The load characteristics of the LED itself greatly affect the reliability of driving it with a switching power supply. The load characteristic of the LED, that is, the volt-ampere characteristic, is a diode characteristic. Within a certain interval, the voltage across the LED rises, causing its current to grow exponentially and exploding. Therefore, many LED lamps driven by switching power supplies exhibit many unstable characteristics. The reason is that the output of the switching power supply is not very clean and smooth DC voltage (current) energy, but a very complex energy signal, which can be roughly regarded as smooth.
The LED is very sensitive to voltage changes. When the LED is operating at a stable current, the voltage across it is generally between 3.0 and 3.6V (the power LED is slightly different). When the voltage applied to the two ends is slightly fluctuated, The current at both ends will change drastically, and the output power of the power supply will change drastically. If there is a sudden increase in the grid voltage, and the output voltage changes little at this time, a large output current will be generated, and the power will increase sharply, and the accident will occur.
Practice has proved that in the circuit, adding various voltage suppression components, such as TVR, TVS, the effect is not very obvious, the damage will still be damaged, the reliability of the LED drive power can never be as good as other power supplies, this is The fact that exists objectively. Although many people say that there is no problem with the LED power supply they do, the actual situation is nothing but pale and powerless self-comfort, because he did not solve the fundamental problem.
Reliability and efficiency are mutually constrained. High-efficiency power supplies, reliability must be reduced, and reliability must be improved. Power efficiency must be sacrificed. Because of the effect of the input voltage on the output voltage, the electrical energy must undergo multiple layers of conversion. To give a simple example, the reliability of the BUCK circuit is usually not too high, but the BUCK-BOOST circuit is better than BUCK, which is proven by practice. Because people who know the principle of power supply know that when the switch tube is turned on, the LED load and inductance are in series with 300V high voltage. At this time, the LED is directly powered by 300V, and the BUCK-BOOST circuit is separately supplied to the inductor. During the turn-off period, the BUCK circuit is the inductor and then the load is freewheeled. When the BUCK-BOOST circuit is turned off, the inductor conducts energy to the LED load. The difference between the two is that the BUCK circuit has a period of time, it is directly powered by 300V, while the latter is stored in the inductor first, and then the energy is transferred from the inductor to the LED load, so the latter is highly reliable because of its passing. The path is long. The long way of transmission will reduce the efficiency. Generally, the efficiency of the BUCK-BOOST circuit is 2-5 percentage points lower than that of the BUCK circuit.
Therefore, the current LED driver power supply is generally better than non-isolated reliability, and the low-voltage reliability is better than high-voltage. It is under the constraint of this law, that is, the efficiency is improved, the reliability is sacrificed, and the reliability is improved. Reliability, we must reduce efficiency.
In fact, the problem is caused by the load characteristics of the LED. The fundamental method is to improve the load characteristics of the LED string, but the method of improving the load characteristics is still the means of sacrificing efficiency. The easiest way to improve the load characteristics is to string in the resistors in the LED string. The larger the resistor string, the more stable the load characteristics. Of course this is to reduce efficiency. Another good way is to add a linear constant voltage device, use a triode, and make a regulating tube. The triode is equivalent to a variable resistor. In this case, the reliability should be higher (in theory, practical experience) not yet). Therefore, it can be basically concluded that the most reliable LED driving method is actually: ordinary constant voltage power supply plus linear constant current device, of course, the efficiency is not too high. When efficiency is high, reliability is down.
Editor: Li Jie
Jinhu Weibao Trading Co., Ltd , https://www.weibaoxd.com