US 8,446,107 B2 · Smart clamp

Abstract

In a circuit that turns off a fluorescent lamp, clamping circuitry is provided to dissipate energy stored in a ballast when the lamp is being turned off. In a normal state in which the lamp is on, or in a normal state in which the lamp is off, clamping is not performed as long the VDS of a power switch is below a voltage A. In a lamp turn off operation, the switch is turned on for a time period to extinguish the lamp, and is then made to operate as a clamp (operate in its linear region) for a second period of time to dissipate energy that was stored in the ballast. Clamping in the linear region continues for VDS voltages down to B as ballast energy is dissipated, where B is smaller than A. By clamping down to the lower voltage B, re-ignition of the lamp is prevented.

Claims26

Dependent claims

A circuit comprising:

a transistor having a source, a gate and a drain, the transistor having a drain-to-source voltage VDS, the transistor having a gate-to-source voltage VGS;
and
a clamp and control circuit that:
(1) in a first mode drives the gate of the transistor such that the transistor is off provided VDS does not exceed a voltage A, (2) in a second mode drives the transistor such that the transistor is on, and (3) in a third mode drives the gate of the transistor such that the transistor operates in its linear region if VDS exceeds a voltage B but is off if VDS is less than B, wherein A is greater than B.

1 more element

Dependencies are inferred from the claim text.

Smart clamp

Life of this patent

Smart clamp

Life of this patent

Abstract

Claims26