Posts Tagged ‘LED power supply’

Basic Knowledge about Different Kinds of LED Power Supplies

01 Dec

Although LED’s power saving efficiency is higher than ordinary light sources, it can not be connected directly to public grid voltage like those ordinary ones. It should be configured with special voltage switching device which can supply it with rated voltage and current, providing a sound condition for it to function in normally. That is the so-called special power supply for LED.

However, LED power supplies with different specifications hold different performance and different switching efficiency. In order to fully bring into play the high efficiency of LED, it is important to choose a proper, high efficiency special power supply for each distinct LED. Low efficiency LED power supplies consume large amount of power supply, which will influence the energy saving trait of LED. Anyhow, the stability, power saving trait and the life-span of LED largely depends on choosing a proper LED power supply.

Different types of LED power supplies

Ⅰ. LED power supply can be classified into two types according to driving modes:

A. Constant current power supply

a. Constant current driving circuit is ideal to drive LED, except for its little bit high cost.

b. Constant current circuit can load short-circuit, but it is forbidden to load fully open circuit.

c. The output current in the constant current driving circuit is constant; however, the output DC voltage changes within a certain range according to different load resistance values.

d. The total amount of LED used in one circuit should be limited, because LED has its maximum current and voltage value restriction.

B. Stabilized voltage power supply

a. After setting each parameter in the stabilized voltage circuit, the output voltage is settled, whereas the output current is variational according to the loading.

b. Stabilized voltage circuit can load open circuit, but it is forbidden to load short-circuit.

c. The luminance of the LED will be influenced by the change of voltage after rectification.

d. Proper resistance should be configured in each series of circuit so that LEDs in stabilized voltage circuit will have uniform luminance.

Ⅱ. LED power supply can be classified into six types according to the structure of the circuit:

a. Conventional transformer step-down
Although the size of this kind of power supply is very small, it is a bit heavy and the efficiency is very low, at about 45%~60%. Also its reliability is not high, so it is seldom used.

b. Electronic transformer step-down
The disadvantages of this kind of power supply is its low switching efficiency, narrow voltage range (about 180~240V) and its strong ripple interference.

c. Capacitance step-down
This kind of LED power supply can easily be influenced by the grid voltage fluctuation and the efficiency is very low. It is inadvisable to use it in flashing LEDs because the charge and discharge process in the capacitance step-down circuit will causing extremely large instant current flow, which can easily damage the chip in the flashing LEDs.

d. Resistance step-down
The power supply efficiency in this kind of circuit as well as its reliability is very low. The circuit is interfered by the grid voltage fluctuation, so it is difficult for the power supply to stabilize its voltage. Large power consumption is another disadvantage for this resistance step-down power supply.

e. RCC step-down switching power supply
Advantages: wide range of stabilized voltage; high power supply efficiency (at about 70%~80%). So it is widely used.
Disadvantages: difficult to control the switching frequency; large ripple coefficient of the load voltage; weak loading adaptability in abnormal condition.

f. PWM control switching power supply
At present, the PWM control switching power supply is much more ideal than other kinds of power supplies. Its output voltage and current are very stable, and the efficiency can reach as high as 80%~90%. This kind of LED power supply is made up of four parts: input rectification filter; output rectification filter; PWM voltage stabilizing control unit; power switching unit. High reliability is another advantage for this power supply because the circuit is well protected.

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