Can LEDs be driven directly from a voltage source?
Direct operation from a voltage source is not recommended even though the LEDs appear to be functioning as required. We can observe from the Forward Current (If) Vs. Forward Voltage (Vf) graph that a slight change in Vf will cause a large change in If leading to a possible electrical over-drive condition. This will reduce LED reliability.Even if over-drive conditions are not reached, swings in If will result in significant luminous intensity variation. The preferred method of operating from a voltage source is via a series resistor which will limit the current flow through the LED.
