Automatic voltage selection for series driven LEDs
AssigneeCalifornia Micro Devices Corporation
InventorsHassan Shami, Adam Whitworth
Life of this patent
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Abstract
An apparatus and method for automatically controlling voltages used to drive LED loads. A battery voltage can be boosted to a selected drive voltage level connected to current sources for driving the LED loads. The drive voltage level is selected by a controller using a headroom detect component to measure a headroom voltage across the current source. The controller adjusts the drive voltage level to maintain the headroom voltage within a predetermined operating range. The drive voltage may be used to drive a variable number of LEDs or a plurality of different LED loads connected in parallel without manual readjustment of drive voltage.
Claims18
A method for automatic voltage selection comprising the steps of:
- providing a voltage to a current source, the current source driving a load;
- measuring a headroom voltage across the current source;
- and
- adjusting the voltage to maintain the headroom voltage within preferred maximum and minimum voltage levels.
An apparatus for controlling a drive voltage comprising:
- a charge pump for boosting a battery voltage to obtain the drive voltage;
- a current source for receiving the drive voltage and providing a desired drive current to one or more LEDs;
- a headroom detect circuit for providing a signal indicative of a voltage measured across the current source;
- and
- a controller for adjusting the drive voltage responsive to information in the signal.
An apparatus for automatically controlling a drive voltage comprising:
- a charge pump for generating the drive voltage;
- one or more current sources coupled to the drive voltage, each current source adapted to drive a corresponding load;
- one or more headroom detectors, each headroom detector configured to provide a headroom signal indicative of headroom voltage measured across a corresponding current source;
- and
- a controller for selecting the drive voltage based on at least one headroom signal.
Dependencies are inferred from the claim text.