The lighting and lighting project of the LED lighting industry is influenced by the global environment as well as its industry specificity.
LED street light power supply is precisely the top priority of LED development. For the related design of LED technology, there are already many solutions and unique design methods. Let's take a look at it one by one.
1. Why does the LED light power supply have to be constant?
The characteristics of LED lighting materials determine that they are greatly affected by the environment. For example, if the temperature changes, the current of the LED will increase, and the voltage will increase, and the current of the LED will also increase. Long-term operation beyond the rated current will greatly shorten the LED bead usage time. The LED constant current is to ensure that the operating current value does not change when environmental factors such as temperature and voltage change.
2, LED light power supply constant current accuracy
The constant current accuracy of some power sources on the market is poor, and the constant current scheme such as the popular recommended scheme on the market has an error of ±8% and the constant current error is too large. The general requirement is ±3%. According to the 3% design. The production power supply should be fine-tuned to achieve ±3% error.
3, LED lamp power supply operating voltage
The recommended operating voltage of general LED is 3.0-3.5V. After testing, most of the work is at 3.2V, so it is reasonable to calculate according to 3.2V. The total voltage of N lamp beads in series = 3.2* N
4, LED lamp power supply is the most suitable working current
For example, the rated working current of LED is 350 mAh. Some factories use it at the beginning and design 350 mA. In fact, the working heat is very serious at this current. After many comparison tests, it is ideal to design 320 mA. . Minimize heat and turn more electrical energy into visible light.
5. How wide are the series and parallel connection of the LED lamp power supply board and the wide voltage?
In order for the LED lamp power supply to operate in the wide range of input voltage range AC85-265V, the LED series-parallel connection of the lamp board is very important. Try not to use a wide voltage, can be divided into AC220V, AC110V as much as possible to classify, in order to ensure power supply reliability. Since the current power supply is generally a non-isolated buck constant current power supply, when the required voltage is 110V, the output voltage should not exceed 70V, and the series number does not exceed 23 strings. The output voltage can reach 156V when the input voltage is 220V. That is to say, the number of series is not more than 45 strings. Do not use too many parallel connections, otherwise the operating current is too large and the power supply is hot. There is also a wide voltage scheme. APFC active power compensation is to first raise the voltage to 400V with L6561/7527, and then step down, which is equivalent to two switching power supplies. This program is only used under certain conditions.
6, Isolated / non-isolated
Generally, the isolated power supply is made into 15W and placed in the LED street lamp power supply tube. The transformer is large in size and difficult to put in. Mainly depends on the specific structure of the space, the isolation can only be 15W, less than 15W, and the price is very expensive. Therefore, the cost performance of isolation is not high, generally non-isolated is more mainstream, the volume can be made smaller, the minimum can be as high as 8 mm, in fact, non-isolated security measures are done, there is no problem. Space can also be used to isolate power.
7. How can the LED light power supply match the lamp bead?
220*1.414=312V, half of the peak voltage is 156V. On the non-isolated basis, the output wave is the upper half wave and there is no lower half wave. Therefore, the LED street light power bead series number is the most customers first design the light board, then find the power supply. It is found that it is difficult to have a suitable power supply, or the current is too large, the voltage is too small (such as 7X1WI>350mA, or V<20V); or the current is too small, the voltage is too high (such as I<200mA or V>25V), resulting in The result is severe heat generation, low efficiency, or insufficient input voltage range. In fact, choosing the best string parallel connection method, the voltage and current applied to each LED is the same, and the power supply effect can achieve the best performance. The best way is to communicate with the power supply manufacturer and tailor it. Or self-produced power.
8, LED series and parallel and PFC power factor
The isolated input AC220V high-voltage electrolytic capacitor capacity is generally 1W=1UF, AC110V1W=2UF. There are three kinds of power supply PFCs on the market: one is a special circuit without PFC without power factor compensation, and its PF value is generally 0. .65 or so; two kinds of passive power factor compensation PFC circuit, that is, passive power factor compensation lamp, also called flow-by-flow circuit board is currently the most widely used reliability, PF value is generally around 0.92; Also use three kinds of active active 7527/6561 circuit, that is, active power factor compensation, called AC220V in APFC circuit, AC110V can use the same capacity of electrolytic capacitor, choose 1W = 1.5UF. The PF value can reach 0.99, but the cost of this solution is slightly less expensive than the second solution. So the second option is more used. For passive PFC circuits: also known as valley-filled PFC circuits, the DC operating voltage range is half of the peak value of the AC input voltage. If the input is 220V, the peak value is more than 45 strings. Therefore, in order to get a relatively large power factor, the number of series connection of the lamp bead should not be too small, otherwise the optimal working condition will not be achieved. The number of series connection on the isolated power supply is related to the number of turns of the auxiliary winding, which must be done. The power supply must meet the output power. The smaller the operating current of the electronic component in the rated voltage operating range, the longer the heating time will be, and the shorter the time will be. LED street light power beads are sensitive to the amount of AC. The higher the AC volume, the worse the light comfort. Generally, an electrolytic capacitor is used to maintain the voltage, and the voltage of the output terminal is reduced as much as possible. The capacity of the electrolytic capacitor at the bottom end cannot be too small, and the ratio of the capacity to the output current is 1 UF < 1.5 MA, otherwise the LED will flicker. The non-isolated input high-voltage electrolytic capacitor is selected in the same way as the isolated type, and the output capacitor is selected to be 1UF<6MA. Dimming LED power supply at the output of the electrolytic capacitor to meet 1UF <0.5MA.
9, LED lamp power efficiency
This parameter is especially important for input power minus output power. The higher the value, the lower the efficiency. This means that a large part of the input power is converted into heat. If it is installed in the lamp, it will produce a very high temperature. In addition, the energy emitted by one of our LEDs will be superimposed to produce a higher temperature. And the time of all the electronic parts inside our power supply will shorten with the increase of temperature. Therefore, efficiency is the most fundamental factor in determining the power supply. The efficiency cannot be too low, otherwise the heat consumed on the power supply is too large. The non-isolated efficiency is higher than the isolation type, generally more than 80%, but the efficiency is related to the matching method of the light board.
10, LED light power supply cooling
The main factor of the heat dissipation scheme is that the LED lamp power supply bead can be used under the hot condition to greatly extend the use time. Generally, the aluminum alloy is used, which is more convenient for heat dissipation. That is, the LED lamp power supply bead is attached to the aluminum substrate, and the external heat dissipation area is maximized.