作者：Blade

OFN package for different low voltage led landscape lights

 

OFN package for different low voltage led landscape lights

 

Chip package is also very important, the QFN chip package is clearly better than the chip in a TSSOP package, thermal resistance is much lower. In the purchase of the module should understand the used chip package (as far as possible in a QFN package, to avoid using the TSSOP package).

 

Now give a concrete example to illustrate: if the solar low voltage led landscape lights uses a 12V battery, the load is 8-string 3 and 1W LED load voltage at the output is roughly 26.4V, the current is 1.05A, the output power of 27.7 W. If the 12V battery, the highest time in the voltage is 14.8V, the step-up ratio is 1.78, then do not have the radiator when the QFN package case temperature is about 60 degrees. Acceptable, but when the battery voltage drops to 10.8V, the step-up ratio becomes 2.44 times, and this time the shell temperature will rise to more than 70 degrees, if the TSSOP package case temperature will rise to about 85 degrees is not allowed!

 

In addition to the need to consider the case temperature, but also consider the maximum input current. SLM2842 the maximum input current of 3A. In the calculation of the maximum input current, we must consider the efficiency of the constant current module itself. Assumed to be 90% at the same time assumes that the output power is 32W, divided by 0.9 is 35.5W.

 

The number of series low voltage led landscape lights should be less than 10, this is because LED lamps have a safety requirements. Voltage led high bay lamps shall not exceed the maximum safety extra low voltage (SELV) according to EU standards of the IEC 61347-2-13 (5/2006), the requirements for DC or AC powered LED module, which is the work output voltage ≤ 25 Vrms (35.3 Vdc), so the total number of series LEDs is not more than 10

Constant current control module for LED street lamps

 

Constant current control module for LED street lamps

 

In the case of electricity, of course, the best AC-DC direct constant current output of the program.

This program can only provide a small power output (<40W) only the United States Power Integration company TOP250YN can provide 75W power output of the program. The circuit is very complicated, expensive, and low flexibility, which is not popular in mains led lighting applications.

 

LED street lamps direct constant current output power supply, but usually only a single output. If you want to multi-channel must be customized (large ones, and each current). On the one hand increases the cost, and will have any change would be very troublesome.

 

So in the case of electricity, the best first constant voltage power supply regulator and then using the constant current of multiple constant current module. The greatest advantage that we can get the highest efficiency in a variety of LED street lamps connection structure. Can choose the output voltage of the constant voltage source to achieve the best match. And high flexibility, it is easy to change their combination.

 

As a light source, the dimming is very important. Not only in order to get a more comfortable environment in the home, today, to reduce unnecessary electric light, in order to further the purpose of energy saving is more important. For the led high bay light source dimmer than other fluorescent lamps, energy saving lamps, high pressure sodium and other easy to implement, so it should be in all types of LED street lamps with dimming function.

The plate cooling of the outdoor LED spotlights

 

The plate cooling of the outdoor LED spotlights

 

LED chip is characterized by high heat in a minimal volume. The heat capacity of the LED itself, it must be the fastest heat conduction out, otherwise it will produce a high junction temperature. Heat leads to the chip outside, a lot of improvements in the outdoor LED spotlights chip structure.

 

In order to improve the heat dissipation of the LED chip itself, the most important improvement is the thermal conductivity of the better substrates. Early outdoor LED spotlights only Si silicon as the substrate. Later changed to sapphire as a substrate. The thermal conductivity of the sapphire substrate is not very good (at 100 ° C is about 25W / (mK)), Cree’s silicon carbide silicon substrate in order to improve the cooling of the substrate, its thermal conductivity (490W / (mK), nearly 20 times) than the sapphire. And sapphire silver plastic solid crystal, the thermal conductivity of the silver plastic is also very poor. Silicon carbide only drawback is the cost more expensive. Cree is the production of silicon carbide substrate led high bay lights.

 

Using silicon carbide as a substrate, can indeed greatly improve its heat, but its cost is too high, and patent protection. Recent domestic manufacturers began to use the silicon material as a substrate. Because the base of silicon materials not subject to patent restrictions. And the performance is better than sapphire. The only problem is the expansion coefficient of GaN and silicon that much difference, but prone to cracking, the solution is to add a layer of aluminum nitride (AlN) as a buffer in the middle.

How the junction temperature is produced in SMD high power LED

 

How the junction temperature is produced in SMD high power LED

 

LED heat because the added energy is not completely converted to light, but part of the conversion into heat. SMD high power LED light effect only 100lm / W, its electro-optical conversion efficiency of only about 20 to about 30%. That is about 70% of electrical energy into heat energy.

 

Specifically, the generation of SMD high power LED junction temperature is caused due to two factors.

 

1. The internal quantum efficiency is not high, and is compound when electrons and holes, and cannot be 100% to generate photons, commonly referred to as “leakage current” which PN carrier in the composite rate. Leakage current multiplied by voltage is the power of this part, which is converted into heat, but this is partially accounted for the main component of the internal photon efficiency is close to 90%.

 

2. Internally generated photons cannot be all shot to the external of the chip and the last is converted into heat, this part is the main, currently known as the external quantum efficiency is only about 30%, most were converted to heat.

 

Although the incandescent light efficiency is very low, around only 15lm / W, but it almost all the electrical energy into light energy radiate out, because most of the radiation is infrared, light efficiency is very low, but exempt cooling problems.

 

The most common civilian light is the incandescent lamp, which is our ordinary bulbs. If the SMD high power LED is to replace incandescent bulbs, it is necessary to develop a in terms of the lamp shape or appearance of similar bulbs and incandescent bulbs, which is often referred to as led high bay bulb. Imagine, Bulb market is very huge.

The heat dissipation of household LED bulbs used in the bathroom

 

The heat dissipation of household LED bulbs used in the bathroom

 

LED cooling is now more and more people attach importance to, this is because the household LED bulbs failure or life is direct and to the junction temperature, heat is not good to high junction temperature, short life of the law of temperature in accordance with Porto Vilnius reduce the life of 10 ℃ will be extended 2 times. Released from Cree, Inc. the light fades and the junction temperature diagram (Figure 1) can be seen, the junction temperature can be controlled at 65 ℃, then the light fades to 70% of the life of up to 100,000 hours! This is the life people dream, but really can be achieved? Yes, as long as to seriously deal with it the heat dissipation problem is likely to do! Unfortunately, the actual cooling of the LED lights, a far cry from this requirement! So that the life of the household LED bulbs into the main problems that affect its performance, it is necessary to be taken seriously!

 

To junction temperature of 25 degrees when the light-emitting 100%, then the junction temperature to rise to 60 degrees, only 90% of the amount of light emitted; junction temperature of 100 degrees down to 80%; 140 degrees, only 70%. Seen to improve heat dissipation, it is very important to control the junction temperature.

 

In addition to the heat of the led high bay light will be making its spectral shift; color temperature increased; forward current increases (constant power); reverse current increases; increased thermal stress; phosphor epoxy accelerated aging problems, so that the household LED bulbs heat dissipation is the most important issue in the design of the LED lamps.

 

 

Requirements for LED streetlight bulbs

 

Requirements for LED streetlight bulbs

 

Because you want to replace incandescent, so at least the following requirements:

Brightness should be very incandescent usually talk about wattage and not talk about the number of lumens. Although the LED also can talk about wattage, but due to the efficiency of LED streetlight bulbs are still evolving, saying only that the wattage does not mean that its lumen. The most commonly used incandescent lamp wattage of 15 watts, 30 watts, 45 watts, 60 watts, 75 watts and 100 watts. If you talk about the number of lumens, you can use incandescent light efficiency. Incandescent lamp luminous efficiency of 7.5-12lm / W The higher the wattage the greater the efficiency.

 

If using LED to replace, and can draw the appropriate wattage. However, because the led high bay luminous efficiency in the rising, it is difficult to give an accurate figure. Assumes the usual LED1, its luminous efficiency of 100lm / W, if the highest luminous efficiency of the LED2 is its luminous efficiency of 130lm / W (warm white light efficiency will be lower than this value). Can be drawn on the wattage of the two luminous efficiency LED. LED streetlight bulbs require constant current source, the constant current source efficiency is assumed to be 85%, In addition, because the LED can not adopt a transparent blister, but only using the milky foam shell. The transmittance of about 85%. They are multiplied together equal to 0.72. After considering the above factors can be drawn and incandescent lamps of equivalent wattage. Can be seen from the table, LED2 in the same brightness can save approximately 10 times the power. It should be of special note.

The applications of LED driver in mains LED lights

 

The applications of LED driver in mains LED lights

 

Very early that there have been a constant current diode, this diode is not a cause for concern, because it’s just as the current standard for some instrumentation. However, recently led the industry to flourish, these diodes are suddenly aroused widespread interest. Many foreign companies have developed products for driving mains LED lights because the led high bay light must be the reason of the constant current source driven. Here we will be in-depth discussion of the properties and applications of the constant current diode.

 

The ideal constant current source is an internal resistance for the infinite devices, irrespective of the voltage across the value, the current flows through will never change. Of course, this device could not exist. Constant-current diode is equivalent to a certain operating voltage range (for example, 25-100V), its current is constant for a particular value (eg 20mA).

 

And high-voltage LED compared discrete low-power mains LED lights. As mentioned earlier, high-voltage LED integrated LED a low-power discrete LED series and high-voltage LED external characteristic. The advantages of discrete LED’s flexibility, users needed the series of any number of LED to get the volt-ampere characteristic. Series and parallel can also be more flexible features. Discrete LED’s emitting surface can adjust (increase) in a certain range, so that luminous uniform, reduce glare. Separation of the mains LED lights heat dissipation area is relatively large, easy to disperse the heat, to simplify the design of the radiator. The integrated high-voltage mains LED lights reduces packaging costs. Integrated high-voltage LED reduce.

Analysis of the power supplier of household LED ceiling lights

 

Analysis of the power supplier of household LED ceiling lights

 

Here, the constant current diode is to input mains voltage changes to maintain the same output current, of course, can be eliminated due to the current caused by the household LED ceiling lights negative temperature coefficient increases. However, due to the pressure of the constant current diode to certain restrictions, so it can be absorbed by the supply voltage change is limited. 100V withstand voltage of the CRD, its operating voltage range is also minus its minimum operating voltage of 10V, the voltage range available, it was only 90V. 220V mains power supply, if the change of +10% to -20%, equivalent to the rectifier 290 ~ 211V, the voltage change of 79V in the range of its pressure. If the household LED ceiling lights 80, if the forward voltage of 3.3V, then the total voltage of 264V, exactly equivalent to 220V after bridge rectifier after the value. At this time there is no voltage drop across the constant current diode, but this time it is unable to work and need at least 10V voltage drop, which is required rectified voltage is 274V, the mains voltage is 228VAC. When the constant current diode voltage drop to a minimum, power consumption is minimum, only 0.03Ax10V = 0.3W, the overall efficiency of up to 96% (of course, but also consider the efficiency of the rectifier, in fact even lower). If power is increased to 242VAC, then the constant current diode voltage increased 26.4V, its power consumption is also increased to 0.79W, the efficiency of this time is equivalent to 91%.

 

Previously assumed that the led high bay light forward voltage drop of 3.3V, in fact even if its rated 3.3V, later in the boot of a period of time, the junction temperature increases, the forward voltage drop is reduced to 3.1V or even 3.0V.

The heat dissipation bathroom ceiling spotlights

 

The heat dissipation bathroom ceiling spotlights

 

Low-power bathroom ceiling spotlights beads, arranged dispersed, can contribute to the heat.

Ceiling structural characteristics conducive to heat dissipation.

 

1. the Internal block the free flow of air. This is the biggest advantages Ceiling compared to other lamps. Closed without the circulation of air is a good thermal insulation properties of the insulator, in turn, to the free flow of air is the best heat sink. All hot objects in the world’s last all the heat into the air to go. Ceiling floor there are a lot of holes in the Ceiling of the shade, the heat generated by the bathroom ceiling spotlights beads through the air immediately to pass to go outside.

 

2. Lampshade good heat dissipation. We know that the convection and radiation heat and the size and materials related to the effect of radiation cooling of the plastic is very good, and shade is thin, so the bad influence of the thermal conductivity of plastics can be ignored.

 

3. A large area: according to a circular area of ​​the formula: S = πr2, or S = π (d / 2) 2, a diameter of 45cm Round Ceiling, floor area is 1590cm2. Because Ceiling typically installed in the room, not too high at room temperature, so you can use the empirical data of 40cm2 / W, as can also be dispersed 40W of power. However, due to the floor near the ceiling, difficult to heat, so the actual cooling effect of the base plate will be worse. The key question is should install led high bay lights beads aluminum plate or PCB copper area has been large enough.

 

The composition and heat dissipation of the high performance led flash light

 

The composition and heat dissipation of the high performance led flash light

 

Not consider the gorgeous crystal ceiling lamps, ordinary high performance led flash light structure and ceiling lamps there is no difference. From the bottom shell, housing, power, light and other four parts.

 

Usually for power greater than 30W more than most of the 1W high performance led flash light beads, less than 30W of most of the low-power led high bay lamp (such as 3020,3014,3528, etc.). The recommended low-power LED chip, so that in the heat, can also increase the luminous uniformity. Lamp beads in accordance with their appearance to arrange, for example, assumes that the shape is round, light beads arranged in a circle, on the contrary, if the shape is square, then arranged in a square. Even so, the arrangement of the lamp beads are still there are many ways. It is 23 0.4W of 5730 high performance led flash light, for a total power of 18W. The middle of the rectangle for its constant current power supply, box the lower right corner, compared with remote control receiver photodiode, in order to receive infrared remote brightness control signal.

 

Need to be raised is still a large number of low-cost LED ceiling lamp with a low-power hat light, However, due to the thermal resistance of the straw hat lamp (450 ° C / W), it is difficult to heat export, and thus the light fades serious, life is very short .

 

The Ceiling Price has a few dozen to several hundred dollars, the foreign brands Ceiling to more than $ 600 As for the ceiling with crystal ornaments, the price is up more than a few thousand dollars everywhere, but its light only. However, at most, a 40W shaped fluorescent lamps. Ceiling unlike the ordinary energy-saving lamps are so cheap.