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IP.com Disclosure Number: IPCOM000005460D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10

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Thomas L. Hopkins


STATEMENT 0F PROBLEM The circuit shown in the attached figure may be used to chop the AC mains to provide pulse width modulated control of an AC machine such as a universal motor or fluorescent lamp (the load). One of the .main problems with thls type of application is that some means must be provided to absorb the inductive energy stored in the load when the transistor turns off to prevent transistor failures. One method of doing this is to use snubber networks. This typically involves costly and bulky components. The other common- ly used method is to clamp the inductive energy in a freewheeling diode. Since the diode is inherently a unipolar device, it would clamp the energy in only one polarity and short circuit the load in the other. To effectively use this technique In AC circuits, some means must be devised to clamp the inductive energy and not short circuit the load half of each cycle.