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LED lamp beads common connection form

1, the overall series form (1) simple series form

In the simple serial connection form, LED1~LEDn are connected end to end, and the current flowing through the LED is equal. For the same-size and batch LEDs, although the voltage on a single LED may have a slight difference, since the LEDs are current-type devices, it is possible to ensure that the respective luminous intensities are consistent, which is a simple series connection. The LED has the characteristics of simple circuit and convenient connection. However, due to the series connection, when one of the LEDs has an open circuit failure, the entire LED string will be extinguished, which affects the reliability of use.

(2) Series form with parallel Zener diodes

Each LED is connected in parallel with a modified series connection of Zener diodes. In this connection, the breakdown voltage of each Zener diode is higher than the operating voltage of the LED. When the LED is working normally, since the Zener diodes VD1~VDn are not conducting, the current mainly flows through the LED1~LEDn. When the LED string is damaged by the LED, the VD1~VDn is turned on, except In addition to the faulty LED, other LEDs still emit current through the current. This type of connection is greatly improved in reliability compared to a simple series.

Overall parallel form (1) simple parallel form

The LEDs 1~LEDn in the simple parallel form are connected in parallel at the beginning and the end, and each LED is subjected to the same voltage during operation. It can be seen from the characteristics of the LED that it is a current-type device, and a small change in the voltage applied to the LED will cause a large change in the current. In addition, due to the limitation of LED manufacturing technology, even the same batch of LEDs, the difference in performance is inherent, so when LED1~LEDn is working, the current of each LED is not equal. It can be seen that the insufficiency of the current distribution of each LED can cause the life of the LED with excessive current to be sharply reduced or even burned out. This connection is simpler. However, the reliability is not high, especially for applications where the number of LEDs is large, which is more likely to cause malfunctions.

(2) Independently matched parallel form

For the reliability problem existing in simple parallel, the independent matching parallel form is a good way. Each LED in this mode has its own current adjustability (driver V+ output is L1~Ln, respectively), ensuring that the current flowing through each LED is within its required range, with a good driving effect, a single LED When the protection is complete and the fault does not affect other LEDs, it can match the characteristics of LEDs with large differences. The main problem is that the structure of the whole driving circuit is complicated, the cost of the device is high, and the occupied volume is too large, which is not suitable for a large number of LED circuits.

Mixed form

The hybrid form is proposed by combining the respective advantages of the series form and the parallel form. The main forms are as follows.

(1) The form of mixing after the first string

When the number of LEDs used is large, simple series or parallel connection is not realistic. The former requires the driver to output a very high voltage (n times the single LED voltage VF), and the latter has to drop the driver to output a large current (single LED). n times the current IF). This causes difficulties in the design and manufacture of the driver, and also involves structural problems of the drive circuit and overall efficiency issues. The product of the number of LEDs in series and the operating voltage VF of a single LED, nVE, determines the output voltage of the driver; the product mf of the number of parallel LED strings and the operating current IF of a single LED determines the driver output current, while mIF* The nVF value determines the output power of the driver.

Therefore, the hybrid mode after the hybrid string is mainly to ensure a certain reliability (the LED fault in each string only affects the normal illumination of the string at most), and the matching with the driving circuit is ensured (the driver outputs a suitable voltage) ), which improves reliability over a simple series. 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.

(2) Mixed form of first and last strings

A number of LEDs are mixed first and last. Since LED1-n~LEDm-n are connected in parallel first, the reliability of each group of LED faults is improved, but the current sharing problem of each group of parallel LEDs is crucial.

For this reason, LEDs with the same working voltage and current as the parallel group can be selected by pairing, or a small current sharing resistor can be connected to each LED in series. Other features and problems with this hybrid form are similar to those of the first string and then the connected form.

(3) Cross array form

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

2. Comparison of different connection forms

Different connection types have different characteristics, and the requirements for the driver are also different, especially in the case of a single LED failure, the operation of the circuit, the reliability of the overall illumination, the ability to ensure that the overall LED can continue to work, and reduce the overall LED failure rate and so on are particularly important.

All in all, the group application of LEDs is an important way of practical application of LEDs. Different LED connections are critical to the ease of use of a wide range of LEDs and the design requirements of the drive circuit. Therefore, in the combination of actual circuits, the correct selection of the appropriate LED connection mode has positive significance for improving the effect of light emission, reliability of work, convenience of design and manufacture of the driver, and efficiency of the entire circuit.

LED lighting module failure and solution

Phenomenon: all LEDs flash;

Problem: poor contact;

Solution: Re-fix or plug in the loose position;

Phenomenon: LED is dim;

Question: 1. The LED polarity is reversed;

2, the LED is too long;

3. The switching power supply and the LED voltage label are inconsistent;

Solution: 1. Ensure correct wiring of positive and negative poles;

2. Reduce the connection of LEDs;

3. Ensure that the switching power supply is consistent with the LED voltage label;

Phenomenon: LED lights of some lines are not bright;

Question: 1. Is the connection direction correct?

2. Whether the power output wiring is correct;

3. The power cord is plugged in and reversed;

Solution: 1. Remove and re-plug in the correct direction;

2. Make sure that the red wire is connected to the positive pole and the black wire is connected to the negative pole;

3, find the part of the inserted line; reconnect;

Phenomenon: all LEDs are not bright;

Problem: 1. The switching power supply has no voltage output;

2. Whether the output of the switching power supply is correct;

Solution: 1. Test power is connected to the input end of the switching power supply;

2. Whether the positive and negative terminals of the power supply are correct;