LEDs are specified to run in a certain current range and the datasheet gives the maximum rated current.
The extract from the Cree C503B datasheet gives us the following guidelines:
- Maximum continuous forward current is 50 mA (1). Take note that this is an absolute maximum rating and is quoted at 25°C. If running in a higher temperature environment the current will have to be reduced to prevent overheating. We should also read Note 1:
1. For long term performance the drive currents between 10mA and 30mA are recommended.
- Peak forward current is quoted at 200 mA (2). To understand this we need to read Note 2:
2. Pulse width ≤0.1 msec, duty ≤1/10.
Some applications such as multiplexed displays the LEDs are blinked on and off fast enough that the eye can’t see. To keep the average light-levels high a very high current pulse is given. In the example above we can see that the pulsed current’s average value is 200 \( 200m \frac {100\mu}{100\mu + 900\mu} = 20 \mathrm mA\). It should end up comparable with the LED run at about 20 mA continuously.
Other applications for pulsed LEDs include strobes and camera flash units.
See Multiplexing – the basics for pulse application.
