3 common connection methods of LED lamp beads
The configuration of LEDs in an application depends on many factors, including application requirements, LED parameters and quantity, input voltage, efficiency, thermal management, size and layout constraints, and optics. The simplest configuration form is a single LE, and there are many application cases using this design, such as car interior dome lights (map lights, reading lights) and so on.
Since the power and brightness of LEDs are not very high at present, and the actual use occasions usually require flat lighting, it is necessary to arrange and combine multiple LEDs as required to meet the needs of large-scale, high-brightness, dynamic display, color conversion and other applications. requirements and matching requirements between LEDs and supporting drivers.
1. Common connection forms
1. Overall series connection
1.1 Simple concatenation form
Generally, in the simple series connection form, LED1~LEDn are connected end to end, and the currents flowing through the LEDs are equal when they work. For LEDs of the same specification and batch, although there may be slight differences in the voltage on a single LED, since the LEDs are current-type devices, they can ensure the same luminous intensity. 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 fault, the entire LED light string will be extinguished, affecting the reliability of use.
1.2 Series Form with Parallel Zener Diodes
A modified series connection of a Zener diode in parallel with each LED. 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 non-conductive, the current mainly flows through LED1~LEDn. Except for the faulty LED, the other LEDs still have current flowing through and emit light. Compared with the simple series connection, this connection method is greatly improved in reliability.
2. Overall parallel connection
2.1 Simple parallel form
In the simple parallel form, LED1~LEDn are connected in parallel end to end, and each LED bears 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 work, who passes the current of each LED is not equal. It can be seen that the impossibility of the current distribution of each LED can drastically reduce the life of LEDs with excessive current, or even burn them out. This connection method is relatively simple. However, the reliability is not high, especially for applications with a large number of LEDs, it is more likely to cause failures in use.
2.2 Parallel form of independent matching
For the reliability problems existing in simple parallel connection, the parallel form of independent matching is a good way. Each LED in this method has its own current adjustability (the V+ output terminals of the driver are L1~Ln, respectively), which ensures that the current flowing through each LED is within its required range, with good driving effect and a single LED. The protection is complete, the failure does not affect the work of other LEDs, and the LEDs with large differences can be matched. The main problems are: the structure of the entire driving circuit is relatively complex, the cost of the device is high, and the volume occupied is too large, which is not suitable for a large number of LED circuits.
3. Mixed form
The hybrid form is proposed by synthesizing the respective advantages of the series form and the parallel form. The main forms are as follows.
3.1 The mixed form of serial first and then parallel
When the number of applied LEDs is large, simple series or parallel connection is unrealistic, because the former requires the driver to output a very high voltage (n times the voltage VF of a single LED), while the latter requires the driver to output a large current (a single LED n times the current IF). This brings difficulties to the design and manufacture of the driver, and also involves the structural problem of the driving circuit and the overall efficiency problem. The product nVE of the number of LEDs connected in series and the operating voltage VF of a single LED determines the output voltage of the driver; the product of the number m of parallel LED strings and the operating current IF of a single LED determines the output current of the driver, and mIF* The nVF value determines the output power of the driver.
Therefore, the method of mixing strings and then parallel is mainly to ensure a certain reliability (the LED failure in each string only affects the normal lighting of the string at most), and to ensure the matching with the driving circuit (the driver outputs a suitable voltage ), which improves the reliability compared to the pure series connection. 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.
3.2 The mixed form of first parallel and then serial
A mixed form of several LEDs in parallel and then in series. Since LED1-n~LEDm-n are connected in parallel first, the reliability of each group of LEDs under fault is improved, but the current sharing problem of each group of paralleled LEDs is therefore very important.
To this end, it can be solved by pairing selection, using LEDs with the same working voltage and current as a group in parallel, or connecting each LED in series with a small current sharing resistor. The other characteristics and existing problems of this hybrid form are similar to those of the series first and then parallel connection.
3.3 Cross Array Form
The cross-array form is mainly to improve the reliability of LED work 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, the three LEDs will light up at the same time; once one or two of the LEDs fail to open, at least one LED can be guaranteed to work normally. In this way, the lighting reliability of each group of LEDs can be greatly improved, and the overall reliability of the entire LED lighting can also be improved.
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