Isolated LED driver power supply series solutions

Against the backdrop of global energy shortages and increasing environmental protection requirements, countries around the world are vigorously developing green energy-saving lighting. LED lighting, as a revolutionary energy-saving lighting technology, is developing rapidly. However, the requirements for LED driver power supplies are also increasing. High efficiency, high power factor, safety isolation, compliance with EMI standards, high current control accuracy, high reliability, small size, and low cost are becoming key evaluation indicators for LED driver power supplies.

Specific requirements for LED driver power supplies

LED is a low-voltage light-emitting device with the advantages of long life, high light efficiency, safety, environmental protection, and convenience. For AC input power drive, isolated output is based on safety regulations. The higher the efficiency of the LED driver power supply, the more it can play the advantages of high light efficiency and energy saving of LED. At the same time, high switching operating frequency and high efficiency make the entire LED driver power supply easy to install in compact LED lamps. High constant current accuracy ensures the brightness and light color consistency when LED lighting is used in large quantities.

Application solutions for LED lamp cups below 10W

At present, LEDs below 10W are widely used, and many integrated products have been launched, that is, LED driver power supplies and LED lamps are integrated in one lamp, which is convenient for users to use directly. Typical lamp specifications include GU10, E27, PAR30, etc.

For this application, we designed the following solution (see Figure 1).


Figure 1 Schematic diagram of LED driver circuit based on AP3766

The features of this solution are as follows.

1 Based on the latest LED dedicated driver chip AP3766, it adopts primary side control mode, without optocoupler and secondary current control circuit, to achieve isolated constant current output, and the circuit structure is simple. The primary current is detected by resistor R5, the primary current peak is controlled to be constant, and the switch duty cycle is controlled at the same time to keep the conduction time of the output diode D1 constant and the ratio of the entire switch cycle time, so as to achieve constant output current.

2 AP3766 adopts proprietary "sub-microampere startup current" technology, which only requires 0.6μA startup current, thus reducing the power consumption on the startup resistors R1 and R2 and improving system efficiency. The typical 5W application efficiency is greater than 80%, and the no-load power consumption is less than 30mW.

3 AP3766 adopts constant current tightening technology to achieve vertical constant current characteristics with high constant current accuracy.

4 The number of circuit components is small. AP3766 adopts SOT-23-5 package, which is small in size. The whole circuit can be installed in a lamp cup of common specifications.

5 It is safe and reliable, with isolated output, and has output open circuit protection, overvoltage protection and short circuit protection functions.

6 The power switch tube adopts a triode, eliminating the high-voltage field effect tube, and the system cost is low.

Figure 2 is a real photo of the 5W application circuit prototype of this solution. Figure 3 is a real photo of the 5W LED driver based on AP3766. Figure 4 is a curve of the full load efficiency of the 5W LED driver circuit based on AP3766 changing with the AC input voltage. Figure 5 is a full load output IV characteristic curve of the 5W LED driver circuit based on AP3766.


Figure 2 Actual photo of the 5W LED driver circuit prototype based on AP3766

Figure 3 Actual photo of the 5W LED driver device based on AP3766

Figure 4 Efficiency curve of the 5W LED driver circuit based on

AP3766 Figure 5 5W10~60W power LED street lamp and LED straight tube lamp application solution based on AP3766

The IEC International Electrotechnical Commission has put forward clear harmonic requirements for lighting fixtures, namely the IEC61000-3-2 standard. Therefore, for higher power LED lighting applications, it is necessary to adopt power factor correction (PFC) control technology. For applications below 60W, there is a cost-effective single-stage PFC control solution, and the circuit schematic of this solution is shown in Figure 6.

Figure 6 Schematic diagram of LED driver circuit based on AP166+AP4313