| 摘要 |
A speed control device is provided such that the speed of DC motors is contr olled to remain constant with varying voltages supplied from a power source. A giv en 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 twofo ld. Power is required for the generation of a welding current to enable the work pieces 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 cons istent welds. The speed control device provided ensures constant power delivery for both p owerrequirements, regardless of variations in the voltag e of a power supply and irrespective of a mechanical load asserted on the welder.
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