Controller for a phase cut dimmable LED driver
View Patent ↗A control scheme for a dimmable lighting driver is provided. The control scheme may operate with a phase cut type dimmer (leading or trailing edge). In an embodiment, the control scheme is programmed or otherwise configured into a controller as a control algorithm. The control algorithm is configured to measure phase cut and zero crossing angles of the input mains waveform, and to subsequently maintain constant LED current commensurate with a user-set dimming level, with no flicker. The control algorithm may be implemented in software, such as a firmware-based routine executable by one or more controllers of a given driver. The one or more controllers may be, for example, an existing general purpose controller of the given driver, or a dedicated dimming controller. Numerous configurations will be apparent in light of this disclosure.
1. A method for control of a phase cut dimmer for lighting systems, the method comprising:
receiving, at a controller of a lighting driver circuit, a representation of an input voltage waveform having a phase cut angle (φ cut ) and a waveform zero angle (φ zero ), as well as a known frequency;
acquiring, by the controller, data representative of a period of the waveform;
determining, by the controller, a plurality of Fourier series coefficients associated with the waveform;
extracting, by the controller, the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) based on the coefficients;
determining, by the controller, a current for one or more light emitting diodes (LEDs) based on at least one of the phase cut angle (φ cut ) and the waveform zero angle (φ zero ); and
adjusting, by the controller, a duty cycle of a pulse width modulation (PWM) signal to provide the determined current to the one or more LEDs.
2. The method of claim 1 wherein determining a plurality of Fourier series coefficients associated with the period comprises determining the two lowest order Fourier series coefficients (0 th and 1 st ) associated with the waveform.
3. The method of claim 1 , further comprising:
storing the data representative of the waveform period.
4. The method of claim 1 wherein acquiring data representative of a period of the waveform comprise acquiring data representative of one period of the waveform.
5. The method of claim 1 wherein extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) based on the coefficients comprises extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) through inversion of an analytical representation of the coefficients, the inversion comprising:
determining the values of cos(φ cut ) and sin(φ cut ); and
determining the value of the waveform zero angle φ zero based on cos(φ cut ) and sin(φ cut ).
6. The method of claim 5 wherein determining the values of cos(φ cut ) and sin(φ cut ) is carried out using the follow equations:
cos
(
ϕ
cut
)
=
±
(
π
a
oM
2
A
-
1
)
;
and
sin
(
ϕ
cut
)
=
1
-
cos
2
(
ϕ
cut
)
,
where A is amplitude of the input waveform, π is the period of the waveform, and
a
0
M
=
2
N
∑
k
=
1
N
d
k
,
where N is a number of data points include in the data representative of the period, d k is the k th data point of the N data points, M indicates a 0 is a measured valued, and the upper + sign of the ± symbol corresponds to leading edge phase cut waveforms and lower − sign of the ± symbol corresponds to trailing edge phase cut waveforms.
7. The method of claim 6 wherein A is assumed based on a nominal RMS (root mean square) level of the waveform together with a division factor based on resistance values of resistors used in a voltage divider to generate the representation of an input voltage waveform.
8. The method of claim 1 wherein determining the value of cos(φ cut ) is carried out using interpolation, and determining the value of sin(φ cut ) is carried out using the follow equation sin(φ cut )=√{square root over (1−cos 2 (φ cut ))}.
9. The method of claim 8 wherein the interpolation is carried out by accessing a pre-computed look-up table (LUT).
10. A non-transitory computer program product encoding instructions that when executed by one or more processors cause a dimming control process for a light system to be carried out, the process comprising:
receiving, at a controller of a lighting driver circuit, a representation of an input voltage waveform having a phase cut angle (φ cut ) and a waveform zero angle (φ zero ), as well as a known frequency;
acquiring, by the controller, data representative of a period of the waveform;
determining, by the controller, a plurality of Fourier series coefficients associated with the waveform;
extracting, by the controller, the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) based on the coefficients;
determining, by the controller, a current for one or more light emitting diodes (LEDs) based on at least one of the phase cut angle (φ cut ) and the waveform zero angle (φ zero ); and
adjusting, by the controller, a duty cycle of a pulse width modulation (PWM) signal to provide the determined current to the one or more LEDs.
11. The computer program product of claim 10 wherein determining a plurality of Fourier series coefficients associated with the period comprises determining the two lowest order Fourier series coefficients (0 th and 1 st ) associated with waveform.
12. The computer program product of claim 10 , further comprising:
storing the data representative of the waveform period.
13. The computer program product of claim 10 wherein acquiring data representative of a period of the waveform comprises acquiring data representative of one period of the waveform.
14. The computer program product of claim 10 wherein extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) based on the coefficients comprises extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) through inversion of an analytical representation of the coefficients, the inversion comprising:
determining the values of cos(φ cut ) and sin(φ cut ); and
determining the value of the waveform zero angle φ zero based on cos(φ cut ) and sin(φ cut ).
15. The computer program product of claim 10 wherein determining the values of cos(φ cut ) and sin(φ cut ) is carried out using the follow equations:
cos
(
ϕ
cut
)
=
±
(
π
a
oM
2
A
-
1
)
;
and
sin
(
ϕ
cut
)
=
1
-
cos
2
(
ϕ
cut
)
,
where A is amplitude of the input waveform, π is the period of the waveform, and
a
0
M
=
2
N
∑
k
=
1
N
d
k
,
where N is a number of data points include in the data representative of the period, d k is the k th data point of the N data points, M indicates a 0 is a measured valued, and the upper + sign of the ± symbol corresponds to leading edge phase cut waveforms and lower − sign of the ± symbol corresponds to trailing edge phase cut waveforms.
16. The computer program product of claim 15 wherein A is assumed based on a nominal RMS (root mean square) level of the waveform together with a division factor based on resistance values of resistors used in a voltage divider to generate the representation of an input voltage waveform.
17. The computer program product of claim 10 wherein determining the value of cos(φ cut ) is carried out using interpolation, and determining the value of sin(φ cut ) is carried out using the follow equation sin(φ cut )=√{square root over (1−cos 2 (φ cut ))}.
18. The computer program product of claim 17 wherein the interpolation is carried out by accessing a pre-computed look-up table (LUT).
19. A lighting driver controller, comprising:
a processor;
a memory accessible to the processor and encoding a plurality of instructions that when executed by the processor cause a dimming control process to be carried out, the process comprising:
receiving a representation of an input voltage waveform having a phase cut angle (φ cut ) and a waveform zero angle (φ zero ), as well as a known frequency;
acquiring data representative of a period of the waveform;
determining a plurality of Fourier series coefficients associated with the waveform;
extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) based on the coefficients;
determining a current for one or more light emitting diodes (LEDs) based on at least one of the phase cut angle (φ cut ) and the waveform zero angle (φ zero ); and
adjusting a duty cycle of a pulse width modulation (PWM) signal to provide the determined current to the one or more LEDs.
20. The controller of claim 19 wherein determining a plurality of Fourier series coefficients associated with the period comprises determining the two lowest order Fourier series coefficients (0 th and 1 st ) associated with the waveform.
21. The controller of claim 19 , further comprising:
storing the data representative of the waveform period.
22. The controller of claim 19 wherein acquiring data representative of a period of the waveform comprise acquiring data representative of one period of the waveform.
23. The controller of claim 19 wherein extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero )based on the coefficients comprises extracting the phase cut angle (φ cut ) and the waveform zero angle (φ zero ) through inversion of an analytical representation of the coefficients, the inversion comprising:
determining the values of cos(φ cut ) and sin(φ cut ); and
determining the value of the waveform zero angle φ zero based on cos(φ cut ) and sin(φ cut ).
24. The controller of claim 19 wherein determining the values of cos(φ cut ) and sin(φ cut ) is carried out using the follow equations:
cos
(
ϕ
cut
)
=
±
(
π
a
oM
2
A
-
1
)
;
and
sin
(
ϕ
cut
)
=
1
-
cos
2
(
ϕ
cut
)
,
where A is amplitude of the input waveform, π is the period of the waveform, and
a
0
M
=
2
N
∑
k
=
1
N
d
k
,
where N is a number of data points include in the data representative of the period, d k is the k th data point of the N data points, M indicates a 0 is a measured valued, and the upper + sign of the ± symbol corresponds to leading edge phase cut waveforms and lower − sign of the ± symbol corresponds to trailing edge phase cut waveforms.
25. The controller of claim 24 wherein A is assumed based on a nominal RMS (root mean square) level of the waveform together with a division factor based on resistance values of resistors used in a voltage divider to generate the representation of an input voltage waveform.
26. The controller of claim 19 wherein determining the value of cos(φ cut ) is carried out using interpolation, and determining the value of sin(φ cut ) is carried out using the follow equation sin(φ cut )=√{square root over (1−cos 2 (φ cut ))}.
27. The controller of claim 26 wherein the interpolation is carried out by accessing a pre-computed look-up table (LUT).