US2875379A - Gas discharge lamp power supply - Google Patents

Description

Feb. 24, 1959 G. T. PORTER GAS DISCHARGE LAMP POWER SUPPLY Filed Feb. 4, 1957 4 .ll'lOlll INVENTOR. GT. PORTER Q H Mom A TTORNEYS 2,875,379 Ice Patented Feb. 24, 1959 2,875,379 GAS DISCHARGE LAMP POWER SUPPLY Grady T. Porter, Dewey, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application February 4, 1957, Serial No. 638,158

6 'Claims. (Cl. 315-106) This invention relates to an improved power supply for gas discharge lamps. 1

Various forms of optical analyzers have recently been developed for the analysis of sample streams in terms of the radiation absorption properties thereof. Someof these analyzers utilize radiation in the ultraviolet spectrum. Such radiation is commonly produced by electrical discharge lamps which are filled with a gas, such as hydrogen or Xenon, for example. When such a gas discharge lamp is employed in an optical instrument, it is important that the radiation produced be of constant intensity. This requires that'a direct current be utilized to energize the lamp. The gas discharge lamp is essentially a current operated device. However, a starting voltage of the order of three times the voltage necessary to maintain the discharge is required. to cause initial ionizationof the gas. For this reason, a conventional power supply utilizing a rectifier and voltage regulator cannot be employed.

In some applications of these optical instruments, it is desirable that the analyzer be as compact as possible and dissipate a minimum amount of heat. It thus becomes xenon, for example.

a discharge lamp 10 which is provided with an anode 11 and. a cathode 12, the latter being in the form of a fila= ment. Tube lll is filled with a gas, such as hydrogen or The power supply circuit is energized by a source of alternating current 13 which is connected across the primary winding 14 -of a transformer 15. The first end terminal of a first secondary winding 17 of transformer 15 is connectedto one terminal of filament 12. The second end terminal and the center tap of transformer winding 17 are connected to terminals 18 and 19, respectively, which are adapted to be engaged by a switch 20. Switch 20 is actuated by a relay coil 21 so as to engage terminal 18 when the relay is deenergized and to engage terminal 19 when the relay is energized.

Transformer 15 is provided with a second secondary winding 22. The first end terminal of transformer winding 22 is connected through an inductor 23 to the anode 11 of discharge tube It). The second end terminal of transformer winding 22 is connected through a capacitor 24 to a terminal 25 which is adapted to be engaged by a switch 26. Switch 26 is connected to a terminal 27 which is connected to filament 12. Switch 26 is also connected to a switch 28. Switch 28 is adapted to engage a terminal 29 which is connected through a capacitor 30 to anode 11. Switches 26 and 28 are operated in important to reduce the initial starting voltage as soon, 7

as the discharge is initiated so as to minimize the heat dissipated in the power supply. For example, in one particular lamp which has been employed in an ultraviolet analyzer, the normal operating power dissipation is of the order of 21 watts. However, the power dissipation in the supply and lamp tiated is of the order of 59 watts.

a In accordance with the present invention, there is provided an improved power supply which automatically reduces the magnitude of the starting voltage when the dis- 1 charge is initiated. The initial starting voltage is provided by means of a series resonant circuit which pro vides the initial high voltage required to fire the tube. The normal operating voltage is supplied from a rectifier which has a current regulator connected to the output thereof. Switching means are provided to remove the resonant circuit from the tube when the discharge is.

initiated so that the normal operating current is supplied from the current regulator circuit.

' Accordingly, it is an object of this invention to provide an improved source of constant intensity radiation for use with optical analyzers.

Another object is to provide apparatus for supplying a constant direct current to a gas filled electrical discharge tube.

A further object is to provide a power supply for a gas discharge tube which automatically reduces the magnitude ,of the voltage across the tube when the discharge 1 is initiated. I A

Other objects, advantages and features should become apparent from the following detailed description, which is taken in conjunction with the accompanying drawings,

which is a schematic circuit diagram of the gas discharge lamp power supply. of this invention. e Referring now to the drawing in detail, there is shown after the discharge is iniunison by a relay coil 31. These switches engage respective terminals 25 and 29 when relay coil 31 is deenergized.

As discussed in detail hereinafter, the circuit thus far described is employed to provide the high voltage required to initiate the discharge through tube 10. During minals of transformer winding 35 are connected through respective rectifiers 36 and 37 to the first terminal of a filter inductor 38. Filter capacitors 39 and 40 are connected between respective end terminals of inductor 38 and terminal 27. This rectifier and filter circuit provides a substantially constant direct potential to maintain the discharge through lamp 10.

A transistor current regulating circuit is employed to maintain an absolutely constant operating current. The second terminal of inductor 38 is connected to the emitter of a P-NP transistor 42. The grounded collector of transistor 42 is connected through a variable resistor 43 to an output terminal 44. The base of transistor 42 is connected to the collector of a N-P-N transistor 45. The emitter of transistor 45 is connected to terminal 27 through a resistor 46. The emitterof transistor 45 is also connected to ground through series connected transistor diodes 47 and 48. These diodes provide substantially constant voltage drops, i. e., the so-called Zener voltage. Terminal 44 is connected to emitter of a P-N-P transistor 50. The collector of transistor 50 is connected to the base of transistor 45 and to terminal 27 through a capacitor 51. The base of transistor 50 is connected to terminal 27 through a resistor 52. The base of transistor 50 is also connected to ground through a transistor diode 53.

This transistor current regulator maintains a constant output current between terminals 44 and 27. If the current between these terminals should increase, for example, the base of transistor 50 becomes less. negative with respect to the emitter so as to decrease the current through the emitter-base junction of transistor 50. This decreases the current flowing from the collector of transistor 50 through the base-emitter junction of transistor 45. As a result, the current through the emitter-base junction of transistor 42 and into the collector of transistor 45 decreases to cause a decrease of current in the circuit from inductor 38 through the emitter-collector path of transistor 42 to terminal 44. This decreases the current between terminals 44- and 27 to compensate for the original increase in output current. Variable resistor 43 controls the bias of transistor 50 to provide an adjustment of the magnitude of the regulated current.

Terminal 44 is connected through a pair of parallel connected rectifiers 56 and 57 to the first terminal of relay coil 31. The second terminal of relay coil 31 is connected to the first terminal of relay coil 21. The second terminal of relay coil 21 is connected to anode 11 through inductor 23. In the absence of a discharge through tube 10, relay coils 21 and 31 remain deenergized so that switches 20, 26, and 28 are in the illustrated positions. This results in the full voltage across transformer winding 17 being applied to filament l2. Inductor 23 and capacitor 30 constitute a high Q series resonant LC circuit which is connected across transformer winding 22. Capacitor 24 is a D. C. blocking condenser and is large compared to capacitor 30 so as to have a negligible effect on the tuning of the resonant circuit. Thus, most of the resonant voltage is developed across capacitor 30 which is connected across discharge tube 10. A relatively small voltage across transformer winding 22 thus develops a sufficiently high voltage across capacitor 30 to cause the lamp to fire. Once the discharge is initiated, a direct current is supplied to the lamp from terminals 44 an 27 of the regulated power supply circuit. 7

The direct current from the power supply circuit energizes relay coils 21 and 31 to disconnect the series resonant circuit from discharge tube 10. Relay coil 21 also operates to reduce the magnitude of the voltage applied across filament l2. Rectifiers 56 and 57 initially prevent the flow of alternating current from transformer winding 22 to ground. A choke coil can serve the same purpose.

The power supply circuit of this invention thus provides an initial voltage of sufiicient magnitude to fire the gas discharge tube. As soon as the tube is fired, the initial starting voltage is automatically removed and a regulated direct current is supplied to the tube. The" amount of heat dissipated by the circuit is thus reduced as soon as the tube is fired. It is desired that the transistors and the voltage regulating circuit be selected so as to dissipate a minimum amount of heat. These transistors should be selected so as to provide elements which are substantially insensitive to temperature changes.

As a specific example of the present invention, the following components were employed in the illustrated circuit.

Component Value 39 125 microfarads. 4t) -c 125 microfarads. 24 2 microfarads. 51 1 microfarad. 30 0.35 microfarad. 23 2 henries. 38 0.8 henry. 46 4,200 ohms. S2 15,000 ohms. 43 100 ohms. 13 110 volts. 35 180 volts. 22 25.2 volts. 17 2.5 volts. 42 MH2N57.

45 T1952. 50 T1305. 48 TI'652-5. 47 TI652-5. 53 TI652-5. Hydrogen lamp.

While the invention has been described in conjunction with a present preferred embodiment, it should be evident that it is not limited thereto.

What is claimed is:

1. A radiation source comprising a gas discharge tube having an anode and a cathode, a. first source of direct potential of sufficient magnitude to maintain a discharge between said anode and cathode, means applying the positive terminal of said firs-t source to said anode and the negative terminal of said first source to said'cathode, a source of alternating current, an inductor and a capacitor connected in series relationship with said source of alternating current, the values of said inductor and capacitor being such as to form a series resonant circuit, switching means to connect said capacitor between said anode and cathode, and means responsive to conduction by said tube to actuate said switching means to disconnect said capacitor from said tube.

2. A radiation source comprising a gas discharge tube having an anode and a cathode, a first source of direct potential of sufiicient magnitude to maintain a discharge between said anode and cathode, means applying the positive terminal of said first source to said anode and the negative terminal of said first source to said cathode, first and second sources of alternating current, said second source of alternating current being of greater magnitude than said first source of alternating current, a third source of alternating current, an inductor and a capacitor connected in series relationship with said third source of alternating current, the values of said inductor and capacitor being such as to form a series resonant circuit, switching means to connect said capacitor. between said anode and cathode and to connect said second source of alternating current to said cathode to supply heat, and means responsive to conduction. by saidtube to actuate said switching means to disconnect said capacitor from said tube and to connect said first source of alternating current to said cathode in place of said second source of alternating current.

3. A radiation source comprising a gas discharge tube having an anode and a cathode, a first source of direct potential of suflicient magnitude to maintain a discharge between said anode and cathode, means applying the positive terminal of said first source to saidanode and the negative terminal of said first source to said cathode, a second source of potential of magnitude sufficient to initiate a discharge between said anode and cathode, first and second sources of alternating current, said second source of alternating current being of greater magnitude than said first source of alternating current, switching means to connect said second source of potential between said anode and cathode and to connect said second source of alternating current to said cathode to supply heat, and means responsive to conduction by said tube to actuate said switching means to remove said second source of potential from said tube and to connect said first source of alternating current to said cathode in place of said second source of alternating current.

4. A radiation source comprising a gas discharge tube having an anode and a cathode, a first source of direct potential of sufficient magnitude to maintain a discharge between said anode and cathode, means applying the positive terminal of said first source to said anode and the negative terminal of said first source to said cathode, a source of alternating current, an inductor having one terminal connected to the first terminal of said source of alternating current, a first capacitor having one ter- 'minal connected to the second terminal of said inductor,

a second capacitor having one terminal connected to the second terminal of said source of alternating current, a first switch connected between the second terminals of said capacitors, means connecting the first terminal of said first capacitor to one of the electrodes of said tube,

' a second switch connecting the second terminal of said second capacitor to the second electrode of said tube, the values of said inductor and said first capacitor being such as to form a series resonant circuit, said second capacitor being substantially larger than said first capacitor, and means responsive to conduction through said tube to open said first and second switches.

5. A radiation source comprising a gas discharge tube having an anode and a cathode, a first source of direct potential of sufiicient magnitude to maintain a discharge between said anode and cathode, means connecting the negative terminal of said first source to the cathode of said tube, a source of alternating current, an inductor having one termnial connected to the first terminal of said source of alternating current, a first capacitor having one terminal connected to the second terminal of said inductor, a second capacitor having one terminal connected to the second terminal of said source of alternating current, a first switch connected between the second terminals of said capacitors, means connecting the first terminal of said first capacitor to the anode of said tube, a second switch connecting the second terminal of said second capacitor to the cathode of said tube, the values of said inductor and said first capacitor being such as to form a series resonant circuit, said second capacitor being substantially larger than said first capacitor, a relay coil to open said switches when energized, and means connecting the positive terminal of said first source to said one terminal of said inductor through said relay coil.

6. A radiation source comprising a gas discharge tube having an anode and a cathode, a first source of potential of suflicient magnitude to maintain a discharge between said anode and cathode, means continuously applying said first source of potential between said anode and said cathode, a second source of potential of magnitude sufiicient to initiate a discharge between said anodeand cathode, said second source of potential being of greater magnitude than said first source of potential, switching means to apply said second source of potential between said anode and cathode, means responsive to conduction by said tube to actuate said switching means to remove said second source of potential from said tube, first and second sources of current, said second source of current being larger than said first source of current, means to connect said second source of current to said cathode to supply heat, and means responsive to conduction by said tube to connect said first source of current to said cathode in space of said second source of current.

References Cited in the file of this patent UNITED STATES PATENTS 707,975 Potter Aug. 26, 1902 780,998 Hewitt Jan. 31, 1905 2,011,969 Cavanaugh Aug. 20, 1935 2,133,152 Schigyo Oct. 11, 1938 2,549,353 Willoughby Apr. 17, 1951 2,564,877 Buckingham et al. Aug. 21, 1951 2,664,541 Henderson Dec. 29, 1953 2,727,188 Rively Dec. 13, 1955 2,728,871 Morin Dec. 27, 1955 2,745,990 Anderson May 15, 1956

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