- an N-channel MOSFET (IRF540N $1.62/10pcs , 30N06, $.1.75/10pcs)
- an NPN transistor (such as S8050)
- 3.9 ohm – 2W resistor, the current limited around 0.5/3.9 = 125mA
- 100kR (1/4W) resistor
- A push-lock switch
- 0.5W 8mm LED, $3.18/100pcs
- A 18660 Lithium battery. I salvaged a few of them from a power bank. Laptop battery (4, 6, 8 cells) made from 18650 cell but careful with that stuff.
- 1 boost-up to 12V board, like this one , $0.56
- 1 lithium charger such asthis one, $0.30
The main difference to the circuit above is using a Lithium battery (18660) with boost up board instead of a mock-up 5V power adapter.
We are going to make a flashlight (v2). first the boost-up board pushes the voltage of the lithium battery (3.7V norminal) to 12V that is sufficient to power 3 LEDs in series.
Let put things together
We can charge the flashlight we needed.
The last photo shows the final flashlight and it was charging from any micro USB source (>1A).
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