LED has become the standard solution for movie lighting and camera flash in mobile phones. For higher image quality and higher resolution requirements, a brighter flash LED solution is required. The challenge is how to squeeze out the best luminous flux from the battery by achieving the most efficient solution. As a result, the operation of absorbing large currents from the battery requires many power-saving operating characteristics and a robust system design. This article describes a system layer flash LED driver design and features that ensure safe operation and integration of the system.
Efficient camera flash LED driver
High-resolution cameras require high-brightness flash to complete photography in the lowest light conditions. The customer requested a flash solution as a standard feature of the phone. Mobile phones with flash units have become an attractive selling point. This feature requires high luminous flux, which presents challenges for efficient LED driver system design.
system design
The high forward voltage and current of the flash LED in the mobile phone and the given battery voltage make the boost converter the best solution. Inductor-based boost converters exhibit satisfactory efficiency when driving large currents. The LED must be driven by current because the forward voltage does not only vary with temperature, but also has its own differences. This change in forward voltage is due to its production process, which varies by ±20%, see Figure 1.
Figure 1 Flash LEDVF/IF diagram
It is a simple method to connect the flash LED in series with a current sense resistor and then drive it through a boost converter. Figure 1 depicts this approach.
Figure 2 Simple LED driving method using an external current detecting resistor
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