Chip improves efficiency of flyback-converter circuits
By Margery Conner, Technical Editor -- EDN, March 10, 2006
Secondary-side SR (synchronous-rectification) circuits in high-power-flyback and half-bridge-converter circuits have drawbacks: They can be difficult to design, and they may be subject to patent and licensing restrictions. In addition, their use of a current-transformer circuit to sense polarity changes in the rectifying MOSFETs results in a large, energy-wasting unused current that oscillates between the transformer and the output-filter capacitor. Addressing these is-sues, International Rectifier’s new IR1167 SmartRectifier IC directly and precisely senses the voltage threshold across the SR MOSFET. The company claims that the chip can increase system efficiency by 1% by halving the losses the MOSFET dissipates and reducing the MOSFET’s temperature by 10°, thus reducing the number of MOSFETs or allowing a change in part size fromTO-220 to SO-8 packages. The device is also available in DIP-8 packages.
The SmartRectifier works with the IRF7853, the IRFB4110, and the IRFB4227 MOSFETs, which feature optimized on-resistance and gate-charge characteristics. The device sells for $1.08 (10,000).
