Method of controlling a ballast, a ballast, a lighting controller, and a digital signal processor
A method of controlling a ballast in a circuit for a lighting application and connected to a mains power supply is disclosed. The method comprises determining whether a dimmer is present in the circuit; in response to detecting that a dimmer is present, determining a zero-crossing of the power supply and setting a bleeder current through the ballast in dependence on the phase of the power supply within a mains half-cycle; and in response to determining that a dimmer is not present, disabling the bleeder current. A ballast which is controlled by such a method is also disclosed. Additionally, a controller, which may include a digital signal processor, for a ballast and operable according to the above method is disclosed.
1. A method of controlling a ballast in a circuit for a lighting application and connected to a mains power supply, the method comprising
determining whether a dimmer is present in the circuit, comprising
determining whether a trailing edge dimmer is present and determining whether a leading edge dimmer is present;
in response to detecting that a dimmer is present,
determining a moment indicative of a zero-crossing of the power supply and setting a bleeder current through the ballast in dependence on the phase of the power supply within a mains half-cycle; and
in response to determining that a dimmer is not present, disabling the bleeder current:
wherein setting bleeder current through the ballast in dependence on the phase of the power supply comprises,
in the case that a trailing edge dimmer is present:
determining a phase of the trailing edge;
setting a first bleeder current during a part of the mains half-cycle including the trailing edge;
and at least one of
setting a second bleeder current, lower than the first bleeder current, during a later part of the mains half-cycle, and disabling the bleeder current during an earlier part of the mains half-cycle.
2. The method of claim 1 , wherein there is a gap between the part of the mains half-cycle including the trailing edge and the later part of the mains half-cycle, during which gap the dimmer current is disabled.
3. The method of claim 2 , wherein setting a bleeder current through the ballast in dependence on the phase of the power supply comprises,
in the case that a leading edge bleeder is present,
determining the phase of the leading edge;
setting a latching bleeder current during a part of the mains half-cycle including the leading edge
and setting a synchronisation bleeder current, lower than the latching bleeder current, during an earlier part of the mains half-cycle.
4. The method of claim 3 , wherein setting a bleeder current through the ballast in dependence on the phase of the power supply further comprises setting a holding bleeder current, lower than the latching bleeder current, during a later part of the mains half-cycle.
5. The method of claim 3 wherein setting a bleeder current through the ballast in dependence on the phase of the power supply further comprises setting a non-zero holding bleeder current, lower than the latching bleeder current, during a later part of the mains half-cycle for some of a group of mains half-cycles, and setting the bleeder current to zero during the respective later part of the mains half-cycle for the remainder of the group of mains half-cycles.
6. The method of claim 3 , wherein the synchronisation bleeder current is lower than the holding bleeder current.
7. The method of claim 1 , wherein determining a moment indicative of a zero-crossing of the power supply comprises determining a moment at which a rectified voltage of the power supply with a reference voltage is less than a reference voltage.
8. The method of claim 1 , wherein a digital circuit is used to effect at least one of
determining whether a dimmer is present in the circuit,
determining a zero-crossing of the power supply,
setting a bleeder current through the ballast in dependence on the phase of the power supply within a mains half-cycle, and
disabling the bleeder current.
9. A ballast circuit for a lighting application and for being supplied by a mains power supply, the ballast circuit comprising
means for determining whether a dimmer is present in the circuit;
means for determining a zero-crossing of the power supply;
and means for setting a bleeder current through the ballast;
the ballast circuit being configured to operate the method of claim 1 .
10. A ballast circuit according to claim 8 , wherein at least one of:
the means for determining whether a dimmer is present in the circuit comprises a dimmer detection circuit;
the means for determining a zero-crossing of the power supply comprises a zero-crossing detection circuit; and
the means for setting a bleeder current through the ballast comprises a controllable current source or a variable resistor.
11. A ballast circuit according to claim 8 , wherein at least one of the means for determining whether a dimmer is present in the circuit and the means for determining a zero-crossing of the power supply comprises a digital signal processing circuit.
12. A lighting controller comprising a ballast circuit as claimed in claim 8 .
13. A digital signal processor configured to operate the method of claim 1 .