as feedback control a normal control for turning on one high-side switch and one low-side arm switch at same time so that the current flows from the power supply to the ground through the DC motor and a current circulation control for turning on one of a) all the high-side arm switches and b) all the low-side arm switches at same time so that the current flows in a same direction as in a normal control time based on energy stored in the DC motor in the normal control time,
wherein the control part performs the feedback control based on the detection value of one of the first resistor and the second resistor in a forward rotation time, the control part performs the feedback control based on the detection value of the other of the first resistor and the second resistor in a reverse rotation time, and the control part performs the feedback control based on one of the detection values of the first resistor and the second resistor that has a same reference potential in the normal control and the current circulation control under a same rotation direction of the DC motor,
the current detection part includes a differential amplifier, which is common to the first resistor and the second resistor, and a selection switch for selectively connecting one of the first resistor and the second resistor and the differential amplifier; and
the control part controls the selection switch in correspondence to the rotation direction of the motor.
2. The motor control unit according to claim 1 , wherein the control part turns on all the low-side arm switches at same time in the current circulation time and performs the feedback control based on the detection value of the current detection resistor, which is at a low-potential side of the DC motor.
3. The motor control unit according to claim 1 , wherein:
the current detection part includes a reference voltage generation part for generating a predetermined reference voltage higher than the ground; and
the differential amplifier is connected to the reference voltage generation part.