Driving High-Power White LED Flash in Camera Phones
Supercapacitors with low ESR (Equivalent Series Resistance) and high capacitance are ideal components for use in pulsed-power applications, such as Flash LEDs and GPRS transmitters, in which the load draws large pulses of current. When connected across the supply, they provide much of the energy needed by each load pulse, reducing voltage ripple, instantaneous supply current and extending battery run time.
The CAP-XX Solutions
CAP-XX proposes 3 solutions using a supercapacitor to support the battery to provide pulse power for the LED Flash and in some cases, also provide pulse power for GPRS transmission. These are:
- A. Place the supercapacitor at the input to a boost or buck-boost converter. This requires a separate current limit between the battery and supercapacitor. The supercapacitor must be a dual cell device rated for 4.5V continuous operation.
- B. Place the supercapacitor at the output of a buck-boost converter. This solution requires a dual-cell supercapacitor rated for 4.5V continuous operation with short excursions up to 5.5V. Select a buck-boost converter whose current limit function can also limit supercapacitor inrush current at power up.
- C. Place the supercapacitor in series with the battery. This requires only a single cell supercapacitor which is thinner and lower cost and there is no inrush current problem, but the battery current = load current.
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