Method and apparatus for starting up
Aspects of the disclosure provide a method. The method includes receiving an input voltage rectified from an alternating current (AC) power supply, detecting a time duration that the input voltage is between a first threshold voltage and a second threshold voltage, determining a line voltage of the AC power supply based on the time duration, and regulating a time for turning on a switch to transfer energy via a transformer based on the detected line voltage.
1. A method, comprising:
receiving an input voltage rectified from an alternating current (AC) power supply;
detecting a time duration that the input voltage is between a first threshold voltage and a second threshold voltage;
determining a line voltage of the AC power supply as a function of a comparison between a threshold value and a ratio of the detected time duration to an AC cycle; and
regulating a time for turning on a switch to transfer energy via a transformer based on the determined line voltage.
2. The method of claim 1 , further comprising:
regulating the time for turning on the switch to transfer energy via the transformer at a power up based on an assumption that the AC power supply is a high line AC power supply with a dimmer.
3. The method of claim 2 , wherein regulating the time for turning on the switch to transfer energy via the transformer at the power up comprises:
regulating the time for turning on the switch to limit a substantially constant peak current flowing through the switch.
4. The method of claim 3 , wherein regulating the time for turning on the switch to limit the substantially constant peak current flowing through the switch further comprises:
generating pulse width modulated pulses based on a sensed current.
5. The method of claim 1 , wherein determining the line voltage of the AC power supply comprises:
determining the line voltage to be a high line voltage when the ratio is lower than a first value; and
determining the line voltage to be a low line voltage when the ratio is higher than a second value that is higher than the first value.
6. The method of claim 1 , further comprising:
determining whether a dimmer exists based on the time duration.
7. The method of claim 6 , wherein determining whether the dimmer exists based on the time duration further comprises:
determining that the dimmer exists when the time duration is smaller than a threshold.
8. A circuit comprising:
a detector configured to receive an input voltage rectified from an alternating current (AC) power supply, and detect a time duration that the input voltage is between a first threshold voltage and a second threshold voltage; and
a controller configured to determine a line voltage of the AC power supply as a function of a comparison between a threshold value and a ratio of the detected time duration to an AC cycle and regulate a time for turning on a switch to transfer energy via a transformer based on the determined line voltage.
9. The circuit of claim 8 , wherein the controller is configured to regulate the time for turning on the switch to transfer energy via the transformer at a power up based on an assumption that the AC power supply is a high line AC power supply with a dimmer.
10. The circuit of claim 9 , wherein the controller is configured to regulate the time for turning on the switch to limit a substantially constant peak current flowing through the switch at the power up.
11. The circuit of claim 10 , wherein the controller is configured to generate pulse width modulated pulses based on a sensed current.
12. The circuit of claim 8 , wherein the controller is configured to determine the line voltage to be a high line voltage when the ratio is lower than a first value and to determine the line voltage to be a low line voltage when the ratio is higher than a second value that is higher than the first value.
13. The circuit of claim 8 , wherein the controller is configured to determine whether a dimmer exists based on the time duration.
14. The circuit of claim 13 , wherein the controller is configured to determine that the dimmer exists when the time duration is smaller than a threshold.
15. An apparatus comprising:
an energy transfer module configured to transfer electric energy from an alternating current (AC) power supply to an output device;
a detector configured to receive an input voltage rectified from the AC power supply, and detect a time duration that the input voltage is between a first threshold voltage and a second threshold voltage; and
a controller configured to determine a line voltage of the AC power supply as a function of a comparison between a threshold value and a ratio of the detected time duration to an AC cycle and regulate a time for turning on a switch of the energy transfer module to transfer energy via a transformer based on the determined line voltage.
16. The apparatus of claim 15 , wherein the controller is configured to regulate the time for turning on the switch to transfer energy via the transformer at a power up based on an assumption that the AC power supply is a high line AC power supply with a dimmer.
17. The apparatus of claim 16 , wherein the controller is configured to regulate the time for turning on the switch to limit a substantially constant peak current flowing through the switch at the power up.
18. The apparatus of claim 17 , wherein the controller is configured to generate pulse width modulated pulses based on a sensed current.
19. The apparatus of claim 15 , wherein the controller is configured to determine the line voltage to be a high line voltage when the ratio is lower than a first value and to determine the line voltage to be a low line voltage when the ratio is higher than a second value that is higher than the first value.
20. The apparatus of claim 15 , wherein the controller is configured to determine an existence of a dimmer when the time duration is smaller than a threshold.