Comparison of Advantages and Disadvantages of Series and Parallel LED Connections
Comparison of Advantages and Disadvantages of Series and Parallel LED Connections
Applications such as LCD backlights, general lighting fixtures, and streetlights require the simultaneous driving of multiple high-brightness LEDs. These LEDs need to be connected in series and parallel and require driving.
For example, when driving 28 LEDs, there are six conceivable connection methods. One is to first connect 14 LEDs in series (LED string) and then connect two such series-connected LED strings in parallel (14 series × 2 parallel). Other methods include 7 series × 4 parallel, 4 series × 7 parallel, 2 series × 14 parallel, 28 series × 1 parallel, and 1 series × 28 parallel.
Which connection method is best? Answering this question requires understanding the advantages and disadvantages of series and parallel connections.
The advantage of series connection is uniform brightness. The advantage of series connection is that the LEDs in the same string have uniform brightness because the current supplied to all LEDs is the same. Furthermore, the driver IC only needs to output a single current to light up all the LEDs in the series, resulting in a simple circuit structure. In addition, its advantage lies in the fact that even if one LED short-circuits, the others can still light up.
The disadvantage is the high driving voltage. With 14 LEDs in series, assuming a forward voltage drop (VF) of 4V per LED, a driving voltage of 56V is required. With 28 in series, this reaches as high as 112V. Except for products from certain semiconductor manufacturers, the selection of LED driver ICs with high driving voltages is extremely limited.
Furthermore, there is the disadvantage that if one LED experiences an open-circuit fault, all the LEDs in series will fail to light up.
Parallel connection has two advantages. One is that it can drive multiple LEDs simultaneously with a low voltage. In a 2-in-series × 14-in-parallel configuration, an 8V driving voltage can drive 28 LEDs. Another advantage is that if one LED in a series connection fails for some reason, the other LEDs in series can continue to light up. In other words, it can form a circuit that is less affected by faults.
There are also two disadvantages. One issue is that controlling the supply current of multiple LED strings connected in parallel to the same value is difficult, which can lead to differences in brightness among the LED strings. Another issue is the increased complexity of the drive circuit. If there are 14 LED strings connected in parallel, wiring is required for all 14 strings. Furthermore, according to the circuit structure, each LED string must be individually controlled for both voltage and current, thus increasing costs.
