Braking of single coil BLDC motors
A method for braking a single coil BLDC motor includes iterating a plurality of times through a sequence of: a braking state which lasts a braking period; and a high impedance state which lasts a cool down period. The current runs through the single coil during the braking state and no current runs through the single coil during the high impedance state. The transiting from the braking state to the high impedance state is done when the motor operates in generator mode.
1. A method for braking a single coil BLDC motor, the method comprising iterating a plurality of times through a sequence of:
a braking state which lasts a braking period, and
a high impedance state which lasts a cool down period, wherein current runs through the single coil during the braking state and wherein no current runs through the single coil during the high impedance state,
wherein transiting from the braking state to the high impedance state is done when the motor operates in generator mode, and
wherein transiting from the high impedance state to the braking state is done when the ratio of the cool down period and the braking period is at least 5%.
2. The method according to claim 1 , wherein transiting from the braking state to the high impedance state is done when a current threshold is reached.
3. The method according to claim 1 , the method comprising a clamping function for absorbing a flyback pulse induced by transiting from the braking state to the high impedance state such that a supply voltage of the motor is clamped to a maximum voltage.
4. The method according to claim 1 wherein the cool down period is adjusted in function of a signal indicative of an operating temperature induced by the clamping function.
5. The method according to claim 2 , wherein the current threshold is adjusted in function of a signal indicative of an operating temperature induced the clamping function.
6. The method according claim 1 , the method comprising connecting a load parallel with the motor when a supply voltage of the motor reaches a first predefined voltage level and disconnecting the load when the supply voltage drops below a second predefined voltage level.
7. A motor driver for driving a single coil BLDC motor, the motor driver comprising:
a controller,
a full bridge output driver comprising a pair of high side transistors and a pair of low side transistors connected with the single coil for controlling a current through the coil,
wherein the controller is configured for switching the transistors of the full bridge driver for braking the motor, thereby iterating a plurality of times through a sequence of a braking state which lasts a braking period and a high impedance state which lasts a cool down period, wherein current runs through the single coil during the braking state and wherein no current runs through the single coil during the high impedance state and wherein transiting from the braking state to the high impedance state is done when the motor operates in generator mode and wherein transiting from the high impedance state to the braking state is done when the ratio of the cool down period and the braking period is at least 5%.
8. The motor driver according to claim 7 , wherein the controller is configured for switching the motor to a braking state by
switching on both high side transistors, both low side transistors, or switching on one high side transistor or one low side transistor, such that the current can recirculate through the transistor which is switched on, and the body diode of the opposing high side, respectively low side transistor, or by
active braking in which the transistors are switched such that a current path is generated by the BEMF voltage of the rotating motor, such that the motor is in generator mode.
9. The motor driver according to claim 7 , the motor driver comprising a current limiter which is configured for triggering the controller to switch from the braking state to the high impedance state when the phase current reaches a current threshold.
10. The motor driver according to claim 7 , the motor driver comprising a clamp which is configured for limiting a maximum voltage which is applied to the full bridge output driver, by providing a drain path to current caused by a flyback pulse induced by transiting from the braking state to the high impedance state.
11. The motor driver according to claim 8 wherein the cool down period is set by the controller.
12. The motor driver according to claim 8 , the motor driver comprising a load, and the controller being configured for connecting the load parallel with the motor when a supply voltage of the motor reaches a first predefined voltage level and disconnecting the load when the supply voltage drops below a second predefined voltage level.
13. The motor driver according to claim 8 wherein control of the cool down period is achieved by a PWM controller.
14. The motor driver according to claim 8 wherein the controller is configured for adjusting the current threshold in function of a signal indicative of an operating temperature of the clamp.