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EETE MAY 2013

Fig. 3: The iW3626 block diagram - a single-stage, non-dimmable PFC LED driver. Fig. 4: The iW3630 block diagram - a two-stage PFC controller with 0 to 10V dimming interface for commercial SSL applications. THD is of particular interest in the US market, while in Europe, the IEC61000-3-2 establishes harmonic requirements for power supplies. When the end application demands low THD, high PF and low output ripple, two-stage approaches fit the bill. The main difference between single-stage and two-stage approaches is the obvious addition of a second conversion stage. The additional conversion stage does the power factor correction while minimizing the total harmonic distortion. Not only does the initial conversion stage remove the line frequency from the main output voltage, removing flicker from the light output, it also adds flexibility for integrating dimming technology and reduces in-rush current which benefits the passive components on the input. Two-stage approaches can use either a boost converter or a simple chopping circuit for the initial stage. The full boost converter offers higher efficiency, higher PF C and lower THD across a broader line voltage range compared to a simple chopper circuit. The iW3630 is an example of a two-stage LED driver for solid-state lighting applications that require high PF (>0.95), low THD (<15%) and low output ripple – see figure 4. The first stage is a full boost converter operated in a constant on time architecture to optimize power factor and minimize THD. This stage converts the mains voltage into an intermediate voltage, decoupling the output from the mains voltage and frequency. The second, main power conversion stage then converts the intermediate voltage into usable DC voltage and current for driving the LEDs. This can be an isolated or nonisolated stage depending upon the needs of the end application. With the iW3630, whether the application is isolated or not, there is no need for an optical feedback device because the main feedback is derived from the primary side of the transformer, using iWatt’s PrimAccurate technology. With regulations dictating power factor requirements for solid state lighting, designers need to incorporate power factor correction circuits into the driver design. A clear understanding of the end requirements based on the intended application of the luminaire determines the type of power factor correction that needs to be implemented. Whether single-stage, costdriven solutions for residential lighting, or two-stage performance driven solutions for commercial and industrial applications, the driver technology now exists to enable a brighter, greener future. www.electronics-eetimes.com Electronic Engineering Times Europe May 2013 23


EETE MAY 2013
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