The importance of power factor to LED lamps

What is the power factor of LED lamps? Power factor is an important parameter of LED lamps. Knowing what power factor will help us further understand LED lamps.

1. Power factor

The power factor characterizes the ability of the lamp to output active power. Power is a measure of the rate of transfer of energy, and in a DC circuit it is the product of voltage V and current A. In the AC system, it is more complicated: that is, part of the AC current circulates in the load without transmitting electrical energy, which is called reactive current or harmonic current, which makes the apparent power (voltage Volt multiplied by current Amps) greater than the actual power. The difference between apparent power and actual power leads to the power factor, which is equal to the ratio of actual power to apparent power. So the real power in the AC system is equal to the apparent power multiplied by the power factor. That is: power factor = actual power / apparent power. Only linear loads such as electric heaters and incandescent light bulbs have a power factor. 1. The difference between the actual power and the apparent power of many devices is small and can be ignored, while the difference between capacitive devices such as LED lamps is very small. big and important. A recent study by American PC Magazine showed that the typical power factor of LED lamps is 0.65, that is, the apparent power (VA) is 50% larger than the actual power (Watts)!

2. Apparent power

Apparent power: the product of AC voltage and AC current. The formula is expressed as: S=UI. In the formula, S is the rated output power, the unit is VA (volt-ampere); U is the rated output voltage, the unit is V, such as 220V, 110V, etc.; I is the rated output current, the unit is A. Apparent power consists of two parts: active power (P) and reactive power (Q). Active power refers to the part that does work directly. For example, to light a lamp, to turn a motor, to make an electronic circuit work, etc. Because this power becomes heat after doing work, it can be directly felt by people, so some people have an illusion, that is, they regard active power as apparent power, but they do not know that active power is only a part of apparent power, which is expressed by the formula : P=Scosθ=UIcosθ=UI F. In the formula, P is the active power, and the unit is W (watt); F=cosθ is called the power factor, and θ is the phase difference when the voltage and current are out of phase when the nonlinear load is present. Reactive power is the part of the power that is stored in the circuit but does not do work directly, expressed by the formula: Q=Ssinθ=UIsinθ. In the formula, Q is the reactive power, and the unit is var.

3. Reactive power

For lamps and other electronic circuits that work on DC voltage, it is impossible to work without reactive power. General users think that devices such as lamps only need active power, not reactive power. Since reactive power does not do work, what is the use of it! So of course they think that the lamps with a power factor. Because it can give the maximum output power. However, this is not the case in reality.

If there is a lamp, when the AC mains is input and rectified, the pulsating DC voltage will be obtained. If the pulsating voltage is not processed, it will be directly supplied to the lamp. There is no doubt that the circuit will not work properly at all. Although the power factor of the lamp is close to 1 at this time, what is the use of this. In order for the lamp circuit to work properly, it must be supplied with a smoothed DC voltage. This “smoothing” must be done by a filter capacitor connected after the lamp rectifier. This filter is like a reservoir, and the capacitor must store a sufficient amount of charge, so that the working voltage on the circuit is still uninterrupted and can maintain a normal level during the blank between the rectified half-waves. In other words, even when there is no input power between the two pulsating half-waves, the voltage level of Uc does not change significantly. This function is realized by the energy storage in the capacitor, and this part of the energy stored in the capacitor is realized reactive power. Therefore, lamps rely on the support of reactive power to ensure that the circuit uses active power correctly to achieve normal use. Therefore, it can be said that lamps not only need active power, but also need reactive power, both of which are indispensable.

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