The LED illuminator/flash that is used on cellphones with cameras is also controlled by flashlight apps. Is the light level controlled by pulse width modulation or is it analog current controlled? In other words, does reducing the illumination also reduce battery drain?
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asked Apr 7, 2019 at 15:31
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1\$\begingroup\$ It would be quite strange to have it current controlled, because it is more complex, expensive and inefficient than simple PWM. \$\endgroup\$– TemeVCommented Apr 7, 2019 at 15:39
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2\$\begingroup\$ I think reducing illumination will reduce battery life in both cases - PWM or analog current control. Do you have a different opinion? \$\endgroup\$– WhiskeyjackCommented Apr 7, 2019 at 15:39
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\$\begingroup\$ Record yourself with the flash light on, slow down the video speed dramatically and see if you have a frequency :) My guess is that it's a PWM to save on battery life. Using analog control sounds like it draws too much current. \$\endgroup\$– user103380Commented Apr 7, 2019 at 15:57
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\$\begingroup\$ Is there an app for Android that can control the illumination of the flash? I tried a few apps but they didn't have that feature. Is it even possible to dim the LEDs? \$\endgroup\$– TemeVCommented Apr 7, 2019 at 16:38
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1 Answer
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PWM and Linear analog current regulators are very inefficient with a wide input battery voltage range >25%. A Boost regulator is preferred with at least 2 LEDs. A boost reg. is essentially the best of both PWM and reactive LC filtering to regulate the boost energy with some variations in current and time limits.
Each mobile phone may have a different solution.
Here is one offered by a product marketing manager at ON Semi reported in EE Times on 06.12.08.
An inductive step-up converter with high power driving circuit of 4.5 W is capable to power two LEDs in series with a driving current of 500mA.
Figure 6. A 4.5W power-flash driver with internal switch and time-out protection
