Electronic – Connecting different specification LEDs in series / parallel combinations


How would you consider connecting two different types of LEDs, a white (6 V @ 150mA) and red (2 V @ 350mA) in a series-parallel combination? (W W R W W R W W) << parallel multiple strings of 8 series connected LEDs.

Similar LEDs will share more or less the same characteristics within a series / parallel circuit using a constant current and a small current balancing circuit (mirror or similar).

If I use a CC driver for the LEDs, it will divide the current to each parral string for instance 150mA per string. But now I have a couple of 350mA LEDs within each series string. This will either cause the efficacy to be next to zero or they will not even light up. Driving all the strings at 350mA will probably create a small electrical fire.

Any insights?

Best Answer

LEDs with different forward current requirements can not be connected in series. Doing so will cause some LEDs to be damaged.

LEDs with different forward voltages can not be connected in parallel. Doing so will cause some LEDs to be dim or completely dark.

LEDs that have the same current requirement can be connected in a series string, with an appropriate resistor to limit current or using a constant-current source.

LED strings can be connected in parallel as long as they are all designed to operate at the same voltage. That is, the current limiting resistor in each string must have been chosen for operation with the same voltage. So, connecting several strings in parallel and driving them with a constant-current driver is not likely to work well...they are not guaranteed to share current equally.