Explore the most reliable LED street light power supply

An LED street lamp lights up 40 1W LEDs. Let's use this as a ratio and list several solutions to compare their advantages.

The first method is non-isolated buck drive, a string of constant current. The biggest advantage of this method is the highest efficiency. 40 in a row, 350MA constant current, but the reliability is not very good, because non-isolated circuits have this weakness. Although the efficiency is high, the reason for the high efficiency is that a large part of the energy in the power grid is directly added to the LED, and the role of the power supply is only to temporarily store part of the energy and then release it at an appropriate time. Therefore, interference in the power grid is easily added to the LED, and the LED is a nonlinear load. When the current is stable, the voltage is at a certain value, which is generally around 3.3V. When there is an instantaneous high voltage in the power grid, it is generally called a surge voltage. Because the LED load is in series with a 300V filter electrolytic, the high voltage will be directly added to both ends of the LED. At this time, due to the characteristics of the LED, a large current will flow instantly, which is equivalent to a short circuit, and the detection part of the constant current power supply will be instantly damaged, and even the constant current source chip will be damaged . Therefore, many current step-down circuits will damage the switch tube , especially the 9910. Many people say that, in fact, step-down power supply drives LEDs with such limitations. Therefore, non-isolated circuits, although efficient and low cost, can only be used in cheap occasions, such as consumer occasions, where the risk of damage can be borne. Therefore, although this method is the most efficient, it is definitely the first to be PASSed.

The second type is the isolated high-voltage constant current source. This method is slightly better, but the efficiency is lower than the non-isolated one. However, the most important point is that the output voltage is too high. If the voltage is too high, there will always be a problem. For example, the power supply will be easily damaged by a short circuit, and its input surge resistance is relatively poor. Facts have proved that the reliability of the LED driver power supply with high-voltage output is not as high as that of the LED driver power supply with low-voltage output. However, the reliability of the LED driver power supply with low-voltage output has been improved, but the efficiency has been reduced. Reliability and efficiency are contradictory, and only a balance point can be selected.

Because high voltage is not good, low voltage is thought of, but low voltage must be divided into several parts, so there is a third method, first constant voltage, then divided into constant current, the reliability of this method is of course better than the above two, but the efficiency is of course lower. However, the risk of street lamps is too great, first of all, of course, the reliability must be high, and the efficiency is second.
But in fact, this method is not the best, it is completely superfluous. The mistake is that the latter stage also needs constant current. For example, what do you want to do with these 40 LEDs? First reduce the voltage to 50V, and then make four-way constant current, ten in the first road. Let's not talk about the increase in cost, put it aside, and talk about efficiency first. Generally, DC/DC, 350MA, is only 90%, right? If you use a constant voltage power supply, the voltage of ten is about 33V, and then make a 5R resistor , the voltage value is just less than 2V, accurately set the voltage, and let the current reach about 350MA. In this way, the efficiency will not be lower than that DC/DC. Let's talk about reliability. As long as the power of a resistor is large enough, it is definitely more reliable than your circuit. In addition, the LED driver circuit is most afraid of surge voltage at the input stage. Adding a resistor directly is good for suppressing surges. Otherwise, the surge will be transmitted to the DC constant current part, and the possibility of damaging the DC part will increase. In fact, it is not necessary to first keep the voltage constant, then keep the current constant, and divide it into several strings. It is better to keep the voltage constant directly and limit the current with resistors, which is more convenient, efficient, and reliable.

The above are just the principle discussion. Let's take a look at the actual situation of the power supply now. This is basically needless to say. It is because of LED that many people began to study and make constant current power supplies. But in general, these constant current sources, whether non-isolated, isolated, high-voltage, or low-voltage, are far inferior to constant voltage power supplies in terms of technical maturity and rich application experience. Especially in conventional constant voltage power supplies, if you want high reliability, you can choose those industrial power supplies, just use 36V industrial-grade power supplies, pick the good brands, use Mingwei or something, if you want to find certification, there are all kinds of certifications, UL has them. Which constant current power supply you see now has any certification? This is very important. Conventional constant voltage power supplies are mature, and constant current power supplies are not mature.

Therefore, whether from the analysis of principle or the actual status of the switching power supply industry, taking into account both reliability and efficiency, it can be said that the best LED street lamp driver power supply with the best reliability and the highest practical feasibility is: conventional 36V industrial-grade constant voltage power supply! (Please indicate the source for original reprints from Power Network)