Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2004-11-23
2008-12-02
Vo, Tuyet (Department: 2821)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S535000, C327S538000, C327S534000, C327S533000, C345S082000, C345S212000, C345S211000
Reexamination Certificate
active
07459959
ABSTRACT:
A plurality of LEDs is driven in parallel, in at least two modes. In a first mode, the LEDs are driven with a first voltage. In subsequent modes, the LEDs are driven with successively higher voltages. The forward voltage drop for each LED is monitored, and the driver switches from the first mode to successive modes based on the largest of the LED forward voltage drops. The current through each LED is controlled by directing a reference current through a first digitally controlled variable resistance circuit, and directing the LED current through a second digitally controlled variable resistance circuit having substantially a known ratio to the first variable resistance circuit and connected in series with the LED. A digital count is altered based on a comparison of the first and second currents, and the first and second variable resistance circuits are simultaneously altered based on the digital count.
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Foran Ryan P.
Rader William E.
Coats & Bennett P.L.L.C.
Semtech Corporation
Vo Tuyet
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