However, as the mains input is converted twice (online UPS are often termed ‘double conversion’) then efficiency is a critical consideration. With rising energy costs, not only are data center operators paying for the cost of any wasted energy, the costs associated with cooling also increase.
Among the biggest contributions to overall losses in a UPS are losses caused by the switching activity of bridge circuits. These switching losses increase as operating frequency increases – and raising operating frequency is an approach that is used to reduce the overall size of the UPS. Toshiba has developed techniques that can significantly reduce these losses in power converters built up by Super Junction MOSFET’s.
The first technique, Synchronous Reverse Blocking (SRB) addresses the reverse recovery charge associated with the freewheeling diode commonly found in half-bridge topologies. By adding a second synchronously controlled switch and a Silicon Carbide (SiC) diode, this contribution to switching losses can be eliminated almost completely.
Recharging the output capacitance of SJ MOSFET’s during every switching cycle is another major source of switching losses. Here, Toshiba’s patented Advanced-SRB (A-SRB) utilizes a charge pump voltage source within a dedicated driver IC to pre-charge MOSFET output capacitance Coss during the deadtime prior to a switching transition, reducing associated losses dramatically.
Toshiba has produced a detailed white paper on improving efficiency in half-bridge based UPS systems covering the theory behind the advances as well as practical realization using Toshiba’s driver modules. To get your free copy of this white paper, please click here: