Motor drive circuit

1. A motor drive circuit configured to supply drive currents to drive coils with a plurality of phases of a motor to drive the motor, comprising:

a trapezoidal wave signal generation circuit configured to output a trapezoidal wave signal whose inclination is changed with a rotation speed of the motor or a target rotation speed of the motor;

a plurality of output transistors configured to output the drive current to the drive coils, respectively, in accordance with the trapezoidal wave signal; and

an amplifier circuit configured to amplify the trapezoidal wave signal in accordance with the rotation speed or the target rotation speed, to be supplied to each of the plurality of output transistors,

wherein the trapezoidal wave signal generation circuit includes a current supply circuit configured to supply a charging/discharging current for charging/discharging a capacitor, in accordance with the rotation speed or the target rotation speed, and the trapezoidal wave signal generation circuit is configured to generate the trapezoidal wave signal including an inclination part whose inclination is according to the inclination of rising or falling of a voltage across the capacitor,

wherein the amplifier circuit is configured to amplify the trapezoidal wave signal in proportion to the rotation speed or the target rotation speed, and

wherein the current supply circuit is configured to supply the charging/discharging current in accordance with an increase in the rotation speed or the target rotation speed, the charging/discharging current increasing more greatly as compared to an increase in proportion to an increase in the rotation speed or the target rotation speed.

2. The motor drive circuit according to claim 1 , further comprising:

an input terminal to which a speed control voltage according to the target rotation speed is inputted,

wherein the trapezoidal wave signal generation circuit is configured to change inclination of the trapezoidal wave signal based on the speed control voltage.

3. The motor drive circuit according to claim 1 , further comprising:

a timing control circuit configured to output an energization timing signal indicating timing for energizing each of the drive coils with the plurality of phases, based on a rotation position of a rotor of the motor corresponding to a phase of said each of the drive coils with the plurality of phases,

wherein the trapezoidal wave signal generation circuit is configured to start rising or falling of the trapezoidal wave signal in accordance with the energization timing signal.

4. The motor drive circuit according to claim 2 , further comprising:

a timing control circuit configured to output an energization timing signal indicating timing for energizing each of the drive coils with the plurality of phases, based on a rotation position of a rotor of the motor corresponding to a phase of said each of the drive coils with the plurality of phases,

wherein the trapezoidal wave signal generation circuit is configured to start rising or falling of the trapezoidal wave signal in accordance with the energization timing signal.

5. The motor drive circuit according to claim 3 , further comprising:

a position detection circuit configured to detect the rotation position by comparing a voltage of each of the phases of the drive coils with the plurality of phases and a voltage of a neutral point of the drive coils with the plurality of phases.

6. The motor drive circuit according to claim 4 , further comprising:

a position detection circuit configured to detect the rotation position by comparing a voltage of each of the phases of the drive coils with the plurality of phases and a voltage of a neutral point of the drive coils with the plurality of phases.

7. The motor drive circuit according to claim 3 ,

wherein the motor includes drive coils with n phases (n is an integer greater than or equal to 3),

wherein the timing control circuit is configured to output the energization timing signal of [180×(n−1)/n] degree energization, and

wherein the trapezoidal wave signal starts rising or falling in timing of the energization timing signal, and stops rising or falling in timing before timing of 180-degree energization, in accordance with the rotation speed or the target rotation speed.

8. The motor drive circuit according to claim 4 ,

wherein the motor includes drive coils with n phases (n is an integer greater than or equal to 3),

wherein the timing control circuit is configured to output the energization timing signal of [180×(n−1)/n] degree energization, and

wherein the trapezoidal wave signal starts rising or falling in timing of the energization timing signal, and stops rising or falling in timing before timing of 180-degree energization, in accordance with the rotation speed or the target rotation speed.

9. The motor drive circuit according to claim 5 ,

wherein the motor includes drive coils with n phases (n is an integer greater than or equal to 3),

wherein the timing control circuit is configured to output the energization timing signal of [180×(n−1)/n] degree energization, and

wherein the trapezoidal wave signal starts rising or falling in timing of the energization timing signal, and stops rising or falling in timing before timing of 180-degree energization, in accordance with the rotation speed or the target rotation speed.

10. The motor drive circuit according to claim 6 ,

wherein the motor includes drive coils with n phases (n is an integer greater than or equal to 3),

wherein the timing control circuit is configured to output the energization timing signal of [180×(n−1)/n] degree energization, and

wherein the trapezoidal wave signal starts rising or falling in timing of the energization timing signal, and stops rising or falling in timing before timing of 180-degree energization, in accordance with the rotation speed or the target rotation speed.