LED lights of the five major technical barriers to break Raiders
This article mainly for the built-in power supply modulator high-voltage driver chip analysis. The purpose is to be able to reduce the loss of MOS tube. Here mainly from the five aspects of the MOS tube burn non-stop reasons, and give a reasonable approach.
1, The chip fever
This content is mainly for built-in power supply modulator high-voltage driver chip. If the chip current consumption of 2mA, 300V voltage added to the chip above, the chip power consumption of 0.6W, of course, will cause the chip heat. The maximum current of the driving chip is derived from the consumption of the driving power MOS tube. The simple calculation formula is I = cvf (consider the charge efficiency of the charge, 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 the power consumption of the chip, you must think of ways to reduce c, v and f. If c, v and f can not change, then think of the chip power to the chip outside the device, The introduction of additional power. Then a little easier, is to consider a better cooling it.
2, Power tube fever
On this issue, but also seen someone posted in the power network forum posted. Power tube power consumption is divided into two parts, switching losses and conduction losses. It should be noted that, in most cases, especially LED mains drive applications, the switch damage is much greater than the conduction loss. Switching losses and power cgd and cgs and the chip drive capacity and operating frequency, so to solve the power tube heat can be resolved from the following aspects:
A, Can not be based on the size of the on-chip resistance to select the MOS power tube, because the smaller the internal resistance, cgs and cgd capacitance greater. Such as 1N60 cgs is about 250pF, 2N60 cgs is about 350pF, 5N60 cgs is about 1200pF, the difference is too big, select the power tube, enough to be on it.
B, The rest is the frequency and chip-driven ability, and here only talk about the frequency of the impact. Frequency and conduction loss is also proportional to, so the power tube fever, the first thing to think about is not a bit high frequency selection. Think of ways to reduce the frequency of it! It should be noted, however, that when the frequency is reduced, the peak current must become large or the inductance becomes large in order to obtain the same load capacity, which may cause the inductance 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 operating frequency down frequency
This is also the user in the debugging process is more common phenomenon, the frequency is mainly caused by two aspects. The input voltage and the load voltage ratio is small, the system interference is big. 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:
A, The minimum current will be set and then small points;
B, wiring clean point, especially the sense of this critical path;
C, the inductance of the choice of small points 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 is a bit big, but for lighting should be enough.
No matter how the frequency is not good, only bad, so be sure to solve.
4, Inductance or transformer selection
Finally talked about the focus, I have not got started, only blindly said the impact of saturation. A lot of user response, the same drive circuit, with a production of the inductor is no problem, with b production of the inductor current becomes smaller. In this case, look at the inductor current waveform. Some engineers did not notice this phenomenon, directly adjust the sense of resistance or operating frequency to reach the required current, this may seriously affect the life of the LED. So, before the design, reasonable calculation is necessary, if the theoretical calculation of the parameters and debugging parameters are a bit far away, to consider whether the frequency down and the transformer is saturated. When the transformer is saturated, L becomes smaller, resulting in a sudden increase in the peak current increment caused by the transmission delay, and the peak current of the LED is also increased. In the average current unchanged under the premise, can only look at the light failure.
5, LED current size
We all know that LEDripple over the General Assembly to LED life is affected, as to how much impact, have not seen which experts said. Previously asked the LED factory this data, they said that within 30% are acceptable, but later did not verify. Suggestions or try to control small points. If the heat to solve the bad, then the LED must be used in derating. Also hope that experts can give a specific indicator, or else affect the promotion of LED.