RETROFIT LED TUBE WITH SAFETY SWITCH

Abstract

The invention further describes tube LED lamp (1) realised to replace a fluorescent tube lamp (70), which tube LED lamp (1) comprises a tube (12) containing an LED arrangement (10) with a number of LEDs (100); a connector arrangement (16A, 16B) with connectors (16) realized for insertion into sockets (50) of a socket arrangement (50A, 50B) of a tube lamp housing (5) incorporating a dimming ballast (20, 21); a driver circuit arrangement (11) for driving the LED arrangement (10), which driver circuit arrangement (11) is realized to output an LED current (I.sub.LED) on the basis of an input current provided by the dimming ballast (20, 21); and a safety switch (S.sub.13, M1) arranged within the tube (12) to electrically isolate connectors (16) of the connector arrangement (16A, 16B), wherein the safety switch (S.sub.13, M1) is arranged between the driver circuit arrangement (11) and the LED arrangement (10). The invention further describes a method of driving a tube LED lamp (1) from a dimming ballast (20, 21) of a fluorescent tube lamp (70).

Claims

1. A tube LED lamp realised to replace a fluorescent tube lamp, which tube LED lamp comprises a tube containing an LED arrangement with a number of LEDs; a connector arrangement with connectors realized for insertion into sockets of a socket arrangement of a tube lamp housing incorporating a dimming ballast; a driver circuit arrangement for driving the LED arrangement, which driver circuit arrangement is realized to output an LED current on the basis of an input current provided by the dimming ballast; and a safety switch arranged within the tube to electrically isolate connectors of the connector arrangement, wherein the safety switch is arranged between the driver circuit arrangement and the LED arrangement.

2. A tube LED lamp according to claim 1, wherein the driver circuit arrangement is realized for connection to a dimming ballast of the PS type.

3. A tube LED lamp according to claim 1, wherein the safety switch comprises a semiconductor device.

4. A tube LED lamp according to claim 1, wherein the safety switch comprises an electromechanical device.

5. A tube LED lamp according to claim 1, wherein the connector arrangement comprises at least one connector at each of two outer ends of a linear tube, wherein a connector is realized for insertion into one of a pair of sockets in a linear tube lamp housing.

6. A tube LED lamp according to claim 1, comprising a switch control circuit realised to close the safety switch only when the connectors of a tube LED lamp are completely inserted into corresponding sockets of a tube lamp housing.

7. A tube LED lamp according to claim 6, wherein the switch control circuit is realised to detect an electrical connection between only one connector of the connector arrangement and one socket of the socket arrangement.

8. A tube LED lamp according to claim 5, wherein the switch control circuit comprises a mains frequency detection circuit for detecting a mains frequency component in a lamp voltage.

9. A tube LED lamp according to claim 5, wherein the switch control circuit is realised to detect a filament voltage at both connectors of the connector arrangement

10. A tube LED lamp according to claim 5, wherein the switch control circuit comprises a DC blocking circuit portion realised to block a DC offset current of the dimmable ballast.

11. A tube LED lamp according to claim 1, comprising a protection circuit module realised to disconnect the LED driver from the LED arrangement in the event of an excessive lamp temperature and/or an excessive lamp current and/or an excessive lamp voltage.

12. A tube LED lamp according to claim 1, realized to retrofit any of a linear fluorescent tube lamp, a circular fluorescent tube lamp, a compact fluorescent lamp.

13. A method of driving a tube LED lamp from a dimming ballast of a fluorescent tube lamp, which method comprises the steps of arranging a number of LEDs in a lamp tube, which lamp tube comprises a connector arrangement with connectors for insertion into sockets of a socket arrangement of a tube lamp housing comprising the dimming ballast; providing a driver circuit arrangement for driving the LEDs, which driver circuit arrangement is realized to output an LED current on the basis of an input current provided by the dimming ballast; and arranging a safety switch between the driver circuit arrangement and the LED arrangement to electrically isolate connectors of the connector arrangement when the connector arrangement is not completely connected to the socket arrangement.

14. A method according to claim 13, comprising the step of maintaining an electrical disconnection between connectors of the connector arrangement until all connectors are correctly inserted into the corresponding sockets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a schematic representation of an embodiment of a TLED according to the invention;

[0029] FIG. 2 shows the TLED of FIG. 1 used to retrofit a conventional fluorescent tube lighting application comprising a first type of dimming ballast;

[0030] FIG. 3 shows the TLED of FIG. 1 used to retrofit a conventional fluorescent tube lighting application comprising a second type of dimming ballast;

[0031] FIG. 4 shows a circuit diagram with a first embodiment of a switch control circuit for a TLED according to the invention;

[0032] FIG. 5 shows a circuit diagram with a second embodiment of a switch control circuit for a TLED according to the invention;

[0033] FIG. 6 shows a circuit diagram with a third embodiment of a switch control circuit for a TLED according to the invention;

[0034] FIG. 7 shows a hazardous removal or insertion of a prior art TLED.

[0035] In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] FIG. 1 shows a schematic representation of an embodiment of a TLED 1 according to the invention. In this exemplary embodiment, the TLED 1 comprises a linear or straight tube 12, which can be made of plastic, glass, etc., with bipin connectors 16 at both ends of the tube 12. The tube 2 can be inserted either way around into a corresponding housing (not shown) for a linear fluorescent tube lamp. For electrical compatibility to a dimming ballast already incorporated into the housing, the TLED 1 comprises a filament emulation circuit 160 at both ends of the tube interior. An LED arrangement 10 fits inside the tube 12 and can comprise any number of LEDs mounted on one or more printed circuit boards. A driver circuit arrangement 11 is also arranged inside the lamp tube 12 and is connected to drive the LED arrangement 10 from an input signal originating from either filament circuit 160. A filter capacitor Cf is connected in parallel across the output of the driver 11 and serves to filter the driver output signal. A switch S.sub.13 is connected between the driver 11 and the LED arrangement 10, and acts to connect or disconnect these according to a control signal originating from a switch control circuit 13. The operation of the switch control circuit 13 will be explained below.

[0037] FIG. 2 shows the TLED of FIG. 1 used to retrofit a conventional fluorescent tube lighting application comprising a first type of dimming ballast 20, namely a dimming ballast realized for connection to the output of a phase-cut dimmer 30, for example a wall-mounted light-switch/dimmer unit. The dimmer 30 is connected between the mains 4 and the dimming ballast 20, and effectively reduces the rms voltage to the dimming ballast 20 by cutting a portion of the mains signal. The diagram also indicates the socket/connector union between sockets 17A, 17B of a lamp housing 5 and pins of a connector arrangement 16A, 16B of the TLED 1.

[0038] FIG. 3 is a simplified block diagram showing the TLED of FIG. 1 used to retrofit a conventional fluorescent tube lighting application comprising a second type of dimming ballast 21, namely a dimming ballast realized for connection to a 0-10V dimmer 31 with a slider for adjusting the desired light output level. In this case, the dimmer 31 is connected at the control input of the dimming ballast 21. The dimming ballast 21 regulates its output current according to the position of the slider. In this case also, the diagram indicates the socket/connector union between sockets 17 of a lamp housing (not shown) and pins 16 of the TLED 1.

[0039] FIG. 4 shows a circuit diagram showing components in a first embodiment of a control circuit for a TLED according to the invention. Here, the circuit diagram shows an LED arrangement 10 comprising a string of LEDs 100 mounted on a board B2. A filament emulation circuit 160 is disposed at each end, and each filament emulation circuit 160 comprises a resistor R.sub.160 in series with a fuse F.sub.160. In this exemplary embodiment, the right-hand side filament emulation circuit 160 is realised on a separate board B3, while the left-hand side filament emulation circuit 160 is realised on a board B1 that also carries the driver circuit arrangement 11, the switch control circuit 13, the safety switch S.sub.13, a protection circuit 14, and various other components. The board B2 carrying the driver circuit arrangement 11 may be realised to fit into one end of the lamp tube in a region that is usually “dark” anyway, corresponding to the location of circuit components of a fluorescent lamp. A simple three-pin connector can be used between the boards B1, B2, B3 to connect—as necessary—high and low LED terminals LED+, LED− and a high-frequency supply terminal HF as indicated in the diagram. The driver circuit 11 also comprises a diode bridge D1, D2, D3, D4 for rectifying the AC signal fed in via the connector pins 16. Capacitor C1 of this embodiment is optional and can be included if it is necessary to shunt a high frequency current in order to reduce the LED current I.sub.LED.

[0040] The safety switch S.sub.13 can be realised as a semiconductor element such as a transistor, or an electromechanical element such as a relay. The switch control circuit 13 is connected between the filament emulation circuits 160. During operation of the TLED 1 in the lamp housing, the switch control circuit 13 will be fed at both ends with high-frequency signals from the dimming ballast. This indicates that the TLED 1 is correctly in place, and the switch control circuit 13 issues an enable signal EN.sub.13 to indicate that the safety switch S.sub.13 can be closed. The diagram also shows further protective circuitry, with a voltage sense resistor R.sub.senseV for sensing an excessively high lamp voltage; a current sense resistor R.sub.senseI for sensing an excessively high lamp current; a thermistor R.sub.temp for sensing an excessively high lamp temperature; and a protective control circuit 14 to generate a switch enable signal from the various inputs supplied by these sense components R.sub.senseI, R.sub.senseV, R.sub.temp and the switch control circuit 13. When none of the abnormal voltage/current/temperature conditions is present, and the switch control circuit 13 has detected that the TLED 1 is correctly inserted, the protective control circuit 14 issues a signal to close the safety switch S.sub.13, so that the driver circuit 11 can drive the LED arrangement 10 at the current level provided by the dimming ballast. FIG. 5 shows a circuit diagram showing details of the switch control circuit 13 of this embodiment. Here, a NPN BJT (bipolar junction transistor) Q1 is used to generate an enable signal EN.sub.13 for the safety switch M1, which in this embodiment is realised as a MOSFET M1. The switch control circuit 13 is realised as an essentially symmetrical network between the filament emulation circuits 160, and comprises a DC blocking capacitor C2, C6 at each end to block an anti-striation DC offset signal generated by the dimming ballast; a low-pass filter C1/R4, C5/R9 to pass a mains-frequency signal and block the high-frequency signals from the electronic dimmer; and a peak voltage detector arrangement D5, D6, C3, R6 for detecting a voltage from the low pass filters C1/R4, C5/R9. If a mains frequency component (e.g. a 60 Hz component in a North America application) is detected, the capacitor C3 will charge, and the enable transistor Q1 will be switched on. A significant mains component will only be detected if one end of the TLED 1 is not properly inserted into the corresponding socket of the lamp housing, so that there is a risk of electric shock to the user. In this situation, the collector of the transistor Q1, which is coupled in some suitable manner to the gate of the MOSFET M1, pulls the gate to “low”, thus keeping the safety switch M1 in the OFF state.

[0041] FIG. 6 shows a circuit diagram with a third embodiment of a switch control circuit 13 for a TLED 1 according to the invention. Here, an AC filament voltage present at one end of the TLED is converted to a DC voltage by means of an isolation transformer T1 and acts to charge a capacitor C4. An AC filament voltage present at the other end of the lamp is rectified and used as an input to an optocoupler T2, which in turn switches on a PNP BJT Q2, which in turn acts to switch on the MOSFET M1. Effectively, the MOSFET M1 can only be switched on if there is a filament voltage at both ends of the TLED 1, i.e. only when the TLED 1 is correctly inserted into both sockets of the lamp housing. In this embodiment, a four-pin connector can be used between the boards B1, B2, B3 to connect—as necessary—high and low LED terminals LED+, LED- and two high-frequency supply terminals HF1, HF2 as indicated in the diagram.

[0042] FIG. 7 shows a hazardous removal or insertion of a prior art TLED 70. Basic elements of a retrofit TLED 70 of the type used to replace a linear fluorescent tube lamp are indicated within the tube. In such a retrofit lamp 70, the driver circuit 71 is realised as an electronic driver such as a switched-mode power supply. Here, the absence of any safety switch or detection circuitry to detect a correct insertion into the housing can result in a high pin leakage current at the exposed end of the retrofit tube lamp 70. A person who inadvertently touches the exposed pins 16 may receive an electric shock.

[0043] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0044] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module.