PCB CONTACT ARRANGEMENT
A printed circuit board (PCB) for mounting electrical components such as LEDs has either contact traces leading to an edge of the PCB, or outward edge protrusions on which an electrically conductive material is deposited, such that the board itself can be used to make electrical contact in a pre-existing, commercially available fitting, such as a wedge or screw-in or bayonet-base fitting designed to receive incandescent light bulbs.
This application is a continuation of U.S. patent application Ser. No. 11/418,919, “PCB Contact Arrangement,” filed 5 May 2006 (which will issue on 11 Nov. 2008 as U.S. Pat. No. 7,450,394), which in turn is a divisional of U.S. patent application Ser. No. 10/714,761, “Bi-Directional LED-Based Light,” filed 17 Nov. 2003 (which issued on 30 May 2006 as U.S. Pat. No. 7,053,560). This application claims priority of and incorporates by reference both of these previous U.S. Patent Applications.
BACKGROUND OF THE INVENTION1. Field of the Invention
This invention relates to lights that use multiple light-emitting diodes, as well as to fixtures for mounting such lights.
2. Description of the Related Art
Incandescent light bulbs are commonly used for indicator lamps, task lamps, general lighting, decorative lamps, warning lamps, traffic lamps and the like. However, incandescent bulbs, and to a lesser extent even plasma-based fluorescent and halogen lights, are generally inefficient in terms of energy use and are subject to frequent replacement due to their limited lifetime. Significant savings can be made by the use light bulbs where the source of light is light-emitting diodes (LED).
LEDs are much more efficient (in terms of lumens per watt) than incandescent and fluorescent lights; moreover, LEDs generally last much longer. This is particularly true of the class of LEDs known as “super-luminescent” or “super-bright,” which have already found uses in such applications as automobile tail lights and traffic signal lights.
Being diodes, one problem with LEDs is that they are direct-current (DC) devices that are easily damaged by too high reverse voltage, whereas the power supplies for many devices that would benefit from the advantages of LEDs deliver alternating current (AC). Even low-voltage light fixtures typically use a 12V AC power source, which is transformed from, for example, 120V AC at 60 Hz.
One common way to provide direct current to LEDs from an AC source is to include in the power-supply circuit a full-wave rectifier and a current-limiting device such as a power resistor. One drawback of this approach is that four rectifying diodes are typically needed and each of these rectifying diodes must carry half the full current load of all the LEDs.
Another known way to provide DC current to LEDs is to include in the power-supply circuit a half-wave rectifier and, again, a current-limiting device such as a power resistor. This is a much simpler circuit than is needed for full-wave rectification, but even it has at least three major drawbacks: First, the light emitted from the LEDs will flicker, for example, at 120 Hz in case the AC power source frequency is 60 Hz. Second, when the supplied voltage is negative, this circuit assumes that the LEDs will evenly divide the reverse voltage among themselves. Failure to do so can lead to a cascade failure of the LEDs; this failure is most prominent in transient conditions. Third, the rectifying diode must carry the full current load of the LEDs.
Even assuming that the power supply problems of the LEDs are overcome, there must still be some convenient way to mount and install the lights themselves. There are of course many different types of light fixtures for the many different common types of incandescent light bulbs. These fixtures feature an array of different types of physical connections with wedge, screw-in, bayonet, flange, bi-pin and other bases. This means that any after-market LED-based light bulb replacement must be able to correctly connect to the different types of existing sockets of the bulbs it is intended to replace. It would be possible to mount LED units within the casings—usually bulbs—of the original lights, but this complicates the manufacture of such LED replacements.
Yet another concern is that incandescent elements can typically be mounted without regard to polarity, whereas existing LED arrangements cannot. When installing an LED replacement in a DC system such as an automobile tail light, there is therefore a risk of incorrect installation because even with a given fitting, the polarity of the wiring is not always the same from one car manufacturer to another.
What is needed is an LED lighting arrangement that eliminates or at least reduces the problems mentioned above. In particular, some fitting is needed to enable easy after-market LED replacement.
In applications that require illumination (such as reading lights) as opposed to simple indication (such as on/off), the LEDs D+ and D− are preferably of the super-luminescent type, for obvious reasons. Even a minimally skillful electrical engineer will be able to choose the actual type of LEDs used, as well as the type and value of the resistor R, to fit the needs of a given application given the specifications of the power source S, in particular, its peak delivered voltage.
Assume for the sake of illustration that when the source S supplies positive voltage, current is flowing in the clockwise direction (viewed as in
Some of the advantages even of the basic embodiment of the invention shown in
The only diodes required are those that actually produce light—no rectifying elements are needed at all.
The invention will work whether the voltage source S delivers alternating or direct current. When operating with a DC voltage source, only one of the LEDs will be active, but on the other hand, the assembly of only three components R, D+ and D− will work equally well regardless of the polarity of the voltage source S.
Each LED D+ and D− is protected from reverse voltage breakdown by the other LED in the pair.
When operating with an AC voltage source, flicker is greatly reduced. In fact, at typical supply frequencies, for example, 60 Hz, D+ and D− will both appear as 120 Hz but totally out of phase with each other; therefore, little flicker will be apparent to a viewer at all.
When powered from an AC source, the peak current of each LED may reach a value higher than the allowed continuous DC current. In such case, the LEDs will emit a higher peak brightness intensity while maintaining lower temperature than when driven at the maximum allowable DC current, which reduces the risk of damage and premature failure.
A separate current-limiting device, Rj, again, usually a resistor, is preferably included in each parallel path in series with the LED pairs. Although not strictly necessary to the invention (a single current-limiting device could be used as shown in
Each LED pair in the array may use the same diode type (and/or color) and be arranged the same as all other pairs, although this is not strictly necessary as long as standard measures (such as adjusting the appropriate resistor values) are taken to ensure proper voltage and current supply to the LEDs. In
The operation of each pair of LEDs in the array will be the same as described above for the single pair D+ and D− shown in
As
After routing, the routes 410-415, 430 are treated, preferably using a standard PCB plating process, to deposit an electrically conductive material such as copper on the inside, upper, and lower surfaces of the routes. The PCB base 300 is then either punched out of the larger PCB 100 by using a pre-designed punch-and-die set or scored and broken along the lines defining the rest (other than the protrusions) of the periphery of the base 300.
Even though LEDs will typically generate less than 0.1 W of power each, applications such as those that have limited space but require high light intensity also require very close packing of multiple LEDs. In existing arrangements, this leads to severe problems of heat dissipation. One advantage of connecting the LEDs in pairs (especially in the multi-LED embodiments of the invention shown below) to form an “AC LED” is that each LED is only “on” about half the time; this reduces generated heat and gives better opportunity for effective heat dissipation. Even disregarding the thermal advantages of the LEDs' 50% duty cycles, the invention still will operate much cooler than a typically halogen bulb, whose operating temperature is as high and potentially dangerous as 200° C.
The width w of the main portion (without the protrusions 410-415) of the base 300 is preferably chosen to be the same or slightly less than the inner diameter of the screw-in fitting 600. When the base 300 is screwed into the fitting 600, the helical inner contact surface 610 of the fitting will electrically contact at least one (and usually all) of the plated protrusions 410-413; the trace T1 will be electrically connected with the other contact 632 of the fitting via the protrusion contact 430. In a different but preferred embodiment of the base 300, the width w is preferably slightly greater than wi; this is described below in conjunction with
The width w of the main portion of the base 300 (not including the protrusions) may then be slightly greater than the inner diameter wi of the fitting 600. When the base 300 is installed, for example, screwed in, it will therefore compress laterally, squeezing together the slots 701, 702. The flexibility of the PCB material itself will bias the protrusions 410-415 outward against the inner contact surfaces 610 of the fitting 600.
Another way to bias the base against the inner contact surface(s) 610 of the fitting 600 would be to mount an electrically conductive compression spring (not shown) on the bottom protrusion 430 and to connect this spring to the trace T1. The biasing force would then be vertical, which would tend to force the upper plated edges of the edges of the protrusions 410-415 into physical and thus electrical contact with the inner contact surface (s) 610 of the fitting 600.
The invention is easily adapted for use in other types of fittings besides the screw-in fitting shown in
The “AC LED” according to the invention may of course also be used in fittings that do not require screwing in or rotation at all.
The usefulness of the configuration shown in
It would also be possible to bend the leads of the LEDs, or to mount them differently, so that they extend laterally out from the base 300 rather than perpendicularly away from its surface.
Still another advantage arises in industries such as the automotive industry. Tail lights in a car are DC devices, but the fittings are usually polarized nonetheless, such that the invention, in particular, the base 300, would be able to fit in the fitting in only one orientation. Because the invention provides an “AC LED,” polarity will not make any difference. On the other hand, the “correct” orientation of the invention for a given car model, or in a given fitting (left as opposed to right, for example) might be such that a single LED pair, as shown in
Note that LEDs are typically so cheap that it would in most cases be better simply to have “idle” LEDs rather than having separate “left-handed” or “right-handed” bases. Rather than allow an LED pair to illuminate to no purpose (for example, the pair facing away from any potential viewers), it would also be possible to route current to the two LED pairs through a switch (double-pole double-throw) so that only one pair is activated at any time; if the PCB is mounted “backwards” then the user can flip the switch and activate the other LED pair.
In this multi-color embodiment of the invention, the LEDs are preferably connected as reversed-polarity pairs as shown in
All LED pairs emitting the same color may comprise one parallel branch of the configuration shown in
At a typical user's normal reading or working distance from the assembly, the light from the LEDs will be so “mixed” that the user will not be able to distinguish any red, green, or blue hues unless he is looking directly at the assembly. When looking at an illuminated object located at distances beyond about 20 cm from the assembly, and possibly even closer, the user will perceive the mixture of red, green, and blue as pure white, or, rather, full-spectrum light illuminating the object. Contrast this with a conventional “white” LED, which is simply a blue-light LED coated with phosphorous so as to introduce a yellow component to the spectrum and produce a “pseudo-white” color.
In one prototype of the multi-element embodiment of the invention illustrated in
It is of course not necessary for the LEDs in the multi-element embodiment shown in
By including the two parallel connected, reverse-polarity LED dies within a single casing, a single component is provided that implements the AC LED according to the invention. Such a component could be used to implement any LED pair described in any embodiment of this invention.
Claims
1. A lighting arrangement comprising:
- a source of electrical power;
- a printed circuit board (PCB) base having front and rear surfaces;
- a plurality of light-emitting diodes (LEDs) driven by the power source and mounted on the PCB base;
- at least two electrically conductive traces on a planar surface of the PCB base leading electrical current between the source of electrical power and the LEDs;
- electrical trace contacts formed on the PCB base in electrical contact with respective ones of the traces and extending to a contact edge of the PCB base such that when the PCB base is inserted into a standard, pre-existing, commercially available wedge-based light fitting designed to receive an incandescent light bulb, each electrical trace contact is pressed into electrical contact with a mating contact element in the wedge-based light fitting, the LEDs thereby replacing the incandescent light bulb.
2. A contact surface arrangement for a printed circuit board (PCB) for mounting at least one electrical component comprising:
- a base cut from a PCB substrate;
- at least one lateral base protrusion mating with at least a first internal, at least partially electrically conductive, surface of a pre-existing, commercially available fitting;
- an electrically conductive material deposited on an outer edge of the lateral base protrusion;
- at least one electrically conductive trace on a planar surface of the base, the trace being in electrical contact with the electrically conductive material deposited on the lateral base protrusion so as to create a first electrical path to at least one of the electrical components; and
- at least one slot in the base extending in an axial direction of the fitting, each slot comprising a physical opening in the PCB board itself;
- in which the base is wider than an internal diameter of the fitting, but by no more than a total width of the slot(s), such that the base, upon installation in the fitting, biases the lateral base protrusions outward and into contact with the first internal surface of the fitting.
3. An arrangement as in claim 2, in which the electrical component is a light-emitting diode and the fitting is a standard fitting designed to receive an incandescent light bulb by insertion of the bulb in an axial direction.
4. An arrangement as in claim 2, in which:
- the fitting is a standard bayonet fitting and the internal surface has indexed indentations; and
- the lateral base protrusions have the same indexing as the indentations.
5. An arrangement as in claim 2, in which:
- the standard fitting is a screw-in fitting and the internal surface has threading with a pitch; and
- on either side of the base portion, the lateral base protrusions have the same pitch as the pitch of the threading.
Type: Application
Filed: Nov 10, 2008
Publication Date: Mar 12, 2009
Inventor: JAMES K. NG (Seattle, WA)
Application Number: 12/268,439