Power factor control for an LED bulb driver circuit

A light-emitting diode (LED) bulb comprising:

• a shell;
• an LED contained within the shell;
• a driver circuit for providing current to the LED, the driver circuit having a power factor control circuit that comprises:
• a tracking circuit connected to a supply line to the LED, wherein the tracking circuit is configured to produce a tracking signal indicative of the voltage of the supply line;
• a switch-mode power supply (SMPS) controller having an input pin and an output pin, wherein the tracking circuit supplies the tracking signal to the input pin,
• wherein, in response to the tracking signal being below a threshold voltage, the SMPS controller is configured to change a frequency of an output signal on the output pin based on the tracking signal, and
• wherein, in response to the tracking signal being above a threshold voltage, the SMPS controller is configured to provide the output signal on the output pin independent of the tracking signal;
• and
• a base attached to the bulb for connecting the LED bulb to an electrical socket.