Constant voltage PWM to constant current PWM led lighting system with thermal and current feedback
A light emitting diode (LED) lighting system has a LED light fixture with a channel having a LED string, and has a controller adapted to receive a power input and a control input, and to provide a constant voltage pulse-width modulated (PWM) power to the channel in response to the control input. The channel has a series regulator operable to convert the constant voltage PWM power to constant current PWM power to regulate current through the LED string. The series regulator proves an internal voltage reference and internal temperature compensation and is operable to regulate the current through the LED string with high precision over a wide temperature range, and is powered solely by the constant voltage PWM power. The lighting system is operable to dim the LED string from 100 percent to zero or near zero percent at high PWM frequencies without perceptible flicker or jitter.
1 . A light emitting diode (LED) lighting system comprising:
an LED light fixture having a first channel including a first LED string of one or more LEDs connected in series;
a controller adapted to receive a power input and a control input, and adapted to provide a first constant voltage pulse-width modulated (PWM) power to the first channel of the LED light fixture in response to the control input;
the first channel of the LED light fixture having a first series regulator operable to convert the constant voltage PWM power to constant current PWM power to regulate current through the first LED string;
the first series regulator providing an internal voltage reference and internal temperature compensation;
the first series regulator being operable to regulate the current through the first LED string with high precision over a wide temperature range;
the first series regulator being powered solely by the first constant voltage PWM power; and
the LED lighting system being operable to dim the first LED string from 100 percent to zero or near zero percent at PWM frequencies at or above 1250 Hz.
2 . The light emitting diode (LED) lighting system as in claim 1 , wherein:
the controller is configured to provide the first constant voltage pulse-width modulated (PWM) power to the first channel of the LED light fixture via a positive conductor and a first negative conductor;
the first LED string having a positive lead coupled to the positive conductor;
the first series regulator having:
first and second resistances, a regulation circuit, a FET, and first and second capacitors;
the first resistance having a positive terminal coupled to the positive conductor;
the first resistance having a negative terminal coupled to a cathode of the regulation circuit and a gate of the FET;
an anode of the regulation circuit being coupled to the first negative conductor:
the first capacitor being connected between the gate of the FET and the first negative conductor;
a drain of the FET being connected to a negative lead of the first LED string:
a source of the FET being connected to a reference terminal of the regulation circuit;
the second resistance having a positive lead coupled to the source of the FET and having a negative lead coupled to the first negative conductor:
the second capacitor having a positive lead coupled to the source of the FET and having a negative lead coupled to the first negative conductor;
the regulation circuit providing an internal voltage reference and internal temperature compensation; and
the regulation circuit being powered solely by the first constant voltage PWM power.
3 . The light emitting diode (LED) lighting system as in claim 1 , wherein:
the LED light fixture includes a second channel including a second LED string of one or more LEDs connected in series;
the controller being adapted to provide a second constant voltage pulse-width modulated (PWM) power to the second channel of the LED light fixture in response to the control input, and independent of the first constant voltage PWM power;
the second channel of the LED light fixture including a second series regulator operable to convert the second constant voltage PWM power to constant current PWM power to regulate current through the second LED string, independent of the first LED string;
the second series regulator providing an internal voltage reference and internal temperature compensation;
the second series regulator being operable to regulate the current through the second LED string with high precision over a wide temperature range;
the second series regulator being powered solely by the second constant voltage PWM power; and
the lighting system being operable to dim the second LED string from 100 percent to zero or near zero percent at PWM frequencies at or above 1250 H.
4 . The light emitting diode (LED) lighting system as in claim 3 , further comprising:
the controller being configured to provide the first constant voltage pulse-width modulated (PWM) power to the first channel of the LED light fixture via a positive conductor and a first negative conductor;
the controller being configured to provide the second constant voltage pulse-width modulated (PWM) power to the second channel of the LED light fixture via the positive conductor and a second negative conductor;
the first LED string having a positive lead coupled to the positive conductor;
the first series regulator having:
first and second resistances, a first regulation circuit, a first FET, and first and second capacitors;
the first resistance having a positive terminal coupled to the positive conductor:
the first resistance having a negative terminal coupled to a cathode of the first regulation circuit and a gate of the first FET;
an anode of the first regulation circuit being coupled to the first negative conductor;
the first capacitor being connected between the gate of the first FET and the first negative conductor;
a drain of the first FET being connected to a negative lead of the first LED string;
a source of the first FET being connected to a reference terminal of the first regulation circuit;
the second resistance having a positive lead coupled to the source of the first FET and a negative lead coupled to the first negative conductor; and
the second capacitor having a positive lead coupled to the source of the first FET and a negative lead coupled to the first negative conductor;
the first regulation circuit providing an internal voltage reference and internal temperature compensation; and
the first regulation circuit being powered solely by the first constant voltage PWM power:
the second LED string having a positive lead coupled to the positive conductor;
the second series regulator having:
third and fourth resistances, a second regulation circuit, a second FET, and third and fourth capacitors;
the third resistance having a positive terminal coupled to the positive conductor:
the third resistance having a negative terminal coupled to a cathode of the second regulation circuit and a gate of the second FET;
an anode of the regulation circuit being coupled to the second negative conductor:
the third capacitor being connected between the gate of the second FET and the second negative conductor;
a drain of the second FET being connected to a negative lead of the second LED string:
a source of the second FET being connected to a reference terminal of the second regulation circuit;
the fourth resistance having a positive lead coupled to the source of the second FET and a negative lead coupled to the second negative conductor; and
the fourth capacitor having a positive lead coupled to the source of the second FET and a negative lead coupled to the second negative conductor;
the second regulation circuit providing an internal voltage reference and internal temperature compensation; and
the second regulation circuit being powered solely by the second constant voltage PWM power.
5 . The light emitting diode (LED) lighting system as in claim 4 , wherein:
the LED light fixture includes means to prevent inductive coupling between the first and second negative conductors.
6 . The light emitting diode (LED) lighting system as in claim 5 , wherein:
the means to prevent inductive coupling between the first and second negative conductors comprises a fifth resistance coupled between the positive conductor and the first negative conductor, and comprises a sixth resistance coupled between the positive conductor and the second negative conductor.
7 . The light emitting diode (LED) lighting system as in claim 4 , further comprising:
means to prevent optically-induced reverse bias between the first LED string and the second LED string.
8 . The light emitting diode (LED) lighting system as in claim 7 , wherein:
the means to prevent optically-induced reverse bias between the first LED string and the second LED string comprises the first LED string including a first diode in series with the one or more LEDs of the first LED string, and comprises the second LED string including a second diode in series with the one or more LEDs of the second LED string; and
the first and second diodes being operable to prevent reverse bias in the first and second LED strings, respectively.
9 . The light emitting diode (LED) lighting system as in claim 1 , wherein:
the lighting system is operable to dim the first LED string from 100 percent to zero or near zero percent at PWM frequencies at or above 1250 Hz without perceptible flicker or jitter.
10 . The LED lighting system of claim 1 , wherein the first series regulator comprises a linear, feedback-controlled current regulation circuit, the regulator including a current-representative feedback path coupled to the first LED string and a series pass device coupled in series with the first LED string and controlled by the regulation circuit in response to the current-representative feedback path, the regulator being powered solely by the first constant voltage PWM power and providing high-precision regulation of the current through the first LED string over a wide temperature range.
11 . The LED lighting system of claim 10 , wherein the current-representative feedback path comprises a sense resistor coupled in series with the first LED string, the voltage across the sense resistor being applied to the regulation circuit to regulate current through the first LED string.
12 . The LED lighting system of claim 10 , wherein the series pass device is a transistor selected from the group consisting of a bipolar junction transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), and an insulated-gate bipolar transistor (IGBT), and wherein the regulation circuit includes a compensation network configured to maintain stability and high-precision current regulation across variations in input voltage, LED forward voltage, and temperature.
13 . A light emitting diode (LED) light fixture comprising:
a first channel including a first LED string of one or more LEDs connected in series;
the LED light fixture being adapted to receive a first constant voltage pulse-width modulated (PWM) power to the first channel of the LED light fixture;
the first channel of the LED light fixture having a first series regulator operable to convert the constant voltage PWM power to constant current PWM power to regulate current through the first LED string;
the first series regulator providing an internal voltage reference and internal temperature compensation;
the first series regulator being operable to regulate the current through the first LED string with high precision over a wide temperature range;
the first series regulator being powered solely by the first constant voltage PWM power; and
the light fixture being operable to dim the first LED string from 100 percent to zero or near zero percent at PWM frequencies at or above 1250 Hz without perceptible flickering.
14 . The light emitting diode (LED) light fixture as in claim 13 , wherein:
the LED light fixture is adapted to receive the first constant voltage pulse-width modulated (PWM) power to the first channel of the LED light fixture via a positive conductor and a first negative conductor;
a positive lead of the first LED string being coupled to the positive conductor;
the first series regulator having:
first and second resistances, a regulation circuit, a FET, and first and second capacitors;
the first resistance having a positive terminal coupled to the positive conductor;
the first resistance having a negative terminal coupled to a cathode of the regulation circuit and a gate of the FET;
an anode of the regulation circuit being coupled to the first negative conductor;
the first capacitor being connected between the gate of the FET and the first negative conductor:
a drain of the FET being connected to a negative lead of the first LED string;
a source of the FET being connected to a reference terminal of the regulation circuit:
the second resistance having a positive lead coupled to the source of the FET and having a negative lead coupled to the first negative conductor;
the second capacitor having a positive lead coupled to the source of the FET and having a negative lead coupled to the first negative conductor;
the regulation circuit providing an internal voltage reference and internal temperature compensation; and
the regulation circuit being powered solely by the first constant voltage PWM power.
15 . The light emitting diode (LED) light fixture as in claim 13 , wherein:
the LED light fixture includes a second channel including a second LED string of one or more LEDs connected in series;
the LED light fixture being adapted to receive a second constant voltage pulse-width modulated (PWM) power to the second channel of the LED light fixture, independent of the first constant voltage PWM power;
the second channel of the LED light fixture including a second series regulator operable to convert the second constant voltage PWM power to constant current PWM power to regulate current through the second LED string, independent of the first LED string;
the second series regulator providing an internal voltage reference and internal temperature compensation;
the second series regulator being operable to regulate the current through the second LED string with high precision over a wide temperature range;
the second series regulator being powered solely by the second constant voltage PWM power; and
the lighting system being operable to dim the second LED string from 100 percent to zero or near zero percent at PWM frequencies at or above 1250 Hz without perceptible flicker or jitter, and independent of the first LED string.
16 . The light emitting diode (LED) light fixture as in claim 15 , wherein:
the LED light fixture is adapted to receive the first constant voltage pulse-width modulated (PWM) power to the first channel of the LED light fixture via a positive conductor and a first negative conductor;
the LED light fixture being adapted to receive the second constant voltage pulse-width modulated (PWM) power to the second channel of the LED light fixture via the positive conductor and a second negative conductor;
the first LED string having a positive lead coupled to the positive conductor;
the first series regulator having:
first and second resistances, a first regulation circuit, a first FET, and first and second capacitors;
the first resistance having a positive terminal coupled to the positive conductor:
the first resistance having a negative terminal coupled to a cathode of the first regulation circuit and a gate of the first FET;
an anode of the first regulation circuit being coupled to the first negative conductor;
the first capacitor being connected between the gate of the first FET and the first negative conductor;
a drain of the first FET being connected to a negative lead of the first LED string;
a source of the first FET being connected to a reference terminal of the first regulation circuit;
the second resistance having a positive lead coupled to the source of the first FET and a negative lead coupled to the first negative conductor; and
the second capacitor having a positive lead coupled to the source of the first FET and a negative lead coupled to the first negative conductor;
the first regulation circuit providing an internal voltage reference and internal temperature compensation; and
the first regulation circuit being powered solely by the first constant voltage PWM power;
the second LED string having a positive lead coupled to the positive conductor;
the second series regulator having;
third and fourth resistances, a second regulation circuit, a second FET, and third and fourth capacitors;
the third resistance having a positive terminal coupled to the positive conductor;
the third resistance having a negative terminal coupled to a cathode of the second regulation circuit and a gate of the second FET;
an anode of the regulation circuit being coupled to the second negative conductor;
the third capacitor being connected between the gate of the second FET and the second negative conductor;
a drain of the second FET being connected to a negative lead of the second LED string;
a source of the second FET being connected to a reference terminal of the second regulation circuit;
the fourth resistance having a positive lead coupled to the source of the second FET and a negative lead coupled to the second negative conductor; and
the fourth capacitor having a positive lead coupled to the source of the second FET and a negative lead coupled to the second negative conductor;
the second regulation circuit providing an internal voltage reference and internal temperature compensation; and
the second regulation circuit being powered solely by the second constant voltage PWM power.