Resistance of LED

  • Thread starter elecz
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Main Question or Discussion Point

Can anyone tell me what is the internal resistance of LED? I mean is that very high or low??? Usually how much current is drawn from it when it is given 5V?
 

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vk6kro
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LEDs and most other diodes are not really like resistors.

The current they draw depends on the voltage across them.

If you put a voltage on the anode that is positive relative to the volatage on the cathode, you can increase this voltage from zero and with a LED, a very small current will flow. (So, if you like, the device has a high resistance.)

As you increase this voltage, the LED current increases very slowly until a voltage is reached where the current starts to increase rapidly and the LED starts to glow.

This voltage is different for different types of LED and it is different for differnt colored LEDs. A red one may start to draw current and glow at about 1.3 volts while a white one may not draw much current until it gets about 3 volts across it.

Above this voltage, the LED starts to draw a lot of current and it is normal to put a resistor in series with it to limit the current it can draw.

If you did put 5 volts across a LED without a series resistor, it would draw a lot of current and probably melt the working part of the diode and it would not work after that.

You could say the apparent resistance of the LED would be very low with a large voltage across it.

You can read more about LEDs here:
http://en.wikipedia.org/wiki/LED
 

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