Triac or bypass circuit and MOSFET power steal combination

摘要

A power supply unit for use with thermostats or other like devices requiring power. A power supply unit may be designed to keep electromagnetic interference emissions at a minimum, particularly at a level that does not violate governmental regulations. A unit may be designed so that there is enough power for a triggering a switch at about a cross over point of a waveform of input power to the unit. Power for triggering may come from a storage source rather than line power to reduce emissions on the power line. Power for the storage source may be provided with power stealing. Power stealing may require switching transistors which can generate emissions. Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum.

主权项

1. A power supply unit for a heat, ventilation and air conditioning thermostat, comprising:
a triac having an input, a gate and an output; a bypass circuit having an input connected to the input of the triac; a stealing circuit comprising an energy storage module and having an input connected to an output of the bypass circuit; and a MOSFET power steal module having an input connected to the output of the triac; and wherein:
the input of the triac and an output of the MOSFET power steal module are primary terminals for connection in a power circuit;the MOSFET power steal module steals energy and the energy goes to the energy storage module; andthe energy is used to trigger the triac at a zero crossing of line voltage from a power source.