Control ICs simplify dimming circuits for energy-efficient CFLs
By Margery Conner, Technical Editor -- EDN, November 14, 2008
Energy-efficient CFLs (compact fluorescent lights) continue to gain in popularity for home and office lighting. However, dimmer switches, which control many incandescent lights, can cause a standard CFL to break down. Dimmer switches vary the voltage to the light by switching the source ac voltage using SCRs (silicon-controlled rectifiers), thus enabling incandescent bulbs to vary their brightness from 0 to 100%. Standard CFLs have steady 120V-ac inputs and hence do not respond well to use with dimmer switches. As a result, controlling the ballast for a CFL to adapt to the switched ac voltage requires a more complex, expensive ballast that, due to the greater number of parts and increased complexity, is more prone to failure. In addition, you cannot adjust most currently available dimmable CFLs to less than 10% of their full-on brightness.
To address this problem, International Rectifier’s 600V IRS2530D and IRS2158D control ICs target CFLs that replace incandescent lights in continuously dimmable- and three-way-lighting applications. The IRS2530D DIM8 linear-dimming-ballast-control IC has a half-bridge driver in an eight-pin package and can dim a CFL to 10% of its full-on light. It is suitable for both linear ballasts and CFLs. The chip has a high-voltage pin to sense the half-bridge current and voltage in ballast-protection functions. The dc dim-input-voltage reference and ac-lamp-current feedback combine to allow the use of one pin for dimming. The combination of these high-voltage control algorithms and simple dimming method in an eight-pin IC results in fewer components, increased reliability, reduced design-cycle time, and high dimming-ballast-system performance. The IRS2530D also features an internal non-ZVS (zero-voltage-switching) and internal-crest-factor protection to prevent lamp failure from damaging the ballast.
For applications requiring dimming of less than 10%, the company offers the 16-pin IRS2158D. The IRS2158D offers additional features, such as an end-of-life window-comparator pin and an internal 60-event current-sense up/down fault counter to accommodate T5-lamp and multilamp ballasts.
The IRS2530D is available in an eight-lead DIP or SOIC package for prices starting at $1.09 (10,000).The IRS2158D is available in 16-pin PDIP and narrow-body SOIC packages for prices starting at $1.29 (10,000). Reference-design kits are available for both devices for prices starting at $99.
