LED drivers determine lighting success

 

LED lighting represents the fastest growing segment of the LED market, and LED driver ICs for lighting are therefore experiencing similar growth. These essential components determine lighting system intelligence and performance, and help to maximise the LEDs’ operating life using features such as short, open and over voltage protection and thermal shut down schemes.

Here’s our pick of some of the best LED drivers available from RS for different lighting applications.

 

Car Headlamps

For automotive headlamps and fog lights, TI has the TPS92690 LED driver IC. This DC-DC controller is suitable for boost, SEPIC, Cuk and flyback topologies with an input range of 4.5 to 75 V. There are two inputs for analogue or PWM signals, which feed the same control method for dimming or thermal foldback.

It also features low-side current sense, adjustable between 50 and 500mV to minimise power loss and provide analogue dimming control. The switching frequency is adjustable up to 2MHz, either set by an internal oscillator or overridden by an external clock for synchronisation with other devices in the design. The part’s adjustable switching frequency and current sense threshold together allow it to be configured optimally for size, efficiency or a balance of both.

The TPS92690 is of course available with AEC-Q100 qualification.

 

GLS bulbs

Also from TI, the TPS92075 and TPS92560 LED drivers are designed for a range of interior light bulbs.

The TPS92075 is for offline 120VAC or 230VAC lamps and downlights such as E14, GU10, A19 and PAR20/30/38 bulbs. It’s extremely space efficient, measuring just 2.9 by 2.9mm in its TSOT package. This part operates as a buck or buck-boost converter, producing a constant current to drive LEDs. Power factor correction is 0.9 or better. The controller is phase-dimmable and works with conventional wall dimmer switches.

 

The TPS92560 is a driver for low-voltage AC or DC lamps like MR16 and AR111 bulbs. To enhance compatibility with electronic transformers, TI has invented a hysteretic input control scheme that doesn’t require any complicated loop compensation. Also integrated are active low-side input rectifiers help improve the application’s efficiency.

 

Displays and Signage

From STMicroelectronics, the LED1642GWQTR is ideal for full colour and monochrome displays and LED signage.

This part is a low-voltage, low-current 16-bit shift register. It has 16 constant-current output channels, which can each provide 3mA to 40mA (programmable via an external resistor). The channels can supply 20V so that several LEDs in parallel may be driven by each channel.  Brightness may be adjusted separately for each channel using a 12- or 16-bit PWM grayscale control. Its clock frequency can go as high as 30MHz to support high data rate transmissions.

The LED1642GWQTR comes with thermal management features too, including an overtemperature alert which triggers thermal shutdown of the output at 170°C. It can detect open and shorted LEDs and the thresholds for this feature are programmable.

 

LCD Backlight

LEDs have long played a key role in backlighting other displays such as LCDs. A prime example of an LED driver for this application is the ADD5211 from Analog Devices. This device can drive four strings of white LEDs and is based on an inductive boost controller topology, offering high efficiency, step-up current mode conversion from 4.5 to 40V.

Four regulated current sinks provide uniform brightness; each one can be driver from 40 to 200mA. A PWM signal may be used to control dimming.

Features of this driver include adaptive output voltage to minimise power dissipation and adjustable operating frequency between 200kHz and 1.2MHz. It also has LED short and open protection, boost output short protection, overvoltage protection, cycle-by-cycle current limit, and thermal shutdown for both the IC and the LED array. An open-drain fault output is also included. A programmable soft start is implemented to reduce inrush current during start up.

 

Portable Products

For battery powered flashlights and other portable products, Microchip makes the MCP1643, which operates from one and two-cell alkaline and NiMH/NiCd batteries. It’s intended for driving one LED, but can supply two red/green/yellow LEDs in series.

This driver is a fixed frequency, synchronous boost converter with constant current output.  Microchip’s low voltage technology allows it to start up from a low 0.65V battery voltage without output voltage and load current overshoot. The enable pin is used to switch the LED on or off, and a 1MHz PWM signal may be used for dimming.

Thermal shut down kicks in at 150°C, with 25°C hysteresis. An over-voltage protection feature limits the output to 5V, in case the LED fails or is disconnected.

 

Reference designs

Apart from the products mentioned above, we also have a complete offer of LED Drivers ICs from On Semiconductor, details together with reference designs are available here.