Lawsuit Charges Power Supply Maker with Patent Infringement

Aug 10, 2005 3:00 PM
By David Morrison, Editor, PETech

Technical Witts (Flagstaff, Ariz.), a supplier of intellectual property, simulation software, and educational and engineering services to the electronics industry, has filed suit against Skynet of Taipei, Taiwan, charging that Skynet violated one of its patents. Technical Witts holds 19 patents in the United States for power conversion technology, which is used in a broad range of electronic system applications and electrical appliances. Technical Witts is seeking damages from infringement as well as an injunction against the importation of infringing products being manufactured by Skynet and sold in the United States. The lawsuit was filed in September of 2004 in federal district court in Phoenix.

The Technical Witts patent (US Patent 5,402,329) teaches the implementation and structure of low-cost single-ended power converters that can operate at very high switching frequencies while also achieving gains in active-on energy efficiency. These benefits are achieved through a zero voltage switching (ZVS) mechanism, which leads to reduction or elimination of switching losses in the power semiconductors and elimination of rectifier reverse recovery effects.

The ZVS mechanism suggests a power semiconductor design optimization process that enables significant reductions in power semiconductor conduction losses. In addition to reduced power semiconductor losses, lower EMI noise generation can be achieved without requiring the use of complex snubbing circuitry. Other power supply improvements include improved cross-regulation of multiple outputs and the ease of incorporating synchronous rectification for lower conduction losses in low-voltage outputs.

The Technical Witts patent (US Patent 5,402,329) teaches a flyback topology, illustrated in Fig. 1, and a forward, or coupled inductor buck, topology, illustrated in Fig. 2. Both of these topologies rely on the energy stored in a small inductor, L1, to provide the energy needed to drive the main switch, S2, to zero volts during the turn on transition of S2.

The switches S1 and S2, shown together with their intrinsic capacitance and body diode, operate alternately (in anti-synchronization) with short dead times between the operation of the switches. During the time that S2 is conducting, the current in L1 flows in the same direction as magnetizing current in the transformer T1. During the time S1 is conducting, current in L1 falls, then reverses, and reaches a maximum current in opposition to the magnetizing current in T1 at the end of the conduction period of S1. The energy stored in L1 at the end of the conduction period of S1 is sufficient to drive S2 to zero volts for a wide range of line voltages and load currents. L1 also forces the current in the secondary circuit to drop gradually to zero amps, thereby eliminating reverse recovery effects that might otherwise afflict D3 and contribute to EMI and switch S2 turn on losses.

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