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US 5,103,154 AGranted
Start winding switch protection circuit
AssigneeTexas Instruments Incorporated
InventorsKevin J. Dropps, Herbert A. Thompson
Life of this patent
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AssigneeTexas Instruments Incorporated
InventorsKevin J. Dropps, Herbert A. Thompson
Estimating the term…
A single phase, capacitor start electric motor is shown in which energization of the auxiliary winding is controlled by a triac. The triac is protected from excessive voltages caused by the vector sum of capacitor, line and induced voltages which can occur at turn-off of the triac. The triac is protected in several embodiments by a gated semiconductor switch serially connected to a current limiting or discharge resistor, both being coupled across the triac. The semiconductor switch has a voltage breakdown device connected in its gate circuit. When voltage across the triac exceeds a selected level the gated semiconductor is turned on thereby drawing sufficient current momentarily to limit the voltage across the triac to a safe level and allowing the capacitor to discharge its voltage through the auxiliary winding circuit. In another embodiment a stack of high voltage bilateral triggering devices is placed across the triac.
A single phase AC induction motor comprising a main winding and an auxiliary winding both connectable to an AC power source, a start capacitor for providing a phase shifted field, auxiliary winding switch means for connecting and disconnecting the start capacitor and auxiliary winding to and from the AC source, auxiliary winding switch protection means including a gated semiconductor switch serially connected to a discharge resistor coupled across the auxiliary winding switch and a voltage breakdown device connected to the semiconductor switch and connected to be directly responsive to the voltage across the auxiliary winding switch, the breakdown device selected to breakdown at a voltage level to prevent excessive voltage appearing across the auxiliary winding switch.
Dependencies are inferred from the claim text.