Today's society, with the continuous progress of science and technology, more and more modern medical equipment has been rapid development, especially direct contact with the human body electronic instruments, in addition to the performance of the instrument itself is more and more demanding, the human body safety considerations are also more and more attention. For example: cardiac puncture monitors, ultrasound, mother and child monitors, infant warming instrument, life monitors and other instruments in close contact with the human body, that is to say, the patient can not use the instrument because of the use of the instrument and the human body caused by electrocution or any other aspects of the danger. Medical electronics, unlike other electronics and power electronics that are targeted at mass-market and cost-conscious consumer electronics and other low-cost product applications, have many more rules to follow. If the designer is responsible for the system power design, the first question to consider for the system power supply portion of the system is whether to buy or manufacture the solution. Since medical electronics production volumes are generally relatively low, the designer must consider the question of whether to buy or build. Designers of medical electronics rarely consider designing their own offline power supplies. Because the investment required for this particular type of design and testing is not commensurate with the size of the final production volume, device manufacturers may find it difficult or impossible to spread the investment made during the design phase over the volume of the product. Therefore, it is more cost-effective to purchase power supplies directly from companies that already have the appropriate design expertise and testing technology.