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Switch mode LED driver...regulating I(in)

Discussion in 'LEDs and Optoelectronics' started by eem2am, Jan 4, 2013.

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  1. eem2am

    eem2am

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    Aug 3, 2009
    Most switch mode LED drivers regulate their output current (= the LED current).

    Though if a LED driver is designed to regulate its INPUT current, then is this likely to mean a more stable situation than a LED driver which regulates its output current?

    i rekkon, if you are regulating the input current, its easier to get stable led current, as you are regulating what goes in before it gets to the switch mode led driver, rather than regulating the output current, where you are having to react to whats gone through the delay of the power stage................if you are regulalating the input current, you dont have any nasty power stage phase changes to think about, because its input current, it hasn't even got to the power stage.

    LED driver with regulated input current:
    http://i49.tinypic.com/2rw6az7.jpg


    .......this one (above) has regulated input current.

    So what do you think?......is "regulating the input current" the best way to easily get a stable led current in the output?
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Why would regulating the input current make a more stable output than regulating the output?

    The input current to a switch mode regulator is switched on and off (hence switch mode), so you can't really mean regulating it (i.e. keeping it constant). I think what you are talking about is limiting the input current, which is done to keep the inductor from saturating. This is a feature on many switch mode controller ICs, and is done in addtion to regulating the output voltage or current.

    Bob
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Actually, some regulators monitor the input current. They do this to switch off the current through the inductor when it reaches a certain value.

    Refer to page 4 of this pdf. The argument here is that it improves the transient response of the regulator. For driving LEDs I would not think that transient response is awfully important.
     
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