Discussion on ACLED constant current control technology

1. ACLED is not a change in the nature of the device

That is to say, there is actually no LED chip with an AC electric field working mechanism. The ACLED that has come out now is a device with a special arrangement of internal chipsets. It is just a change in the internal structure of the LED device. Of course, it is not easy to achieve such a level of technology. Most of the introductions to ACLED now quote the information published by Seoul Semiconductor. From this, it can be seen that it uses the traditional rectifier bridge circuit to solve the problem of AC power supply to the so-called DC LED. It seems that the advantage is that the rectifier diode is saved, but the reverse withstand voltage of the LED is limited. If it is damaged when the surge peak of the power grid is large, it is not necessarily a benefit. Because it is an imitation rectifier bridge circuit, only half of the current flows through the four bridge arms, while the DC load end flows through the entire current, resulting in a very uneven current distribution on each group of LEDs. If there is an undercurrent, it will affect the luminous lumen value and luminous efficiency. If there is an overcurrent, it will cause light decay and affect the life. The solution is also simple. Just remove the LED at the DC end and short-circuit it directly, and the current on the remaining four bridge arms will be consistent. Take a closer look at the circuit again. Now each group of forward and reverse LEDs has been connected in parallel. In fact, it was not necessary to make it too complicated at the beginning. As long as the forward and reverse are connected in parallel, the positive and negative half cycles of the AC can pass. 2. ACLED failed to avoid the indispensable constant current control technology. From the introduction, the current luminous efficiency of ACLED is not high enough compared with the ordinary LED. It is said that it is in the development stage and will be higher in the future. The author believes that the basis of the same type of LED chip itself is the same, and the main factor restricting the amount of light per watt is the type of rectifier bridge circuit. Imagine that only one of the five groups of LEDs can work normally and give full play to the luminous efficiency, and the remaining four groups, accounting for 80%, are working in an under-current state with poor luminous efficiency. No matter how much it develops together, it is naturally much lower than the luminous efficiency of ordinary LEDs. The way to improve it is to abandon the impractical rectifier bridge circuit, and directly connect the forward and reverse parallel connections so that all can work in the best state of luminous efficiency. There is no constant current protection function in ACLED. When using it, an external current limiting resistor must be connected. However, when the current is limited to the upper limit of the power supply voltage, it will work in an under-current low-luminous efficiency state at normal or low voltage. Resistor current limiting is a poor protection method. Not only is the function defective, but it also relies on energy consumption to work, which reduces the power utilization rate, that is, the energy efficiency. If you want to add a PTC to solve the LED constant current problem, you don't have a comprehensive understanding of the performance of this component. PTC is mainly used in overcurrent protection and thermal protection. When the current in the circuit is too large and the PTC reaches the Curie point temperature after heating, the resistance value rises sharply and approaches the circuit break. The demagnetization circuit in the color TV uses it to generate a large current attenuation amplitude demagnetization. When the PTC resistor is affected by the surrounding heat and the temperature exceeds the Curie point, it will be in an open circuit state, which can play a switching type thermal protection role. If you want to rely on the positive temperature coefficient characteristics of the PTC resistor to play a constant current protection role for the LED, you should also think about the following: 1. When the PTC resistor passes current, it takes a heating time to heat up. When the resistance has not increased to a high enough level, the current that may exceed the limit has already damaged the LED. 2. If the self-heating temperature of the PTC resistor is really able to control the constant current, then the influence of the high and low ambient temperature that may change by dozens of degrees will also make the change of this "constant current value" meaningless. If this can be extended to other applications, wouldn't it be possible to simply control the constant current of common LED devices? Unfortunately, it is not possible. Moreover, AC constant current is usually more troublesome than DC constant current. In fact, there are AC LED adaptive constant current drivers with simple circuits, low energy consumption, accurate constant current, surge resistance, high reliability, small size, and low cost, as well as various excellent products from many LED driver manufacturers. Instead of focusing on non-professional circuit technology, LED manufacturers should focus on developing low-cost, high-efficiency LED lighting products to better meet the market's needs.