Importance

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Abstract

In a commutation timing circuit for an electronically commutated motor (ECM), a solid state transconductance amplifier is used to convert the back emf appearing in an unenergized winding stage to a current. The current is then integrated in a capacitor, and at the correct voltage, a comparator generates the timing signal at the instant suitable for commutation of the winding stages. The transconductance amplifier has a differential input stage to which substantial degeneration has been provided to stabilize the transconductance. Subsequent stages of the amplifier, which include three current mirrors, exhibit substantially unity current gain. The circuit is provided with substantial degeneration to insure stability of the transconductance and with automatic self-nulling to correct imbalance of the amplifier. In accordance with a further aspect of the invention, a protective circuit is provided which is active during turn-on and turn-off to insure that the operating voltage applied to the commutation timing circuit is high enough to ensure proper circuit operation before circuit operation is permitted. The invention also concerns a method of timing and a method of operating electronically commutated motor.

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First Claim