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According to the level of the power supply voltage, LED drivers can be divided into three categories: one is powered by batteries, mainly used for portable electronic products, driving small and medium-power white LEDs; the other is powered by a voltage greater than 5, and is powered by a regulated power supply or battery Power supply, such as step-down, step-up and step-down DC converters; the third is directly powered by the mains (110V or 220V) or the corresponding high-voltage DC (such as 40~400V), which is mainly used to drive high-power White LED, such as step-down DC/DC converter.
1. Battery-powered drive solution
The battery supply voltage is generally 0.8~1.65V. This is a common usage situation for low-power lighting devices such as LED displays. This method is mainly suitable for portable electronic products to drive low-power and medium-power white LEDs, such as LED flashlights, LED emergency lights, energy-saving desk lamps, etc. Considering that it is possible to work with an AA battery and have the smallest size, the best technical solution is a charge pump boost converter, such as a boost DC converter (converter or boost (or Buck-boost type) charge pump converters, a few of which use LDO circuit drivers.
2. High-voltage driving scheme
Low-voltage power supply solutions with a voltage higher than 5 use a dedicated regulated power supply or battery. The voltage value that powers the LED is always higher than the voltage drop of the LED tube, that is, it is always greater than 5V, such as 6V, 9V, 12V, 24V or higher. In this case, it is mainly powered by a regulated power supply or battery to drive the LED light. This power supply solution must solve the problem of power supply voltage reduction. Typical applications include solar lawn lights, solar garden lights, and motor vehicle lighting systems.
3.Drive solution powered directly by mains power or high-voltage direct current
This solution is directly powered by mains power (100V or 220V) or corresponding high-voltage direct current, and is mainly used to drive high-power white LED lights. Mains power drive is the most cost-effective power supply method for LED electronic displays and is the development direction for the popularization and application of LED lighting.
When using mains power to drive LEDs, it is necessary to solve the problems of voltage reduction and rectification. It also needs to have relatively high conversion efficiency, smaller size and lower cost. Additionally, security isolation issues should be addressed. Considering the impact on the power grid, electromagnetic interference and power factor issues must also be solved. For medium and small power LEDs, the best circuit structure is an isolated single-ended flyback converter. For high power applications, a bridge conversion circuit should be used.
For LED drivers, the main challenge lies in the nonlinearity of the LED display. This is mainly reflected in the fact that the forward voltage of LED will change with current and temperature. The forward voltage of different LED devices will be different. The LED "color point" will drift with current and temperature, and the LED must be within the specification requirements. work within the range for reliable operation. The main function of an LED driver is to limit current under operating conditions, regardless of changes in input conditions and forward voltage.
For LED electronic display drive circuits, in addition to constant current and steady current, there are other key requirements. For example, if LED dimming is required, PWM technology needs to be provided, and the typical PWM frequency for LED dimming is 1~3kHz. In addition, the LED driver circuit must have sufficient power handling capabilities, be powerful enough to withstand multiple fault conditions, and be easy to implement. It is worth mentioning that because the LED electronic display is always in a state of optimal current, it will not drift.
When it comes to the choice of LED electronic display drive solutions, in the past, the boost DC/DC with inductance was considered. In recent years, the current that the charge pump driver can output has increased from a few hundred milliamps to about 1.2A. Therefore, these two The output of each type of actuator is about the same.
