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auto white led light circuit schematic

Automobile White LED Light

Without any dedicated buck converter/white LED driver IC, you can safely drive many standard Hi-efficieny white LED modules using the battery power available in automobiles. Here is a safe and simple white LED driver designed for 12V automobiles.

In the Automobile White LED Light circuit, fixed voltage regulator IC1 (7805) provides a steady voltage of 5V across C2. Resistors R1 limits the current flow through the white LED D1 (3v6/350mA) with the help of transistor T1 (and T2), ie components R1, T1 (and T2) provide a constant current to D1. Use a good heat sink for T1. This LED unit gives a constant light output for input voltages ranging from 8 to 18 volts!

Auto White LED Circuit Schematic

auto white led light circuit schematic

12 Comments

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  • Edgardo M. Diolola

    Hi Colin Mitchell,
    Thanks a lot for the circuit, very simple to build, with accompanying calculations and illustration.
    This will help many electronics enthusiasts / newbies.

    More power…

  • Colin Mitchell

    Use this circuit:

  • Edgardo M. Diolola

    Hi, Colin Mitchell,,

    Can you kindly post your schematic for the 7805/LED/and the 15 ohms-2 watt resistor? I would be very happy to build it and seems very simple to make, also can be shared to other newbies in electronics.

    Thanks a lot in advance,,

  • Colin Mitchell

    This circuit can be replaced with a single resistor and 7805.
    Use a 15R 2watt resistor and connect the 7805 in constant-current mode.
    T.K.Hareendran does not have a clue about circuit designing.

  • KROKKENOSTER

    The “R”in component values is the only way that the decimal point is in that position a point very easily get overlooked and with wrong components

  • Edgardo M. Diolola

    @kazinator,
    Would you please post a more reliable circuit for the Auto White LED Circuit Schematic?
    I would be very happy seeing it, and also to share your knowledge to everybody who are electronic enthusiasts, be it prof. or newbie..
    Best regards..

  • Kazinator

    The advice to use a heat sink for T1, but not for the 7805 regulator is incorrect, because the load current passes through the regulator and through T1, and the regulator is the component which drops most of the voltage. T1 only drops the difference between 5V and the voltage that develops across the LED, whereas the regulator has to drop 12 to 5V.

    This is not really a great way to drive LEDs, but it’s simple. But it’s not as simple as can be unless you remove the superfluous voltage regulation.

    You see, the 7805 (and its surrounding capacitors) here are actually quite pointless, because the LED is a current-driven device. The two-transistor circuit limits the LED to the same current, regardless of the voltage supply. I.e. the circuit is already regulated enough. Without the 7805, T1 will drop more voltage to keep the LED at the same current. You can use a beefy power transistor in a TO-220 package for T1, and mount it on a heat sink, which you would have to do with the TO-220 7805 anyway.

    Whoever drew this circuit didn’t understand it, and so transplanted the two transistor LED driver from a 5V circuit, cautiously putting in regulation, suspecting that 5V is needed.

    R1 programs the current through the LED, which is approximately 0.7V/R1 or 260mA in the above circuit. Since the LED module will drop about 3V, that leaves 9V across the transistor at 260mA, which means T1 has to dissipate about 2.4W. By suitable choice of T1 (power NPN) and heatsinking, that can be arranged.

    Although T1 is emitter-degenerated by R1, it may still be a good idea to put T2 on the same heat sink, if possible.

  • arulmurugan

    sir Hareendran,
    nice ckt i want to use for my bike.so i need more brightness iwant to use 3watts led 3 nos will pls provide me good alternation in this ckt

  • T.K.Hareendran

    2R7 /2W means 2.7 Ohm/2W.Here R denotes the decimel.Usually if it is in Kilo-Ohm,the value is shown a 2K7/2W (means 2.7Kilo-Ohm/2W).Regarding this circuit,use a 2.7 Ohm resistor as R1 and 6.8 Kilo-Ohm resistor as R2.

  • david

    where do these part numbers come from. i’d like to build but the numbers,where do they come from. for example; r1, 2r7/2w. the 2 watt iget but is it 7ohm or 7k.

    • mowerguy

      2r7 is the relative new waqy of denoting 2.7 Ohms. I don’t care for the new designations, but we are going to have to live with it.

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