According to the power grid rules and the characteristics of LED-driven power supply requirements, in the selection and design of LED driving power to take into account the following nine major performance characteristics requirements:
1. High reliability, especially like LED street lamp driving power supply, installed in the high-altitude, maintenance inconvenient, maintenance costs are also large.
2. High efficiency LED is energy-saving products, the efficiency of driving power is higher. Especially important is the structure of the power supply installed in the luminaire. Because the LED's luminous efficiency decreases with the increase of LED temperature, so the cooling of LED is very important. The efficiency of the power supply is high, its attrition power is small, the calorific value in the lamp is small, also reduces the lamp temperature rise. It is advantageous to delay the LED's light failure.
3. High power factor power factor is the demand of power grid to load. General 70 Watts below the power of the device, there is no mandatory indicators. Although the power factor of a single electrical appliance is low, the effect on the power grid is small, but at night everyone lights up and the same load is too concentrated, which will cause more serious pollution to the power grid. for 30 Watts ~ Watts LED Drive power, it is said that in the near future, may have a certain degree of power factor requirements.
4. Drive mode Now there are two types: one is a constant pressure source for a number of constant current source, each constant current source for each led power supply. This way, the combination of flexible, led failure, do not affect the work of other LEDs, but the cost will be slightly higher one points. The other is direct constant current power supply, led in series or parallel operation. It has the advantage of low cost, but less flexibility, but also to solve an LED failure, does not affect other led operation. These two forms coexist in a period of time. Multi-channel constant current output power supply mode, in the cost and performance will be better. Perhaps the main direction in the future.
5. Surge protection of the ability of the LED surge resistance is relatively poor, especially against reverse voltage. It is also important to strengthen protection in this area. Some LED lights are installed outdoors, such as LED street lamps. Due to the power grid load and lightning induction, from the grid system will invade a variety of surges, some surges will cause damage to the LED. Therefore, the LED power supply to inhibit the intrusion of surges, to protect the ability of the LED is not damaged.
6. The protection function power supply in addition to the regular protection function, it is best to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature too high.
7. Protection of the external installation of lamps, power supply structure to waterproof, moisture-proof, the shell to withstand sun.
8. The life of the driving power supply should be matched with the life of the LED.
9. To meet the requirements of safety and electromagnetic compatibility.
With the increasingly wide application of LED, the performance of LED power supply will be more and more suitable for LED.
Seven principles for determining the quality of LED-driven power supply
1, give up more than 4 outputs, the development of single or two output, give up large current and large current, the development of small current.
The more the output number of the more complex, the different way out of the current interference to solve the cost is high, if not solve the failure rate is higher. In addition, the more output, the greater the total output current, and the current is the main cause of fever, the voltage itself does not directly lead to fever, simply, the heat and the square of the current is proportional, that is, the current increase to twice times the original, the heat will increase to the original 4 times times, the current increased to 3 times times the original, the heat will increase to 9 times To sum up, single or two-way output LED lamp power failure rate will be much lower.
2, intelligent control is one of the advantages of LED lighting, and the power supply is the key to intelligent control.
Intelligent control in LED street lights and LED tunnel lighting application conditions most mature effect most obvious, intelligent control can realize the stepless control of lamp power in different time period, according to the density of road traffic flow, which not only satisfies the application requirement, but also realizes the huge energy saving effect, which can save a lot of funds for the highway supervisor. The application of tunnel illumination can not only save energy, but also automatically adjust the entrance brightness of the tunnel according to the brightness of the tunnel, and provide the driver with an excessive visual phase to ensure the driving safety.
3, give up high-power, ultra-high power, choose the high stability of small and medium-sized power supply.
Because the greater the power, the greater the heat, the more compact parts inside, not conducive to cooling, and the temperature is the main culprit of power failure. In addition, small power supply is relatively mature, stability and cost advantages. In fact, a lot of high-power power solutions have not been verified by time and practice proved that the project is a rush to mount, are experimental products, so the fault is endless. In contrast, small and medium power supply due to the development of earlier, technical solutions to be more mature.
4. Heat dissipation and protection are the main external factors of power failure.
Not only the power itself will be hot, lamps and lanterns will also be hot, the two kinds of heat source how reasonable to emit out is the lamp design engineer must consider the problem, must prevent the excessive concentration of heat, form the heat island effect, affect the power supply life. It is a good choice to adopt the separation power scheme.
5. Maintenance feasibility.
The fault problem of power supply cannot be completely avoided, and the principle of simplicity of maintenance is put forward by Chengdu towards the moonlight. Only the replacement of the power supply with conventional lighting light source replacement is so simple, the user can be happy, even if the power is bad, the mood is not too bad, and the user's mood determines the fate of LED manufacturers.
6. Protection performance.
Protection problem is also very important, water infiltration may cause a short circuit of the power supply, the dust on the shell will affect the cooling of the power supply, exposure is easy to cause high temperature and the aging of wires and other components, from the experience of actual use, the rotating wiring plug failure rate is higher, most of the leakage caused
7. Modular design.
Modular design has become the current trend, must be in the integration of power module, if the power supply can be used to solve maintenance problems, will be welcomed by the user, but also need to establish the interface standardization, so that different manufacturers of LED lamp power can be universal.
Summary: LED light source is best used in Split-style design, at the same time pay attention to the reliability and longevity of power supply, even if the increase of one point cost, only stand in the customer's point of view to design products, enterprises can get long-term development.
Five principles for simplifying led design
This is mainly aimed at the high voltage driver chip of the built-in power modulator. If the chip consumes a current of 2mA, 300V voltage is added to the chip, the chip power consumption is 0.6W, of course, causes the chip to heat up. The maximum current of the drive chip comes from the consumption of the driving power MOS tube, and the simple calculation formula for ISCVF (considering the charging effect of the resistor, the actual I 2Cv, wherein C is the CGS capacitance of the Power MoS tube, V is the gate voltage of the power tube conduction, so in order to reduce the power consumption of the chip, we must find ways to reduce C, V and F. If C, V, and F cannot change, then try to divide the power dissipation of the chip into the device outside the chip, and be careful not to introduce additional power More simply, consider a better heat dissipation.
Power Tube Heating
On this issue, I have seen people posting in the forum. Power Tube's power consumption is divided into two parts, switching loss and conduction loss. It should be noted that most of the occasions, especially the LED mains drive applications, the switch damage is much more than the conduction loss. Switching loss and power tube CGD and CGS, as well as chip driving capacity and operating frequency, so to solve the power tube heating can be resolved from the following aspects: A, can not be one-sided according to the size of the conduction resistance to choose MOS power tube, because the smaller the internal resistance, CGS and CGD capacitance. such as 1n60 CGS for around 250pF, 2n60 CGS around 350pF, 5n60 CGS for 1200pF around, the difference is too big, select Power tube, enough on it. B, the rest is the frequency and chip drive capacity, here only talk about the impact of frequency. Frequency and conduction loss is also proportional, so power tube heating, first of all to think about is not a bit high frequency selection. Try to reduce the frequency! Note, however, that when the frequency decreases, in order to get the same load capacity, the peak current is bound to become larger or the inductance becomes larger, which may cause the inductor to enter the saturated region. If the inductance current is large enough, consider changing the CCM (continuous current mode) to DCM (discontinuous current mode) so that a load capacitance is added.
This is also the user in the debugging process is more common phenomenon, frequency reduction mainly by two of aspects. The input voltage and the load voltage ratio are small, the system interferes greatly. For the former, be careful not to set the load voltage too high, although the load voltage is high, efficiency will be higher. For the latter, you can try the following aspects: A, the minimum current set to a smaller point; B, the wiring clean point, especially sense this critical path, C, the selection of the inductance of the small point or the use of closed magnetic circuit inductance; d, add RC Low-pass filter bar, this effect is a bit bad, C consistency is not good, the deviation is a bit large, but for the lighting should be enough. In any case, the frequency reduction is not good, only bad, so must be solved.
Inductance or transformer selection
Finally talked about the focus, I have not started, can only nonsense point saturation effect. A lot of user response, the same driving circuit, with a production of the inductor is no problem, with the B production of the inductor current becomes smaller. In this case, look at the inductance current waveform. Some engineers do not notice this phenomenon, directly adjust the sense resistance or operating frequency to achieve the required current, this may seriously affect the life of the LED. Therefore, before the design, reasonable calculation is necessary, if the theoretical calculation parameters and debugging parameters are a bit far, to consider whether the frequency reduction and transformer saturation. When the transformer is saturated, l will become smaller, resulting in a sharp increase in the peak current increment caused by the transmission delay, then the peak current of the LED is also increased. On the premise that the average current is unchanged, only the light fades.
LED Current size
We all know Ledripple too big, led life will be affected, the impact of how much, have not seen any experts said. Previously asked the LED factory this data, they said within 30% can accept, but later did not go through the verification. It is advisable to try to control the dots as much as possible. If the heat dissipation solution is not good, the LED must reduce the amount of use. Also hope that experts can give a specific indicator, otherwise affect the promotion of LED.
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