ON Semiconductor's high-efficiency driver power solution for LED street lights

With the increasing support of governments around the world for LED lighting and the further reduction of LED product prices, the LED lighting market has experienced explosive growth in recent years. LED street lights are one of the important applications. Their advantages such as high energy efficiency, environmental protection, energy saving, and easy control have made the trend of replacing traditional street lights more and more obvious. Unlike indoor LED lighting products, LED street lights often have higher power, and the outdoor application environment is more complex. How to drive LED street lights efficiently and reliably has become a key point in the design.

Actively promoting high-efficiency innovation, ON Semiconductor makes full use of its rich experience in the power supply field to provide high-efficiency solutions that meet various regulatory requirements for LED street lamp driver design, including PFC stage and main power stage devices.

Power Factor Correction (PFC) Pre-Boost Conversion Stage Solution

At present, major countries and institutions in the world have put forward corresponding standards for the power factor or total harmonic distortion of LED drivers, such as IEC 61000-3-2 proposed by the International Electrotechnical Commission, EN61000-3-2 of the European Union, JIC-C-61000-3-2 of Japan, GB 17625.1 of China, etc. The US "Energy Star" has power factor requirements for solid-state lighting fixtures with a power level greater than 5 W. The power factor of household drivers must be greater than 0.7, and the power factor of commercial drivers must be greater than 0.9. In the application of street lights, the power factor requirement is usually greater than 0.95.

In order to meet the requirements of power factor and harmonic content limitation in high-power LED street light power supply design, ON Semiconductor provides three operating modes of PFC solutions: continuous conduction mode (CCM), such as NCP1654; critical conduction mode (CrM), such as NCP1608; frequency clamped critical conduction mode (FCCrM), such as NCP1605.

Figure 1. ON Semiconductor offers three-mode power factor correction (PFC) solutions

Among them, the main features of NCP1654 include: average current control mode; fast transient response; SO-8 package , requiring very few external components; low starting current (<75 uA); ±1.5 A push-pull output circuit gate drive; surge current detection, overvoltage protection, undervoltage protection, open-loop protection, as well as precise overcurrent and overpower limiting functions, providing strong protection for the circuit.

Main power stage selection: Half-bridge LLC provides cost-effective, high energy efficiency and easy EMI handling options

There are often multiple topologies to choose from in the design of the main power stage power supply, such as flyback, forward, active clamp forward, half-bridge LLC (dual inductor and single capacitor ), etc. With the increase in power and power density, the half-bridge LLC topology provides a cost-effective, energy-efficient, and easy-to-handle electromagnetic interference (EMI) solution for the design of the main power stage driver power supply for LED street lamps. Compared with other topologies, LLC supports operation under a relatively wide input voltage and output load range; the number of components is limited: the resonant energy storage element can be partially or fully integrated in the main transformer ; the primary switch tube has zero voltage switching (ZVS) under all load conditions; the secondary rectifier has zero current switching (ZCS) under all load conditions; and it has a simple synchronous rectification function.

Figure 2. As power and power density increase, the half-bridge LLC topology becomes an ideal choice for LED street lamp drivers

ON Semiconductor's NCP1397 provides a cost-effective and reliable solution for the main power stage using LLC topology, providing an ideal choice for customers in terms of design considerations such as size constraints, standby requirements and cost. The main features include: high frequency operation from 50 kHz to 500 kHz; 600 V high-voltage floating driver; adjustable minimum switching frequency (3% accuracy); adjustable dead time from 100 ns to 2 us; startup sequence provided by external adjustable soft start; input undervoltage protection combined with latch input; timer-based automatic recovery and immediate latch overcurrent protection; input can be turned off by on/off control (skip cycle mode); 300 uA low standby current; 1A/0.5 A peak current sink/source drive capability; shared collector or emitter optocoupler connection.

Standby circuit selection

In order to effectively improve power efficiency, the product standby power consumption needs to be reduced as much as possible. By using ON Semiconductor's NCP1070 high-voltage switching regulator, a simple peripheral buck circuit can be used to effectively reduce standby energy consumption. The device has a built-in 700V  MOSFET , supports dynamic self-power supply (DSS), provides a lossless startup sequence, and also has short-circuit protection, 1ms soft start, frequency jitter, Vcc pin overvoltage protection and other functions. The circuit is simple and cost-effective.

Constant voltage and constant current control solution

Precise constant voltage and constant current control can ensure uniform light emission between LED particles, thereby better ensuring the life of LED street lights. The NCP4328 provided by ON Semiconductor contains two OTAs, which can achieve precise constant voltage and constant current control on the secondary side.

ON Semiconductor 150W High-Efficiency, Flicker-Free LED Street Light Driver Power Supply Reference Design

ON Semiconductor provides a 150 W LED street light driver power solution reference design. This reference design uses a combination of NCP1654 (PFC) + NCP1397 (LLC) + NCP4328 (constant voltage and constant current control) + NCP1070 (standby control) devices, accepts a wide voltage input of 90 to 265 Vac, provides a 40 V/3.45 A output, can meet the requirements of power factor greater than 0.95, total harmonic content less than 15%, full load average efficiency greater than 90%, and typical current accuracy within 1%. This reference design supports fast startup, with a typical startup time of less than 500 ms, and also provides low output current ripple and no flicker.

Figure 4. The power factor and THD of ON Semiconductor's 150 W streetlight reference design meet the design targets.

Summarize

LED street lamps have high technical content, diverse components, and complex external use environments. Governments of various countries have put forward strict requirements on driver design. Providing high-reliability and high-efficiency power supplies for LED street lamps is also an urgent problem to be solved. ON Semiconductor provides a variety of power supply solutions and topologies, and also provides a reference design with high energy efficiency, high constant current accuracy, no flicker, complete protection functions, high reliability, and simple peripheral circuits, making it an excellent choice for LED street lamp driver solutions.