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Power tool having a universal motor capable of being powered by AC or DC power supply

  • US 10,333,454 B2
  • Filed: 11/20/2017
  • Issued: 06/25/2019
  • Est. Priority Date: 05/18/2014
  • Status: Active Grant
First Claim
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1. A power tool comprising:

  • a housing;

    a universal motor having a positive terminal, a negative terminal, and a commutator engaging a pair of brushes coupled to the positive and the negative terminals, the motor being configured to operate within an operating voltage range;

    a power supply interface arranged to receive at least one of Alternating Current (AC) power from an AC power supply having a first nominal voltage or Direct Current (DC) power from a DC power supply having a second nominal voltage, the DC power supply comprising at least one removable battery pack coupled to the power supply interface, the power supply interface configured to output the AC power via an AC power line and the DC power via a DC power line, wherein the second nominal voltage falls approximately within the operating voltage range of the motor, but the first nominal voltage is substantially higher than the operating voltage range of the motor; and

    a motor control circuit configured to supply AC power from the AC power line or DC power from the DC power line via a common node to the motor such that the brushes are electrically coupled to one of the AC or DC power supplies, the motor control circuit being configured to reduce a supply of power from the AC power line to the motor to a level corresponding to the operating voltage of the operating voltage range of the motor, wherein the motor control circuit comprises;

    a phase-controlled AC switch disposed in series with the AC power line, anda control unit configured to control a phase of the AC switch, the control unit setting a fixed conduction band for the AC switch corresponding to the difference between the first nominal voltage and the operating voltage range of the motor, the fixed conduction band being less than 180 degrees to reduce an average voltage amount on the AC line to a level that falls within the operating voltage range of the motor.

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