Lighting system including a fast low-power startup circuit

1 . A lighting system comprising:

a converter configured to receive a rectified input voltage and to generate an output voltage based on a control signal;

a primary controller configured to generate the control signal to adjust the output voltage of the converter; and

a startup circuit configured to power the primary controller based on the rectified input voltage in response to the output voltage being below a threshold, and to power the primary controller based on the output voltage in response to the output voltage being greater than or equal to the threshold, the startup circuit comprising:

a bootstrap circuit configured to generate a first power signal based on the rectified input voltage;

an input selector configured to receive the first power signal and a second power signal corresponding to the output voltage and to apply one of the first and second power signals to a power input terminal of the primary controller.

2 . The lighting system of claim 1 , wherein the bootstrap circuit is configured to:

receive the rectified input voltage and the output voltage;

set the first power signal based on the rectified input voltage in response to the output voltage being below the threshold; and

set the first power signal based on the output voltage in response to the output voltage being greater than or equal to the threshold.

3 . The lighting system of claim 1 , wherein the bootstrap circuit comprises:

a first transistor comprising a first gate electrode and configured to selectively electrically couple or decouple an input line and the input selector based on a gate voltage of the first gate electrode, the input line being configured to supply the rectified input voltage;

a second transistor comprising a second gate electrode and configured to selectively electrically couple or decouple the first gate electrode to reference ground based on the output voltage; and

a pull-up resistor coupled between the input line and the first gate electrode and configured to activate the first transistor to electrically couple the input line and the input selector in response to the second transistor decoupling the first gate electrode from the reference ground.

4 . The lighting system of claim 3 , wherein the first transistor is coupled between the input selector and the input line, and is configured to activate to electrically couple the input line to the input selector in response to the first gate electrode being at a first voltage, and to deactivate to electrically decouple the input line from the input selector in response to the first gate electrode being at a second voltage,

wherein the second transistor is coupled between the first gate electrode and the reference ground, and the second gate electrode is coupled to an output of the converter,

wherein the second transistor is configured to activate in response to the output voltage being greater than or equal to the threshold, and to deactivate in response to the output voltage being less than the threshold, and

wherein the pull-up resistor is configured to pull up the first gate electrode to the first voltage to activate the first transistor in response to the second transistor being deactivated.

5 . The lighting system of claim 3 , wherein the bootstrap circuit further comprises:

a timer circuit coupled between an output of the converter and the second gate electrode of the second transistor and configured to low-pass filter the output voltage.

6 . The lighting system of claim 5 , wherein the timer circuit comprises an RC filter.

7 . The lighting system of claim 3 , wherein the bootstrap circuit further comprises:

a voltage-drop circuit coupled between an output of the converter and the second gate electrode of the second transistor and configured to generate a reduced output voltage based on the output voltage, and to apply the reduced output voltage to the second gate electrode.

8 . The lighting system of claim 7 , wherein the voltage-drop circuit comprises a zener diode having an anode electrode coupled to the second gate electrode of the second transistor, and a cathode electrode coupled to the output of the converter.

9 . The lighting system of claim 3 , wherein the bootstrap circuit further comprises:

an isolation circuit coupled between an output of the converter and the second gate electrode of the second transistor and configured to prevent back-charging of the output of the converter from the second gate electrode.

10 . The lighting system of claim 9 , wherein the isolation circuit comprises a diode having an anode electrode coupled to the output of the converter, and a cathode electrode coupled to the second gate electrode of the second transistor.

11 . The lighting system of claim 1 , wherein the input selector comprises:

a first diode comprising an anode terminal configured to receive the first power signal and a cathode terminal coupled to the power input terminal of the primary controller; and

a second diode comprising an anode terminal configured to receive the second power signal and a cathode terminal coupled to the power input terminal of the primary controller.

12 . The lighting system of claim 1 , further comprising:

a bias regulator coupled between an output of the converter and the primary controller, and configured to generate the second power signal based on the output voltage of the converter to power the primary controller.

13 . The lighting system of claim 1 , further comprising:

a rectifier configured to receive an AC input signal and to generate the rectified input voltage; and

a light source configured to emit light based on the output voltage of the converter.

14 . The lighting system of claim 1 , wherein the converter is a DC-DC converter, and

wherein the primary controller is a power factor correction controller configured to regulate a DC-level current or a DC-level voltage of an output of the converter.