Which is more Efficient?

Discussion in 'General Electronics Chat' started by cjdelphi, May 31, 2009.

  1. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    272
    2
    ok from a flashlight perspective here.

    2 Lithium's 4.2v fully charged in series, 8.4v volts let's suppose I was going to power a simple 5mm LED.

    8.4-3.0v = 5.4v
    5.4/0.020amps = 270 ohms.

    Now would it be more or less efficient to use PWM? I still can't quite get my head around the heat dissipation from a Resistor over such a small amount of current, at what point does a Resistor become less efficient than say PWM? is there a rule to this?....

    Thanks :)

    As for heat dissipation loss (as anything with large enough currents will create heat)

    5.4v*0.020 = 0.108 watts (1/4watt resistor)
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    PWM does not make a current-limiter be more efficient. Instead it makes the switching device stay cool.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Which is more efficient than using a linear device.

    But if you're talking about LEDs and other solid state devices, you still have to be careful not to exceed the maximum rated current. You can go over a bit, but not too much.
     
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