Introduction of different connection forms and characteristics of LED lights

LED is a solid semiconductor light source based on the principle of electroluminescence. It has rich colors, small size, high brightness, long life, low operating voltage, safe use, fast response time, 0 ~ 100% dimmable light output, shock resistance, shock resistance, Free of many advantages such as ultraviolet and infrared radiation. Therefore, the application range is gradually expanding, and it has a good application prospect.

Introduction of different connection forms and characteristics of LED lights

High power and high brightness LEDs in a single package are costly and are mainly point light sources, so it is practical to use them over a wide range. At present, the power of a single high-brightness LED that has been put into practical use is very small, and in practical applications, most of them require planar light emission. Therefore, multiple LEDs must be arranged and combined in accordance with requirements. High brightness, dynamic display, color change and other application requirements, on the other hand, can meet the drive matching requirements of the driver matched with LED.

1 Common connection form

In applications, there are four main types of connection that are commonly arranged and combined by multiple LEDs according to a certain rule.

Introduction of different connection forms and characteristics of LED lights

1.1 Overall series

1.1.1 Simple tandem form

In general simple series connection, LED1-n are connected end to end, and the current flowing when LED is working is equal. For LEDs of the same specification and batch, although there may be slight differences in the voltages on individual LEDs, since LEDs are current-type devices, they can ensure that their respective luminous intensities are consistent. Therefore, a simple series LED has the characteristics of simple circuit and convenient connection. However, since LED1-n2 is in series, when one of the LEDs has an open circuit fault, it will cause the entire LED string to go out, which will affect the reliability of use.

The series connection method with bypass is an improved method of 1.1.1. Each LED in this manner is connected in parallel with a Zener diode D1-n with a breakdown voltage slightly higher than the operating voltage of the LED. When the LED is working normally, because D1-n is non-conducting, the current mainly flows through the LED1-n string and is equal, the LED1-n string normally emits light; when the LED1-n string is damaged and the lamp string is open, due to D1 The -n conduction ensures that current flows through the entire LED string, so only the failed LED fails, and the entire light string does not go out. Compared with the previous connection method, the reliability of use is greatly improved.

1.2 Overall parallel form

1.2.1 Simple parallel form

LED1-n in simple parallel mode are connected in parallel end to end, and the voltage on each LED is equal when working. It can be seen from the characteristics of the LED that it is a current-type device, and small changes in the voltage applied to the LED will cause large changes in the current. In addition, due to the limitation of LED manufacturing technology, even in the same batch of LEDs, the difference in performance is inherent, so when LED1-n works, the current flowing through each LED is not equal. It can be seen that the uneven current distribution of each LED may cause the life of the LED with excessive current to decrease sharply, or even burn out. Although this connection method is relatively simple, its reliability is not high, especially for applications with a large number of LEDs, it is more likely to cause failure in use.

1.2.2 Independently matched parallel form

Aiming at the reliability problem in 1.2.1, the parallel form of independent matching is a good way. Each LED in this way has its own adjustable current (the driver V + output terminals are L1-n respectively), ensuring that the current flowing through each LED is within its required range. It has the advantages of good driving effect, complete protection of a single LED, and does not affect the operation of other LEDs in the event of a failure, and can match LEDs with large differences. The main problems are: the structure of the entire driving circuit is relatively complicated, the cost of the device is high, and the volume occupied is large, which is not suitable for a large number of LED circuits.

1.3 Mixed form

The mixed form is proposed by combining the respective advantages of the series form and the parallel form. There are two main forms.

1.3.1 The serial connection mode

When the number of LED1-n applied is large, simple series or simple parallel is not realistic, because the former requires the driver to output a very high voltage (n times the single LED voltage VF), and the latter requires the driver to output a large current (single N times of LED current IF). This brings difficulties to the design and manufacture of the driver, and also involves structural problems and overall efficiency problems of the driving circuit. The product of the number of LEDs in series n and the operating voltage VF of a single LED nVF determines the driver output voltage; the product of the number of parallel LED strings m and the operating current IF of a single LED mIF determines the driver output current, and the value of mIF × nVF determines Output power of the driver. Therefore, the first serial-parallel hybrid connection method is mainly to ensure a certain reliability (the LED failure in each string only affects the normal light emission of the string at most), and to ensure the matching with the driving circuit (the driver outputs a suitable voltage) Compared with the simple series connection, the reliability is improved. The whole circuit has the characteristics of simple structure, convenient connection and high efficiency, and is suitable for applications with a large number of LEDs.

1.3.2 Mixed connection mode

(1) The LED connection method of serial-parallel connection is another hybrid connection method different from 1.3.1. Because LED1-n ~ LED1-n are connected in parallel first, the working reliability of each group of LEDs is improved, but the current sharing problem of each group of LEDs connected in parallel is very important. Pairing can be used. The selection method is to select LEDs with the same working voltage and current as a group in parallel, or connect a small current sharing resistor to each LED in series to solve it.

1.3 Cross Array Form

Reliability is proposed to reduce the failure rate. The main structure is: each string is composed of 3 LEDs, which are respectively connected to the Va, Vb, Vc output terminals of the driver. When all three LEDs in a string are normal, the three LEDs emit light at the same time; once one or two of the LEDs fail and open circuit, at least one LED can be guaranteed to work normally. In this way, the reliability of the light emission of each group of LEDs can be greatly improved, and the overall reliability of the entire LED light emission can be improved.

2 Comparison of different forms of connection

Different connection methods have different characteristics, and the requirements for the driver are also different. Especially when a single LED fails, the circuit works, the reliability of the overall light emission, the ability to ensure that the overall LED can continue to work as much as possible, and reduce the overall LED failure rate, etc., are particularly important. Table 1 gives a comparison of relevant wishes under different connection methods, which can be intuitively understood.

3 Concluding remarks

In short, LED group application is an important way for LED practical application. Different LED connection methods are very important for the use of a wide range of LEDs and the design requirements for driving circuits. Therefore, in the combination of actual circuits, correctly selecting the appropriate LED connection mode has positive significance for improving its lighting effect, working reliability, ease of design and manufacture of the driver, and efficiency of the entire circuit.

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