Design of led driver

- Sep 04, 2018-

LED driver power supply design is not difficult, but it must be known. As long as the calculation before commissioning, measurement during commissioning, and aging after commissioning, I believe anyone can do a good job of LED.


1, LED current size
Everyone knows that if the LEDripple is too large, the LED life will be affected, and the impact will be large, but there is no specific indicator.


2, chip fever
This is mainly for the high-voltage driver chip of the built-in power supply modulator, which reduces the power consumption of the chip, and does not introduce additional power consumption to dissipate heat.


3, power tube fever
Regarding this issue, I have also seen people posting in the forum. The power consumption of the power tube is divided into two parts, switching loss and conduction loss. For LED mains drive 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 and the driving capability and operating frequency of the chip. Therefore, to solve the heat generation of the power tube, it can be solved from the following aspects:

A. The MOS power transistor cannot be selected according to the on-resistance of the one-sided surface, because the smaller the internal resistance, the larger the cgs and cgd capacitance.
B. The rest is the frequency and chip drive capability. Here we only talk about the frequency effect. The frequency is also proportional to the conduction loss. Therefore, when the power tube is hot, the first thing to think about is 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 increased or the inductance is also increased, 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), which requires an additional load capacitor.


4, working frequency down frequency

Downsizing is mainly caused by two aspects. The ratio of input voltage to load voltage is small and 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, the minimum point of the minimum current setting;

b, clean wiring, especially the critical path of sense;

c, the small point of the inductor selection or the inductance of the closed magnetic circuit ;

d, add RC low-pass filter, this effect is a bit bad, C's consistency is not good, the deviation is a bit large, but for lighting should be enough.


5, the choice of inductor or transformer
In view of the high-power LED operating voltage of only 3V, 220V AC is converted to DC by full-bridge rectification, the voltage drop across the bridge is about 1.8V, and the power utilization efficiency of driving only one LED is only 60%. More than three LEDs must be connected in series to achieve a total power utilization efficiency of more than 80%.


According to the principle of 3 primary color synthetic white light, three 1W high-power LEDs of red, green and blue are connected in series, and the brightness achieved by the LED equivalent to 3W white light can be obtained. At the same time, it can also combine 6 kinds of colored light to satisfy people's preference for changing color light.