Current limiting Resistor

Discussion in 'General Electronics Chat' started by iONic, Feb 28, 2012.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    I guess the question is not so much, do I need a current limiting resistor, as do I need a voltage dropping resistor.

    Pin 1 of this IC will sink 5mA when the charge voltage fall between .6V and .35V, at which point aprox. 5mA is sinked through D1(LED) and R1(Resistor).

    Not really sure what I need, an LED that lights up well enough at 5mA?
    Will an LED rated at 3V/20mA light up with a 400 ohm resistor in series and only 5mA passing through it?


    [​IMG]

    [​IMG]

    datasheets-LTC4054L-4.2
     
  2. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    You missed a chart. Bottom left of page 4. The charge pin will dump over 20 ma to ground. Keep reading the specsheet.
     
  3. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    Oops! So Pin 1 is a Charge Indicator and not a Charge Complete indicator.
    Actually, both. When LED is lit, the battery is charging, When the Battery is charged, the
    LED should not be lit with only 5mA. Thus a 400 - 500 ohm resistor ought to work fine...
     
    Last edited: Feb 28, 2012
Loading...