Unversal dimming emulator for LED driver
Apparatuses and methods are disclosed for controlling a multicolor LED array. The light engine includes a dimming emulator that supplies high and low supply voltages to a driver dependent on a duty cycle of PWM signals from a control unit. An optical coupler isolates the low supply voltage from ground of the dimming emulator. The control unit receives power for the array from the driver dependent on the supply voltages and controls the array based thereon. The coupler is coupled to a control terminal of an NPN transistor, the PWM signals change the average impedance of the coupler based on the duty cycle and change a voltage divider ratio applied to the control terminal. Other apparatuses and methods are disclosed.
1. A dimming emulator comprising:
an input stage having a control input, the input stage coupled with a control unit to receive control signals from the control unit at the control input, the input stage configured to share ground with the control unit;
an output stage coupled with a light-emitting diode (LED) driver to provide a high supply voltage and a low supply voltage to the LED driver in response to the control signals received at the input stage to permit the LED driver to provide a high LED voltage and a low LED voltage to LED arrays; and
a coupler configured to isolate the low supply voltage from ground and the control signals from the high supply voltage and provide a controllable impedance to adjust the high supply voltage,
the output stage comprising a voltage divider that includes:
a first resistor coupled with a first output terminal of the coupler;
a second resistor disposed between the first resistor and a second output terminal of the coupler, the second output terminal of the coupler configured to provide the low supply voltage to the LED driver via a low output terminal of the output stage; and
a third resistor between a high output terminal of the output stage and a center node between the first resistor and the second resistor.
2. The dimming emulator of claim 1 , wherein the coupler is an optical coupler.
3. The dimming emulator of claim 1 , wherein the control signals are control pulse-width modulation (PWM) signals, and the high supply voltage is dependent on a duty cycle of the control PWM signals by control of the impedance.
4. The dimming emulator of claim 1 , wherein the output stage further comprises a transconductance device having:
a control terminal coupled with the center node;
a first terminal configured to provide the high supply voltage as an amplified voltage of a voltage supplied to the control terminal at a high output terminal of the output stage; and
a second terminal coupled with the low output terminal of the output stage.
5. The dimming emulator of claim 4 , wherein the transconductance device is a bipolar junction transistor.
6. The dimming emulator of claim 4 , wherein:
the transconductance device has a negative temperature dependency; and
the output stage further comprises:
a first negative temperature coefficient (NTC) resistor between the first output terminal of the coupler and the control terminal of the transconductance device; and
a second NTC resistor between the first resistor and the second output terminal of the coupler, the first NTC resistor and the second NTC resistor having resistances and B-values selected to compensate for the negative temperature dependency of the transconductance device.
7. The dimming emulator of claim 4 , wherein the output stage further comprises:
a fourth resistor between the center node and the control terminal of the transconductance device;
an output capacitor between the control terminal and the first terminal of the transconductance device;
a first input capacitor between the center node and the low output terminal of the output stage, the first input capacitor in parallel with the second resistor; and
a second input capacitor between the control terminal of the transconductance device and the low output terminal of the output stage, the first input capacitor and the second input capacitor configured to filter switching noise of the coupler.
8. The dimming emulator of claim 7 , wherein the output stage further comprises:
a fifth resistor between the first terminal of the transconductance device and the high output terminal of the output stage at an output node of the transconductance device, the output capacitor coupled to the output node of the transconductance device; and
another transconductance device having:
a control terminal coupled with the output node of the transconductance device;
a first terminal coupled with the high output terminal of the output stage; and
a second terminal coupled with the low output terminal of the output stage.
9. The dimming emulator of claim 8 , wherein:
the transconductance device is an npn transistor, the first terminal of the transconductance device being a collector and the second terminal of the transconductance device being an emitter; and
the other transconductance device is a pnp transistor, the first terminal of the transconductance device being an emitter and the second terminal of the transconductance device being a collector.
10. A light engine, comprising:
a light-emitting diode (LED) array comprising LEDs of different colors;
a dimming emulator:
configured to supply a high supply voltage and low supply voltage to an LED driver in response to control signals;
a coupler configured to isolate the low supply voltage from ground of the dimming emulator; and
a control unit configured to:
provide the control signals to the dimming emulator; and
receive power for the LED array from the LED driver dependent on the high supply voltage and low supply voltage provided to the LED driver from the dimming emulator and control the LED array based thereon,
the dimming emulator comprising a voltage divider that includes:
a transconductance device having a control terminal and configured to provide the high supply voltage as an amplified voltage of a voltage supplied to the control terminal;
a first resistor between a first output terminal of the coupler and the control terminal of the transconductance device;
a second resistor disposed between the control terminal of the transconductance device and a second output terminal of the coupler, the second output terminal of the coupler configured to provide the low supply voltage to the LED driver via a low output terminal of the dimming emulator; and
a third resistor between a high output terminal of the dimming emulator and the control terminal of the transconductance device.
11. The light engine of claim 10 , wherein the dimming emulator further comprises:
a first negative temperature coefficient (NTC) resistor between the first output terminal of the coupler and the control terminal of the transconductance device; and
a second NTC resistor between the control terminal of the transconductance device and the second output terminal of the coupler, the first NTC resistor and the second NTC resistor having resistances and B-values selected to compensate for a negative temperature dependency of the transconductance device.
12. The light engine of claim 10 , wherein the dimming emulator further comprises:
a fourth resistor between the control terminal of the transconductance device and a center node between the first resistor, the second resistor, and the third resistor;
an output capacitor between the control terminal and a first terminal of the transconductance device coupled with the high output terminal of the dimming emulator through a fifth resistor;
a first input capacitor between the center node and the low output terminal of the dimming emulator, the first input capacitor in parallel with the second resistor; and
a second input capacitor between the control terminal of the transconductance device and the low output terminal of the dimming emulator, the first input capacitor and the second input capacitor configured to filter switching noise of the coupler.
13. The light engine of claim 12 , wherein:
the transconductance device is an npn transistor, the first terminal of the transconductance device being a collector and the second terminal of the transconductance device being an emitter; and
the dimming emulator further comprises a pnp transistor having:
a control terminal coupled with the collector of the npn transistor;
an emitter coupled with the high output terminal of the dimming emulator; and
a collector coupled with the low output terminal of the dimming emulator.
14. The light engine of claim 10 , wherein the control signals are control pulse-width modulation (PWM) signals, and the high supply voltage is dependent on a duty cycle of the control PWM signals.
15. The light engine of claim 10 , further comprising a wireless module to receive wireless signals from a wireless control-device, the wireless signals comprising a correlated color temperature (CCT) value and a distance value (D uv ) of a temperature of the LED array from a black-body line (BBL), the control unit configured to translate the wireless signals and to provide the control signals to the dimming emulator based on the translated wireless signals.
16. A method of driving a multi-color light-emitting diode (LED) array, the method comprising:
receiving wireless signals from a wireless control-device, the wireless signals comprising a correlated color temperature (CCT) value and a distance value (D uv ) of a temperature of the LED array from a black-body line (BBL);
translating the wireless signals into pulse-width modulation (PWM) control signals;
providing PWM control signals to a dimming emulator based on the translated wireless signals;
determining, at the dimming emulator:
a high supply voltage dependent on a duty cycle of the control PWM signals, and
a low supply voltage;
isolating, in the dimming emulator, the low supply voltage from a ground of the dimming emulator using an optical coupler;
supplying the high supply voltage and the low supply voltage to an LED driver; and
receiving power for the LED array from the LED driver, the power dependent on the high supply voltage and low supply voltage and controlling the LED array based on the power received from the LED driver.
17. The method of claim 16 , further comprising:
amplifying the PWM control signals to provide the high supply voltage; and
changing an average impedance of the optical coupler based on the duty cycle to change a ratio of a multiplier used during amplification of the PWM control signals.
18. The method of claim 17 , further comprising:
compensating for a negative temperature dependency of a bipolar junction transistor used for amplifying the PWM control signals using a first negative temperature coefficient (NTC) resistor between the optical coupler and a control terminal of the bipolar junction transistor and a second NTC resistor between the control terminal of the bipolar junction transistor and the low supply voltage.