Power Sources and Supplies: World Class Designs

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157Transformer-isolated Circuits

power is supplied. This causes both heat and a reduction of effi

ciency. The advantage is

that the resistor is an inexpensive part that is also very small compared to an iron core

transformer as used in Figure 6.2 . The bootstrap circuit is an excellent implementation

for universal input supplies. ST produces a line of control ICs with the trade name VIPer

that integrate the bootstrap circuit, as well as a high voltage MOSFET switch for very low

part count operation in low power applications. National, Linear Technology, and other

manufacturers also produce low power (under 20 W) fully integrated ...