[Source: "High-tech LED - Technology and Applications" June issue]
In the past few years, a new generation of street lights based on LED technology has maintained a strong momentum of development. With the expected longevity and higher power efficiency than the prior art, LEDs can be tailored for difficult-to-reach streetlight applications, and their lower operating and maintenance costs provide an attractive return on investment.
Reliability is an important concern in streetlight design. Not only LED lamps are reliable, but power supplies are also reliable. Street lights must be kept in a generally harsh environment, characterized by rapid changes in temperature, humidity and wind conditions during the day and night. Typically, power supplies that supply LEDs for streetlight applications must be capable of operating over an ambient temperature range of -40 ° C to 50 ° C.
Since driving a LED requires a constant current DC source, AC-DC conversion is necessary when powering the LED with AC mains. Early LED streetlight designs used an AC input to connect to a standard high-voltage DC-DC converter and used a balancing circuit to drive multiple LEDs in parallel or in series. Although the power requirements vary depending on the brightness of the LEDs and the number of LEDs in each fixture, in general, these application power supplies must meet current energy regulations, have a power factor of 0.9 or higher, and provide constant current output, waves. Surge protection and low ripple. Most designs require energy efficiency of more than 85%.
Design from a system perspective
Initially, designers relied heavily on flyback topologies to meet the needs of LED streetlight applications. Many vendors offer proven flyback converters that offer low-cost, easy-to-design and fast-to-market solutions compared to more complex LLC converters. However, as global regulators pay more and more attention to reducing energy consumption, new energy efficiency regulations are being introduced. They not only require high efficiency when the power supply is fully loaded, but also require high efficiency in standby mode and different rated load points. The LLC resonant converter uses zero voltage switching technology to reduce switching losses, giving designers the opportunity to maximize efficiency over the entire load range.
Some of the latest LLC converters combine an LLC controller, a lower and upper tube driver, and two half-bridge MOSFETs into one package, further taking advantage of this inherent efficiency advantage. These highly integrated solutions have many advantages. The LLC solution using discrete controllers and MOSFETs forces the designer to set the appropriate dead time for the worst case to avoid breakdown. Designers must overlap the turn-off time of each MOSFET to ensure that they do not turn on and form short conductive loops at the same time. However, the longer the dead time, the lower the efficiency of the converter. By integrating the controller, driver, and MOSFET into a single circuit where all components affecting the switching delay are matched, the LLC converter can more accurately turn the turn-on and turn-off times of the two MOSFETs control. This allows the designer to set shorter, tighter dead times and optimize the performance of the controller to maximize efficiency over a specified frequency range.
A highly integrated solution like this can also significantly improve reliability. To ensure continuous operation of the power supply under all environmental conditions, most LLC converters today feature comprehensive fault detection and compensation. These features include programmable voltage ramp/drop thresholds and hysteresis, undervoltage and overvoltage protection, programmable overcurrent protection (including short circuit protection), and overtemperature protection. Now, some integrated LLC controllers allow designers to replace bulky, less reliable electrolytic capacitors in output loops with more reliable SMD ceramic capacitors. Moreover, by integrating several important functions into one IC, these functions can be fine-tuned during the manufacturing process to optimize the pairing between the MOSFET and the driver to ensure more reliable and efficient performance.
For more information, please refer to the June issue of "High-tech LED-Technology and Applications" magazine.
In the past few years, a new generation of street lights based on LED technology has maintained a strong momentum of development. With the expected longevity and higher power efficiency than the prior art, LEDs can be tailored for difficult-to-reach streetlight applications, and their lower operating and maintenance costs provide an attractive return on investment.
Reliability is an important concern in streetlight design. Not only LED lamps are reliable, but power supplies are also reliable. Street lights must be kept in a generally harsh environment, characterized by rapid changes in temperature, humidity and wind conditions during the day and night. Typically, power supplies that supply LEDs for streetlight applications must be capable of operating over an ambient temperature range of -40 ° C to 50 ° C.
Since driving a LED requires a constant current DC source, AC-DC conversion is necessary when powering the LED with AC mains. Early LED streetlight designs used an AC input to connect to a standard high-voltage DC-DC converter and used a balancing circuit to drive multiple LEDs in parallel or in series. Although the power requirements vary depending on the brightness of the LEDs and the number of LEDs in each fixture, in general, these application power supplies must meet current energy regulations, have a power factor of 0.9 or higher, and provide constant current output, waves. Surge protection and low ripple. Most designs require energy efficiency of more than 85%.
Design from a system perspective
Initially, designers relied heavily on flyback topologies to meet the needs of LED streetlight applications. Many vendors offer proven flyback converters that offer low-cost, easy-to-design and fast-to-market solutions compared to more complex LLC converters. However, as global regulators pay more and more attention to reducing energy consumption, new energy efficiency regulations are being introduced. They not only require high efficiency when the power supply is fully loaded, but also require high efficiency in standby mode and different rated load points. The LLC resonant converter uses zero voltage switching technology to reduce switching losses, giving designers the opportunity to maximize efficiency over the entire load range.
Some of the latest LLC converters combine an LLC controller, a lower and upper tube driver, and two half-bridge MOSFETs into one package, further taking advantage of this inherent efficiency advantage. These highly integrated solutions have many advantages. The LLC solution using discrete controllers and MOSFETs forces the designer to set the appropriate dead time for the worst case to avoid breakdown. Designers must overlap the turn-off time of each MOSFET to ensure that they do not turn on and form short conductive loops at the same time. However, the longer the dead time, the lower the efficiency of the converter. By integrating the controller, driver, and MOSFET into a single circuit where all components affecting the switching delay are matched, the LLC converter can more accurately turn the turn-on and turn-off times of the two MOSFETs control. This allows the designer to set shorter, tighter dead times and optimize the performance of the controller to maximize efficiency over a specified frequency range.
A highly integrated solution like this can also significantly improve reliability. To ensure continuous operation of the power supply under all environmental conditions, most LLC converters today feature comprehensive fault detection and compensation. These features include programmable voltage ramp/drop thresholds and hysteresis, undervoltage and overvoltage protection, programmable overcurrent protection (including short circuit protection), and overtemperature protection. Now, some integrated LLC controllers allow designers to replace bulky, less reliable electrolytic capacitors in output loops with more reliable SMD ceramic capacitors. Moreover, by integrating several important functions into one IC, these functions can be fine-tuned during the manufacturing process to optimize the pairing between the MOSFET and the driver to ensure more reliable and efficient performance.
For more information, please refer to the June issue of "High-tech LED-Technology and Applications" magazine.
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