True or false: If you're a vendor that already designs and builds conventional DC/DC regulators, you can also do LED drivers. The answer: maybe, maybe not.
Let's back up for a moment and look at the driver opportunity for IC vendors. It's not news that LEDs are seeing tremendous growth in all sorts of applications, ranging from targeted uses such as cars and street lamps, to display signage and large-scale displays, and even wide-area interior area illumination. But providing power to every LED array is the less glamorous -- but equally vital -- LED driver, which takes the DC power (usually from a rectified AC line).
How big is this market, and what is its expected growth? As you'd expect, the numbers are all over the place, due to the assessment techniques used and definitions of the market segments (plus the futuristic nature of these reports. (I generally don't give much credence to projections going more than a short time out, and I am always fascinated by the numerical precision and significant figures of the projected data.) Among the report summaries I have seen are these numbers:
Regardless of the numbers you choose to follow, it's clearly a huge opportunity, and that's why just about every vendor of DC/DC regulator ICs is in this market. It makes sense, since there are many similarities between regulators for conventional applications and those for LEDs.
But there are differences that mean that not every vendor automatically has the expertise needed, especially at the higher power levels for high-brightness LEDs (HB LEDs), or LED strings and arrays. Among the major differences are these:
- LEDs need current drive rather than voltage drive. Depending on the number of LEDs in the series string, the voltage at which the driver supplies this current -- the compliance voltage -- can range from a few volts to hundreds of volts. So you need a high-voltage process and design expertise, different than those of the low-voltage, high-current world of many DC/DC ICs.
- In contrast to the largely resistive nature of most loads, perhaps with some inductance or capacitance, the load of the LEDs is inherently non-linear (they are diodes, after all). The output structure of the driver IC must be able to handle this unique kind of load.
- The fault and failure modes, as well as thermal issues, for LEDs as loads are different than other for loads, and the driver must designed for this unpleasant but unavoidable reality.
The list of LED-driver IC vendors is long, and each claims to offer the unique, "better" solution. Among the sources are (in alphabetical order): AnalogicTech, Analog Devices, austriamicrosystems (AMS), Cirrus Logic, Diodes, Inc., Exar, Fairchild Semiconductor, Freescale Semiconductor, Infineon Technologies, Intersil, iWatt, Leadis Technology, Linear Technology Corp., Macroblock, Maxim Integrated Products, Monolithic Power Systems, National Semiconductor (now part of Texas Instruments), NXP Semiconductors, ON Semiconductor, O2 Micro, Power Analog Microelectronics, Power Integrations, Richtek, Rohm Electronics, Semtech, Silicon Touch Technology, Skyworks, STMicroelectronics, Supertex, and Texas Instruments,
Of course, only a detailed analysis of the data sheet, along with some in-depth, hands-on testing of the driver, can confirm those claims. It's enough to make your head go into thermal overload and subsequent shutdown.