US3525012A - Self-contained transformer and low voltage lamp - Google Patents

Description

g- 1970 P. c. DIMITRACOPOULOS ET AL 3,525,012

SELF-CONTAINED TRANSFORMER AND LOW VOLTAGE LAMP Filed Sept. 25, 1967 United States Patent T US. Cl. 315-70 1 Claim ABSTRACT OF THE DISCLOSURE An illumination source converting electric energy to light. A combination of a power transformer and an electric lamp, the secondary winding of the transformer being a part of the light-emitting filament and lying wholly within the lamp, thereby eliminating the leads and contacts which usually connect an electric lamp to its source of electric energy.

FIELD OF INVENTION This invention relates to electric projection lamps, i.c. to lamps used to provide the illumination source of projectors.

DESCRIPTION OF PRIOR ART It is well known that electric incandescent lamps radiate light when an electric current passes through, and thereby heats, their filament. It is also well known that the higher the temperature of the filament, the greater the illumination efliciency. Unfortunately, it is not possible to exceed certain temperatures without melting or sublimating these filaments, and therefore by keeping their tem peratures at a relatively lower value, the major part of the electric energy is converted into unwanted heat. This is a doubly costly process, not only because of the resulting low light efiiciency, but also because of the bulky, heavy and expensive mechanisms that must be provided (such as motor driven blowers) to circulate the air around such lamps and thus avoid excessive heat buildnps, which, in turn, will burn the filaments or melt the lamps and other parts and components mounted or located near them.

It is evident that the heavier the filament (i.e. the greater its diameter) the better it will withstand higher temperatures. Filaments are made today mainly from refractory metals, such as tungsten, each having a certain specific resistivity. It follows that, for a given illumination, the voltage, the filament diameter and its length must be properly adjusted. In order to have a short filament (and thus approximate a point-source of light which is very often ideally suited for projectors), the voltage must be lowered. In order to withstand greater heating, the filament must be heavy. But the mains power line is usual ly 110 volts (or up to 220 volts in some countries), and therefore, lamps had to be built for these voltages, which meant fine and long filaments, which in turn were burning fast and did not approximate a point source of light.

Another approach was the so-called low voltage 3,525,012 Patented Aug. 18, 1970 lamps, usually about 12 or 24 volts. Although this lower voltage is still not sufficiently low, they necessitate quite heavy and bulky transformers, having approximately the weight and size of the blowers and motors that they are supposed to eliminate. Thus, no net gain was possible.

As mentioned briefly above, even 12 or 24 volt operation is still above the desired values. However, there are limitations as to how low this voltage can be dropped: For low voltage, high intensity applications, the amperage becomes excessive, necessitating heavy connecting leads that must pass through the glass envelope of the lamp and this causes considerable sealing problems.

It is evident that the low voltage winding of the transformer must also be of substantially heavy wire and the connecting leads from the transformer to the lamp must also be quite heavy.

OBJECTS OF THE INVENTION It is the object of this invention to provide a novel and unique combination of low voltage lamp and transformer, both the lamp and the transformer forming one single integrated unit.

It is a further object of this invention to provide such lamp-transformer combination that totally eliminates the connecting leads from the secondary of the transformer to the lamp socket.

It is a further object of this invention to provide such a lamp-transformer combination whereby the secondary of the transformer forms part of, and is enclosed inside, the projection lamp.

It is a further object of the present invention to pro vide such lamp-transformer combination, which totally eliminates any and all leads leading from the filament socket pins and/or socket contacts, and thereby eliminates the sealing problems.

It is a further object of the present invention to provide such lamp-transformer combination, which due to its special configuration and attributes, makes possible a low wattage, long life, high temperature and high efficiency filament, which may, if desired, approximate a point source of light, or alternatively, have a desired size and shape.

It is a further object of the present invention to provide such a lamp-transformer combination, fed with electric alternating current of higher than the mains frequency, and/ or chopped portions or such alternating frequency, thereby substantially reducing the size and weight of the transformer primary and transformer iron core.

Other objects of the invention will become evident from the ensuing description, illustration and claim.

SUMMARY The invention achieves its objectives and solves a large part of the problems above-described by providing a lamp whose filament, or a suitable part of such filament, constitutes the secondary winding of a power transformer, such secondary winding being wholly within, or forming a part of, the lamp itself, which lamp is preferably doughnut-shaped and may surround the transformer primary or the transformers iron core.

3 This transformer-lamp combination feeds the lightemitting portion of the filament with as low a voltage as desired, and since the power to the filament is inductively transferred, it does not require the usual heavy connecting wires and contacts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view taken along line 1-1 of FIG. 2.

FIG. 2 is a somewhat simplified view of a preferred em-- bodiment of the invention.

FIG. 3 is a partly sectional, side elevation view of another preferred embodiment of the present invention. FIG. 4 is a sectional view along line 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described by reference to certain preferred specific embodiments thereof, however, it will be understood that the principles of the invention can be carried out by specifically different physical means, and furthermore, in using words of limited meaning, for the better understanding of the particular types and embodiments chosen for description and illustration, it is not intended to exclude variations of those details, which properly fall within the scope of the invention or claims.

As previously stated, the present invention solves the bulk, weight, leads, sealing and other problems associated with the usual type of projection lamps and their associated power supplies. This is achieved by combining the secondary of a power transformer with the filament leads of the lamp itself.

Referring to the accompanying illustrations, 5 and 5 designate the (usually laminated) iron core of a transformer, while 7 is the bobbin containing the primary transformer winding 9.

The low voltage secondary of the transformer is designated by numerals 11 and 13, and forms a complete loop or circle around the transformer core 5 and 5. Part 11 of this loop or circle is of heavy metallic construction, for example a copper wire, while 13 is the filament itself, which may be of tungsten, as is the usual practice today, or other appropriate material. By means of spacers or supports, for example ceramic or mica support plates 17, this secondary loop is held and properly positioned within a glass or quartz envelope 15. In other words, the transparent lamp envelope is doughnut-shaped and envelops one leg of the transformer, while the filament and is metallic support constitute the low voltage secondary of the transformer. In this way, the pins or connectors, usually attached on the socke of the projection lamp are totally eliminated, as are the leads passing through the glass or quartz envelope connecting these pins or contacts to the filament. The usual leads connecting these pins or contacts to the power supply are also eliminated, and thus this transformer-lamp combination makes possible the construction of lamps feeding their filament not only with say 12 volts, but even a small fraction of a volt.

It is well known that:

(l) W: V R or Watts: (Volts) Ohms For higher illumination, it is necessary to pass through the filament as many watts as it is practical, while at the same time, the largest possible percentage of these watts must be converted to light and not unwanted heat. But it must not be forgotten that this is achieved by raising the filament temperature to the highest possible temperature before this high temperature melts or sublimates it. Of course, the larger the diameter of this filament the greater its mechanical strength at a given temperature, but making a filament large in diameter and small in length (for a given wattage dissipation) may only be done, according to the above Formula 1, if the voltage is dropped substantially (since the watts are proportionate to the square of the volts).

It can now readily be seen how this novel lamp permits the feeding of the filament 13 with extremely low voltage, without the associated problems connected with high intensity currents, since:

A reflecting mirror 21 may also be inserted within the lamp envelope, in the usual fashion, or the glass or quartz envelope may be shaped in the proper fashion, just behind the filament, and metalized in order to act as a reflecting mirror, as it is well known in the art. It is evident that this mirror may also be placed outside the glass or quartz envelope, and supported on the transformer core or other appropriate and desired support.

The transformer core may be built in two distinct parts, each being substantially L-shaped, as shown in FIG. 1, part 5 may be hingedly supported on part 5, for example by means of pin 23 or other suitable method. In this fashion, by lifting member 5 in the direction of arrow A, it is possible to withdraw, insert, or replace the doughnut-shaped lamp.

Obviously, other equally suited methods may be employed to open the transformer core in order to remove the lamp.

The usual means power frequency is 60 cycles per second in the American continent and usually 50 cycles per second in Europe and other parts of the world. At these frequencies, in order to arrive at a sufliciently high inductive coupling between the transformer primary and secondary windings and thus obtain an acceptable transformer efiiciency, it is necessary to wind these windings around a fairly substantial amount of iron core. This iron core adds to the bulk and weight of the transformer, which of course, is a most unwanted feature. Fortunately, the higher the current frequency, the lower the amount of iron core, and after a certain frequency level, the coupling of the windings may be achieved without the interposition of any iron core. It is therefore an advantage to increase the mains frequency to a higher level and thereby greatly reduce the iron core, weight and bulk.

When higher frequencies are employed as above described, especially when the looped iron core is not essential, a configuration substantially as that illustrated in FIGS. 3 and 4 is indicated. Numerals indicating various parts are the same used in the preceding description, in connection with FIGS. 1 and 2. The primary 9 may be optionally split in two, and the transparent envelope 15, containing the secondary winding, i.e. lead 11 and illuminating element 13, may be placed between its two parts, as shown in these FIGS. 3 and 4. In FIG. 3, for illustrative purposes, one part of the transformer primary winding is shown in a side elevation view, while the other part and the transparent envelope with its enclosed secondary winding (lead 11 and illuminating element 13) have been shown in a sectional view.

If the power frequency warrants it, the center core 25 may be made of any suitable, magnetically permeable, material, such as sintered or powdered iron, etc., in order to achieve a better magnetic coupling between the windings.

In the above introduction and description it is repeatedly stated or implied that these novel lamps are particularly well suited as illumination sources for projectors and the like. While this is so, it must be made clear that the invention is equally well suited and may be equally well used not only in connection with projectors, but for any and all applications requiring an illumination source, including, of course, any and all lamp applications, like illumination of rooms, streets, etc., etc.

The invention has been described by reference to certain preferred specific embodiments thereof, however, it will be understood that the principles of the invention can be carried out by specifically different physical means, and furthermore, in using words of limited meaning, for the better understanding of the particular types and embodiments chosen for description and illustration, it is V=I x R or Volts=Amperes Ohms not intended to exclude variations of those details, which properly fall within the scope of the invention or claim.

What is claimed is:

1. An electric illumination source comprising a high frequency electric voltage transformer at least a part of Whose secondary winding constitutes the light producing element, comprising a bobbin-shaped transformer primary winding and an annular secondary winding totally enclosed within a substantially annular transparent envelope, a small portion of said secondary winding consituting the light emitting element, said primary winding and secondary winding being substantially coaxially superimposed upon one another and being electromagnetically coupled to one another.

References Cited UNITED STATES PATENTS JAMES W. LAWRENCE, Primary Examiner 10 C. R. CAMPBELL, Assistant Examiner U.S. Cl. X.R.

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