Method for operating a DC motor
Method for operating a DC motor, where the DC motor is supplied with a variable DC voltage via a bridge circuit from a supply voltage and formed by a first, a second, a third and a fourth controllable switch, wherein the DC voltage is varied by pulse width modulation of the control signals driving the controllable switches of the bridge circuit. A control arrangement drives the bridge circuit by pulse width modulation, after the first switch connecting the DC motor to the supply voltage has been switched off, switches on the second switch connected to a ground terminal, or vice versa. The control arrangement automatically inserts a drive pause between the first or second switch being switched off and the second or first switch being switched on, whereby a bridge circuit voltage present at the DC motor is limited by a resultant maximum settable duty cycle to a maximum value.
1. A method for operating a DC motor,
in which the DC motor is supplied with a variable DC voltage via a bridge circuit fed from a supply voltage and formed by a first, a second, a third and a fourth controllable switch, wherein the DC voltage is varied by pulse width modulation of control signals driving the controllable switches of the bridge circuit,
in which a control arrangement drives the bridge circuit by pulse width modulation, which control arrangement, after the first switch connecting the DC motor to the supply voltage has been switched off, switches on the second switch connected to a ground terminal, or vice versa, wherein the control arrangement automatically inserts a drive pause between the first or second switch being switched off and the second or first switch being switched on, as a result of which a bridge circuit voltage present at the DC motor is limited by a resultant maximum settable duty cycle to a maximum value, which is less than the supply voltage, and the control arrangement can also be switched over into a DC mode in which the DC motor is supplied with the supply voltage,
in which method the control arrangement has a control unit, which generates a drive signal in predefined control time durations, said drive signal containing information about a duty cycle of the pulse-width-modulated signal or a supply voltage for the DC motor proportional thereto, wherein a control time duration is a multiple of a period duration of a pulse-width-modulated control signal,
wherein where the bridge circuit voltage to be set for the DC motor is greater than voltage resulting from the maximum value of the duty cycle, the control unit, during a predefined drive time duration, which is a multiple of the control time durations, drives a first number of control time durations, in which the bridge circuit is operated with a pulse-width-modulated signal at a maximum duty cycle, and a second number of control time durations, in which the bridge circuit is operated in the DC mode, wherein a ratio of the first number and the second number of control time durations is derived from a difference value between the bridge circuit voltage to be set and the voltage corresponding to the maximum value.
2. The method as claimed in claim 1 , in which the control unit is formed with a microprocessor, and a circuit arrangement driving the bridge circuit is formed with an integrated circuit.
3. The method as claimed in claim 1 , in which control time durations of the first number of control time durations, in which the bridge circuit is operated with the pulse-width-modulated signal at the maximum duty cycle, and control time durations of the second number of control time durations, in which the bridge circuit is operated in the DC mode, succeed one another alternately within the predefined drive time duration.
4. The method as claimed in claim 3 , in which the control time durations of the first number of control time durations and the control time durations of the second number of control time durations are distributed uniformly within the predefined drive time duration.
5. The method as claimed in claim 2 , in which control time durations of the first number of control time durations, in which the bridge circuit is operated with the pulse-width-modulated signal at the maximum duty cycle, and control time durations of the second number of control time durations, in which the bridge circuit is operated in the DC mode, succeed one another alternately within the predefined drive time duration.
6. The method as claimed in claim 5 , in which the control time durations of the first number of control time durations and the control time durations of the second number of control time durations are distributed uniformly within the predefined drive time duration.