Thermal protection circuit for an led bulb

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.

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.