What are the key points in LED driver power supply?

What are the key points in LED driver power supply?

In order to save energy and electricity, LED has been widely promoted, but LED requires a power driver, which directly affects the lifespan of LED. Therefore, how to do a good LED driver power supply is the top priority for LED power supply designers. This article introduces some issues with LED driver power supplies, hoping to provide some help to engineers.

Guangdong hensoo Power Technology Co., Ltd

1. The driving circuit directly affects the lifespan of LED

The LED driver we refer to includes two types: digital driver and analog driver. Digital driver refers to digital circuit driver, including digital dimming control, RGB full-color transformation, etc. Analogical drive refers to analog circuit drive, including AC constant current switching power supply and DC constant current control circuit. The driving circuit is composed of electronic components, including semiconductor components, resistors, capacitors, inductors, etc., all of which have a service life. The failure of any one component will lead to the failure of the entire circuit or partial functional failure. The service life of LED is 50000 to 100000 hours, calculated as 50000 hours, continuously lit, with a lifespan of nearly 6 years. The lifespan of switch mode power supplies is difficult to reach 6 years. The warranty period of switch mode power supplies sold on the market is generally 2-3 years, and the price is 4-6 times that of ordinary power supplies. It is difficult for general lighting manufacturers to accept. So the faults of LED lamps are mostly caused by driver circuit faults.

2. Heat dissipation issues

LED is a cold light source, and the working junction temperature cannot exceed the limit value. A certain margin should also be left in the design. The design of the entire lighting fixture should consider many aspects such as beautiful appearance, easy installation, light distribution, heat dissipation, etc. A balance point should be sought among many factors, so that the overall lighting fixture is the best The development time of LED lighting fixtures is not long, and there are not many experiences to learn from. Many designs are constantly improved. Some LED lamp manufacturers use outsourced or purchased power supplies, and lamp designers have limited knowledge of power supplies. They provide more heat dissipation space for LEDs and less heat dissipation space for power supplies. Usually, after designing the lighting fixtures, it is necessary to find a suitable power supply to match them, which can bring certain difficulties to the matching of the power supply. It is common to encounter situations where the internal space of the lighting fixture is small or the internal temperature is high, and the cost control is low, making it unable to be matched with a suitable power source. Some LED lighting manufacturers have the ability to research and develop power supplies. By evaluating the initial design of lighting fixtures and synchronously designing the power supply, the above problems can be solved. In the design, it is necessary to comprehensively consider the heat dissipation of LED and power supply, and control the overall temperature rise of the lighting fixtures in order to design better lighting fixtures.

3. Problems in power supply design

a. Power design. Although LED has high light efficiency, there is still 80-85% thermal energy loss, resulting in a temperature rise of 20-30 degrees inside the lamp. If the room temperature is 25 degrees, there will be a temperature rise of 45-55 degrees inside the lamp. If the power supply works in a high-temperature environment for a long time, it is necessary to increase the power margin to ensure its lifespan, usually leaving a margin of 1.5-2 times.

b. Component selection. When the internal temperature of the lamp is between 45-55 degrees, and the internal temperature rise of the power supply is still about 20 degrees, the temperature near the component should reach 65-75 degrees. Some components may experience parameter drift and shortened lifespan under high temperature conditions, so it is important to choose components that can be used for a long time at higher temperatures, with special attention to electrolytic capacitors and wires.

C. Electrical performance design. Switching power supply is designed for LED parameters, mainly constant current parameters. The magnitude of the current determines the brightness of the LED. If the batch current error is large, the brightness of the entire batch of lights will be uneven. Moreover, temperature changes can also cause the output current of the power supply to shift. Generally, batch error control is within+/-5% to ensure consistent brightness of the lamp The forward voltage drop of LED has deviation, and the constant current voltage range of the power supply design should include the voltage range of LED. When multiple LEDs are used in series, the minimum voltage drop multiplied by the number of serial connections is the lower limit voltage, and the maximum voltage drop multiplied by the number of serial connections is the upper limit voltage. The constant current voltage range of the power supply is slightly wider than this range, generally leaving a margin of 1-2V for each upper and lower limit.

d. PCB layout design The size of LED lighting fixtures left for the power supply is relatively small (unless it is an external power supply), so there are many factors to consider in PCB design. Sufficient safety distance should be left, and input and output power sources should be isolated. The primary and secondary circuits should have a voltage resistance of 1500-2000VAC, and a minimum distance of 3mm should be left on the PCB. If it is a metal shell lamp, the distribution board of the entire power supply also needs to consider the safe distance between the high-voltage part and the shell. If there is no space to ensure a safe distance, other measures should be taken to ensure insulation, such as drilling holes on the PCB, adding insulation paper, and sealing insulation adhesive. In addition, the distribution of heating elements should be evenly distributed and not placed in a centralized manner to avoid local temperature rise. Electrolytic capacitors are kept away from heat sources, slowing down aging and extending their service life.

e. Certification issues. At present, there is no standard for LED lighting fixtures in China, and relevant national departments are studying and formulating it. The certification of lighting fixtures sold domestically is based on the standards of lighting fixtures, while those sold abroad are certified with CE or UL, and some are based on foreign LED lighting fixture standards. So, in response to this situation, it is quite difficult for the design of switch mode power supplies to simultaneously meet the above standards. We can only meet different certifications for different requirements.

4. Use parameters.

The selection of external power sources mainly depends on the voltage range of constant current and constant current. The constant current value is selected as below the standard current of the LED. The selection of voltage range should be moderate, and a larger range should be avoided as much as possible to avoid power waste.