Triac or bypass circuit and MOSFET power steal combination
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.
1. A power supply unit for a heat, ventilation and air conditioning thermostat, comprising:
a triac having an input and an output;
a stealing circuit comprising an energy storage module; and
a MOSFET power steal module having an input connected to the output of the triac; and
wherein:
the MOSFET power steal module is configured to steal energy;
the energy storage module is configured to store the energy; and
the energy is used to trigger the triac at a zero crossing of line voltage from a power source.
2. The unit of claim 1 , further comprising:
a first terminal including an input connected to a power source and an output connected to the input of the triac, and
a second terminal including an input connected to an output of the stealing circuit and an output connected to an electrical load.
3. The unit of claim 2 , wherein the electrical load is an electric heating mechanism.
4. The unit of claim 1 , further comprising a bypass circuit having an input connected to the input of the triac.
5. The unit of claim 1 , further comprising a gate signal shaper connected to the MOSFET power steal module.
6. The unit of claim 5 , wherein the gate signal shaper provides a gate signal that results in a soft transition of turning on and off of the MOSFET power steal module.
7. The unit of claim 4 , further comprising a half wave zero cross detect module, wherein the half wave zero cross detect module is connected to:
a line voltage at the input of the triac,
a gate signal shaper, and
a triac gate triggering module.
8. Power supply electronics for a thermostat, comprising:
a triac having an input connected to a power source;
a bypass circuit having an input connected to the input of the triac;
a stealing circuit having an energy storage unit and an input connected to an output of the bypass circuit; and
a power steal module having an input connected to the output of the triac.
9. The electronics of claim 8 , wherein:
the power steal module comprises one or more MOSFETs that are switched on to steal power; and
the energy storage unit stores the power.
10. The electronics of claim 8 , wherein the bypass circuit comprises an RC network.
11. The electronics of claim 8 , wherein the bypass circuit comprises an AC-DC converter.
12. The electronics of claim 8 , further comprising a linear regulator and a super capacitor connected to an output of the energy storage unit.
13. The electronics of claim 8 , further comprising a DC-DC converter connected to an output of the energy storage unit.
14. The electronics of claim 8 , wherein if the power steal module comprises two or more MOSFETs, then a serial MOSFETs power stealing approach is effected.
15. A thermostatic power supply comprising:
a first terminal for connection to a power source;
a bypass circuit having an input connected to the first terminal;
an energy storage module having an input connected to the bypass circuit;
a triggerable switch having an input connected to the first terminal; and
a power steal module having an input connected to an output of the triggerable switch, the power steal module comprising one or more MOSFETs.
16. The supply of claim 15 , further comprising:
a DC-DC converter having an input connected to an output of the energy storage module; and
wherein the bypass circuit comprises an AC-DC converter.
17. The supply of claim 15 , further comprising:
a linear regulator having an input connected to an output of the energy storage module; and
wherein the bypass circuit comprises an RC network.
18. The supply of claim 17 , further comprising a super capacitor connected to the linear regulator.
19. The supply of claim 15 , wherein the triggerable switch is selected from a group consisting of a triac, a thyristor, and a relay.
20. The supply of claim 15 , further comprising a gate signal shaper connected to the power steal module.