The LED power supply is a device that converts alternating current into direct current through a transformer and a rectifier. This device is called a rectifier power supply, also known as a driving power supply. The LED drive power supply is a power converter that converts the power supply into a specific voltage and current to drive the LED to emit light. Usually, the input of the LED drive power supply includes high-voltage power frequency AC (ie mains), low-voltage DC, high-voltage DC, low-voltage high-voltage Frequency AC (such as the output of an electronic transformer), etc.

 LED has the advantages of low energy consumption and long life, so many special applications will use LED as its light source. However, because the power required by LEDs is DC and low voltage, constant current output, energy conversion efficiency and power factor need to be considered in the design of LED drivers for lighting.

1. Low frequency transformer and half-wave or full-wave rectifier circuit

The advantages of low-frequency transformers and half-wave or full-wave rectifier circuits are simple structure and low cost; the disadvantage is that they are large in size, adopt voltage mode, the brightness of LED will change with the change of voltage, cannot provide constant current output, and its surge The current is larger.

Low-frequency transformers and half-wave or full-wave rectification circuits provide LED power in a very simple way, requiring only a low-frequency transformer, rectifier, filter capacitors, and a variable resistor to adjust brightness. The number of LEDs in series is mainly determined by the turns ratio of the transformer. Once the turns ratio is selected, it is difficult to change the number of LEDs in series, and the number of LEDs can only be increased in parallel, but this circuit is difficult to achieve in parallel. The LEDs have the same current flow, resulting in inconsistent brightness across the LEDs.

2. Switching converter circuit

The advantage of the switching converter circuit is that the technology is very mature, and there are many types of integrated switching converters, so it is used by most of the current LED lighting power supplies; Brightness is uneven.

3. Switching current adjustable converter

The switch-mode current-adjustable converter circuit is suitable for the parallel application of LEDs, which can achieve precise matching of currents between the paralleled LEDs, thereby achieving uniform brightness.

In the design of lighting LED power supply, the harmonic distortion of the input current should be as low as possible. The total current harmonic distortion (THD) and power factor will be different due to the adoption of different national standards. Commercial products only meet the design requirements. The standard of this country can be used, and there is no need to make the power factor close to 1 or the THD less than 10%, otherwise the cost of the power supply will increase, and the open-circuit and short-circuit protection circuit of the LED should also be provided in the design.