LED is a solid-state semiconductor light source. Its luminous principle is essentially an electron transition. Led, as a colorful light source, has the characteristics of small size, high brightness, long life, low voltage, high safety, fast response, and so on. At the same time, the output brightness can be adjusted in a wide range. Therefore, it is widely used in daily life, such as billboards, various electronic products, various devices, handheld devices and so on.
Now many LED products use constant current drive method to drive LED. The connection mode of LED also varies according to the actual circuit needs. There are generally four types: series, parallel, hybrid and array.

1. Series Method

This series circuit is relatively simple. The current flowing through the LED during operation is consistent and stable. Since LED is a current-type device, it can basically ensure that the luminous intensity of each LED is consistent. The circuit with this LED connection mode is simple and convenient to connect. However, there is also a fatal disadvantage, that is, when one of the LED open circuit failure, the whole LED string will be extinguished, affecting the reliability of the use. This requires to ensure that the quality of each LED is excellent, so that the reliability will be improved accordingly.
Series method
It is worth noting that if the LED constant voltage drive power supply is used to drive the LED, when one of the LED short-circuit, the circuit current will increase. When a certain value is reached, the LED will be damaged, resulting in all subsequent leds being damaged. However, if the LED constant current drive power supply is used to drive the LED, when a short circuit occurs in an LED, the current basically remains unchanged, and there is no impact on the subsequent LED.

2. Parallel Connection Method

When two leds are connected in parallel, the voltage across each LED is equal. But the current is not necessarily the same, even for leds of the same model, specification and batch. This is due to the manufacturing process and other reasons. This kind of parallel circuit is relatively simple, but not very reliable, especially when the number of leds is high, the possibility of failure is higher.
Parallel method
It is worth noting that the voltage required in parallel is lower, but the brightness of each LED is different due to the different forward voltage drop of each LED. In addition, if one LED is short-circuited, the entire circuit will be short-circuited, and other leds cannot work properly. For an open LED, if a constant current drive is used, the current allocated to the remaining leds will increase, which may cause damage to the remaining leds. However, the use of constant voltage drive does not affect the normal operation of the entire LED circuit.

3. Mixed Connection Method

A hybrid connection is a combination of series and parallel connections. Several leds are first connected in series and then connected in parallel to both ends of the LED drive power supply. When leds are basically the same, using this connection makes all branches have roughly the same voltage and the same current flowing through each branch.
Hybrid connection method
It is worth noting that the use of hybrid method is mainly used in the case of a large number of leds. Compared with the simple series-parallel method, the proposed method can ensure that the LED faults of each branch can only affect the normal luminescence of the branch at most. At present, this method is widely used in many high-power LED lamps and has achieved very practical results.

4. Array Join Method

The main structure of the array mode is as follows: A branch consists of three leds, which are connected to the Ua, Ub, and Uc outputs of the driver respectively. When all three leds in a branch are normal, all three leds will glow at the same time. If one or both leds fail to open, at least one of them can work properly. This can greatly improve the reliability of each group of LED, improve the overall reliability of the entire LED. This method requires more than one input power supply, the purpose is to improve the reliability of LED work, reduce the overall circuit failure rate.

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