Method and apparatus for braking a polyphase DC motor

Abstract

A circuit (10) for braking a polyphase dc motor (12) includes a circuit (38) for producing an output signal indicating that the motor has slowed at least to an actual rotational speed and a braking circuit (42-44, 26-28) to brake the motor (12) when the output signal indicates that the motor has slowed at least to an actual rotational speed. The circuit (38) for producing an output signal indicating that the motor (12) has slowed at least to an actual rotational speed includes a first counter (70) for counting pulses of a speed signal, which may be a standard tach signal. The first counter (70) produces a first output when the first counter (70) reaches a first predetermined pulse count. A second counter (72) counts clock pulses from a clock generator (48) to produce a second output when the second counter (72) reaches a second predetermined pulse count. The first output is connected to restart the first (70) and second (72) counters, and the second output provides an indication when the frequency of the speed signal is lower than a desired ratio to the clock pulse frequency.

Dependencies are inferred from the claim text.