1、 LED power supply can be divided into two categories according to the driving mode:
A. Constant current type:
1. Constant current drive circuit is ideal to drive LED, but the disadvantage is that the price is high.
2. Although the constant current circuit is not afraid of load short circuit, it is strictly prohibited to open the load completely.
3. The output current of the constant current drive circuit is constant, while the output DC voltage varies in a certain range with the load resistance.
4. The number of LEDs used should be limited, because they have the maximum withstand current and voltage values.
B. Stabilized voltage type:
1. After the constant voltage circuit determines the parameters, it outputs a fixed voltage, but the output current changes with the increase or decrease of the load.
2. Although the voltage stabilizing circuit is not afraid of load open circuit, it is strictly prohibited to completely short-circuit the load.
3. The voltage change after rectification will affect the brightness of LED.
4. In order to make LED display brightness of each string driven by voltage stabilizing circuit uniform, appropriate resistance shall be added.
2、 LED power supply can be divided into six categories according to circuit structure:
1. Conventional transformer step-down:
The advantages of this power supply are small size, but its disadvantages are heavy weight and low power efficiency, which is generally 45%~60%. Because of its low reliability, it is rarely used.
2. Electronic transformer step-down:
The disadvantages of this power supply structure are low conversion efficiency, narrow voltage range, generally 180~240V, and large ripple interference.
3. Capacitance step-down:
The LED power supply in this way is easy to be affected by the fluctuation of the grid voltage. The power supply efficiency is low, and it is not suitable for LED to be used when flashing. Because the circuit is depressurized through a capacitor, the instantaneous current passing through the LED is very large due to the effect of charging and discharging during flashing, which is easy to damage the chip.
4. Resistance step-down:
The power supply efficiency of this power supply mode is very low, and the reliability of the system is also low. Because the circuit drops voltage through resistance and is greatly interfered by the change of power grid voltage, it is not easy to be made into a regulated power supply, and the step-down resistor itself also consumes a large part of energy.
5. RCC step-down switching power supply:
The LED power supply in this way has the advantages of wide voltage stabilization range and high power efficiency, which can be generally 70%~80%, and is widely used. The main disadvantages are that the switching frequency is not easy to control, the load voltage ripple coefficient is large, and the load adaptability is poor under abnormal conditions.
6. PWM controlled switching power supply:
At present, the LED power supply designed by PWM control mode is ideal, because the output voltage or current of this switching power supply is very stable. The power conversion efficiency is extremely high, generally up to 80%~90%, and the output voltage and current are very stable. Especially suitable for the driving power supply of LED street lamps The LED power supply in this mode is mainly composed of four parts: input rectifier filtering part, output rectifier filtering part, PWM voltage stabilizing control part, and switching energy conversion part. Moreover, this kind of circuit has perfect protection measures and belongs to high reliability power supply.