Low-loss three-phase ideal diode bridge rectifier eases thermal design

A new low-loss three-phase ideal diode bridge rectifier reference design, demonstrated on evaluation board DC2465, has been announced by Linear Technology. Conventional three-phase rectifiers employ six diodes, but the diodes drop voltage and dissipate significant power at just a few amperes of load current. This requires costly heat sinking and active cooling solutions that complicate thermal design and increase solution size. The DC2465 design replaces the six diodes with three LT4320 ideal diode bridge controllers, driving six low loss N-channel MOSFETs, dramatically reducing power and voltage losses. This enables the overall system to be specified to operate with a smaller, more cost-effective power supply due to the enhanced power efficiency. Low voltage applications benefit from the extra margin afforded by saving the two diode drops inherent in diode bridges. Compared to traditional approaches, the MOSFET bridge enables a rectifier design that is highly space- and power-efficient. The DC2465 board rectifies line-to-line AC voltages from 9VRMS to 48VRMS with frequencies up to 400Hz while sourcing a load of up to 25A without forced airflow. Efficiency at 9V input is raised from 84% for a diode bridge to 97% for the active bridge. The LT4320 ideal diode bridge controller IC is offered in 8-pin MSOP, PDIP, and 3mm x 3mm DFN packages.