Detailed Explanation of 4 Connection Modes for LED Drivers
Currently, most LED products adopt a constant current driving mode to match the operating characteristics of LEDs. To meet the needs of different circuit designs, the common connection modes of LEDs are mainly divided into four types: series, parallel, series-parallel combination, and array. Each mode has its own circuit structure characteristics, application advantages, and limitations, which will be elaborated in detail below.
1. Series Connection Mode
The core structure of series connection is to connect LEDs end-to-end in sequence to form a closed loop. In terms of operating characteristics, the core advantages of this connection mode are simple circuit structure, convenient connection operation, and the current flowing through all LEDs is completely consistent during operation. Since LEDs are typical current-type devices, the consistency of current can directly ensure the uniform luminous intensity of each LED, avoiding brightness differences.
It should be noted that the type of driving power supply will affect the fault impact range of the series circuit: if a constant voltage driving power supply is used, when one of the LEDs is short-circuited, the current of the entire circuit will increase sharply. When the current exceeds the rated bearing value of the LED, the devices around the short-circuited LED will be damaged first, and then all subsequent LEDs will be damaged one after another; if a constant current driving power supply is used, even if one of the LEDs is short-circuited, the circuit current can still remain constant, and will not affect other LEDs. However, regardless of the driving mode adopted, as long as an LED open-circuit fault occurs, the entire light string cannot be lit.
2. Parallel Connection Mode
The structural characteristic of parallel connection is that the ends of all LEDs are converged and connected respectively, that is, the anodes of all LEDs are connected together and the cathodes are connected together. In this connection mode, the voltage across each LED is completely equal, but the current flowing through each LED is not necessarily consistent—even if LEDs of the same model and specification batch are selected, the current distribution will be uneven due to slight differences in production and manufacturing processes. The uneven current distribution will directly affect the service life of LEDs. LEDs with excessive current will age acceleratedly, their service life will be greatly shortened, and they will be easily burned out after long-term use.
In terms of circuit complexity, the parallel connection mode is similar to the series connection mode, both of which are simple circuit structures, but the reliability is also not high. Especially in scenarios with a large number of LEDs, the probability of failure will increase significantly.
It should be noted that the parallel connection mode has low voltage requirements and is more suitable for low-voltage driving scenarios, but there are two key problems: first, the difference in forward voltage drop of different LEDs will lead to inconsistent brightness, affecting the luminous effect; second, the fault impact is special—if one LED is short-circuited, it will cause a short circuit of the entire circuit, and all LEDs cannot work normally; if one LED is open-circuited, when using constant current drive, the current originally allocated to this LED will all be superimposed on the remaining LEDs, leading to overcurrent damage of the remaining LEDs, while using constant voltage drive will not affect the normal operation of the entire LED circuit.
The series-parallel combination mode is a combination of series and parallel connections. Its standard structure is: first, connect several LEDs in series to form a branch, and then connect multiple such series branches in parallel to both ends of the LED driving power supply. On the premise that the parameters of individual LEDs are basically consistent, this connection mode can ensure that the voltage of all parallel branches is equal, and the current in each series branch is uniform, which not only takes into account the advantage of current consistency of the series connection mode, but also integrates the circuit stability characteristics of the parallel connection mode.
It should be noted that the core advantage of the series-parallel combination mode is the improvement of reliability, especially suitable for high-power lamp scenarios with a large number of LEDs. When an LED fault occurs in a series branch, it will only affect the light emission of that branch, and other branches can still work normally. Compared with the simple series and parallel modes, the fault impact range is greatly reduced. At present, most high-power LED lamps (such as LED floodlights, LED industrial and mining lamps, etc.) adopt the series-parallel combination mode, which can not only meet the high-power luminous demand, but also ensure the reliability of use.
The core design idea of the array connection mode is "group redundancy". Its typical structure is: form a branch with 3 LEDs as a group, and each group of branches is connected to the three different output terminals Ua, Ub, and Uc of the driver respectively. From the perspective of working logic, when all 3 LEDs in a branch are normal, the 3 LEDs emit light at the same time; even if 1 or 2 LEDs in the branch fail open, the remaining LEDs can still work normally, thus ensuring that at least one LED in each group emits light.
