LED driver with high dimming compatibility without the use of bleeders
View Patent ↗A switching converter detects when a dimmer circuit supplying power to the switching converter changes from a conducting state to a nonconducting state or from a nonconducting state to a conducting state; an equivalent input resistance of the switching converter is changed to a first, higher value when the dimmer circuit is in the conducting state and to a second, lower value when the dimmer circuit is in the nonconducting state, thereby drawing a minimum current from the dimmer circuit while the dimmer circuit is in the nonconducting state.
1. A circuit for controlling a switching converter, the circuit comprising:
an input voltage or phase analyzer for detecting when a dimmer circuit supplying power to the switching converter changes from a conducting state to a nonconducting state or from a nonconducting state to a conducting state; and
a pulse-width-modulating generator for changing an equivalent input resistance of the switching converter to a first, higher value when the dimmer circuit is in the conducting state and to a second, lower value when the dimmer circuit is in the nonconducting state, thereby drawing a minimum current from the dimmer circuit while the dimmer circuit is in the nonconducting state,
wherein the pulse-width-modulating generator changes the equivalent input resistance at a first point in time prior to a second point in time at which the state of the dimmer circuit changes.
2. The circuit of claim 1 , further comprising a light-emitting diode that receives an output current generated by the switching converter and is illuminated thereby.
3. The circuit of claim 1 , wherein the pulse-width-modulating generator changes the equivalent input resistance by changing a frequency or duty cycle of an output control signal that controls switching characteristics of the switching converter.
4. The circuit of claim 1 , wherein a power drawn from the dimming circuit is approximately equal to a power drawn by a switching converter having a constant equivalent resistance.
5. The circuit of claim 1 , further comprising a feedback analyzer for detecting a current flowing through a light-emitting diode connected to the switching converter, wherein the pulse-width-modulating generator varies a frequency or duty cycle of an output control signal that controls the switching characteristics of the switching converter based on the current.
6. The circuit of claim 1 , wherein the input voltage or phase analyzer detects a current spike in an input current and varies the first point in time to reduce the size of the spike or eliminate the spike.
7. The circuit of claim 1 , wherein the switching converter is a flyback converter or a high-power-factor converter.
8. A method for controlling a switching converter, the method comprising:
detecting when a dimmer circuit supplying power to the switching converter changes from a conducting state to a nonconducting state or from a nonconducting state to a conducting state; and
changing an equivalent input resistance of the switching converter to a first, higher value when the dimmer circuit is in the conducting state and to a second, lower value when the dimmer circuit is in the nonconducting state, thereby drawing a minimum current from the dimmer circuit while the dimmer circuit is in the nonconducting state,
wherein changing the equivalent input resistance includes changing at a first point in time prior to a second point in time at which the state of the dimmer circuit changes.
9. The method of claim 8 , further comprising supplying an output current generated by the switching converter to a light-emitting diode.
10. The method of claim 8 , further comprising changing the equivalent input resistance by changing a frequency or duty cycle of an output control signal that controls switching characteristics of the switching converter.
11. The method of claim 8 , wherein an average power drawn from the dimming circuit is approximately equal to a power drawn by a switching converter having a constant equivalent resistance.
12. The method of claim 8 , further comprising detecting a current flowing through a light-emitting diode connected to the switching converter, wherein a frequency or duty cycle of an output control signal that controls the switching characteristics of the switching converter is varied based on the current.
13. The method of claim 8 , further comprising detecting a current spike in an input current and varying the first point in time to reduce the size of the spike or eliminate the spike.