General Lighting design engineers face many challenges such as power density, power factor correction (PFC), space limitations, and reliability. These LED lighting design challenges are similar to power supply design challenges. Specifically, LED general lighting has several challenges: because of the effects of total effecacy and thermal limitations, even low-power applications are important; in many cases Lower power also requires power factor correction and harmonic processing; in space-constrained applications, especially when replacing bulb applications, the drive power density is critical; overall power reliability is important to improve overall lamp life. The wide input supply voltage range should support up to 277 Vac; compatible with traditional lighting requirements such as TRIAC dimming. In addition, LED general lighting is also subject to evolving standards and safety regulations, such as the US Energy Star and the European Commission's International Electrotechnical Commission (IEC) requirements.
ON Semiconductor has been providing a wide range of solutions for LED lighting, introducing a variety of products that meet the latest LED lighting standards, including AC-DC power ICs, DC-DC drivers, CCR stabilizers, constant current and constant voltage (CCCV). Control, high voltage FET, rectifier, digital interface, ambient light sensor, protection, power line communication (PLC) modem and more. This article mainly introduces AC-DC power supply configuration and related circuits for LED lighting, helping engineers to meet the above challenges and design products that meet general lighting requirements.
ON Semiconductor LED Lighting Solutions
　　 Figure 1 shows the types of products that are available from ON Semiconductor for general LED lighting.
Figure 1: Application diagram of ON Semiconductor's LED lighting solution
In ON Semiconductor's AC-DC power supply configuration for LED lighting, NCP1010~NCP1015 is recommended for lighting applications from 1 to 10 W, and NCP1027/8 is available for 1 to 15 W. These solutions incorporate MOS transistors for isolation. And non-isolated applications, support secondary PWM dimming, analog dimming or dual brightness level dimming, energy efficiency up to 75-80%; 1 to 30 W applications can use LV5026, 5027, 5028, support isolation scheme, typical energy efficiency 85 About 1%; 1 to 40 W recommended to use NCL30000, can be used for primary controllable dimming, suitable for isolation and non-isolation scheme, isolation scheme energy efficiency 80-85%. The 40 to 150 W is recommended for the NCL30001, which is a continuous conduction mode (CCM) control chip. The typical energy efficiency of the isolation scheme is 85-90%; the NCL30051 is recommended for higher power. Figure 2 is a comparison of output power and energy efficiency of these schemes. The functions and features of these solutions are described in detail below.
Figure 2: Comparison of output power and efficiency of AC-DC power supply configuration for LED lighting
LV5026/27/28 Series LED Controller for 1 to 30 W Power AC-DC Applications
The series is the LED controllers of Sanyo Semiconductor, the LV5026M, LV5028TT and LV5027T, which are members of ON Semiconductor. The LV5026M has TRIAC dimming, PWM dimming, analog dimming and power factor correction. The LV5028TT has only TRIAC dimming and power factor. Correction function. The LV5026/7/8 TRIAC dimming circuit is shown in Figure 3.
Figure 3: LV5026/7/8 TRIAC dimming circuit
Take the most functional LV5026M as an example. It is a high-voltage LED controller compatible with different dimming. The dimming mode is TRIAC, analog input or PWM input. The switching frequency (50 kHz, open circuit 70 kHz) can be selected. The solution is a low-noise switching system that uses a 5-band skip mode frequency to step-drive the switch; its reference voltage is selectable (internal 0.605 V and external input voltage) with soft-start and TRIAC stabilization.
The PWM control architecture designed to reduce electromagnetic interference (EMI) has advantages over competing products. It uses a 2-step drive to significantly reduce noise; five levels of frequency in a non-constant period effectively eliminate EMI peaks.
There are two ways to convert low-power AC-DC LED power, one is non-isolated buck, requires mechanical insulation; its design and circuit configuration are simple, the board size is small, the number of components is small, the energy efficiency is high, bill of materials (BOM) The cost is also lower. The other is isolated return, using electrical (magnetic) isolation, easy to meet safety requirements, magnetic design is more complex, suitable for higher power design, requires a larger board size.
LV5026/7/8 is used for non-isolated A19 LED lamps, which can realize the following product features: step-gate driving method, oscillation frequency rotation function, high-gate capability drive circuit, externally adjustable reference voltage, support for multiple dimmers (TRIAC dimming, digital dimming, and analog dimming); soft start, overcurrent protection, thermal shutdown, overvoltage protection, etc. are also supported. The LV5027M/LV5028M is a simplified version of the LV5026M with fewer external components.
Figure 4: LV5026/7/8 for non-isolated A19 LED lights
Low-power step-down solution for high-efficiency and space-constrained applications NCL30100
The NCL30100 is an energy-efficient, peak-current-controlled, self-regulating, fixed-time-down buck controller for low-power, space-constrained applications where space and energy efficiency are critical, such as MR16 LEDs. The scheme has an adjustable oscillation frequency characteristic. The continuous conduction mode (CCM) eliminates the output capacitance, provides higher energy efficiency, and provides natural LED open circuit protection. The NCL30100 utilizes negative current sensing to reduce power loss with a small inductor for low cost, high energy efficiency (100 Vac Vo = 36 V, energy efficiency > 90%) and low component count.
Figure 5: Single Voltage Input Buck Solution NCL30100