PCB transformers, also known as board-mount or circuit-board transformers, perform all the same voltage changing tasks as their larger counterparts. Although some of these little transformers can be constructed using semi-conductor techniques, surprisingly many of them are simply miniaturised versions of the familiar formats, but usually completely sealed in an epoxy resin case. They typically offer a range of output voltages and some feature double primary windings, extending their input voltage capabilities. They are, of course, designed for PCB mounting and usually employ either through-hole technology (THT) for underside soldering or flat-pack (FPAK) for use in surface mount technology (SMT), usually having solder-prepared feet. Selecting the correct PCB transformer is remarkably similar to a full-size universal transformer, with regard being had to primary and secondary voltage along with power rating of both W and VA. Other considerations will be physical dimensions and operating temperature. Many of these small transformers are intrinsically safe and some others are certified as safety transformers, but not all. For applications requiring increased current or voltage, it is often possible to mount transformers in parallel or in series but suitability should always be checked with the manufacturers' specification details.