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| LED flashlight regulated vs unregulated? |
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| drummerdimitri:
I have some flashlight's I'd like to test in terms of having their power supplies. My theory is that a regulated flashlight will try to maintain a constant power draw so as the battery voltage drops with use, it will increase the current draw by a proportional amount correct? Unregulated flashlights would just follow ohms law and act like a resistor right? I could then characterize the LED driver's behavior through my Rigol DP832A if my methodology is correct. |
| BrianHG:
--- Quote from: drummerdimitri on August 12, 2019, 12:31:11 am ---Unregulated flashlights would just follow ohms law and act like a resistor right? --- End quote --- Close, but not quite. Remember, the LED is a diode with a greater than exponential curve in current draw as voltage increases. So, as the battery voltage drops, the current drops far quicker than if it were a resistive incandescent bulb (whose resistance actually decreases as its glow decreases making the battery drain a little faster as well) or a fixed resistor value. In fact as the battery voltage comes close to the LED's turn on voltage, you may be drawing 1-2ma from the batteries while only 0.5v higher, and the LED will draw 20ma or more. |
| Audioguru again:
If you use a Lithium battery (throw away or rechargeable type) then its voltage does not drop much as it runs down then you might not need a voltage regulator. An LED needs a current-limiting resistor or circuit. |
| edavid:
--- Quote from: drummerdimitri on August 12, 2019, 12:31:11 am ---My theory is that a regulated flashlight will try to maintain a constant power draw so as the battery voltage drops with use, it will increase the current draw by a proportional amount correct? --- End quote --- Not necessarily. A 1 cell alkaline/NiMH flashlight will use a boost circuit, and will draw constant power from the battery, and supply constant current to the LED. However, a 1 cell Li-ion flashlight will usually sometimes use a linear current regulator, and draw constant current from the battery. |
| james_s:
Quite a few Li-ion powered flashlights use a buck regulator, at least the decent ones do. |
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