If theįlashlight uses 3 batteries, the lowest voltage will be around 3 volts When the battery is almost empty the voltage is around 0.8V - 1V. Since the red LEDs only need 40mA, a cheap SMD transistor Q2 is used there. The collector voltage drop increases with the current and Will be too low to waste on the voltage drop that a transistor has even when Transistor here because when the batteries are almost depleted the voltage Q3 is an SMD mosfet acting as a variable resistor. LEDs that are driven with 210mA (30mA for each LED) and 2 red LEDs (40mA. In this case I had to fix a headlamp torch that had the main ICīurned out so I made another PCB to drive the LEDs. The circuit is very simple and the working principle can be applied to other For that a transistor mosfet is used here (Q3 For this reason it is preferable to replace the fixed Low light brightness even though there is still potential for a higher current When the battery voltage drops the resistance remains the same leading to a Using a resistor for current limiting in a LED driver is inefficient because
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