In the current life, in order to save energy and electricity, LED has been greatly promoted, but LEDs need to have a Power Supply driver, its quality will directly affect the life of the LED, so how to make a good LED drive power supply is an LED power designer The top priority.
1. The drive circuit directly affects the LED life
The LED driver we mentioned includes two types of digital driver and analog driver. Digital driver refers to digital circuit driver, including digital dimming control, RGB full color change and so on. Analog drive refers to analog circuit drive, including AC constant current Switching Power Supply and DC constant current control circuit. The drive circuit is composed of electronic components, including semiconductor components, resistors, capacitors, inductors, etc. These components have a service life, any one device failure will lead to the failure of the entire circuit or part of the function. The service life of the LED is 50,000-100,000 hours, which is calculated according to 50,000 hours, continuously lit, and has a life of nearly 6 years. The life of the switching power supply is difficult to reach 6 years. The warranty period of the ** switching power supply on the market is generally 2-3 years. The power supply that reaches the 6-year warranty is military grade, and the price is 4-6 times that of the ordinary power supply The lamp factory is difficult to accept. Therefore, the failure of LED lamps is mostly the failure of the driving circuit.
2. Heat dissipation
LED is a cold light source, the working junction temperature cannot exceed the limit, and a certain margin should be left when designing. The design of the whole luminaire should consider the aspects of beautiful appearance, convenient installation, light distribution, heat dissipation and so on. We must find a balance among many factors, so that the overall luminaire is the best. The development time of LED lamps is not long, there is not much experience to learn from, and many designs are constantly improved. Some LED lighting manufacturers use external power supply or outsourcing. The lighting designers don't know much about power supply. The heat dissipation space for LED is large and the power supply space is small. Generally, it is necessary to find a suitable power supply to match after designing the lamp, which will bring certain difficulty to the matching of the power supply. It is often encountered that due to the small internal space of the lamp or the high internal temperature, and the low cost control, it is impossible to allocate a suitable power supply. Some LED lamp manufacturers have power supply research and development capabilities, which can be evaluated at the beginning of the design of the lamp and the design of the power supply can be synchronized to solve the above problems. In the design, the heat dissipation of the LED and the power supply must be comprehensively considered, and the temperature rise of the lamp should be controlled as a whole, so that a better lamp can be designed.
3. Problems in power supply design
a. Power design. Although the LED light efficiency is high, there is still 80-85% of heat energy loss, resulting in a temperature rise of 20-30 degrees inside the lamp. If the room temperature is 25 degrees, the inside of the lamp will be 45-55 degrees. The power supply is in a high temperature environment for a long time. Under the work, to ensure the life, you must increase the power margin, generally leave a margin of 1.5-2 times.
b. Component selection. When the internal temperature of the lamp is 45-55 degrees, the internal temperature rise of the power supply is still about 20 degrees, and the temperature near the component must reach 65-75 degrees. The parameters of some components will drift at high temperature, and some will shorten the life, so the device should be selected to be used at a higher temperature for a long time, pay special attention to electrolytic capacitors and wires.
c. Electrical performance design. The switching power supply is designed for LED parameters, mainly constant current parameters. The size of the current determines the brightness of the LED. If the batch current error is large, the brightness of the entire batch of lamps is uneven. And the temperature change can also cause the power supply output current to shift. Generally, the batch error is controlled within +/- 5% to ensure the consistency of the lamp brightness. There is a deviation in the forward voltage drop of the LED, and the constant current voltage range of the power supply design should include the voltage range of the LED. When multiple LEDs are used in series, the minimum voltage drop times the number of series connections is the lower limit voltage, and the maximum voltage drop is times the number of series connections as the upper limit voltage. The constant current voltage range of the power supply is slightly wider than this range. Leave a margin of 1-2V.
d. PCB layout design. The size of the LED lamps reserved for the power supply is small (unless it is external to the power supply), so the requirements on the PCB design are high, and there are many factors to consider. The safety distance should be sufficient, requiring input and output isolated power supplies, the primary side circuit and the secondary side circuit require a withstand voltage of 1500-2000VAC, and at least 3MM distance must be left on the PCB. If the lamp is a metal shell, the safety distance between the high-voltage part and the shell should also be considered for the layout of the entire power supply. If there is no space to ensure a safe distance, other measures must be used to ensure insulation, such as drilling holes on the PCB, adding insulating paper, and potting insulating glue. In addition, the layout also needs to consider the heat balance, the heating elements should be evenly distributed, can not be placed centrally, to avoid local temperature rise. The electrolytic capacitor is far away from the heat source, slowing down the aging and prolonging the service life.
e. Certification issues. At present, there is no standard for LED lamps in China. The relevant national departments are studying and formulating. The certification of domestically sold lamps is based on the standards of lighting lamps, and the certification of CE or UL is exported, and some are based on foreign LED lamps. Therefore, in view of this situation, it is difficult to design the switching power supply to meet these standards at the same time. We can only meet different certifications for different requirements.
4. Use parameters
The selection of purchased power supply mainly depends on the constant current and the voltage range of the constant current. The constant current value is selected as the standard current of the LED is lower. The choice of voltage range should be moderate, try not to choose a larger range, to avoid waste of power.
APM 120V Smps Power Supply is widely used in automatic testing sector. The average conversion efficiency is 90%, the load regulation is low, which ensure stable output when the load is changing constantly. The Programmable Power Supply supports standard SCPI communication protocol, which is convenient for user`s secondary development.
Some features of the Adjustable Power Supply as below:
- Ultrafast respond time and high efficiency.
- Accurate voltage and current measurement capability
- Constant Power and wide range of voltage and current output
- Equips with LIST waveform editing function
- Support RS232/RS485/LAN/USB (standard) ,GPIB (optional)
- Master/Slave parallel and series operation mode for up to 10 units
- Built-in standard automobile electrical testing curves
- Full protection: OVP/OCP/OPP/OTP/SCP
- Voltage drop compensation by remote sense line.
- Have obtained CE,UL,CSA,FCC.ROHS
120V DC Power Supply,Lab DC Power Supply,DC Regulated Power Supply,High Voltage Power Supply
APM Technologies (Dongguan) Co., Ltd , https://www.apmpowersupply.com