Power Electronics

Adaptive Control IC Powers Halogen Lamps

Combining adaptive control techniques with advances in high-voltage junction isolation (HVJI) process, International Rectifier (El Segundo, Calif.) has readied an unprecedented intelligent control IC that functions as an electronic transformer to drive low-voltage halogen lamps. All necessary features are integrated into a single 8-pin DIP or SOIC package to provide a monolithic solution. In reality, it replaces the age-old magnetics transformer to simplify circuit design and improve reliability. In addition, the integrated half-bridge driver cuts parts count by 20% to lower cost and board space.

Thanks to the innovative adaptive dead time control, the new IR2161 control IC adapts quickly to the changing supply voltage, frequency conditions and lamp conditions, enabling the introduction of highly reliable halogen transformers while streamlining their design and manufacture. Because the dc bus voltage varies during the mains half cycle, the dead time must vary in order to achieve soft switching. The IC has an active dead time circuit that detects the point at which the dc bus voltage in the half-bridge slews to 0 V and sets the low-side driver (LO output) high. An internal sample and hold system allows approximately the same delay to be used to set the high-side driver (HO output) high after LO has gone low. This enables the adaptive dead time control circuit to react on a cycle-by-cycle basis of the oscillator to adjust dead time as necessary to maintain soft switching regardless of external conditions.

Other benefits of adaptive dead time control include cool running MOSFETs, reduced thermal stress in the lamp and improved EMI behavior due to frequency modulation (dither). Furthermore, the chip provides compensation of the output voltage for load regulation, allowing the device to operate with extremely low harmonic distortion over the full range of loads.

Implemented in the company's rugged HVJI process technology, this compact 8-pin device incorporates a 600-V half-bridge driver, advanced overload and short-circuit protection circuitry with high-temperature shutdown and adaptive control techniques. It also includes requisite logic for adaptive dead time control and accommodates output voltage compensation. In addition, it offers a built-in 30-kHz to 125-kHz oscillator. Other features include output drive capability of 250/400 mA, 15.6-V Zener diode clamp on Vcc and micropower startup of less than 300 µA.

Because the HVJI IC technology allows high-voltage circuits to be isolated from low-voltage circuitry, both high- and low-side drive functions can be housed on a single compact chip for controlling various switching converter topologies. And because halogen lighting requires both high- and low-voltage circuits to function, components made with IR's HVJI technology are suited to the application.

In fact, it's a reliable alternative to the traditional approach based upon self-resonating, bipolar transistor half-bridge circuits. The IR2161 also accommodates external dimming with a standard phase-cut, triac-based dimmer. Compared to similar circuits using discrete components, the IR2161 can reduce component count by 20%.

The IR2161 is available in 8-pin DIP, 8-pin SOIC and 8-pin SOIC tape and reel format. In 100,000-piece quantities, the IR2161 is priced at $0.73 each.

The supplier also offers a reference design kit for a 100-W, 220-V input, 12-V output halogen electronic transformer using the IR2161 with a circuit design software that can be downloaded from the company's Web site at www.irf.com/product-info/lighting/indexsw.html.

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