Thermal protection circuit for an led bulb

Abstract

A light-emitting diode (LED) bulb has an LED within a shell. The LED bulb includes a driver circuit for providing current to the LED. The drive circuit has a thermal protection circuit, which includes a first positive thermal coefficient thermistor with a first switching temperature connected in series with a second positive thermal coefficient thermistor with a second switching temperature. The driver circuit includes a switch-mode power supply (SMPS) controller with an input pin and an output pin. The thermistors are connected to the input pin. When either thermistor temperature is above the respective switching temperatures, the thermal protection circuit causes the SMPS controller to produce a signal with a second duty cycle on the output pin. When both thermistor temperatures are below the respective switching temperatures, the thermal protection circuit causes the SMPS controller to produce a signal with a first duty cycle on the output pin.

1 - 25 . (canceled) 
     
     
         26 . A light-emitting diode (LED) bulb comprising:
 a shell;   an LED contained within the shell;   a heat sink for dissipating heat generated by the LED;   a driver circuit for providing current to the LED, the driver circuit having a thermal protection circuit that comprises:
 a switch-mode power supply (SMPS) controller having an input pin, an output pin, and a power supply pin, 
 a MOS transistor having a drain or a source terminal connected to the SMPS input pin, 
 a first thermistor with a positive thermal coefficient and having a first switching temperature, wherein the first thermistor is connected to a gate terminal of the MOS transistor, 
 a pull-up resistor connected between the gate terminal of the MOS transistor and the SMPS power supply pin, 
 a pull-up capacitor connected between the SMPS power supply pin and ground, 
 wherein, when the first thermistor is at a temperature above the first switching temperature, the first thermistor is configured to turn on the MOS transistor, 
 wherein, when the first thermistor is at a temperature below the first switching temperature, the first thermistor is configured to turn off the MOS transistor, 
 wherein, when the MOS transistor is turned off, the SMPS controller is configured to supply a first signal with a first duty cycle on the output pin, and 
 wherein, when the MOS transistor is turned on, the SMPS controller is configured to supply a second signal with a second duty cycle on the output pin, and wherein the second duty cycle is lower than the first duty cycle; and 
   a base attached to the shell for connecting the LED bulb to an electrical socket.   
     
     
         27 . The LED bulb of  claim 26 , wherein the thermal protection circuit further comprises:
 a filter connected to the gate terminal of the MOS transistor.   
     
     
         28 . The LED bulb of  claim 26 , wherein the first thermistor is located adjacent to the heat sink. 
     
     
         29 . The LED bulb of  claim 26 , wherein the driver circuit substantially fits within the base. 
     
     
         30 . The LED bulb of  claim 26 , wherein the thermal protection circuit further comprises:
 a second thermistor with a positive thermal coefficient and a second switching temperature, wherein the second thermistor is connected in series with the first thermistor.   
     
     
         31 . The LED bulb of  claim 30 , wherein the first switching temperature is lower than the second switching temperature. 
     
     
         32 . The LED bulb of  claim 31 , wherein the first thermistor is located adjacent to the heat sink, and wherein the second thermistor is located adjacent to the driver circuit. 
     
     
         33 . The LED bulb of  claim 31 , wherein the thermal protection circuit further comprises:
 a filter connected to the gate terminal of the MOS transistor.   
     
     
         34 . The LED bulb of  claim 33 , wherein the filter comprises a capacitor. 
     
     
         35 . The LED bulb of  claim 26  further comprising:
 an input filter connected to the SMPS controller, wherein the input filter is configured to accept an alternating current (AC) input and the input filter is configured to produce a rectified output, and wherein the input filter is configured to be electrically connected to the base. 
 
     
     
         36 . A thermal protection circuit for a light-emitting diode (LED) bulb, the circuit comprising:
 a switch-mode power supply (SMPS) controller having an input pin, an output pin, and a power supply pin,   a MOS transistor having a drain or a source terminal connected to the SMPS input pin,   a first thermistor with a positive thermal coefficient and having a first switching temperature, wherein the first thermistor is connected to the gate terminal of a MOS transistor,   a pull-up resistor connected between the gate terminal of the MOS transistor and the SMPS power supply pin,   a pull-up capacitor connected between the SMPS power supply pin and ground,   wherein, when the first thermistor is at a temperature above the first switching temperature, the first thermistor is configured to turn on the MOS transistor,   wherein, when the first thermistor is at a temperature below the first switching temperature, the first thermistor is configured to turn off the MOS transistor,   wherein, when the MOS transistor is turned off, the SMPS controller is configured to supply a first signal with a first duty cycle on the output pin, and   wherein when the MOS transistor is turned on, the SMPS controller is configured to supply a second signal with a second duty cycle on the output pin, and wherein the second duty cycle is lower than the first duty cycle.   
     
     
         37 . The LED bulb of  claim 36 , wherein the thermal protection circuit further comprises:
 a filter connected to the gate terminal of the MOS transistor.   
     
     
         38 . The LED bulb of  claim 37 , wherein the filter is configured to provide a time lag. 
     
     
         39 . The LED bulb of  claim 36 , wherein the thermal protection circuit further comprises:
 a second thermistor with a positive thermal coefficient and a second switching temperature, wherein the second thermistor is connected in series with the first thermistor.   
     
     
         40 . The circuit of  claim 39 , wherein the first switching temperature is different than the second switching temperature. 
     
     
         41 . The circuit of  claim 39 , wherein the first thermistor is located adjacent to a heat sink, and wherein the second thermistor is located adjacent to a driver circuit. 
     
     
         42 . The circuit of  claim 36 , further comprising an input filter connected to the SMPS controller, wherein the input filter is configured to accept an alternating current (AC) input and the input filter is configured to produce a rectified output.