Title:
FLUORESCENT LAMP STROBING CIRCUIT
United States Patent 3753040


Abstract:
Strobing circuit for a fluorescent lamp, preferably an ultraviolet lamp, wherein a Triac connects the lamp to a ballast winding, the Triac being controlled by a two transistor multivibrator supplied with DC voltage through a diode connected to a tap of the ballast winding. The resistor is connected in parallel with the Triac to conduct a small amount of current when the Triac is non-conductive and to keep the lamp ionized.



Inventors:
QUENELLE R
Application Number:
05/206606
Publication Date:
08/14/1973
Filing Date:
12/10/1971
Assignee:
IMS CORP,US
Primary Class:
Other Classes:
315/97, 315/105, 315/202, 315/DIG.7
International Classes:
H05B41/34; H05B41/38; (IPC1-7): H05B41/34
Field of Search:
315/241S,DIG
View Patent Images:
US Patent References:
3649869APPARATUS FOR LIGHTING DISCHARGE LAMPS1972-03-14Nomura et al.
3611024SEMICONDUCTOR APPARATUS FOR CONTROLLING THE BRIGHTNESS OF A DISCHARGE LAMP1971-10-05Nakatsu et al.
3609452LAMP DRIVER CIRCUIT1971-09-28Skirvin
3307070Power control system1967-02-28Hutson



Primary Examiner:
Kominski, John
Claims:
I claim as my invention

1. In a strobing circuit for a fluorescent lamp having first and second terminal means at opposite ends thereof, a ballast including a winding having first and second end terminals and an intermediate tap, means connecting said first terminal means of said lamp to said first end terminal of said winding, controlled switching means having a first terminal connected to said second terminal means of said lamp, a second terminal connected to said second end terminal of said winding and a control terminal, means for connecting said intermediate tap and one of said first and second end terminals of said winding to an AC voltage source to develop during non-conduction of said switching means a voltage between said first and second end terminals of said winding substantially higher than the voltage of said source, and a pulsing circuit connected to said control and second terminals of said switching means and arranged to periodically apply a pulse to render said switching means conductive and to apply a high voltage from said winding to said lamp and substantially instantaneously initiate conduction through said lamp, said ballast winding being thereafter operative as an inductive impedance to limit current through said lamp.

2. In a circuit as defined in claim 1, said controlled switching means comprising a solid state device operative to conduct current in either direction upon application of a control signal to said control terminal.

3. In a circuit as defined in claim 1, resistance means connected in parallel relation to said controlled switching means and having a value such as to maintain during periods of non-conduction of said switching means a current through said lamp equal to a small fraction of the current when said switching means is conductive but sufficient to maintain energization of said lamp.

4. In a circuit as defined in claim 3, said resistance means having a value of on the order of 800,000 ohms.

5. In a circuit as defined in claim 1, said winding having a second tap between said first end terminal and said intermediate tap, and said first terminal means of said lamp comprising a pair of terminals connected to a filament within said lamp and connected to said second tap and said first end terminal of said winding.

6. In a circuit as defined in claim 5, said second end terminal of said winding and said intermediate tap thereof being connected to said AC source, said winding having a third tap between said second end terminal and said intermediate tap, a capacitor having one terminal connected to said second end terminal of said winding, a diode connected between said third tap and the other terminal of said capacitor to develop a DC voltage across said capacitor, and means for applying said DC voltage to said pulsing circuit for operation thereof.

7. In a circuit as defined in claim 6, said pulsing circuit comprising a multivibrator including first and second transistors and circuitry for rendering said transistors alternately conductive, said first transistor being operative when conductive to render said switching means conductive and said second transistor being operative when conductive to render said first transistor non-conductive.

8. In a circuit as defined in claim 7, adjustable resistance means for controlling the duration of the time interval of conduction of said second transistor, said first transistor being conductive for a time interval of generally fixed duration independent of the time of conduction of said second transistor and sufficient to insure conduction of said switching means.

9. In a circuit as defined in claim 8, each of said transistors comprising a base electrode and first and second output electrodes, means including capacitors providing cross-connections between said base electrodes and said first electrodes for rendering said transistors alternately conductive, said controlled switching means comprising a solid state device operative to conduct current in either direction, said control electrode of said switching means being connected directly to said second output electrode of said first transistor.

Description:
This invention relates to a fluorescent lamp strobing circuit and more particularly to a relatively simple circuit which uses standard parts and is economically manufacturable while being highly reliable and efficient and readily adjustable.

Strobing circuits have heretofore been proposed for periodically flashing a fluorescent lamp for various purposes. For example, a "black light" or ultraviolet fluorescent lamp may be strobed to periodically illuminate a poster or other display imprinted or painted with designs or indicia of fluorescent materials, to attract attention thereto or to produce exciting and entertaining visual effects. In general, such strobing circuits have operated by applying a high voltage impulse between opposite end connections of the fluorescent lamp, of sufficient magnitude to cause ionization within the lamp and to generate a flash of light. For example, the circuit has been proposed in which the secondary winding of a step-up transformer is connected to the end connections of a lamp with the primary of the transformer being connected through a silicon controlled rectifier to a low voltage DC source including a capacitor connected through a diode to the secondary winding of a step-down transformer having a primary winding connected to an AC supply line. The silicon controlled rectifier is controlled from a timing circuit, also energized from the DC source. This type of circuit is relatively complex, requires special parts and is inefficient and unreliable, particularly with respect to the required flashing of a cold lamp. Other types of prior art circuits have similar disadvantages.

This invention was evolved with the general object of overcoming the disadvantages of prior circuits and of providing a circuit which is relatively simple in construction and operation while being efficient, readily adjustable and reliable.

According to an important feature of the invention, a conventional type of ballast is employed having a tapped winding, with one end terminal of the winding and one tap being connected to an AC supply and with end connections of the lamp being connected to end terminals of the winding through controlled switching means. A pulsing circuit is connected to a control terminal of the controlled switching means and is arranged to periodically render the controlled switching means conductive to energize the lamp. With this comparatively simple arrangement, using standard types of parts, highly efficient and reliable operation is possible.

An important feature of the invention is in the connection of resistance means across the controlled switching means, the resistance means having a value such as to maintain during periods of non-conduction of the switching means a current through the lamp equal to a small fraction of the current therethrough when the switch means is conductive, but sufficient to maintain ionization of the lamp. With this arrangement, much more efficient and reliable operation is possible since the lamp is never completely de-ionized.

In accordance with another specific feature, one filament of the lamp is connected between an end terminal and a tap of the ballast winding in a manner such as to heat the filament initially and also during times between strobing of the lamp, to facilitate the initial strobing of the lamp and to further assist in keeping the lamp ionized between strobing times.

A further feature of the invention is in the connection of the pulsing means to a tap of the ballast winding to supply operating voltage thereto, a diode and capacitor being preferably utilized to supply a DC operating voltage. Preferably, the pulsing circuit may comprise a pair of transistors connected as a free-running multivibrator. The switching means preferably comprises a Triac, conductive in both directions, and having a gate electrode directly connected to an output electrode of one of the transistors.

Specific features relate to the construction of the multivibrator circuit and to the provision of means for adjusting the period of operation thereof, to adjust the time interval between flashing of the lamp.

Another feature of the invention is that by the simple provision of a switch, manually operable, across the controlled switching means, the operation can be readily changed from strobe to continuous, this feature being possible because of the use of the ballast which may be a standard commercially available ballast.

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate a preferred embodiment and in which:

FIG. 1 is a front elevational view of a fluorescent lamp unit incorporating a strobing circuit according to the invention;

FIG. 2 is a rear elevational view of the unit of FIG. 1, but illustrating a support member in a position different from that illustrated in FIG. 1;

FIG. 3 is a side elevational view of the unit of FIG. 1, showing the support member positioned for supporting the unit from a flat surface;

FIG. 4 is a side elevational view similar to FIG. 3 but illustrating the support member positioned in supporting the unit from a wall; and

FIG. 5 is a schematic diagram of the strobing circuit of this invention.

Reference numeral 10 generally designates a fluorescent lamp unit which incorporates a strobing circuit constructed in accordance with the principles of this invention. In general, the unit 10 comprises a lamp 11 which may preferably be a "black light" or ultraviolet lamp, mounted in a housing 12 which supports, behind the lamp 11, a reflector 13 including a central section 14 and two side angularly disposed sections 15 and 16.

The housing 12 is supported by means of a specially formed support member 18 which includes inwardly turned end portions 19 and 20 inserted into sockets in opposite ends of the housing 12, a pair of portions 21 and 22 which, in the position shown in FIG. 1, extend downwardly, and a pair of portions 23 and 24 which extend angularly from the lower ends of the portions 21 and 22 to ends integrally joined together. In the position shown in FIG. 1, and as also depicted in the side view of FIG. 3, the portions 23 and 24 rest on a flat surface to support the housing 12, which may be tilted to any desired position by rotation about the common axis of the portions 20 and 19.

Alternatively, the support member 18 may be positioned as shown in FIGS. 2 and 4 to hang the unit from a screw 25, or the like, affixed in a wall 26. In this case, also, the unit may be adjustably rotated about the common axis of the portions 19 and 20 to point the lamp in a desired direction.

As shown in the rear view of FIG. 2, two controls are provided. A slide switch 27 is provided for selectively obtaining continuous or strobe operation and a knob 28 is provided, rotatable in a clockwise direction to initially close a switch and energize the unit with further rotation being effective to adjust the rate of the strobing operation, when the slide switch 27 is positioned for a strobing operation.

Referring now to FIG. 5, reference numeral 30 generally designates the electrical circuit of this invention. The circuit 30 comprises a ballast 31 which includes a suitable core of magnetic material and a winding 32 thereon, the winding 32 having end terminals 33 and 34, a pair of filament taps 35 and 36 and a supply line tap 37. In the circuit as illustrated, the end terminal 34 is connected to one supply line 39 while the tap 37 is connected to a second supply line 40 through an on-off switch 41, operable by the knob 28, above described. Lines 39 and 40 may be connected to a conventional 117 volt 60 cycle supply line.

The end terminal 33 and the tap 35 are connected to terminal prongs 43 and 45 of one end connection of the lamp 11, such prongs 43 and 44 being connected to one filament of the lamp 11. The end terminal 34 is connected through a controlled switching means in the form of a Triac 45 to prongs 47 and 48 at the opposite end connection of the lamp 11. Prongs 47 and 48 may be connected to a filament within the lamp 11 but with the circuit as illustrated, no heating current is applied to the filament.

A gate or control electrode of the Triac 45 is connected to the emitter of a transistor 49 which with a second transistor 50 forms a free-running multivibrator circuit. The collector of the transistor 49 is connected through a resistor 51 to a line 52 and is also connected through a capacitor 53 to the base of the transistor 50 which is connected through a resistor 54 to a line 52. The base of the transistor 49 is connected through an adjustable resistor 55 in a fixed resistor 56 to the line 52 and is also connected through a capacitor 57 to the collector of the transistor 50 which is connected through a resistor 58 to the line 52. The emitter of the transistor 50 is connected to a line 60 which is connected to one electrode of the Triac 45, the end terminal 34 of the winding 32 and to the supply line 39.

A DC voltage is applied between the lines 52 and 60. For this purpose, line 52 is connected through a diode 61 to the tap 36 of the winding 32 and a capacitor 62 is connected between the lines 52 and 60. Diode 61 operates as a rectifier to convert the relatively low voltage between tap 36 and terminal 34 into a DC voltage across capacitor 62.

The adjustable resistor 55 is operated by the knob 28 and the slide switch button 27 operates a switch 63 which is connected in parallel with the Triac 45. A resistor 64 is also connected in parallel with the Triac 45 for the purpose of maintaining ionization of the lamp 11 during strobing operation, as hereinafter described.

The operation will first be described with the assumption that the slide switch button 27 is positioned to close the switch 63. When the switch 41 is closed, by rotating the knob 28 clockwise, the ballast 31 operates as a transformer to apply current to the filament connected to the prongs 43 and 44 and at the same time, a relatively high starting voltage, which may be on the order of 175 to 200 volts RMS is applied between the end connections of the lamp 11 through the combination of the starting voltage and the heating of the filament, the lamp ignites, the gas therewithin being ionized. The lamp 11 then conducts relatively heavily and the voltage thereacross drops to a relatively low value, on the order of 60 volts RMS, maintained fairly constant and independent of current. The excess voltage, i.e. the difference between the line voltage and the operating voltage of the lamp is absorbed by the ballast winding which operates essentially as an inductance.

Such operation is, of course, similar to that of a conventional fluorescent lamp with a rapid start ballast.

When the switch 63 is opened, for strobe operation, the Triac 45 operates as a periodically closed switch, the Triac 45 being highly conductive whenever a signal of sufficient amplitude is applied to the control or gate electrode thereof, from the transistor 49. An important feature is that when the Triac 45 is non-conductive, a small current flows through the resistor 64 to keep the gas within the lamp 11 ionized so that the lamp can be instantaneously flashed with a very high degree of reliability whenever the control signal is applied to the gate electrode of the triac 45. The value of the resistor 64 is preferably high enough, however, to produce very little light output from the lamp.

In describing the operation of the multivibrator, it may be assumed that the transistor 50 is initially conductive while the transistor 49 is non-conductive. With transistor 50 conductive, the collector is at a relatively low potential and through the capacitor 57, the base of the transistor 49 is held at a potential less than that of the emitter thereof, so that the transistor 49 does not conduct. However, the charge of the capacitor 57 is gradually changed through current flowing through the resistors 55 and 56 and at a certain time, the base of the transistor 49 goes positive with respect to the emitter thereof, initiating conduction of the transistor 49. When transistor 49 starts to conduct, the potential of the collector thereof drops and through the capacitor 53, the potential of the base of the transistor 50 is dropped to cut off conduction of the transistor 50. With transistor 49 heavily conductive, enough current flows through the gate electrode of the Triac 45 to cause conduction thereof and flashing of the lamp 11.

With transistor 49 conducting and transistor 50 non-conducting, the charge of the capacitor 53 is gradually changed by current through the resistor 54 until the base of the transistor 50 is at a potential above that of the emitter thereof, whereupon the transistor 50 again starts to conduct, cutting off conduction through the transistor 49. It will be observed that the "on" time, i.e. the time during which the transistor 49 is conducting, is of substantially fixed duration, the capacitor 53 and the resistor 54 having fixed values. A fixed "on" time is desirable, to insure proper flashing of the lamp 11. The "off" time, i.e. the time during which the transistor 49 is non-conducting, is however adjustable by adjustment of the resistor 55, so that the rate at which the lamp is flashed or strobed is adjustable. The resistor 55 preferably has a logarithmic taper such as used in conventional audio potentiometers, which provides a more linear relationship between the degree of rotation of the knob 28 and the rate of flashing or strobing of the lamp.

It is important to note that the ballast 31 may be a conventional type of rapid-start ballast and all of the other components may be standard types, no special components being required. By way of illustrative example and not by way of limitation, the various components may be of the following types or have the following values:

Referance Numeral Value or Type 49,50 2N5172 51 2200 ohms 53 0.047 microfarads 54 820,000 ohms 55 500,000 ohms 56 10,000 ohms 57 5 microfarads 58 22,000 ohms 61 1N4003 62 60 microfarads 64 820,000 ohms

It is noted that the multivibrator in the illustrated circuit acts as a pulsing circuit to periodically apply a pulse to the control or gate electrode of the triac, but other forms of pulsing circuits may be used and in particular, the circuitry may be used in a music follower operation, wherein the pulsing circuit is controlled from suitable filters connected to the output of an audio amplifier, to pulse the triac in synchronism with the "beat" of the music, for example.

It will be understood that other modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.