Basic question about driving LEDs

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AmatSaragih

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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
 

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.
 

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).
 

Basic LED question

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

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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