Lighting circuits, luminaries and methods compatible with phase-cut mains supplies
Lighting circuits and luminaires and methods are disclosed which are operable with a phase-cut dimmer. A circuit includes a rectifier having a low side output and a high side output, a switched mode converter including a switch and an inductor, having a high side input connected to a bus rail, and having a configuration to draw current across a complete mains cycle, a controller for the switched mode converter, a filter circuit connected between the rectifier high side output and the bus rail and including a capacitor connected between the high side output of the mains rectifier and ground, and a resistance connected between the low side output of the rectifier and ground. The value of the resistance may be such the RC time constant of the resistor and filter circuit is greater than the time required for any ringing in the circuit to fall to no more than 20 mA.
1. A lighting circuit for mains LED lighting applications operable with a phase-cut dimmer, wherein the mains has a maximum voltage which is at least 200V, the circuit comprising:
a rectifier having a low side output and a high side output;
a switched mode converter comprising a switch and an inductive element, having a high side input connected to a bus rail, and having a configuration so as to draw current from the mains across a complete mains cycle;
a controller for the switched mode converter;
a filter circuit connected between the rectifier high side output and the bus rail and comprising a capacitor connected between the high side output of the rectifier and ground; and
a combined damping/latch resistance connected between the low side output of the rectifier and ground;
wherein the value of the combined damping/latch resistance is such that the RC time constant of the combined damping/latch resistance and filter circuit is greater than the time required for any ringing in the circuit to fall to no more than 20 mA.
2. A lighting circuit according to claim 1 , wherein the value of the combined damping/latch resistance is at least one of between 150Ω and 1 kΩ, and between 150 Ω and 560 Ω.
3. A lighting circuit according to claim 1 , wherein the switched mode converter is a one of a buck-boost converter and a fly-back converter.
4. A lighting circuit according to claim 1 , wherein the controller is configured to operate the switched mode converter in boundary conduction mode.
5. A lighting circuit according to claim 1 , wherein the RC time constant of the combined damping/latch resistance and filter circuit is between 50 μs and 300 μs.
6. A lighting circuit according to claim 1 , further comprising a waveform shaping circuit arranged to provide a higher input current to the converter when a momentary phase of the mains input signal exceeds 90°.
7. A lighting circuit according to claim 1 , wherein the controller is configured to operate the switched mode convertor using on-time control.
8. A lighting circuit according to claim 1 , wherein the filter circuit further comprises an inductor between the rectifier high side output and the bus rail and a further capacitor connected between the bus rail and ground.
9. A lighting circuit according to claim 1 , further comprising a bypass switch, arranged and configured to, in use, provide a bypass path to bypass the combined damping/latching resistance at the end of a predetermined interval from a moment the dimmer starts conducting.
10. A lighting circuit according to claim 1 , further comprising one or more LEDs.
11. A populated driver circuit board comprising a mains rectifier, a switched mode converter and a filter circuit, each as claimed in claim 1 , and mounted on a common printed circuit board, and configured and adapted to operate in a lighting circuit.
12. A lighting circuit comprising a populated a driver circuit board as claimed in claim 11 , and a populated LED circuit board comprising at least one LED and the combined damping/latch resistance.
13. A lighting circuit as claimed in claim 12 , wherein electrical connection between the populated driver circuit board and the populated LED circuit board is provided by three conductors.
14. A luminaire comprising a lighting circuit as claimed in claim 12 in a housing.
15. A lighting circuit for mains LED lighting applications operable with a phase-cut dimmer, wherein the mains has a maximum voltage which is at least 200V, the circuit comprising:
a rectifier having a low side output and a high side output;
a switched mode converter comprising a switch and an inductive element, having a high side input connected to a bus rail, and having a configuration so as to draw current from the mains across a complete mains cycle;
a controller for the switched mode converter;
a filter circuit connected between the rectifier high side output and the bus rail and comprising a capacitor connected between the high side output of the rectifier and ground; and
a combined damping/latch resistance connected between the low side output of the rectifier and ground;
wherein the RC time constant of the combined damping/latch resistance and filter circuit is between 50 μs and 300 μs.
16. A lighting circuit for mains LED lighting applications operable with a phase-cut dimmer, wherein the mains has a maximum voltage which is at least 200V, the circuit comprising:
a rectifier having a low side output and a high side output;
a switched mode converter comprising a switch and an inductive element, having a high side input connected to a bus rail, and having a configuration so as to draw current from the mains across a complete mains cycle;
a controller for the switched mode converter;
a filter circuit connected between the rectifier high side output and the bus rail and comprising a capacitor connected between the high side output of the rectifier and ground;
a combined damping/latch resistance connected between the low side output of the rectifier and ground; and
a waveform shaping circuit arranged to provide a higher input current to the converter when a momentary phase of the mains input signal exceeds 90°.