Power supply solutions for LED lighting (Figure)-EEWORLD

Collect

With the progress of the times and the improvement of life functions, the modern society's requirements for lighting are no longer just the pursuit of brightness. The new generation of lighting concepts have entered the stage of energy saving, environmental protection, ergonomics, computerization, and compactness. The most noteworthy products of the new generation of lighting are light emitting diodes (LEDs), which meet the above requirements.

LEDs have the advantages of low energy consumption and long life, so many special applications will use LEDs as their light sources; however, because the power supply required by LEDs is DC and low voltage, the power supply traditionally used to drive tungsten filament bulbs or fluorescent lamps is not suitable for directly driving LED lamps.

Traditional constant voltage converters must be modified before they can be used to drive LED lamps; circuit modifications need to consider constant current output, energy conversion efficiency, power factor, etc., which will test the design technology of electronic circuits. This article will introduce the two most common solutions currently on the market and a newly developed solution. Two common solutions: 1. Low-frequency transformer and half-wave or full-wave rectifier circuit

Advantages: simple circuit, low cost

Disadvantages: large size, voltage mode, LED brightness will change with the supply voltage; cannot provide constant current output; large surge current.

As shown in Figure 1, this method of providing LED power is very simple. It only requires a low-frequency transformer, a rectifier, a filter capacitor, and a variable resistor for adjusting the brightness. The number of LEDs in series is mainly determined by the turns ratio of the transformer. Once the turns ratio is fixed, it is not easy to change the number of LEDs to get the same brightness. The only way to increase the number of LEDs is by connecting them in parallel, but this power supply architecture makes it difficult to achieve the same brightness for parallel LEDs.

2. Switching power supply - provides fixed voltage

Advantages: The technology is very mature and easy to obtain; the current power supply mode of most LED lighting has good voltage load and stable change.

Disadvantages: It is not easy for the switching power supply to provide fixed power for the series or parallel connection of LEDs, and the current load varies greatly; therefore, whether the LEDs are used in series or in parallel, the current flowing through each LED is different, which is reflected in the actual application, that is, the LED brightness is also difficult to control, so the solution is not conducive to the LED lighting power supply .

In addition, this power supply adopts switching technology, so its volume is much smaller than the previous solution. The VR is a variable resistor used to adjust the brightness of the LED. If a power supply with adjustable output voltage is used, it will be much more convenient for the series and parallel application of LEDs. Currently, the price of power supplies with adjustable output voltage is relatively high or the volume is larger than that of fixed voltage mode. Latest technology

3. Switching constant current power supply

Based on the inconvenience of using in the past, a constant current mode power supply was developed as a power supply for LED lighting. It allows the application of LED series and parallel connection, and it is easier to control the current flowing through the LED, that is, it is easier to control the brightness of the LED.

As shown in Figure 3, the constant current power supply with adjustable output current is very suitable for LED lighting applications. Because there is no additional variable resistor VR, the power utilization rate is higher than the first two solutions. It is very convenient to use LEDs in series because the current flowing through the LEDs is fixed and is not affected by the number of LEDs. For the parallel use of LEDs, the current sharing effect of the LEDs in the parallel path cannot be guaranteed.

At present, most of the high-current LED lighting power supplies adopt the first two solutions, but in comparison, the constant current output mode of the switching constant current supply is more suitable because it can easily control the current of each LED in both series and parallel applications to achieve consistent brightness; in addition, the harmonic distortion of the input current is as low as possible. The total harmonic distortion (THD) and power factor value will vary depending on the standards of different countries. Commercial products only need to meet the standards of the country of application in design, and there is no need to achieve a power factor close to 1 or THD less than 10%, otherwise the cost will increase a lot and lose product competitiveness. As for the THD specification, please refer to IEC1000-3-2 class D. When designing, special attention should also be paid to the open circuit and short circuit protection of LEDs.

Reference address：Power supply solutions for LED lighting (Figure)

Previous article：Principles of drawing electrical diagrams
Next article：Technical features and applications of new lighting and display power supplies (picture)

Popular Resources
Popular amplifiers