LED Driver: Everything You Need To Know
by Penglight | Date: 26th-Mar, 2023
LED is one of the most sensitive semiconductor components. Due to its negative temperature characteristics, it needs to be stabilized and protected during the application, thus giving rise to the concept of LED driver, also known as LED power supply. LED applications are almost ubiquitous in every field of electronic applications. And because of its unpredictability in luminous intensity, light color, on-off control, etc, LED drivers have become almost one-to-one servo devices, making the members of this device family diverse. From this point of view, it is necessary to have a deep understanding of the parameters of LED drivers. Let’s delve into it together!
What Is LED Driver?
LED driver is an electrical device that regulates the power to an LED or a string of LEDs. It provides a constant current or voltage to the LED(s) to ensure that they operate within their specified operating range and prevent them from burning out. LED drivers are essential components in LED lighting systems and are available in various types, such as constant-current, constant-voltage, and dimmable drivers.
The core components of the LED driver, aka power supply, include input filter components, switch controllers, inductors, MOS switch tubes, feedback resistors, output filter components, etc. In addition, some power supplies also have input Overvoltage/Undervoltage protection, open circuit protection, overcurrent protection, etc.
Basic Knowledge about LED Driver
Input Voltage Range
The user sees that the input voltage range marked on the power supply is 85-265VAC, but in actual use, it is 100-240VAC. In fact, during the testing of safety certification, it will carry out a so-called +10% more strict test (IEC60950 is a +6%- 10% more strict test). Therefore, there is no problem in using the voltage range defined in the power supply specification, and the indication on the power supply is to meet the safety regulations and ensure that the user can input the power correctly.
Power Factor (PFC)
PFC (Power Factor Correction) is mainly used to improve the ratio of effective power to apparent power at the input of the power supply. Generally, for models without a PFC circuit, the power factor at the input end is only 0.4-0.6, while those with active PFC circuits can achieve 0.95 or higher, and the relevant formula is as follows:
Apparent power = input voltage x input current (VA)
Effective power = input voltage × input current × power factor (W)
From an environmental perspective: power plants operated by power companies must generate electrical energy greater than the apparent power in order for their generators to provide a stable supply of electricity to meet market demand.The actual use of electricity is measured in effective power.
If the power factor is 0.5, it means that the generator must produce more than 2 VA of power to safely supply 1W of electricity demand, resulting in poor energy efficiency. On the contrary, if the power factor is improved to 0.95, the power plant only needs to generate more than 1.06 VA of power to supply 1W of electricity demand without any problems, resulting in better energy efficiency.
Overvoltage/overcurrent/overload/overtemperature fault protection refers to the protection action triggered by the relevant circuit function of the power supply when the safety of the power supply is threatened due to changes in internal and external conditions such as input power, load, environment, cooling circuit or device failure, and the power supply cannot work normally.
- OVP (Over Voltage Protection): A feature of switching power supply circuits that protects the switching power supply and the load when an abnormal high voltage appears at the output.
- Undervoltage protection: When the power supply voltage of the protected circuit is lower than a certain value, the protector cuts off the circuit; when the power supply voltage returns to the normal range, the protector automatically reconnects.
- OCP: Over Current Protection is used in DC switch power circuits to prevent the regulating tube from being burned out in case of circuit short-circuit or current increase. The basic method is that when the output current exceeds a certain value, the regulating tube is in a reverse bias state, thus cut off and automatically cut off the circuit current.
- Short Circuit Protection: It limits the output current of the switch power supply to a safe value during a short circuit to protect the switching power supply from damage.
- OTP: Over Temperature Protection circuit should be set in high power DC switching power supply, due to the high integration and small volume of switch regulator in the power supply, the power density per unit volume is greatly improved. Therefore, if the temperature requirements of the internal components of the power supply device are not correspondingly improved, the circuit performance will inevitably deteriorate and the components will fail prematurely.
Protection (action) has the following methods:
- Restart (automatic and manual) after the power is off and on, the power will return to normal.
- Hiccup (intermittent output).
- Fold back limiting (linearly reducing the output current to normal value when the load approaches a short circuit)
- Constant current limiting, or constant current, can limit the output current from increasing indefinitely due to overload or short circuit of the load. Even if the load is short-circuited, it will not cause equipment shutdown and power supply damage).
- Downtime overcurrent, overload, overvoltage, and overtemperature fault usually refer to dangerous states when the output current/power/(or input) voltage and heatsink temperature exceed the rated values of the power supply protection threshold.
The switching power supply will experience a brief surge of high current (approximately 20-60A depending on the product design, please refer to the product specifications) when the input power is turned on (for 1/2 to 1 power cycle, e.g. 1/120 to 1/60 seconds for a 60Hz power source). After the product is turned on, the current input returns to normal, and this phenomenon only occurs during the moment when the power is supplied to the input of the power supply.
This is a normal phenomenon and will not damage the power supply. However, it is not recommended to continuously turn the power supply on and off. It should also be noted that if multiple power supplies are turned on at the same time, it may cause the system’s protective switch to trip. It is recommended to delay the power-on of multiple power supplies or use the remote control function of the power products to turn them on in sequence.
Output Voltage Accuracy
The output voltage accuracy refers to the difference between the actual output voltage and the rated output voltage. This error is the sum of the line stability and load stability. Usually, this parameter is +/-1% Line stability refers to the percentage of output voltage deviation from rated voltage when the input voltage varies between the maximum and minimum allowable values. Load stability refers to the percentage deviation of the output voltage from the rated voltage when the output load current changes between the maximum and minimum values allowed.
Why Use Constant Current Power Supplies for LED Lights?
The lifespan of LED refers to the time when light decay occurs. Constant current LED driver controls the current of the LED, ensuring that the junction temperature of the LED chip will not be too high, and preventing the abnormal aging of the semiconductor chips, packaging materials, and fluorescent materials. As a result, the luminous intensity of the LED will not decrease too quickly (i.e. light decay). The use of other types of power supply cannot control the current of the LED to be constant, and its temperature rise is not easy to control, leading to light decay.
The luminous intensity of LED is proportional to the current. Therefore, the LED power supply needs to have a constant current output characteristic to ensure that the LED can obtain stable luminous intensity and the manufacturer’s long lifespan guarantees during use. In order to ensure a constant current operating circumstance for LEDs, the LEDs must be connected in series to ensure that the current of each LED in the circuit is equal and constant.
As the power demand of the LED light group increases, the number of LEDs connected in series will be more and more, and the voltage demand will be proportional to the number of series connected, resulting in higher and higher voltage, which makes safety issues more likely to occur. Then, the manufacturing and usage requirements will become more stringent, which will increase the cost and difficulty of using the power supply. Therefore, the demand for low-voltage power supply has emerged for high-power LED use.
The CV+CC power supply can work at a constant voltage or constant current.
IP rating: IP rating defines whether the LED driver is waterproof or not. Take the example of IP65, the first digit means protection against solids and the second digit means protection against liquids. The larger each digit is, the greater the protection. For more info, please refer to IP Rating – Complete Guide.
Efficiency: The ratio of total output power expressed as a percentage to active input power. That is efficiency = output power/input power * 100%.
Rated wattage: refers to the maximum output power of the power supply (the product of voltage V and current A).
EMC: Electromagnetic compatibility refers to the ability of devices or systems to operate in their electromagnetic environment in compliance with requirements without causing intolerable electromagnetic interference to any devices in their environment. EMC includes two departments: EMI (Electromagnetic Interference) and EMS (Electromagnetic Susceptibility). EMI refers to the harmful energy conducted or radiated by switching power supplies, while EMS refers to the ability of LED power supplies to perform their functions without being affected by the surrounding electromagnetic environment.
Ripple: Due to the fact that a DC stable power supply is generally formed by rectification and voltage stabilization of the AC power supply, it is inevitable that there will be some AC components in the DC stable quantity. This AC component superimposed on the DC stable quantity is called ripple.
Output ripple and Noise: Within the specified bandwidth, the amplitude of the AC voltage output by the switching power supply is usually expressed in millivolt peak-to-peak value or RMS value.
Total Harmonic Distortion (THD): It is a measure of the additional harmonic components (including their multiples) in the output signal compared to the input signal when using a signal source. It is usually expressed as a percentage. In general, THD is the lowest at a frequency of 1000Hz, so many products use this frequency as their benchmark for measuring THD. Therefore, when testing THD, a sound with a frequency of 1000Hz is emitted to detect it, and the lower the value, the better.
Overshoot and Undershoot: Overshoot is the first peak or valley that exceeds the set voltage — For the rising edge, it refers to the highest voltage, and for the falling edge, it refers to the lowest voltage. Undershoot refers to the next valley or peak. Excessive overshoot can cause the protection diode to operate and lead to premature failure. Excessive undershoot can cause false clock or data errors.
Operating Ambient Temperature: The temperature range within which the electrical indicators and stability of the switch power supply can be reasonably operated. Unless otherwise specified, do not assume that the power supply can output full power throughout the entire temperature range, nor that the power supply can maintain the same electrical indicators throughout the entire working temperature range.
Pulse Width Modulation (PWM): A voltage adjustment method used in switching power supplies, which refers to controlling the output by changing only the width of the pulse sequence.
9 Features of A Good LED Driver
1. High reliability: Especially like the power supply used for LED street lights, they’re installed at a high altitude that is around 8-12m, which it’s not easy to repair and the maintenance cost is expensive. Thus, a high-reliability driver is a must for the street light series.
2. High efficiency: LED is an energy-saving product, so the efficiency of the LED driver should be high. Heat dissipation is very important for power supplies installed in luminaires. If the power supply has high efficiency, then its power consumption is small, as a result of generating less heat and the temperature rise of the lamp is also small, which is beneficial for delaying the light decay of the LED.
3. High power factor: Power factor is a requirement of the power grid for the load. Generally, there is no mandatory requirement for electrical appliances less than 70 watts. Although the low power factor of a single electrical appliance with a small power has little impact on the power grid, the high lighting electricity demand at night, and the same type of load is too concentrated, it will seriously pollute the power grid. Now, many lighting and driver manufacturers also supply high power factor LED drivers of 30W~40W or even smaller power supply.
4. Driving mode: At present, there are generally two driving modes: one constant voltage source supplies multiple constant current sources, and each constant current source independently supplies power to each LED. This method is flexible in combination, and if one LED fails, it does not affect the operation of other LEDs, but the cost is slightly higher.
Another driver mode is direct constant current power supply, LEDs run in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and the problem of solving the failure of a certain LED without affecting the operation of other LEDs needs to be solved.
5. Surge protection: The ability of LED to withstand surge is relatively poor, especially the ability to withstand reverse voltage. It is very important to strengthen the protection in this respect. Some LEDs installed outdoors, such as LED street lights, are invaded by various surges from the power grid system due to the start of the power grid load and the induction of lightning strikes. Some surges can cause damage to the LED. Therefore, the LED drive power supply should have the ability to suppress the invasion of surges and protect the LED from damage.
6. Protection function: In addition to the conventional protection function, the power supply should preferably add LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high.
7. Protection aspect: For lamps installed outdoors or in complex environments, the power supply structure needs to have requirements such as waterproof, moisture-proof, and high-temperature resistance.
8. Safety regulations: LED driver power supply products need to comply with safety regulations and electromagnetic compatibility requirements.
9. Others: For example, LED driver power supplies need to be matched with LED life expectancy.
3 Types of LED Power Supplies
1. According to the driving mode, it can be divided into constant current type and constant pressure type.
- Constant current type: The characteristic of constant current circuit is that the output current is constant, and the output voltage changes with the size of the load resistance. Constant current power supply is an ideal solution for driving LED and is not afraid of short circuits of load. The consistency of LED brightness is better. However, the disadvantage is the cost is expensive, load cannot be completely open, and the number of LEDs should not be too many, because the power supply has a maximum withstand current and voltage.
- Constant voltage type: The characteristic of constant voltage type drive circuit is that the output voltage is constant, and the output current changes with the size of the load resistance. The voltage will not be very high. Disadvantages: load cannot be completely short-circuited, and voltage fluctuations will affect the brightness of LEDs.
2. According to the circuit structure, it can be divided into capacitor voltage reduction, transformer voltage reduction, resistor voltage reduction, RCC voltage reduction, and PWM control type.
- Capacitive voltage reduction: LED power supplies that use capacitive voltage reduction are easily affected by fluctuations in the power grid voltage, the impact current is too large, and the low power supply efficiency, but the structure is simple.
- Transformer voltage reduction: This method has low conversion efficiency, low reliability, and bulky transformer.
- Resistive voltage reduction: This method is similar to the capacitive voltage reduction method, but the resistor needs to consume more electricity, so the power supply efficiency is also relatively low;
- RCC voltage reduction: this method is more widely used because of its wide voltage stabilization range, and its power utilization efficiency can reach more than 70%, but its load voltage ripple is larger.
- PWM control type: the use of PWM control is worth mentioning because for now, LED power supplies designed with PWM control are relatively ideal. This LED driver power supply outputs stable voltage or current, and the power conversion efficiency can reach 80% or even more than 90%. It is worth noting that this type of power supply can also be equipped with multiple protection circuits.
3. It can be divided into the isolated driver and non-isolated driver according to whether the input and output are isolated.
- Isolated driver: Isolation is for safety reasons, and the input and output are isolated through the transformer. Common topologies include forward, flyback, half-bridge, full-bridge, and push-pull. Forward and flyback topologies are mostly used in low-power applications, with few devices and simpler implementation. Among them, the flyback has a wide input voltage range and is often combined with PFC. Its application is more extensive as a flyback isolated driver.
- Non-isolated type: Isolated drivers are generally powered by batteries, storage batteries, and regulated power supplies, and are mainly used in portable electronic products, mining lamps, automobiles, and other electrical equipment.
How to Choose a Good LED Driver for Lighting Fixture?
When it comes to choosing a good LED driver for your lighting fixture, there are several factors that need to be considered. The LED driver is an essential component of the lighting system, as it regulates the power supply to the LED lights. A good LED driver ensures that the LED lights operate efficiently and effectively, providing the desired lighting output while maintaining energy efficiency. Here are some of the factors to consider when choosing a good LED driver for your lighting fixture:
1. Compatibility with LED lights: The LED driver must be compatible with the LED lights that are being used. The voltage and current requirements of the LED lights must match the output of the LED driver. It is important to check the specifications of both the LED lights and the LED driver to ensure compatibility.
2. Power output: The power output of the LED driver must be sufficient to power the LED lights. The power output is measured in watts and must be chosen based on the total wattage of the LED lights that are being used. It is important to choose an LED driver with a power output that is slightly higher than the total wattage of the LED lights to ensure optimal performance.
3. Efficiency: The efficiency of the LED driver is an important factor to consider. A good LED driver should have high efficiency, which means that it converts the input power to LED lights with minimal losses. The efficiency of the LED driver is measured in terms of a percentage, and it is important to choose an LED driver with high efficiency to ensure energy efficiency and cost savings. Generally, LED driver efficiency can be 95-98%.
4. Dimming capability: If the lighting fixture requires dimming capabilities, then it is important to choose an LED driver with dimming capabilities. The LED driver must be compatible with the dimmer switch that is being used, and it must be able to provide smooth and flicker-free dimming. There are Triac, 0/1-10V, DALI, DMX, and PWM dimming drivers to choose from.
5. Quality and reliability: The quality and reliability of the LED driver are important factors to consider. A good LED driver should be made of high-quality materials, such as aluminum for better heat dissipation and should be designed to last for a long time. It is important to choose an LED driver from a reputable manufacturer to ensure quality and reliability.
6. Flicker-Free: Flicker-free LED power supplies typically use high-frequency switching technology to regulate the current, which helps to eliminate any visible flicker. And it ensures that the light output is consistent and without any flicker. This is important because flickering can cause eye strain, headaches, and other health issues, especially for those who spend a lot of time in the presence of LED lights.
7. Waterproof function: If the lighting application is in outdoors or a wet environment such as the bathroom or balcony, a waterproof power supply is a must. It protects the driver from water damage, which can cause the driver to malfunction or fail completely, resulting in the light fixture may not be able to function properly or may pose a safety hazard. Additionally, a waterproof driver can extend the lifespan of the LED light fixture by preventing water damage and corrosion.
8. Safety: Ensure that the LED driver has appropriate safety certifications, such as UL or CE, to ensure that it is safe to use and meets industry standards.
Penglight is a professional LED lighting sourcing agent in China. We specialize in the sourcing and development of lighting products since 2016, our services are mainly light fixtures sourcing and development, LED light testing and quality inspection, lighting shipment consolidation and delivery. We help our customer implement their lighting project from start to finish, whether it’s indoor lighting or outdoor landscape lighting, we offer a turnkey lighting solution to meet your project requirements. If you have an ongoing project that needs light fixtures, feel free to contact us.