The LED driving power supply converts the power supply into a specific voltage and current to drive the voltage converter of the LED. Usually: the input of the LED driving power supply includes high-voltage power frequency AC, low-voltage DC, high-voltage DC, low-voltage high-frequency AC, etc. So today I will show you the LED constant voltage power supply.
Constant voltage power supply driving method
Constant voltage power supply
1. After the voltage stabilizing circuit determines various 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 the load opening, it is strictly forbidden to completely short-circuit the load.
3. The voltage change after rectification will affect the brightness of the LED.
4. To make each string of LEDs driven by a voltage stabilizing circuit display uniform brightness, a suitable resistor needs to be added.
5. Constant voltage driving circuit is more ideal for driving LED, and constant voltage is the future trend.
Characteristics of constant voltage power supply
(1) High reliability
Especially like the driving power supply of LED street lights, it is installed at high altitude, making maintenance inconvenient and expensive.
(2) High efficiency
LED is an energy-saving product, and the efficiency of the driving power supply must be high. It is very important to dissipate heat from the junction where the power supply is installed inside the luminaire. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which also reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LED.
(3) High power factor
Power factor is the requirement of the power grid for the load. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the low power factor of a single electrical appliance with small power will have little impact on the power grid, the large amount of lighting used at night and the concentration of similar loads will cause serious pollution to the power grid. For 30- to 40-watt LED driving power supplies, it is said that there may be certain index requirements for power factors in the near future.
(4) Surge protection
LED’s ability to withstand surges is relatively poor, especially its ability to withstand reverse voltage. Strengthening protection in this area is also important. Some LED lights are installed outdoors, such as LED street lights. Due to the activation of the grid load and the induction of lightning strikes, various surges will invade from the grid system, and some surges will cause damage to the LED. Therefore, it is analyzed that the driving power supply of “Zhongke Huibao” should have certain deficiencies in surge protection. As for the frequent replacement of power supplies and lamps, the LED driving power supply must have the ability to suppress the intrusion of surges and protect the LED from damage.
(5) Protection function
In addition to the conventional protection functions of the power supply, it is best to add LED temperature negative feedback to the constant current output to prevent the LED temperature from being too high; it must comply with safety regulations and electromagnetic compatibility requirements.
Constant voltage power supplies can be divided into six categories according to circuit structure
1. Conventional transformer step-down:
The advantage of this kind of power supply is its small size. The disadvantage is that it is heavy in weight and the power efficiency is also very low, generally between 45% and 60%. Because the reliability is not high, it is rarely used.
2. Capacitor voltage reduction:
This type of LED power supply is easily affected by grid voltage fluctuations, and the power supply efficiency is low. It is not suitable to use the LED when it is flashing, because the circuit reduces the voltage through the capacitor. When used in flashing, due to the effect of charging and discharging, the instantaneous current passing through the LED Very large and can easily damage the chip.
3. Electronic transformer step-down:
The shortcomings of this power supply structure are low conversion efficiency, narrow voltage range, generally 180~240V, and large ripple interference.
4. Resistor voltage reduction:
The power efficiency of this power supply method is very low, and the reliability of the system is also low. Because the circuit reduces voltage through resistors, it is greatly disturbed by changes in grid voltage, so it is not easy to make a regulated power supply, and the voltage-reducing resistor itself consumes a large portion of energy.
5. RCC step-down switching power supply:
The advantages of this type of LED power supply are a relatively wide voltage stabilization range and a relatively high power efficiency, which can generally be 70% to 80%, and it is widely used. The main disadvantages are that the switching frequency is difficult to control, the load voltage ripple coefficient is large, and the load adaptability is poor under abnormal circumstances.
6. PWM controlled switching power supply:
Currently, LED power supplies designed with PWM control are ideal because the output voltage or current of this switching power supply is very stable. The power conversion efficiency is extremely high, generally as high as 80%~90%, and the output voltage and current are very stable. This method of LED power supply mainly consists of four parts: input rectification and filtering part, output rectification and filtering part, PWM voltage stabilization control part, and switching energy conversion part. Moreover, this circuit has complete protection measures and is a high-reliability power supply.
Eight performance characteristics requirements of constant voltage power supply
According to the power usage rules of the power grid and the characteristic requirements of the LED drive power supply, the following nine performance characteristics should be taken into consideration when selecting and designing the LED drive power supply:
1. High reliability, especially the driving power supply of LED street lights, which is installed at high altitude, making maintenance inconvenient and expensive.
2. High-efficiency LEDs are energy-saving products, and the efficiency of the driving power supply must be high. This is especially important for structures where the power supply is installed inside the lamp. Because the luminous efficiency of LEDs decreases as the temperature of the LED increases, the heat dissipation of the LED is very important. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which also reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LED.
3． High power factor Power factor is the requirement of the grid for the load. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the low power factor of a single electrical appliance with small power will have little impact on the power grid, if everyone lights up lights at night and the same type of load is too concentrated, it will cause serious pollution to the power grid. For 30- to 40-watt LED driving power supplies, it is said that there may be certain index requirements for power factors in the near future.
4． Surge protection LED’s ability to withstand surges is relatively poor, especially its ability to withstand reverse voltage. Strengthening protection in this area is also important. Some LED lights are installed outdoors, such as LED street lights. Due to the activation of the grid load and the induction of lightning strikes, various surges will invade from the grid system, and some surges will cause damage to the LED. Therefore, the LED driving power supply must have the ability to suppress surge intrusion and protect the LED from damage.
5. Protection function In addition to the conventional protection functions of the power supply, it is best to add LED temperature negative feedback to the constant current output to prevent the LED temperature from being too high.
6. In terms of protection, if the lamp is externally installed, the power supply structure must be waterproof and moisture-proof, and the outer casing must be light-resistant.
7. The life of the driving power supply must match the life of the LED.
8. Must comply with safety regulations and electromagnetic compatibility requirements.
As the application of LED becomes more and more widespread, the performance of LED driving power supply will become more and more suitable for the requirements of LED.
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Post time: Apr-25-2024