TUBULAR DEVICE FOR FITTING TO A TUBULAR LIGHT FITTING

Abstract

A lamp comprises an input for connection to a high frequency ballast for gas discharge lamps. A power supply unit obtains power from a LED on voltage of the LED of the lamp, and the power supply unit powers an isolation switch at the input. During a preheat stage of the ballast, the power supply unit does not close the isolation switch, but the isolation switch is closed when the high frequency ballast is in a later state, i.e. the ignition phase.

Claims

1. A lamp, comprising: an input adapted to be connected to a high frequency ballast for gas discharge lamps; a light emitting unit, comprising LEDs, for receiving power from the input and establishing a LED on voltage across the LEDs when the LEDs are on; at least one isolation switch coupled between the input and the light emitting unit; and a power supply unit adapted to obtain power from the established LED on voltage and to use the power for powering the at least one isolation switch to close the switch and thereby electrically connect the input to the light emitting unit, wherein the lamp is configured to: be unable to establish the LED on voltage sufficient for the power supply unit to close the at least one isolation switch when the high frequency ballast is in a preheat state; and establish the LED on voltage sufficient for the power supply unit to close the at least one isolation switch when the high frequency ballast is in a later state after the preheat state.

2. The lamp of claim 1, wherein the at least one isolation switch is adapted to be open in the preheat state such that the lamp is adapted to be seen as a high impedance by the high frequency ballast to allow the high frequency ballast to start up, and further comprising an output capacitor in parallel with the light emitting unit.

3. The lamp of claim 1, further comprising: a detection circuit adapted to detect that the lamp is connected to the high frequency ballast; and a control circuit to enable the power supply unites when the detection circuit detects that the lamp is connected the high frequency ballast; wherein the lamp optionally has a further input to be connected with a low frequency power comprising at least one of AC mains and an electromagnetic ballast's output, the detection circuit optionally comprises a frequency detector to detect a frequency of an input to determine whether the lamp is connected to the high frequency ballast, and the control circuit optionally comprises a switch to couple the LED on voltage to the power supply unit when the detection circuit detects that the lamp is connected the high frequency ballast, otherwise to decouple the LED on voltage from the power supply unit.

4. The lamp of claim 1, wherein the current from the high frequency ballast to the light emitting unit in the preheat state is in the range 10% to 20% of the nominal current in a normal driving state, which nominal current is in the range 100 mA to 1 A.

5. The lamp of claim 1, wherein the later stage comprises an ignition state of the high frequency ballast, wherein an ignition current in the ignition state to the light emitting unit is in the range of 100% to 200% of the nominal current in a normal driving state, which ignition current is between 200 mA to 1 A, and the light emitting unit is adapted to establish the sufficient LED on voltage in a period of 1 ms to 20 ms.

6. The lamp of claim 5, wherein the at least one isolation switch is provided with a parallel bypass capacitor to allow a high frequency ignition current to flow before the at least one isolation switch is closed.

7. The lamp of claim 1, wherein the power supply unit comprises a switch mode power supply or alternatively a voltage-dividing power supply or a direct power supply, wherein said voltage-dividing power supply comprises a resistor voltage dividing circuit or a capacitor-resistor voltage dividing circuit, and the at least one isolation switch comprises at least one relay.

8. The lamp of claim 7, wherein when the power supply unit comprises the switch mode power supply, the switch mode power supply comprises an IC controller, to operate the switch mode power supply, which IC controller is activated by a voltage supply above a threshold voltage corresponding to the sufficient LED on voltage, wherein the lamp further comprises a voltage divider for generating the voltage supply from the LED on voltage.

9. The lamp of claim 5, comprising a tubular LED lamp, and the lamp comprises: a first pair of input terminals of the input at one end and a second pair of input terminals of the input at an opposite end; and a first isolation switch of the at least one isolation switch at the first pair of input terminals and a second isolation switch of the at least one isolation switch at the second pair of input terminals.

10. The lamp of claim 9, wherein one of the at least one isolation switch at each pair of input terminals is provided with a respective parallel bypass capacitor to allow the ignition current, which is high frequency, to flow before the one isolation switch is closed.

11. The lamp of claim 9, further comprising a rectifier arrangement between the input and the light emitting unit, which rectifier arrangement comprises a first bridge rectifier connected to the first pair of terminals through the first isolation switch and a second bridge rectifier connected to the second pair of input terminals through the second isolation switch.

12. The lamp of claim 9, wherein the power supply unit has a single output for controlling the first and second isolation switches.

13. The lamp of claim 9, comprising first and second filament emulation circuits, wherein, when the first and second isolation switches are open: the first filament emulation circuit is connected between the first pair of input terminals at one end of the lamp; and the second filament emulation circuit is connected between the second pair of input terminals at another end of the lamp.

14. The lamp of claim 13, wherein when the first and second isolation switches are closed the first and second filament emulation circuits are electrically floating.

15. A lighting fixture comprising: an electronic fluorescent lighting ballast for gas discharge lamps; and a lamp as claimed in claim 1 fitted to the fluorescent lighting ballast.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0064] FIG. 1 shows a basic known tubular LED lamp;

[0065] FIG. 2 shows an example of an electromagnetic ballast;

[0066] FIG. 3 shows a relate control circuit based on a switch mode power supply;

[0067] FIG. 4 shows a lighting circuit;

[0068] FIGS. 5A and 5B show another lighting circuit; and

[0069] FIGS. 6A to 6C shows other implementations for the power supply unit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0070] The invention will be described with reference to the Figures.

[0071] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0072] The invention provides a lamp which comprises an input for connection to a high frequency ballast for gas discharge lamps. A power supply unit obtains power from a LED on voltage of the light emitting unit of the lamp, and the power supply unit powers an isolation switch at the input. During a preheat state of the ballast, the power supply unit does not close the isolation switch, but the isolation switch is closed when the high frequency ballast is in a later state, i.e. the ignition phase. The selection is done automatically by whether a sufficient voltage is established on the light emitting unit, in the different preheat and later states.

[0073] The invention relates in particular to a lamp in which an electric pin safety solution making use of an isolation switch such as a relay is adopted to enable a tubular LED to be used with a high frequency fluorescent tube ballast.

[0074] Conventionally, such a relay is driven by a circuit of discrete components, resulting in a complex circuit which is difficult to place in the limited space of the PCB of a TLED, especially for a T5 tube.

[0075] A low drop out, LDO, circuit can instead be used as the supply for a relay, but the circuit efficiency is poor which risks excessive heat generation, and there are compatibility issues with some ballasts such as dimming ballasts. The LDO circuit uses a MOSFET operating in the linear mode, and thus has high power loss at a high bus voltage (Vbus) condition.

[0076] The invention is based on the use of a switch mode power supply circuit, including a switch mode power supply IC, as a relay control circuit. This provides a solution suitable for the limited PCB space of TLED lamp. It also enables a high efficiency, and thus better lumen output, without a risk of overheating.

[0077] FIG. 3 shows a relay control circuit based on the pulse switch modulating IC controller 30 of a switch mode power supply. The IC controller 30 is for example a buck converter including a main converter switch and feedback control circuitry.

[0078] The IC controller has a sense terminal VSEN for receiving a feedback control voltage, and the circuit controls the switching of the main converter switch (which is integrated in the controller IC 30) to regulate the feedback voltage.

[0079] The buck converter circuit comprises inductor L0, diode D0, and load in the form of resistor R0 and capacitor C0.

[0080] The relay control voltage V_RELAY is the output voltage of the converter.

[0081] The feedback voltage for the sense terminal is obtained by resistor divider R1, R2, R3 between the output V_RELAY out and the ground terminal of the IC controller.

[0082] The IC controller has a ground terminal GND, a supply terminal VIN, a voltage sense input VSEN, a current setting input ISET and a terminal LX which connects to the drain of the main switch (a high voltage MOSFET).

[0083] The controller IC 30 is supplied by a voltage to terminal VIN based on a resistive divider R4, R5 between the voltage V_LED and ground, GND. Note that the voltage supplied to the controller IC may instead be a tapped voltage an intermediate location along the LED string, as long as the forward voltage is enough to power the power supply. The voltage divider R4, R5 in the example shown determines when V_LED is sufficient to turn on the IC. The capacitor C5 buffers the result of the divider to remove jitter or spikes.

[0084] The input to the buck converter is V_LED. The current flows in via terminal LX, and flows out via ISET and to the inductor L0. The feedback control implemented by the controller IC is for providing voltage regulation of the output voltage V_RELAY. The current setting input ISET is used for setting a current limit.

[0085] The lamp current of the ballast between the two ends of a TLED (shown in FIG. 4) is very small during the preheat stage. Typically, it will last for less than 2 seconds. The current is about 10%-20% of the normal operation current. The normal operating current is for example several hundred mA. The current during the preheat stage is not enough to build sufficient voltage across the LEDs (on the storage capacitors C7, C8 shown in FIG. 4) to turn on the LEDs. Thus the LED voltage V_LED is very small.

[0086] Some intelligent ballasts will detect the circuit impedance during the preheat stage, and if the lamp impedance is too low, the ballast cannot start up normally. If an isolation relay is off, the circuit will have a high impedance, and this assists in ballast detection and operation.

[0087] The controller IC also typically implements an under voltage protection voltage (Vuvp). This can be set based on the equation below:

Vuvp=(R4+R5)/R5*VIN_on

[0088] VIN_on is the voltage at which the IC turns on.

[0089] Vuvp can for example be set to around 80% of the normal LED string voltage. When the voltage across the capacitor C5 is less then Vuvp, the IC 30 stops working and the relay will be switched off (i.e. the relay will be open).

[0090] The circuit is for example designed such that the LED string voltage is less than 50% of the normal LED string voltage during the preheat stage. As a result, the IC stops. The lamp will start operating when the capacitor C5 is charged to VIN_on, and this takes place during the ballast ignition phase.

[0091] Thus, during the preheat stage, the voltage V_LED only reaches for example 50% of the normal LED string voltage and hence does not reach Vuvp and the voltage VIN does not reach VIN_on.

[0092] The voltage reached by V_LED depends on the current delivered, as a result of the charging of capacitor capacitors C7, C8 (in FIG. 4). Thus, the circuit is designed based on the known current flow during the preheat stage and the known duration (or range of durations for different types of ballast) of the preheat stage, such that the divided voltage VIN_on is not reached during the preheat stage.

[0093] By way of example only, VIN_on=15V, R5=50 kΩ, R4=250 kΩ. In this case, Vuvp=90V, V_LED (nominal)=120V (so Vuvp is approximately 80% of V_LED).

[0094] During the preheat stage, V_LED reaches 50% of the nominal LED string voltage, i.e. 60V, so Vuvp is not reached by V_LED and VIN_on is not reached at VIN (VIN is at about 10V).

[0095] During ignition, V_LED rises quickly. When it passes 90V, the IC 30 turns on, and the isolation switches close.

[0096] The setting of Vuvp to around 80% of the nominal value of V_LED (rather than a lower value as would conventionally be the case) is so that the IC 30 will not mis-trigger during the preheat stage, and the IC will be triggered by the under voltage protection only during the normal operating condition.

[0097] FIG. 4 shows a lighting circuit in accordance with the invention.

[0098] The lighting circuit is integrated within a tubular lamp of the type shown in FIG. 1. The tubular lamp has a first (left) end with external connectors PinL1 and PinL2 and a second (right) end with external connectors PinR1 and PinR2. Each external connector defines an input adapted to be connected to a high frequency ballast for gas discharge lamps.

[0099] Each pin is connected in series with a respective electrical isolation switch in the form of a relay. The relay Relaya_L is at pin PinL1, the relay Relayb_L is at pin PinL2, the relay Relaya_R is at pin PinR1 and the relay Relayb_L is at pin PinR2.

[0100] The relay Relaya_L at one pin at one end has a parallel Y-capacitor CyL, and the relay Relaya_R at the corresponding pin at the other end also has a parallel Y-capacitor CyR.

[0101] These capacitors provide a high frequency conduction path when the isolation switches are turned off.

[0102] Each end of the TLED lamp has a filament emulation circuit. The first end has a filament emulation circuit F1, in the form of a resistor, which is connected between the pins at the first end when the isolation switches are open. Similarly, the second end has a filament emulation circuit F2, in the form of a resistor, which is connected between the pins at the second end when the isolation switches are open. The filament emulation circuits F1 and F2 are only used for lamp detection at preheat stage. The real load seen by the ballast is the LED loading at normal operation (after ignition).

[0103] The pair of pins at each end connects to a full bridge diode rectifier with a buffer capacitor at the output. A first rectifier D1 to D4 and buffer capacitor C7 is at the first (left) end and a second rectifier D5 to D8 and buffer capacitor C8 is at the second (right) end.

[0104] At the first end, the output of the rectifier D1 to D4 defines the LED voltage V_LED. This is the LED on voltage across a light emitting unit, in the form of LEDs LED1 to LEDn. There may be a series circuit of LEDs or a combination of series and a parallel LEDs. This LED on voltage provides the supply voltage to the buck converter 40. The buck converter is one example of possible power supply unit which obtains power from the established LED on voltage and uses the power to control the isolation switches. Closing the isolation switches electrically connects the respective input to the light emitting unit.

[0105] At the second end, the external terminals connect to the rectifier D5 to D8 through coils EE8a and EE8b. These are matching inductors for adjusting LED current when connected to different ballasts.

[0106] The output of the rectifier D5 to D8 also defines the LED voltage V_LED.

[0107] The buck converter 40 comprises all of the parts shown in FIG. 3. Thus, the supply voltage is converted by a resistive divider before being supplied to the controller IC 30 of the buck converter 40.

[0108] The output voltage V_RELAY drives two relay coils Relaycoil_L and Relaycoil_R. One coil drives the pair of relays in synchronism at one end, and the other coil drives the pair of relays in synchronism at the other end.

[0109] The isolation switches (relays) are turned off (i.e. the switches are open) during the preheat stage of the ballast, and they are turned on at the ignition stage. During the preheat stage, the current from the high frequency ballast to the light emitting unit in the preheat state is for example in the range 10% to 20% of the nominal current in a normal driving state. The nominal current is for example in the range 100 mA to 1 A so the current to the light emitting unit during the preheat stage is thus tens of mA. This small current will flow between PinL1 and PinR1. During the preheat stage a current typically of several hundred mA will flow through the filament emulation circuits F1 and F2.

[0110] The capacitors CyL and CyR are in series with the LED string. The circuit thus has a high impedance, which is beneficial for correct operation of the ballast.

[0111] The small current of tens of mA is unable to establish a voltage amplitude on the buffer capacitors C7, C8 and the LEDs sufficient for the power supply unit 40 to turn on and thereby close the isolation switches.

[0112] After the preheat stage, the ballast delivers the ignition current. During the preheat stage, most of the current flows from one pin to the other pin at the same terminal (e.g. PinL1 to PinL2, and PinR1 to PinR2). The ignition current instead flows between the two ends (intended for ionizing the gas in a gas lamp). This current flows through part of the diode bridge at one end, through the LED arrangement and through part of the diode bridge at the other end.

[0113] This ignition current is sufficient that the voltage amplitude sufficient for the power supply unit 40 to be powered is reached. The isolation switches are then closed. The first and second filament emulation circuits are then electrically floating. They then play no role in the normal functioning of the lamp.

[0114] Thus, only when the ignition phase is reached does the power supply close the isolation switches. Thus, the lamp is safe to touch until the preheat stage is complete.

[0115] More practically, during the ignition state of the high frequency ballast, an ignition current in delivered to the light emitting unit is in the range of 100% to 200% of the nominal current in a normal driving state. The ignition current is for example between 200 mA and 1 A.

[0116] The light emitting unit is then able to establish the voltage amplitude to turn on the power supply unit 40 in a period of 1 ms to 20 ms.

[0117] The capacitors C2, C4, C5 and C6 are matching capacitors, used to adjust the LED current when connected to different ballasts.

[0118] FIGS. 5A and 5B shows a circuit diagram of another LED tube lamp using the concept of the invention. The additional capability of the LED tube in FIG. 5A is that it can support AC mains input or electromagnetic ballast input between pin1 and pin2 at the left end. For AC mains input or electromagnetic ballast input, the energy come into the rectifier formed by diodes D6, D7, D8 and D9 and to a DCDC converter to power the LEDs. Besides, it can support high frequency ballast input between the left end to right end similar as described above. For high frequency ballast input, pin1 and pin2 are the same voltage, and pin3 and pin4 are the same voltage, the energy first comes in via the Ycap and the diodes, and turn on the LED, the LED on voltage between the V+ and V− then powers the relay driver to turn on the relay and bypass the Ycap, similar as described above.

[0119] The inventors realizes that, the relay does not need to be driven in case of AC mains input or electromagnetic ballast input. However, since the relay driver obtains the LED on voltage to drive the relay, the relay driver would still be powered when the LED is turned on by the AC mains input or electromagnetic ballast input. This results in wasted power. Moreover, in the hi-pot test, an AC frequency high voltage is applied between the left end and the right end, this high voltage may go through the Ycap and also turn on the LED. In this case the LED on voltage will power the relay driver and close the relay, the closed relay results a low impedance path for the hi-pot test voltage, and the hi-pot test would fail. The inventors also want to avoid this problem.

[0120] To solve at least these two problems, the inventors proposes that the relay driver is powered by the LED on voltage only when the input to the LED tube lamp is a high frequency ballast, excluding the case of low frequency AC mains or electromagnetic ballast input, or low frequency hi-pot test voltage. There is a detection circuit to detect the presence of a high frequency ballast, more specifically, the detection circuit could be a frequency detector to detect a high frequency signal of the input. The implementation of a frequency detector to recognize the high frequency and filter out the low frequency is well known for those skilled in the art, such as a high pass filter. And as shown in FIG. 5B, there is a switch SW1 to close to couple the LED on voltage to the power supply unit/relay driver 40 when the detection circuit detects that the lamp is connected the high frequency ballast, otherwise to the switch SW1 is open and decouple the LED on voltage from the power supply unit/relay driver 40. The switch SW1 could be implemented by a MOSFET, a bi-polar transistor, or even a relay. The output of the detection circuit may be converted properly to drive the switch SW1, and the driving of a switch is also a quite common implementation for those skilled in the art. The description will not give further details.

[0121] Instead of implementing the power supply unit by switch mode power supply, we can implement it by a voltage dividing or even a direct power supply.

[0122] The direct power supply means there is a direct electrical connection without substantially voltage dropping, so that the LED on voltage is substantially all used to drive the isolation switch. This provides simpler implementation for the power supply unit than the switch mode power supply implementation. FIG. 6A shows this implementation.

[0123] The voltage dividing power supply means there is an impedance component to take some voltage and provide the remaining LED on voltage to drive the isolation switch. As shown in FIG. 6B, we can select one or more LEDs whose ON voltages sum is higher than the drive voltage. One resistor R1 is used to take some portion of the LED ON voltage and leave the remaining portion of the LED on voltage to drive the isolation switch. The voltage dividing power supply has better efficiency.

[0124] In further improved solution, a capacitor-resistor voltage dividing circuit is used, as shown in FIG. 6C. Capacitor-resistor voltage dividing circuit means a parallel connection of a capacitor and a resistor. The capacitor, since it intends to suppress the voltage built on it, gives a larger portion of the LED on voltage to drive the isolation switch. This provides a strengthened actuation to close the isolation switch such as relay. As time goes by, the voltage on the capacitor increases, the remaining portion of LED on voltage, being taken by the isolation switch, is sufficient to keep the close state of the isolation switch. Thus the efficiency is also high.

[0125] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

[0126] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0127] If the term “adapted to” is used in the claims or description, it is noted the term “adapted to” is intended to be equivalent to the term “configured to”.

[0128] Any reference signs in the claims should not be construed as limiting the scope.