Solid-state lighting with reduced light flickering
An LED luminaire comprising LED arrays, a buck circuit with a switching portion comprising a transformer, and an LED driving circuit comprising a feedback control circuit is used to replace a conventional luminaire with a severe temporal light artifact. The buck circuit with the switching portion is configured to generate a variable DC voltage with a low-frequency ripple associated with AC mains. The feedback control circuit is configured to feedback a mixed voltage and current control signal to the buck circuit with the switching portion to compensate the low-frequency ripple so as to regulate an LED driving voltage with a ripple-reduced LED current to drive the LED arrays with a flicker-reduced light emission that may protect users of the LED luminaire from possible health hazards such as seizures, headaches, eyestrain, reduced visual performance, migraines, etc.
1. A light-emitting diode (LED) luminaire, comprising:
one or more LED arrays;
at least one full-wave rectifier configured to couple to alternate-current (AC) mains and convert a line voltage from the AC mains into a first direct-current (DC) voltage;
a buck circuit with a switching portion comprising a first control device, a primary diode circuit, a first electronic switch controlled by the first control device and configured to modulate the first DC voltage into a variable DC voltage at a switching frequency, a transformer comprising a primary winding and a secondary winding, and a first ground reference; and
an LED driving circuit comprising a second ground reference electrically isolated from the first ground reference, a feedback control circuit, and a first rectifier circuit and a second rectifier circuit both coupled to the secondary winding, wherein the first rectifier circuit and the second rectifier circuit are respectively configured to convert the variable DC voltage into a second DC voltage and a third DC voltage via the transformer, wherein the second DC voltage is configured to produce a feedback control signal transmitted to the first control device via the feedback control circuit, and wherein the third DC voltage is configured to drive the one or more LED arrays with a flicker-reduced light emission,
wherein:
the feedback control circuit comprises an optocoupler circuit comprising an LED and a photo-transistor optically coupled to the LED,
the LED comprises a cathode and is configured to convert the feedback control signal into a light signal,
the photo-transistor is configured to convert the light signal into an electric signal, and
the optocoupler circuit is configured to provide an electrical isolation between the buck circuit with the switching portion and the LED driving circuit but to allow the feedback control signal to transmit.
2. The LED luminaire of claim 1 , wherein the feedback control circuit further comprises a second control device coupled to the optocoupler circuit and configured to abstract voltage and current variations associated with the second DC voltage and the third DC voltage and to send to the first control device via the optocoupler circuit to compensate and to control the variable DC voltage, thereby regulating the third DC voltage according to a predetermined LED driving voltage and a predetermined LED driving current.
3. The LED luminaire of claim 2 , wherein the second control device comprises a first operational amplifier and a second operational amplifier, wherein the first operational amplifier is configured to receive a first portion of the second DC voltage and to regulate the third DC voltage, wherein the second operational amplifier is configured to receive a second portion of the second DC voltage and to regulate an LED driving current to drive the one or more LED arrays, and wherein double regulations of the third DC voltage and the LED driving current lead to an average current flowing in the secondary winding with the reduced low-frequency current ripple.
4. The LED luminaire of claim 3 , wherein the feedback control circuit further comprises a first diode coupled to a first output of the first operational amplifier and a second diode coupled to a second output of the second operational amplifier, wherein each of the first diode and the second diode comprises an anode, and wherein the anode of the first diode and the anode of the second diode are electrically connected and further coupled to the cathode of the LED to control an electric current flowing in the LED.
5. The LED luminaire of claim 1 , wherein the LED driving circuit is further configured to drive the one or more LED arrays with the flicker-reduced light emission with a percent flicker less than 6% at a nominal flicker frequency of 100 Hz or 120 Hz.
6. The LED luminaire of claim 1 , wherein, responsive to detecting zero current in the primary winding, the first control device is configured to generate a zero current detection signal to control the first electronic switch on and off with a constant on-time and a varied off-time with a duty cycle controlling the third DC voltage and the LED driving current via the transformer to drive the one or more LED arrays.
7. The LED luminaire of claim 6 , wherein the feedback control circuit is further configured to control the switching frequency and the duty cycle to compensate a low-frequency voltage ripple of the second DC voltage, consequently producing the third DC voltage with a ripple-reduced LED driving current to drive the one or more LED arrays.
8. The LED luminaire of claim 1 , wherein the switching frequency is no less than 30 kHz.
9. The LED luminaire of claim 1 , wherein the primary diode circuit is coupled between two terminals of the primary winding and configured to generate energy pulses in the primary winding and to yield the variable DC voltage with a constant current control.
10. The LED luminaire of claim 1 , wherein the LED driving circuit further comprises an output capacitor and a common-mode choke coupled between the output capacitor and the one or more LED arrays and configured to reduce a differential interference but to allow the LED driving current to pass and to operate the one or more LED arrays with the flicker-reduced light emission.
11. The LED luminaire of claim 2 , wherein the feedback control circuit further comprises a first transistor circuit coupled between the first rectifier circuit and the second control device and configured to receive the second DC voltage and to provide a power to both the second control device and the LED.
12. The LED luminaire of claim 11 , wherein the feedback control circuit further comprises a voltage divider coupled to the first transistor circuit to receive the second DC voltage and configured to provide the first portion and the second portion of the second DC voltage to the second control device to produce the feedback control signal to transmit to the first control device via the optocoupler circuit.
13. The LED luminaire of claim 1 , wherein the transformer further comprises an auxiliary winding magnetically coupled to the primary winding, and wherein the buck circuit with the switching portion further comprises a voltage feedback circuit coupled to the auxiliary winding and configured to draw energy from the auxiliary winding to sustain operation of the first control device.
14. The LED luminaire of claim 13 , wherein the voltage feedback circuit comprises a third diode and a voltage regulator, and wherein the voltage regulator comprises a first voltage reference and a second transistor configured to supply a voltage and a current to the first control device.