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    LED Car indicator lights must be done with linear LED driver?

    Is it true that LED car indicator lights (flashers) have to be done with linear LED drivers because switch mode LED drivers cause too much ringing on the power wires feeding the indicator lights.?

    Basically, all switch mode LED drivers need to have fairly large capacitors at their input, and when the indicator light flashes on, a sudden pulse of current is drawn through the power wires, and this instigates a resonance between the power wiring inductance and the input capacitors of the switch mode LED driver............this ringing causes disturbance to other circuitry in the car, including the car radio.?

    Linear LED drivers, on the other hand, dont need as much input capacitance, so they dont suffer this problem, and this is why LED car indicator lights are done with linear LED drivers....

    is this correct?

    I say this because when working at a place where they designed LED car indicator lights, (and other car LED lights), the senior engineer asked me to find out how he could stop the ringing between the car's power wiring and the input caps of the switch mode led drivers.

    Also, there was more ringing because the switch mode led drivers had input LC filters.

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    Re: LED Car indicator lights must be done with linear LED driver?

    not really..

    You can use strings of 9V LEDs which is 3 whites or 6 reds and PWM series switch to regulate the current from 14.2V
    an LC Pi filter prevents ripple currents getting out and filter current coming in at a 10KHz rate so that it is both efficient and low in EMI. twisted pairs helps egress.

    With a buck -boost regulator you do the same protective 2V zener diodes or 3 silicon diodes can prevent strings from failing when one Led fails or similar cct. (for Red and double that for white)
    Last edited by SunnySkyguy; 14th April 2013 at 02:57.
    A best design is easily achieved with good test specs™
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    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

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    Re: LED Car indicator lights must be done with linear LED driver?

    LED Lights for cars has a low power consumption and long and predictable lifetime.The lifetime of LED street lights is usually 10 to 15 years, three times the life of current technologies adopted. LEDs also have low maintenance cost.


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    Re: LED Car indicator lights must be done with linear LED driver?

    Quote Originally Posted by treez View Post
    Is it true that LED car indicator lights (flashers) have to be done with linear LED drivers because switch mode LED drivers cause too much ringing on the power wires feeding the indicator lights.?.
    It is quite likely PWM would radiate a lot of noise in the AM band so filtering would absolutely necessary.
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto


    1 members found this post helpful.

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