Bypass switch for in-line power steal
A power supply unit for use with thermostats or other like devices. The power supply unit may keep electromagnetic interference emissions and harmonics at a minimum. A unit may have enough power for 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. Power for the storage source may be provided with power stealing which require switching transistors which can generate emissions. In-line thermostats using MOSFETS power steal may do the power steal during an ON state (triac, relay or silicon controlled rectifier activated). Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum. All that may be needed, during an OFF state as a bypass, is a high voltage controllable switch. The need may be achieved using high voltage MOSFETS.
1. An in-line thermostat power system comprising:
a bypass switch;
a power stealing circuit connected to the bypass switch;
an energy storage circuit connected to the power stealing circuit;
an SCR interface circuit connected to the energy storage circuit; and
an SCR circuit connected to the SCR interface circuit; and
wherein the bypass switch is a controllable switch for line voltage, the line voltage controllable switch comprising a positive bypass switch and a negative bypass switch, the positive bypass switch comprises one or more line voltage MOSFETs, and the negative bypass switch comprises one or more line voltage MOSFETs.
2. The system of claim 1 wherein:
the positive bypass switch comprises a positive protect circuit; and
the negative bypass switch comprises a negative protect circuit.
3. The system of claim 1 further comprising:
a half wave zero crossing detection circuit connected to the energy storage circuit; and
a gate signal shaping circuit connected to the half wave zero crossing detection circuit, the bypass switch, and the power stealing circuit; and
wherein:
the power stealing circuit comprises one or more switching MOSFETs; and
the gate signal shaping circuit provides a gate signal that results in a softer transition of turning on and off of the one or more MO SFETs of the power stealing circuit.
4. An in-line thermostat power system comprising:
a bypass switch;
a power stealing circuit connected to the bypass switch;
an energy storage circuit connected to the power stealing circuit;
an SCR interface circuit connected to the energy storage circuit; and
an SCR circuit connected to the SCR interface circuit;
wherein the bypass switch is a controllable switch for line voltage;
wherein the SCR interface circuit has a first input connected to an output of the energy storage circuit, a second input connectable to a line voltage, a third input connectable to a control signal source, and an output for outputting one or more gate signals; and
wherein the SCR circuit has a first input for gate signals from the SCR interface circuit, a second input connectable to a line voltage, and an output of a controlled line voltage.
5. The system of claim 4 , further comprising:
a thermostat comprising:
a temperature sensor;
a temperature setting adjuster; and
a processor connected to the temperature sensor and a temperature setting adjuster; and
wherein the processor comprises the control signal source that provides a signal to the SCR interface circuit which in turn outputs the gate signals to the SCR circuit, with a goal to bring a temperature indication from the temperature sensor and a temperature setting of the temperature setting adjuster to a same value.
6. The system of claim 4 , further comprising:
a heater having terminals connected to a line voltage and an output of the SCR circuit; and
wherein:
the temperature sensor is situated in a space that contains the heater; and
the gate signals to the SCR result in the output of the SCR circuit to control heat from the heater to achieve the goal to bring the temperature indication from the temperature sensor and the temperature setting of the temperature setting adjuster to a same value.
7. A thermostatic power supply mechanism comprising:
a first terminal for connection of a power source;
a bypass switch having an input connected to the first terminal, the bypass switch comprising one or more MOSFETs that are switched;
an SCR circuit having a first connection connected to the first terminal, an input for a control signal, and a second connection for a load;
a second terminal for connection to the load;
a stealing circuit having an input connected to an output of the bypass switch, and an output connected to the second terminal, the stealing circuit comprising an energy storage unit; and
a power steal module having an input connected to the second connection of the SCR circuit and an output connected to the second terminal, the power steal module comprising one or more MOSFETs that are switched to steal power, wherein the stolen power goes to the energy storage unit.
8. The mechanism of claim 7 , wherein the energy storage unit comprises one or more super capacitors.
9. The mechanism of claim 7 , further comprising a MOSFET gate signal shaper that provides a gate signal to the power steal module that softens a transition of turning on or off of the one or more MOSFETs.
10. The mechanism of claim 7 , further comprising:
an SCR control signal circuit having an output that provides the control signal to the input of the SCR circuit; and
wherein the control signal provided to the input of the SCR circuit results in making power available or not available at the second connection of the SCR circuit.
11. The mechanism of claim 10 , wherein:
the second connection of the SCR circuit is connected to the load; and
the load is a heater.
12. A thermostatic power supply mechanism comprising:
a first terminal for connection of a power source;
a bypass switch having an input connected to the first terminal;
an SCR circuit having a first connection connected to the first terminal, an input for a control signal, and a second connection for a load;
a second terminal for connection to the load;
a stealing circuit having an input connected to an output of the bypass switch, and an output connected to the second terminal; and
a power steal module having an input connected to the second connection of the SCR circuit and an output connected to the second terminal;
wherein the bypass switch has circuitry that comprises:
a positive bypass switching MOSFET; and
a negative bypass switching MOSFET.
13. A power supply unit for a thermostat and electric heater comprising:
a bypass switch circuit having an input for connection to a first line voltage, the bypass switch circuit comprising one or more MOSFET switches;
a power steal device having an input connected to an output of the bypass switch circuit;
an energy storage having an input connected to an output of the power steal device;
an SCR gate signal circuit having an input connected to an output of the energy storage;
an SCR circuit having an input from an output of the SCR gate signal circuit and an input connectable to a second line voltage, and having an output for providing a controlled second line voltage; and
a linear regulator connected to the output of the energy storage.
14. The unit of claim 13 , wherein the power steal device comprises one or more MOSFET switches.
15. A power supply unit for a thermostat and electric heater comprising;
a bypass switch circuit having an input for connection to a first line voltage;
a power steal device having an input connected to an output of the bypass switch circuit;
an energy storage having an input connected to an output of the power steal device;
an SCR gate signal circuit having an input connected to an output of the energy storage;
an SCR circuit having an input from an output of the SCR gate signal circuit and an input connectable to a second line voltage, and having an output for providing a controlled second line voltage; and
a zero crossing detector having an input connectable to the second line voltage.
16. The unit of claim 15 , further comprising a FET gate signal shaping circuit having an input for receiving zero crossing information from the zero crossing detector and having an output for providing a sync signal to the bypass switch circuit.
17. The unit of claim 16 , further comprising a reverse wave protection circuit having an input connected to the first line voltage, a second input connected to the output of the energy storage, and having an output for providing a protect signal to the FET gate signal shaping circuit.