Lamp Half-Bridge Driver Chips Boost Efficiency, Need Fewer Parts

A pair of half-bridge driver ICs raises efficiency and slashes parts count in controllers for compact fluorescent lamps (CFLs) and low-voltage halogen lamps. These chips from International Rectifier are based on the company's proprietary high-voltage junction-isolation IC technology.

The CFL ballast and the halogen converter-control ICs integrate high-frequency switching regulators to efficiently convert a rectified mains voltage. Both add soft-start and protection circuitry. The IR2520D CFL ballast controller and the IR2161 halogen converter controller use similar 600-V half-bridge drivers with internal voltage-controlled oscillators (VCOs).

In the CFL chip, when the supply voltage exceeds the undervoltage-lockout threshold, the VCO frequency ramps down toward the resonance frequency of the high-Q ballast. The frequency keeps decreasing until the lamp ignites. If the lamp ignites successfully, the VCO runs at a minimum frequency programmed by an external resistor.

The halogen controller has one key difference. To maximize lamp lifetimes, its VCO runs at about 120 kHz at startup, using the reactance of the external transformer to hold down the converter's output voltage. In RUN mode, the oscillator then runs from approximately 30 kHz at maximum load to 55 kHz at no load. This regulates without the need to monitor the output.

Other differences relate to special features. The CFL chip incorporates adaptive zero-voltage switching (ZVS), internal crest-factor overcurrent protection, and an integrated bootstrap diode. The halogen-lamp chip includes adaptive dead time to allow cool-running MOSFETs in the bridge and reduces electromagnetic interference by dithering the VCO frequency.

Key specifications for both ICs include an output drive capability of 250/400 mA, a 15.6-V Zener diode clamp on V_CC, and micropower startup current.

The IR2520D Adaptive CFL IC and the IR2161 converter IC are available in eight-pin DIPs and eight-pin SOIC packages. Unit pricing begins at $0.57 for the IR2520D and $0.73 for the IR2161, both in 100,000-piece quantities.