"High-voltage LED" is a kind of low-power LED that is provided by LED manufacturers in series. As shown in Figure 1, it is a kind of integrated LED; and the main difference between the integrated LED and the former shown in Figure 2 is: the former is All are connected in series, the latter being in series and parallel. The integrated LED is characterized by a slotting method on a large wafer, which is cut into a number of small LEDs, and then the trenches are filled with an insulating layer, and the wires connecting the LEDs are laid in accordance with the series and parallel requirements. 
Figure 1 High voltage LED (all in series)
Figure 2 High voltage LED (serial and parallel)
The linear high-voltage LED driver scheme discussed in this article is a smaller current (less than 100mA), higher voltage LED driver scheme.
The load characteristics of the LED are shown in Figure 3. According to the load characteristics of the LED, the high voltage LED needs to have a controlled constant current source to control. After rectifying the power frequency AC voltage, if this voltage is directly applied to the output LED, constant current cannot be achieved, that is, the LED current is not constant throughout the power frequency cycle: 1. The brightness can not be controlled; 2. LED lamp beads Life expectancy is greatly reduced. According to different control requirements, the main constant current control methods are: switching power supply drive, RC capacitor, constant current diode and linear high voltage drive.
Second, the technical route "PK"
1, linear high voltage drive vs high frequency switching power supply driver
The MOSFET is connected in series with the LED lamp bead load, so that the MOSFET is closed-loop controlled by the LED load current and operates in the linear region, so that the line produces a "constant current-transformation" effect, so that the LED load passes through a constant current, and the series connection The MOSFET is subjected to varying voltages. This is similar to the working principle of LDO (Low Dropout Regulator low dropout linear regulator). Simply put, this is how linear high voltage drive LEDs work.
The high-frequency switching power supply driver converts the AC mains into the voltage and current required by the LED through high-frequency switching and magnetic components. The high frequency switching power supply driver is divided into two types: isolated and non-isolated.
Compared with the high-frequency switching power supply, the advantages of the linear high-voltage scheme are mainly: the circuit is simple, the circuit works in the power frequency linear mode, not in the high-frequency mode, eliminating the high-frequency inductance, and there is no EMI problem, eliminating the EMC. Circuit.
The high-frequency switching power supply drive is much more complicated than the linear high-voltage scheme, but it can flexibly realize various load output requirements. The two applications are different and are not comparable in the strict sense. We next focus on comparing the linear high voltage solution with its main competitors: the traditional RC solution and the diode drive solution.
2, linear high voltage drive VS resistance-capacitance buck drive VS diode drive
The working principle of RC is to limit the maximum operating current by the capacitive reactance generated by the capacitor at a certain AC signal frequency. The capacitor buck is actually using the capacitive reactance current limit, while the capacitor acts as a limiting current and dynamically distributing the capacitor and the load. The role of the voltage. As shown in Fig. 4, since the on-resistance of the rectifier tube is only a few ohms, the dynamic resistance of the Zener diode VS is about 10 ohms, the current limiting resistor R1 and the load resistance are generally 100-200 ohms, and the filter capacitor is generally 100 uF-1000 uF. Its capacitive resistance is small and can be ignored. If R is used to represent the equivalent resistance of all components except C1, you can draw the AC equivalent circuit as shown in the following figure in Figure 4, and satisfy the condition of >R, so you can draw the voltage vector because R is very small, R The voltage drop across is also much smaller than the voltage drop across C1, so VC1 is approximately equal to the supply voltage V, ie =V. According to the electrician principle, taking 1uF and 50Hz AC as an example, the series capacitor capacitance is 3185 ohms (1/2*3.14*50*10e-6), and the average DC current after the rectification is Id.
The constant current diode scheme uses a constant current diode to directly drive the LED, but we must pay attention to selecting the proper current and withstand voltage when using the constant current diode for LED driving.
1, the lowest voltage. Since the constant current diode requires a certain voltage Vk to enter the constant current, the too low power supply voltage cannot work. Usually this Vk is about 5-10V, so most battery-powered LEDs don't work.
2. Maximum current Because the power consumption of the constant current diode is limited, excessive current is not suitable. For example, a 1W LED usually requires 350mA, and a constant current diode is difficult to provide.
3. At present, the most suitable use occasion is to exchange AC power supply LED lamps. It is most suitable to use a series of small power LEDs in series, that is, high voltage and small current.
Figure 5 is a constant current diode driving source for a bulb lamp. The load is 80 3014, the total power is 8W, and the constant current diode used is also constant current at 30mA. If the constant current diode at hand is only 5 mA, 6 parallel connections are required.
Here, the role of the constant current diode is to keep the output current constant when the input mains voltage changes. However, since the withstand voltage of the constant current diode is limited, the variation of the power supply voltage that it can absorb is also limited. For the CRV with 100V withstand voltage, it can only deal with limited voltage changes in 220VAC mains power supply. After 220VAC is bridge rectified, its output DC voltage is about 311V. If the mains changes by -10%-+20%, it is equivalent to 280V-373V after rectification, and the voltage changes by 93V. If the number of LEDs used is 80, the total voltage is 240V. When the mains voltage fluctuates to 264VAC, it is 373V after bridge rectification. At this time, the voltage difference has exceeded the withstand voltage of the constant current diode, and the safety is greatly reduced, so the voltage of the LED is severely limited in use.
Figure 3 LED load characteristics
Figure 4: Resistor-capacitor step-down drive high-voltage LED
Figure 5 uses a constant current diode as the LED driver
III. Program test PK
1. Resistor-capacity application (using 60 60MA 2835 lamp beads for load)
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2, diode solution application
Example: 80 3014 series bulbs were used, and 5 Semitek S-562Ts were connected in parallel. When it inputs different mains voltages, the measured results are shown in the table below.
3, the use of linear drive Solutions
ORG5910 constant power scheme application line:
Test data (45V for 6V/30mA lamp beads):
ORG5910 constant current solution application line:
Test data (90V for 3V/30mA lamp beads):
ORG5910 full patch high PFC solution application line:
Test data (13 18V 3020 lamp beads as load):
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