With the rise and continuous improvement of the solid-state lighting industry, light-emitting diodes ( LEDs ) have become an alternative to today's lighting technology due to their high efficiency, energy saving, long life and environmental protection, and are gradually being applied to lighting. A key factor driving attention to LED lighting technology is that it greatly reduces energy consumption and enables long-term, reliable work.
Of course, the first thing to consider when using LED lighting is its brightness, cost and longevity. Because the main reason that affects the life of LED is the current impact of its frequent startup, the various surge pulses of the outside world, and the current limitation during normal operation, the circuit introduced in this paper combines these factors and avoids the circuit design. The impact of high current on LED lighting fixtures, and its operating current is stabilized within a certain range, solving the problem of brightness degradation of current LED lighting fixtures, thereby effectively extending its service life.
The LEDs are all driven by DC, so a power adapter, LED driver , is required between the mains and the LEDs. Its function is to convert AC mains into DC power suitable for LEDs. Usually, the LED is driven by a dedicated constant current source or a driver chip, which is easily limited by factors such as volume and cost. The most economical and practical method is to use a capacitor buck power supply. It uses it to drive low-power LEDs, has the advantages of not being short-circuited by load, simple circuit, etc., and a circuit can drive 1 to 70 low-power LEDs (however, the current impact when starting this power circuit, especially frequent startup, will give LED Cause damage. Of course, proper protection can avoid this kind of impact).
A typical circuit for a capacitive buck power supply is shown in Figure 1. C1 is a step-down capacitor (using a metallized polypropylene capacitor) and R1 provides a discharge loop for C1. Capacitor C1 provides a constant operating current for the entire circuit. Capacitor C2 is an electrolytic capacitor, and its withstand voltage depends on the number of LEDs connected in series (about 1.5 times its total voltage). Its main function is to suppress voltage abrupt changes caused by energization moments, thereby reducing voltage shock to LEDs. The impact of life. R4 is the bleeder resistor of capacitor C2, and its resistance should be increased as the number of LEDs increases.
It should be noted that the circuit must select the appropriate capacitor according to the current of the load, instead of the voltage and power of the load. Generally, the relationship between the capacity C of the step-down capacitor C1 and the load current Io can be approximated as: C=14.5Io, The unit of capacity of C is uF, and the unit of Io is A. The current limiting capacitor must use a non-polar capacitor, and the capacitor's withstand voltage must be above 630V.
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