Retrofit light emitting diode, LED, tube for reducing audible noise originating from a high frequency electronic ballast

Patent metadata

Field	Value
Publication number	US-10904972-B2
Application number	US-201816607471-A
Country	US
Kind code	B2
Filing date	Apr 18, 2018
Priority date	Apr 24, 2017
Publication date	Jan 26, 2021
Grant date	Jan 26, 2021

Abstract

A retrofit Light Emitting Diode, LED, tube for connecting to a High Frequency, HF, ballast, which LED tube comprises a switchable capacitor arrangement for ensuring that the ballast does not go into over current protection mode, wherein the switching is controlled based on a desired dimming level of the LED tube. The switchable capacitor arrangement is provided in parallel with said input of said rectifier, and comprises at least a first capacitor and a second capacitor in series, and said control circuit is adapted to configure said switchable capacitor arrangement to conduct the AC power and switch at least one of the first capacitor and the second capacitor between the rectifier and the LED array to block the DC power to said LED array.

First claim

The invention claimed is:

1. A retrofit Light Emitting Diode, LED, tube for connecting to a High Frequency, HF, ballast, said retrofit LED tube, comprising:
an LED array (LED 1 ) for emitting light;
a rectifier (DB 1 , DB 2 , DB 3 , DB 4 ) having two AC terminals (A, B) and two DC terminals (C, D), wherein the rectifier is arranged to receive AC power at its AC terminals from a connected HF ballast and, in use, to convert said AC power to DC power, and to provide said DC power to said LED array via the two DC terminals (C, D);
a dimming unit arranged for receiving an input dimming level;
a switchable capacitor arrangement (C 3 , C 4 , S 1 ) arranged for introducing a capacitance to said connected HF ballast; and
a control unit arranged for controlling the switching of the switchable capacitor arrangement based on said received input dimming level,
wherein the switchable capacitor arrangement comprises a switch (S 1 ), at least a first capacitor (C 3 ) and a second capacitor (C 4 ), and said control circuit is adapted to control the switch (S 1 ) to switch alternate one of the first capacitor and the second capacitor in series between alternate one of AC terminals (A, B) of the rectifier and the LED array and cut off a connection of the LED array to one of the two DC terminals (C, D) thereby blocking the DC power to said LED array in opposing half cycles of the AC power;
wherein the first capacitor and the second capacitor have a junction between them, and wherein the control unit is adapted to control a connection between the junction and one of the DC terminals of the rectifier, and wherein
the control circuit is adapted to control the switch (S 1 ) to switch the other one of the first capacitor and second capacitor in parallel with the other one of the AC terminals (A, B) and the series connection of the one of the first capacitor and the second capacitor and the LED array;
wherein the junction is further connected to the anode or the cathode of the LED array, and the switch (S 1 ) is between the junction with the anode or the cathode of the LED array and the one DC terminal of the rectifier.

2. A retrofit LED tube as claimed in claim 1 , wherein said switch (S 1 ) comprises any of a bipolar transistor and a power Metal Oxide Semiconductor, MOS, Field Effect Transistor, FET, and
said control circuit is adapted to allow the one of the first capacitor and the second capacitor to discharge in one subsequent phase after the one of the first capacitor and the second capacitor is switched in series between an output of the rectifier and the LED array to block the DC power to said LED array in one phase.

3. A retrofit LED tube as claimed in claim 1 , wherein the control unit is adapted to be controllable between:
a first mode in which the junction and the LED array (LED 1 ) are isolated from the output of the rectifier such that the alternative one of the two capacitors is in series between the LED array and the output of said rectifier to block the DC power; and
a second mode in which the junction and the LED array (LED 1 ) are connected to the output of the rectifier thereby to allow the LED array to be powered by the DC power.

4. A retrofit LED tube as claimed in claim 3 , wherein said control unit comprises a detection circuit for detecting the current flowing through the LED array or the current at the output of the rectifier, and is arranged to switch between the first and second modes according to said received input dimming level and the detected current.

5. A retrofit LED tube as claimed in claim 4 , wherein said control unit is adapted to be controllable to switch between the first and second modes at a frequency of greater than 20 kHz, and at a duty cycle according to said received input dimming level and the detected current.

6. A retrofit LED tube as claimed in claim 1 , wherein said rectifier comprises a full bridge diode rectifier, with a first AC terminal (A) and a second AC terminal (B), and a positive DC terminal and a negative DC terminal (C, D), wherein said positive DC terminal and said negative DC terminal are respectively adapted to connect to an anode and a cathode of the LED array (LED 1 ), and wherein the switchable capacitor arrangement is provided in parallel with the first AC terminal and the second AC terminal, and the switch (S 1 ) is connected between said positive DC terminal (C) or said negative DC terminal (D) and a corresponding electrode of the LED array.

7. A retrofit LED tube as claimed in claim 1 , further comprising a dummy load (R 3 ) and a smoothing capacitor (C 5 ) each in parallel with the LED array.

8. A lighting system, comprising:
a high frequency electronic ballast; and
a retrofit LED tube as claimed in claim 1 ,
wherein the retrofit LED tube is connected to said high frequency electronic ballast.

9. A lighting system according to claim 8 , further comprising a dimmer switch arranged for setting, by a user, an input dimming level, and arranged for transmitting said input dimming level to said dimming unit comprised by said retrofit LED tube.

10. A method of operating a retrofit LED tube, which is connected to a high frequency, HF, ballast, said retrofit LED tube comprising an LED array (LED 1 ) for emitting light, a rectifier having two AC terminals (A, B) and two DC terminals (C, D), and a switchable capacitor arrangement, and arranged for introducing a capacitance to said connected HF ballast, wherein the method comprises:
receiving AC power from a connected HF ballast and using the rectifier to convert said AC power to DC power;
receiving an input dimming level; and
controlling switching of said switchable capacitor arrangement based on said received input dimming level,
wherein the switchable capacitor arrangement comprises a switch (S 1 ), at least a first capacitor (C 3 ) and a second capacitor (C 4 ), and said step of controlling comprises:
controlling said switch (S 1 ) to switch an alternative one of the first capacitor and the second capacitor in series between an alternate one of the two AC terminals (A, B) of the rectifier and the LED array and cut off a connection of the LED array to one of the two DC terminals (C, D) thereby blocking the DC power to said LED array in opposing half cycles of the AC power;
wherein the first capacitor and the second capacitor have a junction between them, the step of controlling comprises switching the other one of the first capacitor and second capacitor in parallel with the other one of the AC terminals (A, B) and the series connection of the one of the first capacitor and the second capacitor and the LED array, and
wherein controlling the switching comprises switching between:
a first mode in which the junction and the LED array are isolated from the output of the rectifier such that the alternative one of the two capacitors is between the LED array and the output of said rectifier to block the DC power; and
a second mode in which the junction and the LED array are connected to the output of the rectifier thereby to allow the LED array to be powered by the DC power,
wherein during the first mode, allowing the one of the first capacitor and the second capacitor to discharge in one subsequent phase after the one of the first capacitor and the second capacitor is switched in series between an output of the rectifier and the LED array to block the DC power to said LED array in one phase.

11. A method as claimed in claim 10 , comprising detecting the LED current or the output current of the rectifier, and switching between the first and second modes according to said received input dimming level and the detected current.

12. A method as claimed in claim 11 , wherein sai

Assignees

• Signify Holding Bv

Inventors

• Chen Zhi Quan
• Zhang Xianhui
• Tao Haimin

Classifications

• Y02B20/30

  Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED] · CPC title

• H05B45/357 Primary

  specially adapted for retrofit LED light sources · CPC title

• H05B45/39

  Circuits containing inverter bridges · CPC title

• H05B45/382

  with galvanic isolation between input and output · CPC title

• H05B45/3725 Primary

  Switched mode power supply [SMPS] · CPC title