Electronic switch having an in-line power supply

Abstract

A two-wire smart load control device, such as an electronic switch, for controlling the power delivered from a power source to an electrical load comprises a relay for conducting a load current through the load and an in-line power supply coupled in series with the relay for generating a supply voltage across a capacitor when the relay is conductive. The power supply controls when the capacitor charges asynchronously with respect to the frequency of the source. The capacitor conducts the load current for at least a portion of a line cycle of the source when the relay is conductive. The load control device also comprises a bidirectional semiconductor switch, which is controlled to minimize the inrush current conducted through the relay. The bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the capacitor of the power supply, and the relay is rendered non-conductive in response to an over-temperature condition in the power supply.

What is claimed is: 
     
       1. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:
 a latching relay adapted to he coupled in series electrical connection between the source and the load, the latching relay arranged to conduct a load current through the load when the relay is conductive; 
 a controller configured to control the relay to be conductive and non-conductive to turn the load on and off, respectively; 
 an output capacitor arranged to develop a DC supply voltage for powering the controller; and 
 an in-line power supply coupled in series electrical connection with the relay, the in-line power supply further coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the power supply configured to conduct the load current through the output capacitor for at least a portion of a line cycle of the AC power source when the relay is conductive; 
 wherein the relay is rendered non-conductive in response to an over-temperature condition in the electronic switch. 
 
     
     
       2. The two-wire electronic switch of  claim 1 , wherein the power supply comprises a bidirectional semiconductor switch coupled in series with the relay and in parallel with the output capacitor, the power supply configured to render the bidirectional semiconductor switch non-conductive to charge the output capacitor when the relay is conductive. 
     
     
       3. The two-wire electronic switch of  claim 2 , wherein the controller is configured to provide a relay-set control signal to a SET coil of the relay to render the relay conductive, and a relay-reset control signal to a RESET coil of the relay to render the relay non-conductive, the power supply further comprising a thermistor responsive to a temperature of the power supply, the thermistor electrically coupled to the RESET coil of the relay for rendering the relay non-conductive in response to an over-temperature condition in the power supply. 
     
     
       4. The two-wire electronic switch of  claim 3 , wherein the thermistor comprises a PTC thermistor thermally coupled to the bidirectional semiconductor switch of the power supply. 
     
     
       5. The two-wire electronic switch of  claim 4 , wherein the PTC thermistor is coupled in series electrical connection with the output capacitor of the power supply, and the a the voltage across the series combination of the output capacitor and the PTC thermistor is electrically coupled to the RESET coil of the relay, the controller configured to control the relay-reset control signal to render the relay non-conductive in absence of the over-temperature condition in the power supply; and
 wherein the voltage across the series combination of the output capacitor and the PTC thermistor increases during the over-temperature condition in the power supply, and the relay is rendered non-conductive independent of the a magnitude of the relay-reset control signal. 
 
     
     
       6. The two-wire electronic switch of  claim 2 , wherein the power supply further comprises a control circuit coupled to the a bidirectional semiconductor switch for rendering the bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to the a magnitude of the DC supply voltage to render the bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold. 
     
     
       7. The two-wire electronic switch of  claim 6 , wherein the control circuit of the power supply is configured to render the bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold. 
     
     
       8. The two-wire electronic switch of  claim 2 , further comprising:
 an off-state power supply coupled in parallel with the series combination of the relay and the in-line power supply, the off-state power supply coupled to the output capacitor for controlling when the output capacitor charges to generate the DC supply voltage across the output capacitor when the relay is non-conductive. 
 
     
     
       9. The two-wire electronic switch of  claim 8 , further comprising:
 a communication circuit configured to receive digital messages; 
 wherein the controller is configured to turn the load on and off in response to the digital messages received via the communication circuit. 
 
     
     
       10. The two-wire electronic switch of  claim 1 , wherein the bidirectional semiconductor switch of the power supply comprises two FETS in anti-series connection. 
     
     
       11. The two-wire electronic switch of  claim 1 , further comprising:
 a triac coupled in parallel with the series combination of the relay and the power supply, the controller configured to turn on the load by first rendering the triac conductive and then rendering the relay conductive, the controller configured to turn off the load by first rendering the relay non-conductive and then rendering the triac non-conductive; 
 wherein the triac is rendered conductive in response to an over-current condition in the output capacitor of the power supply. 
 
     
     
       12. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:
 a latching relay adapted to be coupled in series electrical connection between the source and the load for turning the load on and off; 
 a first bidirectional semiconductor switch coupled in parallel electrical connection with the relay, the first bidirectional semiconductor switch comprising a control input; 
 a controller configured to turn on the load by first rendering the first bidirectional semiconductor switch conductive and then rendering the relay conductive, the controller configured to turn off the load by first rendering the relay non-conductive and then rendering the first bidirectional semiconductor switch non-conductive; 
 an output capacitor arranged to develop a DC supply voltage for powering the controller; and 
 an in-line power supply coupled in series electrical connection with the relay, the first bidirectional semiconductor switch being electrically connected in parallel with the series combination of the relay and the power supply, the in-line power supply being coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the power supply being configured to conduct the load current through the output capacitor for at least a portion of a line cycle of the AC power source when the relay is conductive; 
 wherein the first bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the output capacitor of the power supply. 
 
     
     
       13. The two-wire electronic switch of  claim 12 , wherein the power supply comprises a second bidirectional semiconductor switch electrically connected in series with the relay and in parallel with the output capacitor, the power supply being configured to render the second bidirectional semiconductor switch non-conductive to charge the output capacitor when the relay is conductive. 
     
     
       14. The two-wire electronic switch of  claim 13 , further comprising:
 a drive circuit coupled between the controller and the control input of the first bidirectional semiconductor switch, the drive circuit being configured to render the first bidirectional semiconductor switch conductive in response to a control signal provided by the controller. 
 
     
     
       15. The two-wire electronic switch of  claim 14 , wherein the power supply comprises a resistor coupled in series with the output capacitor, the resistor being coupled to the drive circuit, the drive circuit being configured to render the first bidirectional semiconductor switch conductive in response to the a current through the resistor exceeding a predetermined current threshold. 
     
     
       16. The two-wire electronic switch of  claim 14 , wherein the first bidirectional semiconductor switch comprises a triac. 
     
     
       17. The two-wire electronic switch of  claim 13 , wherein the latching relay is coupled to the power supply, and the relay is rendered non-conductive in response to an over-temperature condition in the power supply. 
     
     
       18. The two-wire electronic switch of  claim 17 , wherein the controller is configured to provide a relay-set control signal to a SET coil of the relay for rendering the relay conductive, and a relay-reset control signal to a RESET coil of the relay for rendering the relay non-conductive, the power supply further comprising a PTC thermistor thermally coupled to the second bidirectional semiconductor switch of the power supply, the PTC thermistor being coupled in series electrical connection with the output capacitor of the power supply, the a voltage across the series combination of the output capacitor and the PTC thermistor being electrically being coupled to the RESET coil of the relay, the controller being configured to control the relay-reset control signal to render the relay non-conductive in absence of the over-temperature condition in the power supply; and
 wherein the voltage across the series combination of the output capacitor and the PTC thermistor increases during the over-temperature condition in the power supply, and the relay is rendered non-conductive independent of the a magnitude of the relay-reset control signal. 
 
     
     
       19. The two-wire electronic switch of  claim 13 , wherein the power supply further comprises a control circuit coupled to the second bidirectional semiconductor switch for rendering the second bidirectional semiconductor switch conductive and non-conductive, the control circuit being responsive to the a magnitude of the DC supply voltage to render the second bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold. 
     
     
       20. The two-wire electronic switch of  claim 19 , wherein the control circuit of the power supply is configured to render the second bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold. 
     
     
       21. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:
 a latching relay adapted to be coupled in series electrical connection between the source and the load for turning the load on and off; 
 a first bidirectional semiconductor switch coupled in parallel electrical connection with the relay, the first bidirectional semiconductor switch comprising a control input; 
 a controller configured to turn on the load by first rendering the first bidirectional semiconductor switch conductive and then rendering the relay conductive, the controller configured to turn off the load by first rendering the relay non-conductive and then rendering the first bidirectional semiconductor switch non-conductive; 
 an output capacitor arranged to develop a DC supply voltage for powering the controller; and 
 an in-line power supply coupled in series electrical connection with the relay, the first bidirectional semiconductor switch being electrically connected in parallel with the series combination of the relay and the power supply, the in-line power supply being coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the power supply comprising a second bidirectional semiconductor switch electrically connected in series with the relay and in parallel with the output capacitor, the power supply being configured to render the second bidirectional semiconductor switch non-conductive to charge the output capacitor when the relay is conductive; 
 wherein the first bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the output capacitor of the power supply, and the relay is rendered non-conductive in response to an over-temperature condition in the power supply. 
 
     
     
       22. The two-wire electronic switch of claim 21, wherein the in-line power supply further comprises a thermistor responsive to a temperature of the in-line power supply, and wherein the thermistor is electrically coupled to the latching relay to render the latching relay non-conductive in response to an over-temperature condition in the in-line power supply. 
     
     
       23. The two-wire electronic switch of claim 22, wherein the thermistor is coupled in series electrical connection with the output capacitor, and a voltage across the series combination of the output capacitor and the thermistor is electrically coupled to the latching relay. 
     
     
       24. The two-wire electronic switch of claim 21, wherein the in-line power supply further comprises a control circuit coupled to the second bidirectional semiconductor switch for rendering the second bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to a magnitude of the DC supply voltage to render the second bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a first DC supply voltage threshold. 
     
     
       25. The two-wire electronic switch of claim 24, wherein the control circuit of the in-line power supply is further configured to render the second bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage reaches a second DC supply voltage threshold. 
     
     
       26. The two-wire electronic switch of claim 21, further comprising:
 a communication circuit configured to receive messages;   wherein the controller is further configured to turn the electrical load on and off in response to the messages received via the communication circuit.   
     
     
       27. A load control device for controlling power delivered from an AC power source to an electrical load, the load control device comprising:
 a controllably conductive device adapted to be coupled in electrical connection between the AC power source and the electrical load, the controllably conductive device arranged to conduct a load current through the electrical load when the controllably conductive device is conductive;   a controller configured to control the controllably conductive device to be conductive and non-conductive to conduct and not conduct, respectively, the load current through the electrical load;   a capacitor arranged to develop a DC supply voltage for powering the controller; and   a power supply coupled in electrical connection with the controllably conductive device, the power supply further coupled to the capacitor for generating the DC supply voltage across the capacitor when the controllably conductive device is conductive, the power supply configured to conduct the load current through the capacitor for at least a portion of a line cycle of the AC power source when the controllably conductive device is conductive;   wherein the controllably conductive device is rendered non-conductive in response to an over-temperature condition in the load control device.   
     
     
       28. The load control device of claim 22, wherein the power supply comprises a bidirectional semiconductor switch coupled in series with the controllably conductive device and in parallel with the capacitor, the power supply configured to render the bidirectional semiconductor switch non-conductive to charge the capacitor when the controllably conductive device is conductive. 
     
     
       29. The load control device of claim 23, wherein the power supply further comprises a thermistor responsive to a temperature of the power supply, and wherein the thermistor is electrically coupled to the controllably conductive device to render the controllably conductive device non-conductive in response to an over-temperature condition in the power supply. 
     
     
       30. The load control device of claim 24, wherein the thermistor is coupled in series electrical connection with the capacitor, and a voltage across the series combination of the capacitor and the thermistor is electrically coupled to the controllably conductive device. 
     
     
       31. The load control device of claim 28, wherein the power supply further comprises a control circuit coupled to the bidirectional semiconductor switch for rendering the bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to a magnitude of the DC supply voltage to render the bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a first DC supply voltage threshold. 
     
     
       32. The load control device of claim 31, wherein the control circuit of the power supply is further configured to render the bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage reaches a second DC supply voltage threshold. 
     
     
       33. The load control device of claim 27, further comprising:
 a communication circuit configured to receive messages;   wherein the controller is further configured to turn the electrical load on and off in response to the messages received via the communication circuit.   
     
     
       34. The load control device of claim 27, further comprising:
 a bidirectional semiconductor switch coupled in parallel with a series combination of the controllably conductive device and the power supply, the controller further configured to turn on the electrical load by first rendering the bidirectional semiconductor switch conductive and then rendering the controllably conductive device conductive, the controller further configured to turn off the electrical load by first rendering the controllably conductive device non-conductive and then rendering the bidirectional semiconductor switch non-conductive.   
     
     
       35. The load control device of claim 34, wherein the bidirectional semiconductor switch is rendered conductive in response to an over-current condition. 
     
     
       36. The load control device of claim 34, wherein the bidirectional semiconductor switch comprises a first bidirectional semiconductor switch; and
 wherein the power supply comprises a second bidirectional semiconductor switch coupled in series with the controllably conductive device and in parallel with the capacitor, the power supply configured to render the second bidirectional semiconductor switch non-conductive to charge the capacitor when the controllably conductive device is conductive.