Patent ID: 6118239
Filing Date: 2000-09-12
Classification: H02P

Abstract:
A speed control drive circuit for providing to the armature of an ac-powered motor a train of bipolar drive pulses whose pulse amplitude and pulse frequency are controlled in accordance with a selection of motor speed, comprising:a source of ac power having at least first and second ac conductors;controlled rectifier means having ac inputs connected respectively to said first and second ac conductors, dc output rails at which a rectified dc voltage is provided, and at least one gate for controlling the ac power through the rectifier means thus to control the level of voltage at said dc output rails;bridge inverter circuit means having dc inputs connected to said dc rails and outputs providing said bipolar drive pulses to the armature of said motor;selector means for selecting a speed in a range including at least a low speed and full speed; andcontrol circuit means having an input coupled to said selector means, a drive output providing an output drive signal to said bridge circuit means at a frequency corresponding to said selected speed, and pickoff voltage selecting means having an output coupled to the gate of said controlled rectifier means so that the level of said rectified dc voltage corresponds with the selected motor speed, wherein said pickoff voltage selecting means detects zero crossings of said ac power and computes a time to the point at which the ac voltage is at a desired pickoff voltage.