Drives and Controls Magazine

Mosfets make redundant supplies redundant

03 November, 2010

The power supply manufacturer Puls has launched a redundancy module which can be used, by itself, as a redundant 40A, 24V power supply system. Instead of conventional diodes, the YR80 module uses Mosfet (metal oxide semiconductor field effect transistor) devices, which have much lower losses and need less cooling.

“Traditional diode-based redundancy modules waste enormous amounts of energy, produce excessive heat and require a lot of hardware to achieve the level of protection needed for vital equipment,” explains Puls’ managing director, Harry Moore. “The YR80’s use of Mosfet technology represents a step change in the design of these devices, giving customers the opportunity to build leaner, more efficient systems at significantly lower cost.”

Conventional redundancy systems incorporate two power supplies connected in parallel, each capable of handling the load if the other fails. This is known as 1+1 redundancy. For higher output currents, N+1 redundancy systems are used, so for a 120A load, four 40A power supplies are used, so that if one fails the remaining three can safely supply the required power.

The diodes traditionally used to protect these power supplies consume large amounts of energy, especially in high-load applications. These losses create heat problems and require large heatsinks to dissipate the heat.

The Mosfets used in the new module have a low on-resistance, resulting in much smaller voltage drops than for diodes. For a 40A output current, diodes produce a voltage drop of at least 500mV between the input and output terminals. With Mosfets, the drop is just 50mV, saving energy and making cooling easier. The YR80’s losses for a 40A output are only 2.7W, so a heatsink is not needed.