Four major problems of LED drive power design are summarized

Time:2018-10-20 Views:344

The quality of LED drive power will directly affect the life of LED. Therefore, how to make an LED drive power is the top priority of LED power designers.

In the current life, in order to save energy and power, LED has been widely popularized, but LED needs to have a power driver, and its quality will directly affect the life of LED. Therefore, how to do a good LED driver is the top priority of LED power designers.This article introduces some problems of LED drive power supply, hoping to provide some help to engineers.

1. Drive circuit directly affects LED life

The LED drivers we talked about include digital drive and analog drive, digital drive exponential circuit drive, including digital dimming control, RGB full color changing and so on.Analog drive refers to analog circuit drive, including AC constant current switching power supply, DC constant current control circuit.The driving circuit is composed of electronic components, including semiconductor components, resistances, capacitors, inductors, etc., all of which have a service life. Failure of any device will result in failure of the whole circuit or partial function.The service life of LED is 5,000-100,000 hours, and it is continuously lit by 50,000 hours, with a life of nearly 6 years.The service life of switching power supply is very difficult to reach 6 years. The quality warranty period of ** switching power supply on the market is generally 2-3 years. The power supply that reaches 6 years is military grade, and the price is 4-6 times of the ordinary power supply.Therefore, the LED lamp‘s fault is mostly the driver circuit fault.

2. Heat dissipation

LED is a cold light source, the working junction temperature shall not exceed the limit value, and a certain amount shall be left in the design.The design of the whole lamp should consider many aspects such as beautiful appearance, convenient installation, light distribution, heat dissipation, etc. The balance point should be sought among many factors, so that the overall lamp is the best.Some LED lighting manufacturers use power supplies that are outsourced or purchased. The lighting designers do not know much about power supplies, and the heat dissipation space for leds is large, while the heat dissipation space for power supplies is small.After designing lamps and lanterns to look for appropriate power source to come form a complete set commonly, bring certain difficulty to the form a complete set that gives power source so.Often encounter because luminaire interior space is lesser or internal temperature is higher, and cost control is inferior, cannot match appropriate power source.Some LED lighting factories have the power r&d ability, which can be evaluated at the beginning of the design of lamps, and the power design can be carried out synchronously to solve the above problems.In the design, the heat dissipation of LED and the heat dissipation of power supply should be considered comprehensively, and the overall temperature rise of lamps should be controlled, so that better lamps can be designed.

3. Problems in power design

A. power design.Although the LED has high efficiency, it still has 80-85% thermal energy loss, resulting in 20-30($10.6626) temperature rise inside the lamp. If the room temperature is 25 degrees, the inside of the lamp will be 45 to 55 degrees. The power supply will work in the high temperature environment for a long time.

B. component selection.When the internal temperature of the lamp is 45 to 55 degrees, the internal temperature rise of the power supply is about 20 degrees, so the temperature near the element should be 65 to 75 degrees.Some components will drift at high temperatures and some will shorten their life, so choose devices that can be used at higher temperatures for longer periods, paying special attention to electrolytic capacitors and wires.

C. electric performance design.The switch power is designed for LED parameters, mainly constant current parameters. The current size determines the LED brightness. If the batch current error is large, the brightness of the whole batch of lamps is not uniform.Changes in temperature can also offset the output current of the power supply.Generally, the batch error is controlled within +/-5% to ensure consistent brightness of the lamp. The forward voltage drop of the LED has deviation, and the constant current voltage range of the power supply design shall include the voltage range of the LED.When multiple leds are connected, 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.

D. design of PCB sheet. The size of LED lamp reserved for power source is small (unless it is external to power source), so the PCB design requires higher requirements and more factors to be considered.The safety distance shall be enough, and the power supply isolated from input and output shall be required. The primary side circuit and secondary side circuit shall be able to withstand voltage of 1500-2000vac, and the PCB shall be at least 3MM away.If it is a metal case of lighting, then the entire power supply cloth plate should also consider the high pressure part and the shell of the safety distance.If there is no space to guarantee a safe distance, other measures should be used to guarantee the insulation, such as punching holes on the PCB, adding insulation paper, pouring and sealing insulation glue, etc.In addition, heat balance should also be considered for the cloth plate. The heating elements should be distributed evenly and cannot be placed in a centralized place to avoid local temperature rise.Electrolytic capacitors stay away from heat, slow aging and extend service life.

E. certification issues.At present, there is no standard for LED lamps in China, and relevant departments of the country are working on it. The certification of lamps sold in China refers to the standards of lighting lamps, and the certification of CE or UL is made for export, and some are made according to the standards of foreign LED lamps.Therefore, it is difficult for the switch power supply design to meet the above standards at the same time. We can only meet different certification requirements.

4. Usage parameters

The selection of the external power supply mainly depends on the constant current and constant current voltage range.The constant current value is selected as the LED‘s standard current deflection.The choice of voltage range should be moderate, do not choose a larger range as far as possible, avoid power waste.