Patent Application
20090200955
This application relates to a lamp assembly, and more particularly a combined lamp assembly incorporating a fluorescent lamp and more preferably a compact fluorescent lamp (CFL) light source and at least one light emitting diode (LED) light source. More particularly, this application relates to a combined arrangement for operating the lamp assembly, and particularly a combined driver circuit for the two light sources. However, it will be appreciated that the disclosure may find use in related environments and applications.
It is generally known to provide a lamp assembly having combined light sources. For example, different types of light sources may be combined in a lamp assembly where each light source provides a different type of light output, and the combined output provides a mixture of light that cannot be achieved by either light source on its own. Commonly owned and co-pending application (Attorney Docket No. 226177/GECZ 2 00824 (U.S. Ser. No. 12/021,880, filed 29 Jan. 2008) discloses a combined lamp assembly that includes a CFL light source and at least one LED light source and the disclosure thereof is expressly incorporated herein by reference. Particularly, the LED is preferably one that emits red light. The red light of the LED is mixed with the output of the CFL to advantageously provide an enriched, red color to the combined light output.
Known lamp assemblies that combine light sources usually employ separate, first and second driver circuits, namely a dedicated first driver circuit for controlling the CFL and a dedicated second driver circuit for controlling the LED. The CFL requires a high voltage, AC source and the first driver circuit or ballast associated therewith is an area of continued development and improvement. The LED, on the other hand, usually requires a DC power source and a low voltage. Thus, although combining the different types of light sources in a single lamp assembly is advantageous for light output, the combination presents unique issues since the needed driver circuits are so different. As will be appreciated, separate driver circuits add undesired cost and complexity to the lamp assembly.
Still another consideration is the space requirement of the lamp assembly. It is difficult to include separate LED and CFL driving circuits in the limited volume associated with the lamp assembly. Likewise, if the driving circuits are combined, then the same concerns with space requirements still exist.
There are several ways of driving a LED from a line-AC source. For example, one proposal uses a transformer for low voltage driving, and a resistor or capacitor for current limiting, that is before or after the transformer. Another option is to employ a current generator circuit using a switching power supply with a current limiter or generator. The switching power supply is connected with several LEDs. The current is limited by a capacitor and/or resistor.
One proposed solution to an integrated or combined circuit is disclosed in published international application WO2007/066252 A1. An LED circuit is connected in series with the fluorescent lamp and the high frequency alternating current that drives the fluorescent light source is supplied to the LED circuits. Each LED circuit has at least three parallel branches, namely, a first branch includes an impedance circuit while the second and third branches contain the LEDs which are connected in anti-parallel relation. The impedance circuit controls the amount of current flowing through one of the second and third branches at any one time (i.e., if there is high impedance, then a large part of the AC flows through the second or third branches, and vice versa if there is low impedance, then a small portion of the AC current flows through the second and third branches). Since the LED allows current to flow in only one direction, and the LEDs are arranged in anti-parallel relation in the second and third branches, the alternating current can flow through one of the second and third branches at any one time.
This solution is not as desirable since the LED and the fluorescent lamp are connected in series. Since, as noted above, an individual LED is usually driven by DC current, and fluorescent lamps are driven by AC current, the combined lamp assembly necessarily requires at least two LEDs—one operable in each current direction, Moreover, since the components are arranged in series relation, the current that flows through the fluorescent lamp and the LED driver circuit is necessarily the same. Further, ignition of the fluorescent lamp requires high voltage (on the order of 100 volts, for example, for a compact fluorescent lamp assembly). This voltage level is not desired for LEDs since it could potentially damage the LED light source.
Thus, a need exists for an inexpensive, compact, low power, efficient combined light assembly and associated combined driver circuit that addresses the competing, disparate requirements of the different types of light sources and overcomes the deficiencies identified above.
The present application discloses a combined lamp assembly that incorporates different, first and second light sources (e.g., a fluorescent lamp and an LED) with a combined driver circuit wherein the LED is not driven by line AC.
The light assembly driver circuit for driving a fluorescent lamp and at least one light emitting diode (LED) preferably includes an integrated driver circuit including an alternating current (AC) circuit that includes at least one ballast coil for driving the fluorescent lamp, and a direct current circuit having a secondary winding inductively coupled with the ballast coil for driving the LED.
In another embodiment, a charge pump circuit is added to a conventional fluorescent lamp circuit. A soft-switching capacitor is included in the charge pump capacitor. The current that is supplied to the LED is determined by the value of the capacitor, the switching frequency, and the DC bus voltage, and thus provides for a delay in current supply to the LED. This delay advantageously protects the LED from the large voltage required to ignite the fluorescent lamp.
A method of driving a lamp assembly that includes at least one fluorescent lamp and at least one light emitting diode (LED) sued a combined driver circuit for supplying both the fluorescent lamp and the LED, includes supplying high voltage AC to a first portion of the driver circuit for the fluorescent lamp; supplying low voltage DC to a second portion of the driver circuit for to the LED; and providing a secondary winding in the second portion of the driver circuit that is inductively coupled with a ballast coil in the first portion of the driver circuit that drives the fluorescent lamp.
A primary benefit is the ability to efficiently integrate the driver circuits for the combined lamp assembly.
Another benefit relates to a low cost solution to the disparate needs of the different light sources.
Yet another benefit is associated with protecting the LED from the high voltage operatively associated with the fluorescent lamp driver circuit.
Still another benefit resides in the compact, low-power dissipating LED driver combined with the fluorescent lamp driver.
A further benefit results from ease of igniting the lamp since the circuit is not loaded during ignition.
A still further benefit is provided by overvoltage protection for the LED.
Further benefits and advantages will become apparent to those skilled in the art from reading and understanding the following detailed description.
Turning first to
An envelope such as a glass envelope or outer bulb 120 may encompass the fluorescent discharge lamp arrangement 102. The outer envelope is secured to one end of the housing and the other end of the housing typically includes a base such as an Edison-style threaded base 122 for mechanically and electrically connecting the lamp assembly to an associated lamp fitting or lamp holder (not shown). An LED 124 is provided in the base and may be connected to a heat sink such as brass ring 126 to dissipate the heat. In addition, a light guide 128, shown in this embodiment as an elongated linear light guide, receives light from the LED disposed in the base and conveys the light (for example, red light emitted by the LED) into the vicinity of or along the exposed length of the discharge tube(s) 108 where the LED red light is advantageously mixed with the white light from the CFL.
The lamp electronics are oftentimes enclosed within the base. The fluorescent lamp is driven by a conventional AC power supply, and includes a ballast coil 130 and associated electronics to initiate an arc in the discharge tube and provide for steady state operation of the CFL. Since the details and operation of the CFL electronics are well known in the art, further discussion is deemed unnecessary to a full and complete understanding of the present disclosure. It is further understood that the discharge tube requires an elevated voltage level (for example, in the range of 100 volts or more) in order to initiate an arc, and thereafter the continued operation of the arc discharge requires a lower voltage level. As noted above, however, the high voltage level can have an adverse impact on a LED light source.
This disclosure uniquely integrates the driving circuits for the fluorescent lamp and LED into a combined solution that advantageously connects the LED driver to the CFL ballast. More particularly, and with reference to
First and second field effect transistors (FET) Q1, Q2 are incorporated into the circuit to protect the LED during ignition of the CFL. As is known, the transistors rely on an electric field to control the conductivity of a channel, particularly the gate terminal controls electron flow from the source to the drain. Here, the resistor bridge R3, R4 controls the gate voltage of field effect transistor Q2 that is supplied by diode D3 and capacitor C1. When the voltage through the ballast coil is high during CFL ignition, the gate voltage of Q2 rises to the level of opening the FET Q2. When Q2 is opened, the gate of Q1 is pulled low, so that Q1 is closed. Accordingly, no current can flow through FET Q1 and the LED is off.
After lamp ignition, however, the voltage in the ballast primary coil is reduced to a steady state operation and likewise the voltage on the secondary winding 136a, 136b is reduced. As a result of the reduced voltage level, field effect transistor Q2 closes because the gate voltage thereof as set by R3 and R4 is lower than the opening voltage. Consequently, the gate voltage of Q1 is then set by R2, R3 so that Q1 is now open and the LED is illuminated as a result of current flow. The circuit arrangement of
These relationships are graphically illustrated in
Co serves as the soft-switching capacitor and the charge pump capacitor. The current that is supplied to the LED is determined by the value of Co, the switching frequency and the DC bus voltage V. Thus, this arrangement provides for a delay in current supply to the LED and thereby advantageously protects the LED from the large voltage required to ignite the fluorescent lamp since the charge pump circuit only provides current flow to the LED after the ignition voltage has subsided.
A relatively simple, alternative LED circuit 160 is shown in
Still another embodiment of a ballast circuit 180 for a fluorescent lamp 182 and a LED 184 in a combined lamp assembly is shown in
The four diodes 196a-d provide the desired rectification of the square wave voltage. Moreover, the RC network 198 in the fluorescent lamp portion of the combined circuit is configured so that Q10 is not turned on until after lamp ignition. Again, this delay and the coupling via the secondary winding protects the LED from the high voltage associated with fluorescent lamp ignition.
The disclosure has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. For example, the LED may be indirectly connected to the secondary winding via a voltage rectifier where the voltage rectifier may include a current generator, a voltage/current generator, a voltage regulator, a timer, and/or an overvoltage protector as is generally known in the art, and without departing from the scope and intent of the present disclosure. It also bears mention that in electronics practice, high voltage generally means in the range of 120-750 kilovolts, and low voltage means 0 to 700 volts. Therefore, the range of high voltage associated with the present disclosure should not be misconstrued with this general understanding of high voltage in the electronics practice. Further, in the present disclosure, the operating current of the LED and the CFL are both on the scale of a few hundred milliamps. Generally, and in the present disclosure, the LED is driven by higher current than the CFL. It is intended that the disclosure be construed as including all such modifications and alterations.
