Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Run it from a current limited switched mode power supply. Linear Tech and Nat Semi do many that will meet this requirement.
OR
Assuming a car when running is putting 14V out of the alternator, (14-10)/.9 is close to 4.7ohm as a preferred value resisor. Make it a 5Watt one on a small heatsink and you should be fine.
No need to worry about effiency as it's running from a car battery unless you have other ideas like leaving it on for a few weeks without using the car.
Using only a resistor for current regulation will produce a huge difference in light output as car voltage varies from 12.2V (engine stopped) to 14.6V (engine running fast).
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