Patent Application
20100181925
The present invention relates to a ballast/line detection circuit for fluorescent replacement lamps.
LED light sources are rapidly becoming competitive with fluorescent lamps with respect to luminous efficacy. Known LED light sources typically require rewiring the fixture so that line voltage is directly connected to the LED lamp connectors, bypassing the ballast. LED light sources have been developed that connect the replacement LED lamp to the output of the ballast. Accordingly, it has become more difficult to replace existing fluorescent lamps, since it may not be readily apparent if a fixture has been rewired to bypass the ballast, or is still wired through the ballast without at least partial disassembly of the light fixture.
It is desirable to be able to replace existing fluorescent lamps with LED sources without replacing the fixture that contains the lamps, due to the cost, time, and disruption caused by replacing a fixture as opposed to replacing a lamp. When replacing fluorescent lamps in this way, it is possible to either connect the replacement lamp to the output of the ballast, or to rewire the fixture so that line voltage is directly connected to the lamp connectors, bypassing the ballast. Each of these configurations has advantages and disadvantages. The ballast connection, for example, permits lamp replacement by untrained personnel, has a very quick relamp time, permits mixing of LED and fluorescent lamps in the same fixture, and permits easy relamping back to fluorescent. The ballast-free (direct to AC line) connection, for example, permits the elimination of the ballast and its noise, lifetime limit, and heat production. It also can eliminate the power that is necessarily wasted in the ballast. Since both configurations have advantages in different situations, it is desirable for non-fluorescent replacement lamps to be usable without change with or without a fluorescent ballast.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.
The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:
Referring to
As one non-limiting example, the normal operating point of replacement lamp 30 can be around 120V and 220 mA. Of course, other replacement lamps can operate at different operating points. When replacement lamp 30 is operating from ballast 34, the power in lamp 30 increases as the current in lamp 30 decreases, and vice versa, because the operating point voltage of lamp 30 is below the maximum power point of the ballast. This is because a small decrease in current can result in a relatively large increase in voltage, as illustrated in
On the other hand, when replacement lamp 30 is operating from the AC line source 32, the power in lamp 30 increases as the lamp current increases, and vice versa, because the voltage does not change with current. As a result of the fundamental incompatibility of the two types of power sources, any control scheme that attempts to operate with both of these power sources must be able to handle the differences between a ballast source and an AC line source.
Accordingly, it is important to correctly detect which power source 14 is present. While the embodiments described herein refer to identifying the power source as an AC line or ballast, reference to the ballast 34 does not necessarily mean the absence of an AC line connection but yet refers to a power source that may contain both the AC line and the ballast. If a control scheme suitable for AC line 32 source is used with the ballast 34, the input voltage can increase to the maximum available from ballast 34. It may be impractical to provide components that can withstand the maximum voltage ballast 34 can deliver (e.g., up to 1200V) when the normal operating point of the replacement lamp 30 is, for example, around 1/10 of that value. Conversely, if a control scheme suitable for ballast 34 is employed when connected to the AC line 32, the current into the lamp 30 may increase without limit, until component failure or another limit intervenes.
Referring now to
The rectified voltage is smoothed by a filter 18, which is connected across rectifier 16. Filter 18 can be realized by capacitor C1. Alternatively, filter 18 can be realized by any other suitable number of capacitors. A shunt regulator 12 and a current-limiting resistor 20 are placed in parallel with filter 18. Shunt regulator 12, as illustrated in
To identify the type of power source 14, the circuit 10 detects when Zener diode D5 is conducting by detecting the current flowing therein. Input signal 36 can be latched because the normal operating point of the lamp 30 can be very similar for both AC line 32 and ballast 34 operation. It is the incremental change that is different. However, in other embodiments, input signal 36 will not be latched.
The Zener diode D5 can be chosen so that it does not conduct when the power source 14 is AC line 32 without ballast 34. For example, if the line voltage is 120 VAC, the Zener breakdown voltage can be set higher than a peak line voltage (e.g. 168V). Accordingly, for example, the Zener breakdown voltage can be 200 V. Since the Zener diode is set up to not conduct, the voltage across a resistor 20 will be below that of a reference voltage V2. Accordingly, an inverting input (V−) of a voltage comparator U2 will be at a greater voltage than a non-inverting input (V+). In turn, the output of comparator U2, which is connected to a clock input (CLK) of an integrated circuit 24, outputs a value (e.g., negative or zero voltage) that will not set clock input (CLK). Integrated circuit 24, as illustrated in
As is well known in the art, if clock input (CLK) is not set, non-inverted output (Q) of D flip-flop A1 will output a signal representing that ballast 34 has not been detected. In other words, for example, the non-inverted output (Q) will be set to a logical 0 and in turn, control circuitry 22 can be configured to operate as if AC line 32 is the power source 14 without ballast 34.
On the other hand, when the power source 14 includes the ballast 34, the rectified voltage will rise until the Zener diode D5 conducts. When the Zener diode D5 current is sufficiently high that the voltage across resistor 20 is above reference voltage V2, non-inverting input (V+) of voltage comparator U2 will be at a greater voltage than inverting input (V−). In turn, the output of the comparator U2, outputs a value (e.g., positive voltage) that will set clock input (CLK). Accordingly, when clock input (CLK) is set, non-inverted output (Q) will output a signal representing that ballast 34 has been detected. For example, non-inverted output (Q) will be set to a logical 1 and in turn, control circuitry 22 can be configured to operate as if the ballast 34 is included in the power source 14.
Once power source 14 is identified, the correct control algorithm or circuit can be engaged. The control circuit 22 can then set and maintain the correct operating point of the lamp 30 to avoid damage to components. For example, if power source 14 does not include ballast 34, control circuit 22 will operate in a manner in which increasing current drawn from the power source 14 increases the power drawn from the AC line 32, and vice versa. Further, for example, if ballast 34 is detected, as discussed above, control circuit 22 will operate in a manner in which increasing current drawn from the power source 14 decreases the power drawn from the ballast 34, and vice versa.
Control circuit 22 can be any suitable controller device that can provide current regulation to LED D6 through power converter 26. The manner in which the current is regulated, as discussed previously, can depend on whether ballast 34 is part of power source 14. Further, although controller circuit 22 is shown as including IC U1, other suitable control circuits are available that may not utilize an integrated circuit or have a different configuration.
The control scheme used when the AC line mode controller 52 is selected can be any suitable control scheme for providing power to LED D6 from AC line 14. For example, the control scheme can include peak current control, average current mode control, PWM duty cycle control and/or any other suitable control scheme. The AC line mode controller 52 may optionally receive current, power, or light output feedback from LED D6. As illustrated and as will be discussed in more detail below, AC line mode controller 52 receives current feedback from LED D6. When the multiplexer has detected that ballast 34 has not been detected, the AC line mode controller 52 provides a gate signal through the multiplexer and through a gate driver 56. The gate driver 56 provides a gate driver signal to a power converter 26, as will be discussed in more detail below.
The control scheme used when the ballast mode controller 54 is selected can be any suitable control scheme for providing power to LED D6 from ballast 34. For example, the control scheme can include providing a control scheme where the AC Line mode controller 52 provides a constant gate signal (i.e. turning on switch M1 at 100% duty cycle) so that the current through LED D6 may be regulated by the ballast 34. Alternatively, any other control scheme may be used through. Again, similar to that AC line mode discussed above, the ballast mode controller 54 may optionally receive current, power, or light output feedback from LED D6. As illustrated and as will be discussed in more detail below, ballast mode controller 54 receives the same current feedback as AC line mode controller 52. Other suitable control scheme schemes are also available that may be used in lieu of or in addition to the ballast mode control scheme discussed above. For example, one such control scheme includes PWM duty cycle control with reverse feedback gain. The reverse feedback can provide the average current across LED(s) and invert a signal representing the average current so that, at any given operating point, increasing a current drawn from the source will increase LED power and decreasing the current drawn from the source will decrease LED power. Another such control scheme includes the addition of a shunt regular to limit the voltage from the ballast 34. Of course, other control schemes are available.
Power converter 26 is shown in
If ballast 34 is included in the power source 14 and is wrongly identified as an AC line 32 source due to, for example, low voltage of input signal 36, detection circuit 10 can switch to the “ballast detected” mode of operation when the voltage eventually rises. As discussed previously, once the voltage rises to the Zener voltage, the Zener diode D5 will conduct, and the ballast 34 can correspondingly be detected. If the Zener diode D5 energy and power capacity is sufficiently high, the protective action of the Zener diode D5 can permit a delayed start of the control circuitry 22 without damaging other electrical components.
The detection circuit 10 can be associated with or built into the fluorescent replacement lamp 30, as shown in phantom line in
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/146,164, filed Jan. 21, 2009, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61146164 | Jan 2009 | US |
