US 6,741,049 B2 · Low voltage start up circuit for brushless DC motors

Abstract

A local oscillator and logic circuit pulses the open winding of a brushless DC motor at start up and the back EMF is used to generate a voltage to boost the voltage available to the control circuit for optimizing performance when starting with low supply voltage. As the rotor of a motor rotates and the windings are commutated by the drive electronics there is generated in each winding a voltage caused by the collapse of the current and the inherent inductance of the winding. These voltages exceed the normal operating voltage of the motor. The energy in these voltages is used to generate a regulated power feed to the analogue circuitry of the control circuit at a suitable voltage level. During steady state conditions, when the motor is running, the commutation of the windings is continual and there is ample energy available to power analogue electronics, and, if required, associated digital electronics as well. At start up, however, when the motor is stationary, there is no commutation and thus no additional voltage pulses from which to generate a supply for the analogue circuitry. Accordingly, additional circuitry is included to drive one of the motor windings with short voltage pulses such as to create inductive voltages that can be used to create the desired regulated power feed for the analogue circuitry. This feed, once established, enables the analogue circuitry to accurately determine the state and position of the rotor and cause the correct winding to be driven. The motor will then start and usual steady state conditions will become established.

Claims19

Dependent claims

A circuit arrangement for driving at low voltage a brushless dc motor having a rotor and at least two windings for driving one or more permanent magnets on the rotor, the arrangement comprising:

drive circuits configured to provide drive signals to the windings;
one or more sensors arranged to determine the rotational position of the rotor;
an analogue processing circuit configured to process signals received from the one or more sensors so as to provide a feedback signal;
a regulation circuit configured to extract energy from inductive voltages produced by the windings and to generate a voltage power source for the processing circuit;
an oscillator circuit configured to provide a pulse signal;
and
a control circuit configured to receive the feedback signal and the pulse signal, the control circuit being further configured to control the drive circuits such that:
in a first mode of operation, when the rotor is turning, the drive circuits are selectively enabled based on the feedback signal;
and
in a second mode of operation, when the rotor is not turning, the drive circuits are pulsed based on the pulse signal so as to generate inductive voltages in the windings.

7 more elements

Dependencies are inferred from the claim text.

Low voltage start up circuit for brushless DC motors

Life of this patent

Low voltage start up circuit for brushless DC motors

Life of this patent

Abstract

Claims19