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What's the circuit in LED flash light?

Discussion in 'Electronic Components' started by peter, Sep 26, 2004.

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  1. peter

    peter Guest

    In all the white-LED flashlights I bought, they all have some sort of
    circuit attached to the LEDs. I thought all you needed is a resistor for
    each LED to limit the current. What does the circuit do? Is it functionally
    similar to a resistor but has higher efficiency (perhaps a switching current
  2. Dave Platt

    Dave Platt Guest

    In all the white-LED flashlights I bought, they all have some sort of
    Yes, it's probably a boost-mode switching regulator. White-light LEDs
    have a fairly high threshold voltage... they need 4-5 volts across
    them to conduct, and this is more than a two-cell battery can provide.
    The switching circuit boosts the voltage, and delivers a consistent
    and stable current to the LEDs.

    You can run white LEDs from a higher-voltage DC source (e.g. 6-9
    volts) with just a series resistor. However, this is rather wasteful
    of power (a good deal of the battery's power is dissipated as heat in
    the resistor) and the brightness of the LEDs will vary significantly
    as the battery runs down.
  3. Depends on how many cells the light has. If it has two 1.5V cells or
    less, then the light needs the circuit to boost the voltage up to 3.4VDC
    or so to drive the white LED.

    The Dorcy 4 white LED flashlights are only $16 or so at OSH, so you can
    get a reasonably priced flashlight for under $20. If you buy one of
    those 'torches' that use a lithium cell or two, then you end up paying
    double for the batteries. And you keep on paying for the life of that
    light. new.htm just a satisfied customer.
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