Electrical theory 1.3e - Series or parallel LED connections

In this section we’ll look at connecting LEDs in either series or parallel and the use of a current limiting resistor.

LEDs are electronic devices so they behave differently to light bulbs – after digesting all this info you’ll understand what's happening!

 

Key points:

 A LED has roughly a constant voltage behaviour which means they must be operated at their typical voltage to get plenty of light. (See detailed explanation for those interested.) Also too much voltage (across its terminals) causes too much current to flow - this causes LEDs to prematurely fail!

 

Here's an easy to understand graph which shows LED relative brightness for various voltages across it. It's for a RED LED with typical voltage of 1.9 to 2.0V - other colour LEDs have similar graphs BUT their own typical voltages.

Looking at blue markers on graph:

• No light is emitted for a voltage of less than 1.55 - 1.60VDC.
• A miniscule of light is emitted around 1.60V.
• The amount of light increases above 1.7V in a linear manner. This is why 2.0V for red LEDs is used.
• The upper limit of voltage (2.15V) is limited by current and overheating the LED (around 25mA for 5mm LED). Currents above say 25mA will proportionally shorten the LED’s life and very high currents will blow it up!

 

The above is general information and the manufacturer's data should be used. Note there can be a variation of 10-15% between LEDs of same colour.

The voltages stated above are the voltages across the LED's 2 terminals - not the supply voltage.

So you have a rough understanding and it will become clearer after looking at discussions on SERIES and PARALLEL .

NEXT >> SERIES