Disclosure of Invention
Accordingly, an object of the present invention is to provide an LED lamp having good lighting performance when assembled in various lighting apparatuses regardless of the kind of ballast used in the lighting apparatuses (e.g., whether the lighting apparatuses have a magnetic ballast, a constant current ballast, a constant power ballast, or no ballast).
According to an aspect of the invention, a LED lamp suitable for a lighting device, in particular a lighting device designed for a fluorescent lamp, is proposed, the LED lamp being adapted to receive power from the lighting device and comprising one or more LEDs. The LED lamp includes: a first power supply circuit including a ballast protection circuit including an impedance; and a second power supply circuit comprising a filter circuit and a switched mode power supply. The first power supply circuit is connectable to receive power from the lighting device and supply power to the one or more LEDs through the ballast protection circuit. The second power circuit is connectable to receive power from the lighting device and to supply power to the one or more LEDs through the switch mode power supply.
The LED lamp further comprises: a switching circuit connected to sense power received from the lighting device and to switch between a plurality of operating modes depending on whether the power received from the lighting device is provided by the magnetic ballast, the electronic ballast operating as a constant current ballast, the electronic ballast operating as a constant power ballast, or not provided by the ballast.
The plurality of operating modes include: a first mode of operation in which the second power supply circuit is connected to supply power to the one or more LEDs and the first power supply circuit is not connected to supply power to the one or more LEDs; and a second mode of operation in which the first power supply circuit is connected to supply power to the one or more LEDs and the second power supply circuit is not connected to supply power to the one or more LEDs.
The switching circuit of the LED lamp may be adapted to switch to the first mode of operation when the switching circuit detects that the power received from the lighting device is provided by the magnetic ballast or not provided by the ballast. The LED lamp may be configured such that: in a first mode of operation, the switched mode power supply operates at an operating frequency and the filter circuit is connected to filter noise generated by the switched mode power supply (e.g., in the second power supply circuit to enable filtering of noise). In this mode, the LED is driven by the switched mode power supply and the ballast protection circuit (which is part of the first power supply circuit) is not required and can be switched off.
The switching circuit of the LED lamp is adapted to switch to a second mode of operation when the switching circuit detects that the power received from the lighting device is provided by the electronic ballast. The LED lamp may be configured such that: in the second mode of operation, the switch mode power supply is off or inoperative and the filter circuit is open (e.g., disconnected from the second power supply circuit). In this mode, the LED is driven by the ballast protection circuit. The switched mode power supply (and associated filter circuitry) need not be, and may be, turned off, or placed in a non-operational mode.
In an embodiment, the LED lamp is configured such that: in a second mode of operation, when the ballast protection circuit is connected to supply power to the one or more LEDs, an impedance is connected in series with the LEDs if power received from the lighting device is provided by the electronic ballast operating as a constant power ballast, and the impedance is bypassed if power received from the lighting device is provided by the electronic ballast operating as a constant current ballast.
In an embodiment, the switching circuit comprises a first sensing circuit adapted to generate a first output signal for operating a first switch, wherein the first switch is arranged to connect the first power supply circuit to supply power to the one or more LEDs through the ballast protection circuit.
In an embodiment, the switching circuit comprises a second sensing circuit comprised in the switched mode power supply, wherein the second sensing circuit is adapted to sense a voltage or a current supplied to the switched mode power supply and to operate the second switch in dependence of the sensed voltage or current.
In an embodiment, the second sensing circuit causes the switched mode power supply to operate when a voltage or current received by the switched mode power supply exceeds a predetermined threshold.
In an embodiment, the second sensing circuit operates the switch mode power supply when the LED lamp receives operating power from the lighting device and the first power supply circuit is not connected.
In an embodiment, the switching circuit comprises a third sensing circuit adapted to generate a third output signal for operating a third switch arranged to switch off the filter circuit when the first power supply circuit is enabled to supply power to the one or more LEDs.
In an embodiment, the switching circuit comprises a fourth sensing circuit adapted to generate an output signal for operating a fourth switch arranged to bypass the impedance.
In an embodiment, the fourth switch is arranged to switch the ballast protection circuit from the low impedance mode to the high impedance mode when the sensed voltage or current exceeds a predetermined threshold. In an embodiment, the impedance of the ballast protection circuit has an inductive impedance between 0.12mH and 0.3mH, preferably an inductive impedance of 0.18 mH.
In an embodiment, the LED lamp further comprises: an auxiliary circuit defining a conductive path connected in parallel with the one or more LEDs, wherein the auxiliary circuit comprises: is arranged to bypass the capacitor in the conductive path of the burst current from the LED and further comprises a circuit for not discharging the capacitor through the LED.
In an embodiment, the sensing circuit has an impedance of at least 2MOhm for a period of at least 75msec when receiving power from the lighting device.
According to another aspect of the present invention, there is provided an LED lamp suitable for a lighting device, comprising: one or more LEDs; a ballast protection circuit comprising an impedance connectable in series with the one or more LEDs to supply power to the one or more LEDs; a switched mode power supply connectable in series with the one or more LEDs to supply power to the one or more LEDs; a filter circuit connectable to filter noise generated by the switched mode power supply; one or more sensing circuits connected to measure power received from the lighting device and to generate at least one output in accordance with the power received from the lighting device indicating whether power is provided by the magnetic ballast, the electronic ballast operating as a constant current ballast, the electronic ballast operating as a constant power ballast, or not by the ballast (referred to herein as "direct mains"); and a plurality of switches for defining a plurality of operating modes of the LED lamp and switching between the plurality of operating modes based on at least one output from the sensing circuit.
The plurality of operating modes include: a first operating mode in which the switched mode power supply operates at an operating frequency, the filter circuit is connected to filter noise generated by the switched mode power supply, and the ballast protection circuit is disconnected; a second mode of operation in which the switched mode power supply is inactive, the filter circuit is disconnected, the ballast protection circuit is connected, and the impedance is bypassed; and a third mode of operation in which the switched mode power supply is inactive, the filter circuit is disconnected, the ballast protection circuit is connected, and the impedance is connected in series with the LED.
The LED lamp may be adapted to switch to the first mode of operation when the power received from the lighting device indicates that power is provided through the magnetic ballast or not through the ballast. In this mode, the LEDs are powered by a switched mode power supply.
The LED lamp may be adapted to switch to the second mode of operation when the power received from the lighting device indicates that power is being provided by an electronic ballast operating as a constant current ballast. In this mode, the ballast protection circuit is connected and the impedance in the ballast protection circuit is bypassed. A switched mode power supply is not required and is not operational and the filter circuit can be disconnected to avoid bypassing high frequency components of the current supplied from the electronic ballast and to avoid compatibility issues with some designed electronic ballasts during the ballast ignition phase. The filter circuit may comprise a surge protection circuit or device to prevent surges in the power supplied to the LED lamp by the magnetic ballast or direct mains, and preferably also to disconnect the surge protection circuit or device in the second mode of operation.
The LED lamp may be adapted to switch to the third mode of operation when the power received from the lighting device indicates that power is provided by an electronic ballast operating as a constant power ballast. In this mode, the ballast protection circuit is connected and the impedance in the ballast protection circuit is connected in series with the LED. This provides increased impedance in series with the LED to reduce the current flowing through the LED.
The LED lamp may include: a first power supply circuit for supplying power to the one or more LEDs through the ballast protection circuit; and a second power supply circuit for supplying power to the one or more LEDs via the filter circuit and the switched mode power supply. The first power circuit supplies power to the LED when the LED lamp operates in the third operating mode, and the second power circuit supplies power to the LED when the LED lamp operates in the first operating mode or the second operating mode.
The one or more sensing circuits may comprise a first sensing circuit for generating a first output signal for operating a first switch, wherein the first switch is arranged to connect the first power supply circuit to supply power to the one or more LEDs through the ballast protection circuit. The first sensing circuit may be arranged to sense a frequency of a voltage supplied by the lighting device and may be arranged to connect the ballast protection circuit to a rectified voltage supplied to the LED lamp.
The switched mode power supply may comprise a second sensing circuit for sensing a voltage or current supplied to the switched mode power supply and operating the second switch in dependence on the sensed voltage or current. The second sensing circuit may be arranged to: the switch mode power supply is operated when a voltage or current received by the switch mode power supply exceeds a predetermined threshold, and the switch mode power supply may be operated when the LED lamp receives operating power from the lighting device and the first power supply circuit is not connected. The LED lamp may be configured such that connection of the first power supply circuit may cause the sensed voltage or current supplied to the switched mode power supply to drop or remain below a predetermined threshold.
The one or more sensing circuits may comprise a third sensing circuit for generating a third output signal for operating a third switch, wherein the third switch is arranged to disconnect the filter circuit when the first power supply circuit is enabled to supply power to the one or more LEDs. The third sensing circuit may be arranged to sense the magnitude of the rectified voltage or current supplied to the LED lamp and to generate the output signal, and the third switch may comprise an electromagnetic relay. The filter circuit may include a surge protection circuit or device, and the third switch may also open the surge protection circuit or device.
The one or more sensing circuits may include a fourth sensing circuit for generating an output signal that operates a fourth switch that bypasses the impedance. The fourth sensing circuit may be arranged to sense a voltage or current indicative of current flowing through the one or more LEDs, and the fourth switch may be arranged to switch the ballast protection circuit from the low impedance mode to the high impedance mode when the sensed voltage or current exceeds a predetermined threshold.
The LED lamp may further comprise an auxiliary circuit defining a conductive path connected in parallel with the one or more LEDs, wherein the auxiliary circuit comprises a capacitor in the conductive path arranged to bypass the burst current from the LEDs, and further comprises a circuit for not discharging the capacitor through the LEDs.
Detailed Description
The following is a more detailed description of exemplary embodiments of the present description.
FIG. 1 is a schematic diagram of an embodiment of the present invention. The LED lamp 1 is configured to be compatible with a lighting device 2 designed for a fluorescent tube, preferably having the same length and shape as a standard fluorescent tube, so that the LED lamp 1 can be fitted into the lighting device without modification. Two electrical connectors 3 (typically in the form of pins) are provided at each end of the LED lamp 1 for releasable connection to respective connectors 4 of the lighting device. The lighting device 2 may comprise a ballast 5 or may be without a ballast. If ballast 5 is included in the lighting device, ballast 5 may be a magnetic ballast, an electronic ballast operating as a constant current ballast, or an electronic ballast operating as a constant power ballast.
The lighting device 2 supplies power to the LED lamp 1 through the connector 4. The power input to the LED lamp 1 provided by the lighting device 2 varies depending on the design of the lighting device (i.e., whether the lighting device has a ballast, and if so, what type of ballast).
Ballasts-free luminaires typically provide an AC mains voltage (e.g. 120Vac or 230Vac at 50Hz or 60Hz) at connector 4. Although the lighting device may comprise some circuit components between the AC mains input and the connector 4 of the lighting device, it is also referred to as "direct mains".
Magnetic ballasts use inductive elements to regulate the current supplied by the lighting device, typically providing power at connector 4 at a mains frequency and voltage similar to that of the direct mains case.
Electronic ballasts typically convert AC mains voltage power (mains voltage power) to DC and then back to a variable frequency AC voltage to provide high frequency power (e.g., 100 + 110Vac at 20kHz to 200 kHz) at connector 4. Electronic ballasts are typically designed to: a constant current ballast designed to provide current at a substantially constant amplitude; or a constant power ballast, designed to deliver a substantially constant power and whose output current will vary according to the load impedance in an attempt to maintain the designed power output. If the load voltage (e.g., across the LED lamp 1) is lower than the expected fluorescent lamp voltage, the constant power ballast typically attempts to increase the output current to more closely approach the design power level.
Fig. 2 is a schematic view of the LED lamp 1 of fig. 1. A rectifier 6, preferably a full wave rectifier, is connected to the connection pin 3 and is used to rectify the AC voltage applied to the connection pin 3 (i.e. supplied by the connector 4 of the lighting device 2) to produce a DC voltage for powering the LED lamp 1.
The LED lamp 1 includes one or more LEDs 7 for emitting light. Although three LEDs are shown in the drawings, any number of LEDs may be suitably used in consideration of the specifications of the LEDs used, the amount of light emitted, and the overall design of the LED lamp. The LED7 may be connected in series or in parallel, or may be multiple series strings of LEDs connected in parallel, or any other combination of connections as desired.
The LED lamp 1 includes: a ballast protection circuit 10 for powering the LED7 when the LED lamp 1 detects that it is receiving power from a lighting device having an electronic ballast, and includes: a filter circuit 20 and a switched mode power supply 30 for supplying power to the LED7 when the LED lamp 1 detects that it is receiving power from a lighting device that does not have a ballast or that has a magnetic ballast. A switching circuit 40 is also included for sensing the received power and switching the various circuits according to the characteristics of the received power. The switching circuit 40 may be implemented as a centralized circuit for generating a plurality of switching signals, or as a plurality of individual circuits each generating a switching signal, wherein the plurality of signals together perform the function of the switching circuit 40. The switching circuit 40 may be implemented as one or more simple circuits formed by separate circuit elements, or may be implemented as one or more integrated circuits or microcontrollers or the like. An integrated circuit or microcontroller may additionally be used to ensure that the switching signal does not switch the circuitry of the LED lamp 1 to an unsafe or undesirable configuration.
In this embodiment, the LED lamp 1 includes two parallel power supply circuits for supplying power to the LEDs 7, although in other embodiments the two power supply circuits may be arranged differently (e.g., in series). The first power supply circuit 50 includes the ballast protection circuit 10, and supplies power for operating in the lighting apparatus having the electronic ballast through the ballast protection circuit 10. The second power supply circuit 51 includes the filter circuit 20 and the switch mode power supply 30, and is supplied with power for operation in the lighting device without ballast or with magnetic ballast from the switch mode power supply 30.
When the LED lamp 1 is installed in a lighting device without ballast, the connector 3 typically receives an AC mains voltage and the output of the rectifier 6 (preferably a full-wave rectifier) is a pulsating DC voltage, which has a maximum voltage typically close to 170Vpk and 325Vpk, respectively, for 120Vac and 230Vac applications, and a ripple frequency that is twice the mains frequency (e.g. 100Hz or 120Hz (for full-wave rectification)).
When the LED lamp 1 is installed in a lighting device with a magnetic ballast, the connector 3 typically receives an AC mains voltage modulated by an inductive element in the ballast, and during steady state operation the output of the rectifier 6 (preferably a full wave rectifier) is a pulsating DC voltage similar to that without the ballast.
When the LED lamp 1 is installed in a lighting apparatus having an electronic ballast, the connector 3 receives a high-frequency AC voltage generated by the electronic ballast. When an electronic ballast starts, a high output voltage is first generated, typically around 400Vac, designed to light a fluorescent lamp. After ignition, the output voltage drops and, depending on the load impedance, typically has a voltage lower than the AC mains voltage (e.g. in the range of 40-80Vac, depending on the load) and a much higher frequency than the AC mains voltage (e.g. in the range from 20kHz to 200 kHz). The output of the rectifier 6 is therefore a high frequency pulsating DC voltage, with a low maximum voltage (after ignition) typically in the range 40-80Vac (depending on the load), and with a high frequency ripple typically 40kHz to 400 kHz.
The switching circuit 40 detects the type of ballast (if any) supplying power to the LED lamp 1 and switches the LED lamp 1 between different operating modes depending on the detection. In one embodiment, the switching circuit 40 is designed to distinguish between direct mains power or power supplied from a magnetic ballast and power supplied from an electronic ballast.
In one embodiment, the switching circuit 40 senses the voltage supplied to the LED lamp 1 to distinguish the electronic ballast from the magnetic ballast or direct mains. For a magnetic ballast or direct mains, the voltage supplied to the LED lamp 1 is substantially the mains voltage (e.g. 120Vac or 230 Vac). This is significantly higher than the typical output voltage of an electronic ballast, which is typically in the range of 40-80Vac, depending on the number of LEDs 7 in series. This allows the switching circuit 40 to be implemented using simple, compact and low cost circuitry to detect when the supply voltage is above or below a threshold (e.g., 100Vac) to distinguish the type of ballast used.
In another embodiment, the switching circuit 40 senses the frequency of the voltage or current supplied to the LED lamp 1 to distinguish the electronic ballast from the magnetic ballast or direct mains. For a magnetic ballast or direct mains, the frequency of the AC voltage and current supplied to the LED lamp 1 is substantially the mains frequency (e.g. 50Hz or 60 Hz). This is much lower than the typical output frequency of an electronic ballast (typically in the range of 20 to 200 kHz). Thus, the switching circuit 40 may be designed to detect when the supply frequency is above or below a threshold to distinguish the type of ballast used.
The sensing of the supply voltage or frequency may be performed on the AC side of the rectifier, measuring the amplitude or frequency of the AC voltage received from the lighting device, or may be performed on the DC side of the rectifier, measuring the amplitude or ripple frequency of the rectified DC voltage supplied to the LED lamp 1.
When the switching circuit 40 detects that the LED lamp 1 receives power supplied from the electronic ballast, then the switching circuit 40 connects the first power supply circuit 50 to supply power received from the lighting device 2 to the LED7 through the ballast protection circuit 10 (e.g., connects the first power supply circuit 50 to conduct power from the output of the rectifier 6 to the LED 7). The switching circuit 40 also opens or disables the second power supply circuit 51 so that the second power supply circuit 51 does not supply power to the LED7 (e.g., by disconnecting the second power supply circuit 51 from the rectifier 6 or LED7 or disabling or disconnecting the operation of the switched mode power supply 30 from the circuit). In this operating mode, the ballast protection circuit 10 operates and preferably turns off the filter circuit 20 and preferably disables the switched mode power supply 30, i.e. is placed in a non-operating mode.
It should be noted that the terms "switch" and "connect", "close" or "On" and "open", "open" or "Off" include digital On/Off switches such as those produced by electromechanical relays, but also analog switches involving impedance changes such as those produced by transistors or MOSFETs, i.e., changes between an On or connected state with relatively low impedance and an Off or open state with relatively high impedance. As such, the switching circuit 40 determines the current path for supplying power to the LED 7.
When the switching circuit 40 detects that the LED lamp 1 receives power supplied from a magnetic ballast or direct mains, the switching circuit 40 connects and/or enables the second power supply circuit 51 to supply power to the LED7 through the switched mode power supply 30 and connects the filter circuit 20 to enable the filter circuit 20 to filter noise generated by the switched mode power supply 30 (e.g. by connecting the filter circuit 20 to the output of the rectifier 6 or to the input or output of the switched mode power supply 30, connecting the filter circuit across the output of the rectifier 6 or the input or output of the switched mode power supply). The switching circuit 40 also disconnects the first power supply circuit 50 such that the first power supply circuit 50 does not supply power to the LED7 (e.g., by disconnecting the first power supply circuit 50 (or ballast protection circuit 10) from the rectifier 6 or LED 7). In this mode of operation, ballast protection circuit 10 is disconnected, switched mode power supply 30 is enabled, and filter circuit 20 is connected to filter noise.
The switched mode power supply 30 may be of conventional design for converting rectified DC power from the rectifier 6 to produce a switched DC output suitable for driving the LED 7. The filtering circuit 20 provides filtering for electromagnetic interference (EMI) generated by the switched mode power supply 30.
The filter circuit 20 may also preferably comprise a surge protection circuit or means for preventing surges in the AC mains supply when the second power supply circuit 51 is connected to operate under magnetic ballast or direct mains conditions. A Metal Oxide Varistor (MOV) or similar circuit element may be used as a surge protection device (typically with a clamping voltage in the range of 275V to 400V). When the first power supply circuit 50 is connected to operate under the condition of the electronic ballast, since the electronic ballast is generally internally provided with surge protection, the surge protection is not necessary. In addition, due to the design features of rapid start fluorescent tubes, electronic ballasts typically include a lighting mechanism that generates a high trigger voltage when turned on. When the LED lamp 1 is installed in a lighting fixture equipped with an electronic ballast, repeated exposure to the initial high voltage each time the LED lamp 1 is turned on may cause premature failure of the surge protection device. Therefore, when the switching circuit 40 detects that the LED lamp 1 receives the power supplied from the electronic ballast, the switching circuit 40 turns off the filter circuit 20, and also turns off the surge protection circuit or device.
Thus, the switching circuit 40 switches the LED lamp 1 between different operating modes depending on whether the LED lamp 1 receives power from a magnetic ballast or direct mains or from an electronic ballast. If the LED lamp 1 receives power supplied from the electronic ballast, the first power supply circuit 50 is connected to supply power to the LED 7. The ballast protection circuit 10 then operates and can switch the LED lamp 1 between other operating modes depending on whether the LED lamp 1 receives power from an electronic ballast operating as a constant power ballast or an electronic ballast operating as a constant current ballast.
Fig. 3 is a more detailed schematic diagram of the LED lamp 1 of fig. 2, showing details of one embodiment of a switching circuit 40 and one embodiment of a ballast protection circuit 10, both of which may be used in the LED lamp 1.
Switching circuit 40
In this embodiment, the switching circuit 40 includes four sensing circuits 41-44 implemented as separate circuits. The first sensing circuit 41 generates an output 41a for operating a first switch 45, the first switch 45 for connecting and disconnecting the first power supply circuit 50 to provide current to the LED7 through the ballast protection circuit 10. The second sensing circuit 42 (implemented in an internal circuit of the switched mode power supply 30 in this embodiment) generates an output to enable or disable the switched mode power supply 30 (e.g., by enabling or disabling the operating switch 46 of the switched mode power supply 30). The third sensing circuit 43 generates an output 43a for operating the third switch 47 to connect or disconnect one or more components in the filter circuit 20. The fourth sensing circuit 44 generates an output 44a for operating a switch 48 of the ballast protection circuit 10.
The switches 45-48 may be any type of suitable switch, for example, electromechanical switches such as relays, or semiconductor switches such as transistors, MOSFETs, or the like. It should be noted that the terms "open" and "closed" when referring to any switch described in this specification should also be understood to mean "open" and "on" or "disable" and "enable", respectively.
The first sensing circuit 41 provides an output for controlling the operation of the first switch 45. When the LED lamp 1 is detected to receive power from the electronic ballast, the first power circuit 50 is connected to supply power to the LED7 when the first switch 45 is closed. The first switch 45 connects the LED7 directly to the DC power supply, i.e., to the DC power supply line 9, through the ballast protection circuit 10. When the first switch 45 is turned off, the first power supply circuit 50 is turned off. In one embodiment, the first switch 45 is normally in a closed position and when the first sensing circuit 41 detects that the LED lamp 1 receives power through the magnetic ballast or direct mains, its output causes the first switch 45 to open, thereby opening the first power circuit 50. In another embodiment, the first switch 45 is normally in the open position and when the first sensing circuit 41 detects that the LED lamp 1 is receiving power through the electronic ballast, its output closes the first switch 45 so that the first power circuit 50 is connected to the LED7 through the ballast protection circuit 10. In the present embodiment, the first sensing circuit 41 senses on the AC side of the rectifier to measure the frequency of the AC voltage received from the lighting device 2. Because the frequency varies greatly between the relatively low frequency of the direct mains or magnetic ballast and the relatively high frequency of the electronic ballast, the first sensing circuit 41 can easily distinguish between these conditions. Although the voltage can also be sensed, it is more difficult because the voltage to be measured is floating. Sensing can also be done on the DC side, but requires more complex circuitry.
In this embodiment, the second switch 46 is part of the switched mode power supply 30, i.e., is a switch in the power supply that generates a switched output to drive the LED 7. In this embodiment, the switched mode power supply 30 includes a second sensing circuit 42 to enable or disable operation of the switched mode power supply 30 by sensing the magnitude or frequency of the power received by the switched mode power supply 30. In one embodiment, the second sensing circuit 42 detects the voltage at the input of the switched mode power supply 30 and/or the current flowing through the switched mode power supply 30 and generates an output to initiate operation of the switched mode power supply 30 when the voltage across the switched mode power supply 30 or the current flowing through the switched mode power supply 30 exceeds a certain threshold. For example, operation of the switched mode power supply 30 may be initiated when the input voltage of the switched mode power supply 30 is in the range of 40-60V.
When the first switch 45 is closed to connect the first power supply circuit 50 while supplying power to the LED lamp 1, the voltage across the switched mode power supply 30 and the current through the switched mode power supply 30 drops, and the sensing circuit 42 generates an output that disables operation of the switched mode power supply 30, and the switch 46 is placed in an open state. When the first switch 45 is open while supplying power to the LED lamp 1, the voltage across the switched mode power supply 30 and the current through the switched mode power supply 30 rise, and the sensing circuit 42 generates an output that enables operation of the switched mode power supply 30.
When the switch mode power supply 30 is enabled, the second switch 46 is switched at a high frequency (typically about 50kHz) to produce an output for driving the LED 7. When the switched mode power supply 30 is disabled, the second switch 46 is placed in an open position such that the switched mode power supply 30 does not supply power to the LED7 (i.e., the connection through the DC power line 9 of the switched mode power supply 30 and the LED7 is broken). In another embodiment, the switched mode power supply 30 receives a signal from the switching circuit 40 to enable or disable operation of the switched mode power supply 30. In another embodiment, an additional switch separate from the switched mode power supply 30 is provided to connect or disconnect the second power supply circuit 51 (and the switched mode power supply 30).
The third sensing circuit 43 provides an output for controlling the operation of the third switch 47. The filter circuit 20 is connected and used to filter EMI generated by the switched mode power supply 30 when the third switch 47 is closed, and at least some components of the filter circuit 20 are disconnected or bypassed when the third switch 47 is open. In one embodiment, the third switch 47 connects the filter circuit 20 across the DC power supply (i.e., between the DC power supply line 9 and ground (0V) at the output of the rectifier 6) to enable the filter circuit 20 to filter out EMI generated by the switch mode power supply 30. The third switch 47 turns off the filter circuit 20 when the first power supply circuit 50 is in use (i.e., when the LED lamp 1 receives power from the electronic ballast) and the second power supply circuit 51 is not in use. This is done because the front-end capacitance in the filter circuit (connected across the DC power supply, between the DC power supply line 9 and ground) may prevent proper operation of the ballast protection circuit 10 by bypassing high frequency components (at least some high frequency components) of the current supplied from the electronic ballast to ground, and may also result in a loss of system efficiency due to current shunting from the LEDs 7. The capacitor may also cause compatibility problems with some designs of electronic ballasts during the ballast ignition phase. Some electronic ballasts sense the presence of a lamp at its output before starting the ignition phase by passing current through the filament and sensing the return current to confirm that a lamp is installed in the lighting fixture. This small current charges the front-end capacitance of the filter circuit 20, the ballast will not detect a return current, and may shut down. This will result in poor compatibility when the LED lamp 1 is used with such a ballast. Switch 47 solves these problems.
In the present embodiment, the third sensing circuit 43 senses on the DC side of the rectifier to measure the magnitude of the rectified DC voltage supplied to the LED lamp 1. Since the operating voltage varies greatly between the relatively high peak voltage of the direct mains or magnetic ballast and the relatively low voltage of the electronic ballast (referenced to ground (0V)), a simple circuit can be used to distinguish between these cases. This design enables the use of simple and economical circuitry. Sensing frequency and/or sensing on the AC side of the rectifier is also possible, but results in a more complex circuit.
In one embodiment, the third switch 47 is normally in the open position with the filter circuit 10 open, and when the third sensing circuit 43 detects that the LED lamp 1 receives power through the magnetic ballast or direct mains, its output closes the third switch 47, so that the filter circuit 20 is connected. In another embodiment, the third switch 47 is normally in a closed position and when the third sensing circuit 43 detects that the LED lamp 1 is receiving power through the electronic ballast, its output turns the third switch 47 off, causing the filter circuit 20 to turn off. The third switch 47 is preferably an electromagnetic relay, rather than a semiconductor switch such as a transistor or MOSFET. Relays typically have a very low impedance when closed, while semiconductor switches have a relatively high impedance, e.g., several hundred milliohms, even when turned on. This higher "on" impedance of the semiconductor switch results in higher EMI emissions from the circuit, which is avoided by using a relay switch.
In one embodiment, the closing of the first switch 45 is delayed for a short period of time (e.g., several hundred milliseconds) to simulate the ignition behavior of a fluorescent lamp. When the LED lamp 1 is turned on and the electronic ballast is detected to supply power to the LED lamp, the switching circuit 40 will operate to connect the first power circuit 50 to supply power to the LED 7. However, when the impedance of the LED lamp 1 as seen from the ballast is high, applying a short delay between turning on the electronic ballast and closing the first switch 45 results in a short period of time. This short delay may be implemented in the first sensing circuit 41 to apply a predetermined delay before closing the first switch 45. This simulates the starting behavior of a fluorescent lamp with a high impedance before the fluorescent tube is ignited. This feature avoids problems in operation of the LED lamp 1 with an electronic ballast that is set to have a high load impedance at start-up and that may shut down or operate erratically if the load impedance is too low. This feature thus improves the compatibility of the LED lamp 1 with an electronic ballast.
Ballast protection circuit 10
When the LED lamp 1 detects that the power supplied by the lighting device is supplied from the electronic ballast, the filter circuit 20 and the switched mode power supply 30 are bypassed and the LED7 is powered through the ballast protection circuit 10. The ballast protection circuit 10 operates as a variable impedance arranged in series with the LED 7. When the current drawn by the LED lamp 1 or the voltage across the LED lamp 1 is within a desired range, the impedance of the ballast protection circuit 10 is low, but when the current or voltage exceeds a threshold value, the impedance of the ballast protection circuit 10 increases, thereby increasing the impedance of the LED lamp 1 across the lighting device 2 and the output of the ballast 5 powering the LED lamp. When operating an LED lamp using some type of electronic ballast that operates as a constant power ballast, the increased impedance reduces the problem by, for example, reducing the system power of such a ballast by about 15% by increasing the impedance in the circuit.
The ballast protection circuit 10 can be switched between at least two impedance values to conduct current in at least a low impedance mode and a high impedance mode, and optionally other modes (e.g., in two or more discrete operating modes). Alternatively, the ballast protection circuit 10 may include a variable impedance that may continuously vary the effective impedance to conduct current at different impedance values.
The ballast protection circuit 10 is connected in series with the LED7 such that a change in the impedance of the ballast protection circuit 10 will change the total impedance of the LED lamp 1 appearing across the output of the lighting device 2 and the ballast 5. The ballast protection circuit 10 varies the impedance in dependence on the current drawn by the LED lamp 1 and/or the voltage across the LED lamp 1. In this embodiment, when the current drawn from the ballast 5 and/or the voltage provided by the ballast 5 exceeds a predetermined threshold, the ballast protection circuit 10 is set to automatically switch from the low impedance mode to the high impedance mode such that the current flowing through the ballast protection circuit 10 and the LEDs 7 is reduced, thereby reducing the current drawn from the lighting device 2, and thermal runaway and other detrimental effects of the ballast 5 can be avoided, and the life of the ballast 5 can be increased.
In this way, even when the lighting device 2 is equipped with a constant power ballast, the LED lamp 1, which draws low power, can be safely installed in a lighting device 2 designed for higher power fluorescent lamps (e.g., a 28W LED lamp instead of a 58W fluorescent tube). The LED load impedance of the LED lamp 1 is much lower than that of a fluorescent lamp. A constant power ballast will attempt to maintain the design output power (e.g., 58W). The output voltage across the ballast load (LED lamp 1) will be lower and the ballast will react by driving a higher output current to maintain a constant output power level. The ballast protection circuit 10 is designed to react to higher ballast output current or voltage and automatically increase impedance. The current flowing from the ballast flows through the ballast protection circuit 10 and the LED7 and a change in the impedance of the protection circuit 10 will affect the total impedance at the ballast output. The increase in the total impedance of the LED lamp 1 increases the voltage on the ballast output and reduces the ballast output current to avoid damage to the ballast.
The ballast protection circuit 10 is arranged to measure or react to a current and/or a voltage, wherein a change in the measured value is indicative of a change in the total current drawn from the ballast and/or the voltage across the LED lamp 1. The ballast protection circuit 10 may include sensors (e.g., voltage or current sensors), or may use electrical components having different characteristics at different current/voltage values, or electrical components that react or "trip" when a certain current or voltage threshold is reached.
In the embodiment of fig. 3, the ballast protection circuit 10 comprises an impedance 11 and a fourth switch 48 arranged in parallel, which together form a variable impedance. The impedance 11 may be an inductive element, a resistive element, an active element or any combination of these elements. The impedance 11 is preferably an inductive impedance having an inductance between 0.12mH and 0.3mH (preferably, 0.18 mH). The fourth switch 48 may be a fuse or circuit breaker element that combines a circuit breaking function with a current sensing function that senses the current flowing through the fourth switch 48, i.e., the fuse blows or the circuit breaker trips when the current flowing through the fuse or circuit breaker exceeds a predetermined threshold. Alternatively, the fourth switch 48 may be any suitable type of switch, such as an electromechanical relay or a semiconductor switch such as a transistor or MOSFET, which is operated (opened/closed and closed/on) by the separate fourth sensing circuit 44.
The separate fourth sensing circuit 44 may measure a current (representing the current drawn by the LED lamp 1 from the lighting device) and/or a voltage (representing the voltage supplied from the lighting device to the LED lamp 1). In one embodiment, the fourth sensing circuit 44 includes an active sensing component (e.g., provided with one or more operational amplifiers, and/or one or more transistors, and/or one or more MOSFETs, and/or a microcontroller or microprocessor) to monitor the current drawn from the ballast and/or the voltage supplied by the ballast. The fourth switch 48 may be designed for one-time use (e.g., a fuse) or may be resettable (e.g., a circuit breaker). Temperature operated switches (e.g., thermal switches) may also be used.
The ballast protection circuit 10 may be arranged to switch from the low impedance mode to the higher impedance mode by opening the fourth switch 48. In the illustrated embodiment, in the low impedance mode, the fourth switch 48 is closed and the impedance 11 is shorted (bypassed) by the switch. The impedance of the fourth switch 48 is preferably low such that in the low impedance mode, the ballast protection circuit 10 has a negligible effect on the operation of the ballast 5 and the LED lamp 1. In the higher impedance mode (as shown), the fourth switch 48 is open so that substantially all of the current drawn from the ballast 5 flows through the impedance 11. The impedance 11 is of sufficient magnitude to increase the total impedance across the LED lamp 1 and across the output of the ballast 5, preferably by a factor of at least 20-30. As an example, the load impedance of the LED7 is typically a few tens of ohms, while the ballast protection circuit 10 adds about 100 ohms in the high impedance mode.
In a preferred embodiment, the low impedance mode is predominantly resistive and preferably a default operating mode, and the ballast protection circuit 10 is arranged to switch from the low impedance mode to the higher impedance mode only if the increase in measured current and/or voltage exceeds a threshold. This ensures that the LED lamp 1 operates in a low impedance mode, for example when the ballast 5 is a constant current ballast. Constant current ballasts typically have a self-protective/self-correcting mechanism to avoid the potential problem of maintaining a constant current. If the impedance of the LED lamp 1 deviates too much from the usual fluorescent tube impedance (e.g. with a large or complex impedance such as inductive or capacitive), there is a risk that the ballast will automatically shut down or enter a safe mode. By designing the LED lamp 1 to operate in a low impedance mode by default, the risk of this occurring can be reduced.
In one embodiment, the fourth switch 48 or the fourth sensing circuit 44 is arranged to determine whether the current flowing through the fourth switch 48 and/or the voltage across the fourth switch 48 exceeds a predetermined threshold.
For example, when the current and/or voltage is below a threshold (e.g., when a constant current ballast is connected to the LED lamp 1), the fourth switch 48 remains closed such that the effective impedance of the ballast protection circuit 10 is of an order of magnitude determined by the impedance of the fourth switch 48 (low impedance mode). When the current/voltage exceeds a threshold (e.g., when the ballast is a constant power ballast, which may produce, for example, twice the current of the ballast relative to a constant current ballast), the fourth switch 48 is opened so that the effective impedance of the ballast protection circuit 10 is of an order of magnitude determined by the impedance 11. Thus, the ballast protection circuit 10 switches from the low impedance mode to the higher impedance mode to reduce the current drawn from the ballast to avoid thermal runaway.
Fig. 4 is an alternative embodiment of the LED lamp 1 of fig. 3. In the present embodiment, the third switch 47 is arranged in series with the filter circuit 20. When the third sensing circuit 43 detects that the LED lamp 1 receives power from the direct mains or the magnetic ballast, the third sensing circuit 43 provides an output for closing the third switch 47 to connect the second power supply circuit 51, i.e. the filter circuit 20 and the switched mode power supply 30. Many types of electronic ballasts are designed to perform internal diagnostic checks when turned on. When the LED lamp 1 receives power from the electronic ballast, preferably, the LED lamp 1 presents a high impedance load to the electronic ballast for a sufficient time for the ballast to perform an internal diagnostic check (i.e., similar to the initial high impedance of a fluorescent tube). Thus, in the embodiment shown in fig. 4, the sensing circuit 43 preferably has an impedance of at least 2MOhm for a period of at least 75msec when the mains supply is switched on (with or without a ballast).
Fig. 5 is a simplified circuit diagram of an embodiment of an LED lamp 1 that can be used as in fig. 2 and 3.
The filter circuit 20 includes: an inductor L1 in series with the switched mode power supply 30, a resistor R1 in parallel with the inductor, a capacitor C1 between the DC supply line 9 and ground, and a capacitor C2 between the output of the filter circuit 20 and ground, both capacitors being grounded through an electromagnetic relay K1 (acting as a third switch 47). The filter circuit 20 further comprises a metal oxide varistor MOV1 providing surge protection connected between the DC supply line 9 and ground through a relay K1. Therefore, when the relay K1 is opened (i.e., the switch 47 is opened), the capacitors C1 and C2 and the surge protector MOV1 are all opened to avoid problems in operating the LED lamp 1 with the electronic ballast.
The relay K1 is controlled by a signal generated by the third detection circuit 43. In this embodiment, the third sensing circuit 43 functions as a current sensing circuit to turn on or off the relay K1 according to the output current of the switched mode power supply 30 measured through the transformer T1. This serves as a discriminator between the direct mains or magnetic ballast mode of operation and the electronic ballast mode of operation.
The switch mode power supply 30 includes a transistor Q1 (serving as the second switch 46) that performs the switching function of the power supply to produce the desired output for driving the LED 7. The transistor Q1 is connected through a resistor R2, a transformer T1, and a diode D2 connected in series to drive the LED 7. The switched output of the switched mode power supply 30 is smoothed by the inductance of the transformer T1 and the capacitance C4. The diode D3 acts as a freewheel and the diode D2 serves to electrically disconnect the switched mode power supply 30 from the ballast protection circuit 10 and the transistor Q2 (first switch 45). This makes the load impedance of the LED lamp 1 resistive and provides good compatibility with different types of ballasts. For an electronic ballast, resistor R4 is used to discharge capacitor C4 after LED lamp 1 turns off. Transistor Q1 is controlled by the microcontroller to provide the required switching function to produce the required output for driving LED 7. The microcontroller also includes a sensing circuit for sensing the voltage across resistor R2 to enable and disable operation of the switched mode power supply. Signals from a separate sensing circuit may be used as an input to the microcontroller to enable or disable the switched mode power supply (e.g., to place transistor Q1 in an off state).
A transistor Q2 (serving as the first switch 45) is connected in series with the ballast protection circuit 10. When the transistor Q2 is turned off, the power supply to the LED7 through the ballast protection circuit 10 is turned off, and when the transistor Q2 is turned on, the power supply to the LED7 through the ballast protection circuit 10 is connected. Transistor Q2 may be controlled by the first sensing circuit 41 described above or other sensing circuit that performs the sensing function.
The ballast protection circuit 10 includes a diode D4 and a transistor Q3 (serving as the fourth switch 48) connected in series, the diode D4 and the transistor Q3 being connected in parallel with an inductor L2. When the transistor Q3 is turned off, the impedance of the inductor L2 appears in series with the LED7, such that the impedance across the LED lamp 1 (i.e., between the DC power supply line 9 and ground) includes the impedance of the inductor L2 added to the impedance of the LED 7. When the transistor Q3 is turned on, the inductor L2 is shorted by a diode D4 in series with the transistor Q3. Since the forward impedance of the diode D4 and the impedance across the transistor Q3 are both much smaller than the impedance of the inductor L2 in the on state, the impedance across the LED lamp 1 (i.e., between the DC power supply line 9 and ground) is reduced by effectively removing the impedance of the inductor L2. Transistor Q3 may be controlled by the fourth sensing circuit 44 described above or other sensing circuits that perform the sensing function.
In some electronic ballast designs, the ballast continues to output power for a short period of time after lamp shut-down, particularly in the form of voltage spikes, pulses, or bursts of voltage spikes or pulses (hereinafter referred to as bursts). These bursts do not cause problems when the ballast drives a fluorescent lamp, but can cause the LED lamp to flash when the user turns off the lamp, which is undesirable. The embodiment of fig. 5 includes additional circuitry to reduce or avoid these flashes when the LED lamp 1 is used with this type of electronic ballast.
In this embodiment, the auxiliary circuit 60 provides a conductive path connected in parallel with the LED7 such that current generated by the burst is conducted through the conductive path to bypass the LED 7. To bypass the burst current, the conductive path should have a lower impedance than the LED. In this embodiment, the conductive path includes capacitor C5. The capacitor is preferably used to provide a low impedance at high burst frequencies. The capacitance of capacitor C5 is preferably high enough to sink a burst of current, e.g., to avoid quickly approaching a maximum state of charge when a burst is received, and low enough that the capacitor is sufficiently discharged during the time interval between bursts so that the capacitor can sink current from the next burst. Preferably, capacitor C5 has a capacitance in the range of 10 μ F-50 μ F.
When a burst voltage occurs, particularly during the peak of each burst, capacitor C5 conducts current and bypasses LED 7. Thus, only a small or no burst of current flows through the LED7, causing the LED to produce very little or no light. Therefore, the flash caused by the burst can be avoided or reduced.
In the embodiment shown, the auxiliary circuit 60 is arranged to discharge the capacitor C5 during the time interval between bursts (typically in the range from 1 to 300 milliseconds). When the capacitor C5 charges above the threshold voltage of diode D6, the resistor R5 and zener diode D6 conduct to discharge the capacitor C5, and diode D5 prevents the capacitor C5 from discharging through the LED7, which may produce a flash of light.
While the principles of the invention have been described above in connection with specific embodiments, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention, as defined in the appended claims.