Daniel M Sable, 66Concord, VA

4884183, Nov 28, 1989

Mar 29, 1989

7/330388

Daniel M. Sable - Blacksburg VA

General Electric Company - East Windsor NJ

H02M 3156

363 41

A pulse width modulated control signal for use in motor control and with power supplies is generated by a dual-mode controller having variable frequency control in a discontinuous current operating mode. The controller also provides control in a continuous current operating mode, and makes a smooth transition therebetween.

5999433, Dec 7, 1999

Jan 12, 1998

9/005669

Guichao Hua - Blacksburg VA
Xinfu Zhuang - Blacksburg VA
Daniel M. Sable - Pearisburg VA

VPT, Inc. - Blacksburg VA

H02M 75387
H02M 3335

363132

A method and apparatus for maintaining relatively low ripple current in a dc-dc converter while minimizing the size of an inductive line filter utilizes a transformer having at least a pair of secondary windings in which the secondary windings are selected to have different numbers of winding turns depending on the specific design of the ideal duty factor at which the converter will be operated. In addition, the converter is provided with an active pre-load which establishes a continuous conduction current when load current is below some selected minimum value in order to provide control stability during light load conditions without converter oscillations. In an illustrated embodiment, the active pre-load circuit comprises a resistor connected in series with a transistor across the voltage output of the converter with the gate terminal of the transistor connected through a zener diode to the control circuit so that when the control voltage feedback signal drops to a selected low value, the transistor is biased into conduction to connect the resistor as a load to maintain a minimum load current. Alternatively, the transistor can be connected across one of the diodes in the transformer secondary and arranged so as to conduct current in a direction opposite to the direction of current through the diode so that under low current conditions, a current loop is formed through the transformer to maintain continuous current flow and allow the converter to operate at very light loads.

6084792, Jul 4, 2000

Aug 18, 1999

9/376616

Wei Chen - Campbell CA
Guichao Hua - Hangzhou, CN
Daniel M. Sable - Blacksburg VA
Stephen J. Butler - Blacksburg VA

VPT, Inc. - Blacksburg VA

H02M 7217

363127

A power converter using a switching signal having at least three levels of amplitude, one of which amplitude levels has a zero amplitude level during a predetermined switching interval, is provided. The power converter includes a circuit module having first and second input terminals for receiving the switching signal. The circuit module in turn is made up of a first power transistor and second power transistor. Circuitry is electrically coupled to a predetermined one of the power transistors for maintaining a predetermined voltage level across the gate terminal of the predetermined one of the power transistors during the switching interval of zero amplitude. The predetermined voltage level is chosen to enable that predetermined power transistor to continue in a respective "on" state notwithstanding of the presence of the switching interval of substantially zero amplitude. The circuitry further allows for removing or discharging the predetermined voltage upon termination of the switching interval of zero amplitude level to enable the predetermined power transistor to transition to a respective "off" state. The power converter may be conveniently used to extend a self-driving synchronous rectification technique to a broader range of output voltages and circuit topologies and provides over-voltage protection to the gates power transistors, and the capability to directly parallel additional modules.