There are three common types of high-frequency machines. In the late 1990s, a BOOST boost chopper circuit was added to the SCR rectifier backend to increase the DC to the voltage required for UPS output, thereby eliminating the need for output transformers. It can be simply understood as replacing the AC boost of the previous power frequency UPS transformer with DC boost, which not only reduces the cost but also greatly reduces the volume and weight of UPS. It can be said to be a major technological innovation in the UPS industry. This type of UPS without a transformer, although the first half of the rectifier is still an SCR device, the second half of the rectifier contains an IGBT high-frequency boost chopper circuit. From the domestic definition, this also belongs to high-frequency machines. At present, there are fewer and fewer BOOST boost chopper high-frequency models, and only some small and medium-sized UPS will continue to use them.