For feeding low-voltage soldering iron from a household outlet uses simple adapters, which are, as a rule, the quenching capacitance (capacitor for a specific value). However, the use of such a device for installation of equipment with microprocessors, field-effect transistors and other electronic components afraid of static electricity is undesirable. Too high risk of breakdown due to the direct connection of the heating element with electricity of high voltage. Need galvanic isolation. For example, in the form of a step-down transformer.
The best solution is to use an adapter with electrical isolation with electrical grid, toroidal power transformer (from the equipment on the low-voltage vacuum fluorescent displays). In addition to the network, and 40-V he has other windings: for chips, filament lamps and other purposes. As they say, there is an ideal opportunity for the creation of compact multifunctional devices, the output of which is easily variable voltage AC/DC (Fig. 1).