Speed control device for DC motors
First Claim
1. A speed control circuit for controlling the rotational speed of a direct current (DC) motor to remain constant, said circuit comprising:
- a positive rail connected to a positive polarity side of a power source;
a ground rail connected directly to electrical ground and to said positive rail through a Zener diode, wherein a first electrical potential remains constant between said positive rail and said ground rail;
a negative rail connected to a negative polarity side of said power source and further connected to said ground rail through a first resistor, wherein a second electrical potential exists between said negative rail and said positive rail; and
a DC motor connected between said positive rail and said negative rail through a switching MOSFET, wherein a motor potential across said DC motor remains constant.
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Accused Products
Abstract
A speed control device is provided such that the speed of DC motors is controlled to remain constant with varying voltages supplied from a power source. A given application for such a speed control device is in the use of portable, hand-held Metal Inert Gas (MIG) welders. The power requirements of a portable MIG welder are twofold. Power is required for the generation of a welding current to enable the workpieces to be sufficiently heated and thus, welded together, and power is also required to drive a wire spooler which provides wire at a constant rate, leading to accurate and consistent welds. The speed control device provided ensures constant power delivery for both power requirements, regardless of variations in the voltage of a power supply and irrespective of a mechanical load asserted on the welder.
35 Citations
13 Claims
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1. A speed control circuit for controlling the rotational speed of a direct current (DC) motor to remain constant, said circuit comprising:
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a positive rail connected to a positive polarity side of a power source; a ground rail connected directly to electrical ground and to said positive rail through a Zener diode, wherein a first electrical potential remains constant between said positive rail and said ground rail; a negative rail connected to a negative polarity side of said power source and further connected to said ground rail through a first resistor, wherein a second electrical potential exists between said negative rail and said positive rail; and a DC motor connected between said positive rail and said negative rail through a switching MOSFET, wherein a motor potential across said DC motor remains constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A speed control circuit for a portable, hand-held MIG welder comprising:
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a Zener diode connected between a positive rail and a ground rail, wherein said positive rail is further connected to a positive polarity side of a power source; a DC motor connected between said positive rail and a negative rail for supplying a constant power to a wire drive device, wherein said constant power is not effectcd by variations in a voltage supplied to said speed control circuit from a power supply; and a trigger for initiating a delivery of said constant power to said wire drive device and said trigger concurrently initiates an opening of a gas valve, wherein said opening occurs slightly before said delivery.
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Specification