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  1. #1
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    Basic LED question

    Suppose I have a HC logic gate that can sink 20mA at 5V.
    I'm sure I can use it to drive a 2V 20mA Led (with 100ohm Resistor).

    But I wonder if I use it to drive a 3V 30mA Led (with R).
    Is this 30mA Led can destroy my logic IC ?

    Amat Saragih

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  2. #2
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    Re: Basic LED question

    You should look at the details of the logic data sheet. The maximum current is frequently quoted for the highest voltage that will be interpreted as a logic zero. There is probably also another absolute maximum current limit.

    You can also parallel two HC gates in the same package to double the output current ratings.



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  3. #3
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    Re: Basic LED question

    Most of logic ICs are designed in such a way that you can safely shorten their outputs to GND line (but not to +V) so don't worry you wll not damage your driver and, as Flatulent said, you can parallel 2 or more HC gates if you wish to drive 1, 2 or more high current LEDs (each with R).



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  4. #4
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    Basic LED question

    Or simply drive your LED at reduced current. It won't be quite as bright.



  5. #5
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    Re: Basic LED question

    You could also drive the LED through a BJT Transistor, to keep the LED bright and the Logic safe.



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