Introduction to non-isolated buck power supply design method
The non-isolated step-down power supply is a commonly used power supply structure, accounting for almost 90% of the fluorescent lamp power supply. Many people think that the non-isolated power supply is only a kind of buck type. Whenever it is said that it is not isolated, it thinks of the buck type, and it is thought that the lamp is not safe (refer to the power supply damage). In fact, the buck type is not just one type, there are two basic structures, namely boost, and buck-boost, ie BOOST AND BUCK-BOOST, even if the latter two power supplies are damaged. Will not affect the benefits of LED . The buck power supply also has its advantages. It is suitable for 220, but it is not suitable for 110. Because the voltage of 110V is low, the drop is lower, so the output current is large, the voltage is low, and the efficiency is not too high. The buck type 220V AC is about 300V after rectification and filtering. After the step-down circuit, the voltage is generally reduced to about 150V DC, so that high-voltage and small-current output can be realized, and the efficiency can be made higher. Generally, MOS is used as a switch tube to make power of this specification. My experience is that it can be as close as 90%, and it is difficult to go up. The reason is very simple, the chip generally has a self-loss of 0.5W to 1W, and the fluorescent tube power supply is only about 10W. So it is impossible to go up again. Now that power efficiency is a virtual thing, many people are blowing, and the actual situation is not at all.
Some people often say that 3W's power efficiency is 85 percent, and it is still isolated. Tell everyone that even in the frequency hopping mode, the no-load power consumption is the smallest, it is 0.3W, and what is the output 3W low voltage, which can reach 85%, in fact, 70% is very good, anyway now Many people brag about not drafting drafts, can fool the layman, but now do not know much about LED power.
I said that to be efficient, we must first do non-isolated, and then output specifications and high voltage and small current, which can save the conduction loss of power components, so the main loss of such LED power supply, one is the chip itself. Loss, this loss generally has a fraction of a few W to a W, and one is the switching loss. Using MOS as the switching transistor can significantly reduce this loss, and the loss of the triode is much larger. So try not to use a triode. There is also a small power supply, it is best not to save too much, do not use RCC, because the general manufacturers of RCC circuits simply do not do quality, in fact, the chip is also cheap, ordinary switching power supply chip, integrated MOS tube, up to two yuan Money, there is no need to save a little bit, RCC only saves material costs, in fact, the cost of processing and repairing is higher, and it is not worth the loss.
The basic structure of the buck power supply is to string the inductor and load into the high voltage of 300V. When the switch is switched, the load is lower than 300V. There are many specific circuits and many online. I will not draw a picture. Now 9910, there are generally constant current ICs on the market that are basically implemented with this circuit. But this kind of circuit is when the switch tube breaks down, the whole LED light board is finished, which should be regarded as the worst place. Because when the switch tube breaks down, the entire 300V voltage is applied to the lamp board. The lamp board can only withstand more than one hundred volts, and now it is three hundred volts. This happens. The LED must be burned. Therefore, many people say that non-isolation is not safe. In fact, it means bucking, just because the vast majority of non-isolated is buck, so it is considered that non-isolated damage must be bad LED. In fact, the other two basic non-isolated structures, the power supply is damaged, will not affect the LED.
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