LED drive power design

by:MOSO     2019-12-11
It's not difficult, but we must know something. As long as the calculation before debugging, measurement during debugging, aging after debugging, I believe anyone can do a good job of LED. 1. LED current Everyone knows that if the LEDripple is too large, the life of the LED will be affected, and how much the impact is, but there is no specific indicator. 2. Chip fever This is mainly for the high-voltage driver chip with built-in power modulator, to reduce the power consumption of the chip, do not introduce additional power consumption, and do a good job of heat dissipation. 3, power tube heating Regarding this issue, I have also seen people post in the forum. The power consumption of the power tube is divided into two parts, switching loss and conduction loss. For LED mains driving applications, the switching damage is much greater than the conduction loss. The switching loss is related to the cgd and cgs of the power tube, as well as the driving ability and operating frequency of the chip, so to solve the heat generation of the power tube, it can be solved from the following aspects: A. The MOS power tube cannot be selected according to the on-resistance, because the smaller the internal resistance, the larger the cgs and cgd capacitance. B. The rest is the frequency and the chip's driving ability. Here we only talk about the impact of frequency. The frequency is also proportional to the conduction loss, so when the power tube heats up, you must first think about whether the frequency selection is a bit high. When the frequency is reduced, in order to obtain the same load capacity, the peak current must be larger or the inductance also larger, which may cause the inductor to enter the saturation region. If the inductor saturation current is large enough, you can consider changing the CCM (continuous current mode) to DCM (discontinuous current mode), so you need to add a load capacitor. 4.Frequency reduction of working frequency Frequency reduction is mainly caused by two aspects. The ratio of input voltage to load voltage is small, and the system interference is large. For the former, be careful not to set the load voltage too high, although the load voltage is high, the efficiency will be high. For the latter, you can try the following aspects: a. Set the minimum current point again; b. Clean the wiring, especially the critical path of sense; c. Select the small point of the inductor or use a closed magnetic circuit inductor ; D, add RC low-pass filtering, this effect is a bit bad, the consistency of C is not good, the deviation is a bit large, but it should be enough for lighting. 5, the choice of inductor or transformer In view of the working voltage of the high-power light-emitting diode is only 3V, the full-bridge rectification is used to convert 220V AC power to DC power. The voltage drop across the full-bridge is about 1.8V, and the power utilization efficiency of driving only one LED is only 60%. More than three light-emitting diodes must be connected in series to make the total power utilization efficiency exceed 80%. According to the principle of 3 primary colors to synthesize white light, three red, green, and blue 1W high-power light-emitting diodes are connected in series to work, and the brightness equivalent to 3W white-emitting LED can be obtained. At the same time, six kinds of colored light can be combined to meet people's preference for changing colored light.
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