LED lighting requires electrolytic capacitors

[Source: LED Engineering magazine's "good LED products," September issue text / Yen Kuang Shi Xiaofan] interior lighting LED lamps need to have a good cheap price, thus optimizing the product design is very important.

Based on the difference in voltage of the power supply grid around the world, LED lamps are divided into two types: wide voltage input and constant voltage input. In order to be able to be used in different regional grid voltages, wide voltage input LED lamps become mainstream products, wide voltage input. The LED lamp power supply needs to use the power supply of the switching constant current source. When the power supply network voltage changes from AC84-280V, it relies on the switching power supply automatic buck-boost control to output a constant DC current. LED lamp beads must work in a constant current environment to illuminate normally and efficiently without flicker.

LED switch constant current power supply

The switching constant current source power supply relies on the switching frequency of the machine and the transformer to automatically raise and lower the voltage, and responds to the fluctuation of the grid voltage, and outputs a constant direct current, which is provided to the LED lamp bead to make it normally emit light.

The grid current enters the LED drive power source, and is preferably processed by EMC. After the rectifier bridge stack, the AC is converted into DC; secondly, the power supply control chip and the transformer reduce the high-voltage DC voltage to the operating voltage required by the LED lamp bead, and the output is constant. The working current; with the appropriate working voltage, to meet the VF voltage and IF constant current requirements of the LED lamp bead string, the LED lamp bead can normally emit light.

However, the grid voltage is 50 Hz or 60 Hz power frequency AC, the voltage waveform is a sine wave, so after the rectification is obtained a pulsating DC power rich in 50 Hz power frequency and its octave ripple, the ripple is the residual AC component, must pass After the electrolytic capacitor is filtered, stored, charged and discharged, a relatively smooth DC current can be obtained. The basic principle is shown in Figure 1.

The main chip control IC of the switching constant current source requires a clean power supply without ripple, and the ripple in the working circuit needs to be eliminated, so a bypass filter capacitor is required. The switching constant current power supply drives the LED drive current through the transformer in the circuit, and is simply rectified into DC by the diode, so it will contain a lot of ripples. The low frequency ripple will cause the human eye to see the flicker, and the ripple filter must be used with the electrolytic capacitor. net.

>>>Unfinished , please refer to the September issue of Gaogong LED 's " LED Good Products" magazine.

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