Shenzhen Lux Lighting Co.,Ltd.



Shenzhen Lux Lighting Co.,Ltd.

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LED lights of the five major technical barriers to break Raiders

This paper mainly for high-voltage driver chip with built-in power supply modulator analysis. The purpose is to be able to reduce the loss of MOS tube. The following analysis of the main aspects of the MOS tube burning from the reasons for non-stop, and gives a reasonable approach.
1, the chip fever
This content mainly for the built-in high-voltage power supply driver chip modulator. If the chip current consumption of 2mA, 300V voltage added to the chip above, the chip's power consumption is 0.6W, of course, will cause the chip fever. The maximum current of the driving chip is from the consumption of the driving power MOSFET. The simple calculation formula is I = cvf (considering the charge resistance of charging, the actual I = 2cvf, where c is the cgs capacitance of the power MOS tube, v is the power tube conduction When the gate voltage, so in order to reduce chip power consumption, we must think of ways to reduce the c, v and f. If c, v and f can not be changed, then think of ways to chip power is divided into devices outside the chip, The introduction of additional power consumption. And then simply, is to consider a better heat it.
2, the power tube fever
On this issue, have seen someone posted in the power network forum posted. The power dissipation of the power transistor is divided into two parts, switching loss and conduction loss. It should be noted that most occasions, especially LED drive applications, switching damage is much greater than the conduction losses. Switching loss and power of the cgd and cgs and chip driving ability 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 resistance to select the MOS power transistor, because the smaller the resistance, cgs and cgd larger capacitance. Such as 1N60 cgs for 250pF or so, 2N60 cgs for about 350pF, 5N60 cgs for 1200pF or so, the difference is too large, select the power tube, enough on it.
B, the rest is the frequency and chip-driven, and here only talk about the impact of frequency. Frequency and conduction loss is also proportional to, so the power tube heat, we must first think about is not a bit high frequency selection. Try to reduce the frequency of it! It should be noted, however, that when the frequency is reduced, the peak current must be larger or the inductance will become larger in order to obtain the same load capacity, which may cause the inductor to enter the saturation region. If the inductor saturation current is large enough, consider changing the CCM (continuous current mode) to DCM (discontinuous current mode), so you need to add a load capacitor.
3, the working frequency down
This is also the user in the debugging process is more common phenomenon, mainly by the two leading frequency down. The input voltage and load voltage ratio is small, the system interference. For the former, be careful not to set the load voltage is too high, although the load voltage is high, the efficiency will be high. For the latter, you can try the following aspects:
A, the minimum current set to a small point;
B, clean wiring, in particular the sense of this critical path;
C, select the inductance of the small point or use the closed magnetic circuit inductance;
D, plus RC low-pass filter it, this effect is a bit bad, C consistency is not good, the deviation a bit large, but for lighting should be enough.
In any case there is no benefit down, only bad, so we must solve.
4, the choice of inductance or transformer
Finally talked about the key, and I have not started, can only be blind to the effect of saturation. Many users reaction, the same drive circuit, with a production inductor no problem, with the production of b inductor current becomes smaller. In this case, to look at the inductor current waveform. Some engineers did not notice this phenomenon, directly adjust the sense resistor or operating frequency to achieve the required current, this may seriously affect the LED life. So, before the design, a reasonable calculation is necessary, if the theoretical calculation of the parameters and debugging parameters are a bit far, to consider whether the frequency and the transformer is saturated. Transformer saturation, L will become smaller, resulting in transmission delay caused by a sharp increase in the peak current increase, then the peak current LED also followed. In the average current under the premise of the same, can only watch the light fades.
5, LED current size
We all know LEDripple over the General Assembly to make LED life affected, as the impact of how much, have not seen which experts said. LED plant previously asked the data, they said within 30% can be accepted, but later failed to verify. Suggestions or try to control the small points. If the cooling solution is not good, LED must be derated use. Also hope that experts can give a specific indicator, or else affect the promotion of LED.
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