LED driver solutions for medium voltage general lighting applications

Many medium voltage LED applications are powered by off-line AC-DC power supplies, batteries, or electronic transformers with low voltage AC outputs. But some of these power supplies, such as lead-acid batteries, are only simply regulated. Therefore, there is a need for an LED driver solution that can operate over a wide input voltage range and can be configured with a variety of topologies to support LED load requirements. Depending on the LED current and operating conditions, linear or switching regulator LED driver solutions can be used. ON Semiconductor provides solutions in a variety of topologies for medium voltage LED applications to meet a variety of general lighting needs such as landscape lighting, low voltage track lighting, solar-powered lighting, automotive lighting, emergency vehicle lighting, marine lighting, 12 Vac/Vdc MR16 lamps, aircraft interior lighting, sign backlighting, billboard text circuits and signs.

Figure 1: Example of LED landscape lighting

Medium Voltage LED Common Topologies and Power Supplies

Medium voltage LED lighting applications require optimized driver solutions. ON Semiconductor provides medium voltage LED driver solutions with three different topologies: inductive, charge pump, and linear, to meet different application requirements of users, as shown in Figure 1.

Figure 2: Examples of three topologies

There are several types of power supplies for medium voltage LED applications, each with its main purpose. Among them, offline AC voltage regulator adapters, common voltages are 12, 24, 36, 48 Vdc, and the voltage regulation accuracy is ±5%, which is suitable for low to medium power applications with low safety requirements. Sealed lead-acid batteries, with only simple voltage regulation, 8 to 14 Vdc, are widely used in automotive lighting; 7-27 Vdc, used for automotive, solar, and marine lighting. 12 Vdc and 12 Vac power supplies are common in indoor lighting, track lights, outdoor lighting, landscape lighting, etc.

ON Semiconductor Medium Voltage LED General Lighting Solutions

1) Linear LED driver solution

Linear solutions are the preferred approach for many lighting applications because their design is simple and intuitive and allows the LED to be driven with a precisely regulated current regardless of variations in the LED forward voltage or input supply.

Because these LED drivers are linear, they must match the power consumption requirements of the application. ON Semiconductor offers a wide range of constant current linear LED drivers from 10 mA up to 1 A. The channel output currents of 10 to 50 mA include NSI50010Y, NSI45020JZ, NSI45020, NSI45020A, NSI45025, NSI45025A, NSI45025AZ, NSI45025Z, NSI45030, NSI45030A, NSI45030AZ, NSI45030Z, NSIC2020B, NSIC2030B, NSIC2050B and NCV7680; the channel output currents of 60 to 350 mA include NSI45060JD, NUD4011, NSI45090JD and CAT4104; and the channel output currents of NUD4001 (500 mA) and CAT4101 (1000 mA) are larger.

Figure 3: NSI45 application circuit

Take the NSI45 series of linear constant current regulators as an example. This is a two-terminal or three-terminal linear constant current regulator based on the self-biased transistor technology of ON Semiconductor's pending patent. It is very suitable for a wide range of LED applications with different input voltages, such as driving current in LED lighting applications for buildings, automobiles and industrial signs. It can operate over a wide input voltage range, providing engineers with a simple, cost-effective current regulation solution suitable for their applications without sacrificing performance. This constant current regulator series can maintain a stable current over a wide range, ensuring constant brightness within the operating voltage range, and has a negative temperature coefficient characteristic, protecting the LED from thermal runaway at extreme voltages and operating temperatures.

Another typical application of NSI45 is as a constant current regulator linear LED driver for display screens and billboard text circuits. Its features include low startup voltage, precise current regulation regardless of changes in forward voltage (Vf), and negative temperature coefficient characteristics to protect the LED.

Figure 4: NSI45 display and billboard text circuit application example

2) LED MR16 bulb solution

NCL30100 is a buck LED driver controller with high efficiency, peak current control, adaptive fixed off time, which can be used in low power and space-constrained applications where space and high efficiency are critical. The solution has adjustable oscillation frequency and adopts continuous conduction mode (CCM), which can save output capacitors, with energy efficiency up to 95%, and provides natural LED open circuit protection.

The driver controller has a switching frequency of up to 700kHz, does not require output capacitors, and has a Vcc operating range of 6.35 to 18 V. It can drive one or more high-power LEDs and is mainly used in applications such as MR16 LED lighting, ambient lighting, solar LEDs, traffic lighting, outdoor lighting, and LED light strips. The PCB using the NCL30100 is very small and can be installed in the lamp holder of an MR16 lamp. The hysteresis control feature of the NCL30160 provides fast response during load transients without the need for small signal control loop compensation components. Protection features include resistor-settable LED current, LED short-circuit protection, undervoltage lockout, and thermal shutdown.

Using the NCL30100, negative current sensing can be used to reduce power losses with small inductors, achieving low-cost, high-efficiency and low-component applications. The device uses a low-side N-FET switch topology and continuous conduction mode operation, eliminating the need for output capacitors. Therefore, the circuit can be placed in an MR16 lamp holder using the evaluation boards NCL30100ADLMGEVB and NCL30100ASLDGEVB provided by ON Semiconductor, the latter of which can also achieve PWM dimming.

Figure 5: NCL30100 LED driver controller circuit

Figure 6: NCL30100 evaluation board

In addition, for 12 V AC-DC designs of 3 to 4 LED modules, the evaluation board NCP3065BBGEVB provided by ON Semiconductor for NCP3065 can be used. It can be used to drive Sharp ZENIGATA?, Cree XLamp?MC-E and other LED modules in 12 Vac/Vdc applications. Since the module forward voltage overlaps with the input voltage range, only one switch buck-boost configuration is used. It is characterized by small size, wide input and output operating voltage, output current is regulated, and it also has LED open circuit protection and output short circuit protection capabilities. This solution is suitable for MR16 bulbs, landscape lighting, traffic lighting, etc.

Figure 7: Buck-boost MR16 lamp LED and reference design demonstration board

3) Solar powered LED road sign solution

The NCL30160 is a switching regulator for high-power LEDs that uses a constant voltage from a power supply based on the NCL30051 to step down the voltage, thereby providing a constant current for the LED string. By utilizing a low on-resistance internal MOSFET of only 30 mΩ and the ability to operate at 100% duty cycle, it can provide an energy efficiency of up to 98%.

The device operates with an input voltage range of 6.3V to 40V and a switching frequency of up to 1.4 MHz, making it an excellent solution for industrial and automotive applications. The high switching frequency allows designers to use smaller external components, helping to minimize board size and cost. The NCL30160 includes a hysteresis control feature that provides fast response during load transients, eliminating the need for small signal control loop compensation components. Protection features include resistor-settable LED current, LED short-circuit protection, undervoltage lockout, and thermal shutdown. There is also a dedicated PWM dimming pin/low-power shutdown function.

Working together with the NCP30160 IC, the NCL30051 simplifies the power circuit design with minimal external components. This architecture enables the chipset to be integrated into a more compact and cost-effective LED lighting power supply for general lighting applications such as outdoor lighting (such as LED road signs, street lights, parking lot lights).

Figure 8: Solar-powered LED road sign and driver solution

Promote LED to replace incandescent lamps

According to the Announcement on the Gradual Prohibition of Import and Sale of General Lighting Incandescent Lamps jointly issued by the National Development and Reform Commission and other departments, the import and sale of general lighting incandescent lamps will be gradually banned in stages according to the power size starting from October 1, 2012. ON Semiconductor uses its core expertise and advantages in power management, high-efficiency power supplies and packaging to develop dedicated LED drivers for different application fields, as well as solid-state lighting solutions that meet or exceed regulatory requirements around the world, providing a wealth of options for realizing the lighting revolution and will play a positive role in promoting this process.