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The Power Supply of the Flexible LED Strip

Currently, energy conservation, emission reduction, and low-carbon economy are widely advocated all over the world. LED industry, which corresponds to these ideas perfectly, has huge development potentials. Thereinto, the flexible LED strip is the most outstanding product and has been very popular among customers. A complete LED strip should consist of two parts: the strip itself and the driving power supply, and the quality of the power supply determines the lifespan and performance of the flexible LED strip to a certain degree. Thus customers should first know some relevant knowledge about power supplies before purchasing, and then they could have a better judgment about the product.

Why we must adopt low-voltage power supply for the flexible LED strip? First, the constant current could protect LEDs from being burned or damaged by over-current, which may shorten the lifespan of LED products. The matched switching power supply should be able to output constant current and voltage regardless of the voltage fluctuations of the power grid. Second, the low-voltage power supply is safe, the output voltage of which is only 12V. Unlike the products which adopt 220V, the whole LED strip is safe to touch. Third, the low-voltage power supply could only drive small amount of LEDs, so it could reduce the possibility of breakdown efficiently. Four, the low-voltage power supply has high efficiency and low power consumption.

The features of the driving power supply for the flexible LED strip

1. Protection function. Besides the common protection function, the power supply of the flexible LED strip should better add LED temperature negative feedback in the constant-current output to avoid the over-heating of LEDs. Meantime, it should also correspond to the safety regulation and electromagnetic compatibility requirements.

2. Drive methods. There are generally two kinds of drive methods now: the first method is to adopt one constant voltage source to drive multiple constant current sources, and each constant current source power one LED circuit. This kind of method is flexible. The failure of one LED circuit will not damage others. But the cost is a little high. The other method is to adopt constant current directly to power LEDs in series or in parallel. This method costs less but is not as flexible as the first method. The failure of one LED will influence the normal working of other parts of the flexible LED strip. These two methods coexist for a time. However, the first method is better in terms of cost and performance, so maybe it will become the mainstream in the near future.

3. High power factor. The power factor reflects the requirements of the power grid upon loads. Generally speaking, for low-voltage electrical equipment (under 70W), we do not have any mandatory indexes. However, though the small power factor of one low-power electrical equipment has little influences upon the power grid, the power grid may be polluted seriously at night because the electricity consumption is large and similar loads are too concentrated. For LED driving power supplies of 30W-40W, there will be certain indexes in terms of power factors in the near future.

4. High efficiency. As the flexible LED strip is an energy-saving product, the efficiency of the driving power supply should be high. The higher the efficiency, the smaller the power dissipation, and the smaller the heat production, thus the temperature rise of the LED strip could be also reduced. It is good for delaying the lumens depreciation of LEDs.

5. High reliability. As the flexible LED strip is usually installed in the suspended ceiling or at high places, the maintenance is not convenient, so the power supply should be highly reliable. A good power supply should be able to protect the product and extend its lifespan. Customers should bear this mind during purchasing process.

The classification methods of the driving power supply for the flexible LED strip

The LED strip must cooperate with the driving power supply, and different working environments also have different requirements upon driving power supplies. For now, there are many categories of power supplies in the market. Here we classify them according to the driving method and circuit structure.

1. According to the driving method, there are mainly two kinds of power supplies for the flexible LED strip.

(1) The constant-current type: a. The current output by the constant-current driving circuit is steady, while the output voltage varies along with the load resistance within a certain range. The smaller the load resistance, the lower the output voltage; vice versa. b. The constant-current circuit has no load short circuit problems, but it must strictly prohibit open circuit. c. The constant-current driving circuit is ideal to drive LEDs, but the price is relatively high. d. Please pay attention to the maximum bearing current and voltage, which limits the number of LEDs.

(2) Voltage-stabilizing type: a. When the parameters of the voltage-stabilizing circuit are confirmed, the output voltage is steady, while the output current fluctuates along with the load. b. The voltage-stabilizing circuit has no open circuit problems, but it must avoid dead short circuit. c. If we adopt voltage-stabilizing circuit to drive LEDs, appropriate resistance is needed to make the brightness of LEDs uniform. d. The brightness may be influenced by fluctuations of the rectified voltage.

2. According to the circuit structure, there are six kinds of power supplies for the flexible LED strip.

(1) Capacitance buck type. During working, the instantaneous current may become so large that the chip will be damaged. This kind of power supplies may be easily influenced by the voltage fluctuation of the power grid. They have low efficiency and reliability.

(2) Resistance buck type. This kind of power supplies also will be influenced greatly by the voltage fluctuation of the power grid. Buck resistance needs to consume large quantity of energy, so this kind of powering method has low efficiency and reliability.

(3) Common transformer buck type. This kind of power supplies for the flexible LED strip has small volume, heavy weight, and low efficiency, generally 45%-60%. So they are not usually adopted and have low reliability.

(4) Electronic transformer buck type. The efficiency is low, and the voltage range is not wide, generally 180-240V. Meantime, the corrugated interference is large.

(5) RCC buck type switching power supplies. The voltage-stabilizing range is wide, and the efficiency is high, generally 70—80%. As the oscillation frequency is discontinuous, the switching frequency could not be easily controlled. The ripple ratio of the load voltage is large, and the adaptability of the abnormal load is bad.

(6) Switching power supplies of PWM control mode. They mainly consist of four parts: the input rectifier filter, output rectifier filter, PWM voltage-stabilizing control part, and switching energy conversion part. The efficiency of the power supply is high, which is about 80-90%. The output voltage and current is stable. Generally, this kind of circuit has perfect protection measures and belongs to highly reliable power supplies.

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