Importance

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Abstract

A circuit for operating a polyphase dc motor, for example of the type having a plurality of 'Y' connected stator coils, has circuitry for unambiguously determining the actual instantaneous position of the rotor of the motor, circuitry for determining a desired rotor position precedent to executing a desired commutation sequence, and circuitry for executing the desired commutation sequence when the circuit for determining the actual instantaneous position of the rotor detects that the rotor is actually in the desired rotor position. The circuitry for unambiguously determining the actual instantaneous position of the rotor includes a back emf amplifier switchably connected to at least one floating coil in accordance with sequence signals received directly from a sequence generator, and circuitry for determining when the voltage received by the back emf amplifier crosses zero from a predetermined direction. In one embodiment, the circuit includes mask circuitry for inhibiting the zero crossing detection circuitry for a predetermined time after a change in the commutation sequence. The mask circuitry includes clocked up and first and second down counters, the second down counter being inhibited to be clocked until the first down counter has reached a predetermined count, and the zero crossing circuitry being inhibited until at least the second down counter has completed its count. When a zero crossing is detected, the count of the up counter is loaded into both the first and second down counter, then the up counter is reset to begin a new commutation period count.

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First Claim