First, ACLED is not a fundamental change in the device.
That is to say, there is actually no LED chip for the working mechanism of the alternating electric field. The ACLED that is now available is a special arrangement of internal chip sets, which is only a change in the internal structure of the LED device. Of course, this level of technology is also required. not easy.
Most of the introductions to ACLEDs are quoted from Seoul Semiconductor. It can be seen that it uses the traditional rectifier bridge circuit to solve the problem of AC so-called DC LED power supply. It seems that the advantage is that the rectifier diode is omitted, but the reverse voltage withstand voltage of the LED is limited. If the surge peak of the power grid is large, it will not be beneficial.
Because it is an analog rectifier bridge circuit, only half of the current flows through the four bridge arms, and the DC load terminal flows through the entire current, causing the current distribution on each group of LEDs to be quite uneven. For example, the undercurrent will affect the luminous lumen value. And luminous efficiency, such as overcurrent, causes light decay and affects life.
To solve the problem is also simple, just remove the DC terminal directly after the short circuit, the remaining four bridge arm current can be consistent. Looking at the circuit carefully, it has now become a parallel connection between the forward and reverse LEDs of each group. In fact, it didn't have to be too complicated in the first place. As long as the forward and reverse parallels, the exchange can pass both positive and negative for half a week.
Second, ACLED failed to avoid the essential constant current control technology
From the introduction, the current LED light efficiency and the usual LED ratio is not high enough, it is said to be the development stage, will be higher in the future. The author believes that the basis of the same LED chip itself is the same, the main limitation of the amount of watts per watt is the rectifier bridge circuit type. Imagine that only one of the five groups of LEDs can work normally, giving full play to the light effect. The remaining four groups, which account for 80%, work in the under-current state with poor light efficiency. How to develop along with it, it is also inherently better than the ordinary LED's luminous efficiency. The method of improvement is to abandon the unusable rectifier bridge, and the direct forward and reverse parallel connections can all work in the state with the best luminous efficiency.
There is no constant current protection function in ACLED. When used, it must be connected with a current limiting resistor. However, when it is limited to the upper limit of the power supply voltage, it will work in the low light effect state of undercurrent at normal or low voltage. Resistor current limiting is a poor protection method. It not only has functional defects, but also relies on energy consumption to make the power utilization rate lower.
If you want to add a PTC to solve the LED constant current problem, it is not comprehensive enough to understand the performance of the 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 open circuit. The degaussing circuit in the color TV uses it to generate a large current attenuation amplitude. Degaussing.
When the PTC resistor is affected by the surrounding heat, the temperature will become an open state when the temperature becomes above the Curie point, which can function as a switch type thermal protection.
If you want to rely on the positive temperature coefficient of the PTC resistor to protect the LED from constant current, you should also think of it:
1. The PTC resistor passes the current. There is a heating time process to heat up. When the resistance has not increased enough, the current that may have been exceeded has already damaged the LED.
2, the self-heating temperature of the PTC resistor body can really control the constant current, then the effect of high and low ambient temperature changes of several tens of degrees should make this "constant current value" change meaningless.
Can be widely used, isn't the current LED device now simple and constant? Unfortunately, it can't be done. And usually AC constant current is more troublesome than DC constant current.
In fact, there can be support for various types of excellent products such as circuit simplification, control energy consumption, constant current accuracy, surge resistance, high reliability, small size, low cost, and many excellent products of LED driver manufacturers. . LED manufacturers and their efforts to focus on non-professional circuit technology, it is better to focus on the development of low-cost, high-efficiency LED lighting products will be more able to meet the market demand.
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