US 3497768 A
Description (OCR text may contain errors)
Feb. 24, 1970 v A. MATHISEN I 3,497,768
ONE SHOT OPERATION CIRCUIT F 'Q R A GAS DLSCHARGE LAMP Filed Match 5. 1968 gan INVENTOR.
United States Patent 3,497,768 ONE SHOT OPERATION CIRCUIT FOR A GAS DISCHARGE LAMP Henry A. Mathisen, Northhrook, Ill., assignor to Addressograph-Multigraph Corporation, Mount Prospect, 11]., a corporation of Delaware Filed Mar. 5, 1968, Ser. No. 710,482 Int. Cl. H05!) 41/00, 41/36, 41/14 US. Cl. 315183 6 Claims ABSTRACT OF THE DISCLOSURE A control circuit to flash a xenon lamp includes a silicon controlled rectifier (SCR) that is placed in conduction by a one-shot trigger circuit to connect the lamp across an alternating current potential source for a single half cycle. A normally charged capacitor is discharged through a pulse transformer and the conductive SCR to pulse the starter electrode of the lamp in synchronism with the connection of the lamp to the potential supply.
This invention relates to electrical controls for a high intensity radiation source, and more particularly, to a control for controlling the short duration energization of a high intensity radiation source or lamp using an alternating current supply.
The high intensity radiation sources or lamps with which this invention can be used are usually of the gas filled type, such as xenon, and are particularly useful in photo imaging processes, although they can be used in other applications where high intensity radiation is required over a very short time span. Electrical control systems heretofore known for energizing a high intensity radiation source for a short duration of time relied upon one or a bank of capacitors to provide the source of energy to energize the radiation source. The use of such a control system was costly, required a great deal of space, and from the standpoint of safety did not lend itself for use in equipment to be operated by untrained personnel. Hence, they were not suitable for incorporation into equipment designated for general oflice use.
It is a general object of this invention to provide an improved electrical control for energizing a high intensity radiation source that is compact, economical, and simple to operate.
It is an object of this invention to provide an improved electrical control for energizing a high intensity radiation source for a short duration that is powered by an alternating current potential source.
It is another object of this invention to provide a high intensity radiation source that can be energized for very short periods of time for use in conjunction with a photo exposure system.
Another object is to provide a control circuit for connecting a high intensity lamp with an alternating current potential source, which circuit includes means for synchronizing the energization of a starter electrode for the lamp with the connection of the lamp to the potential source.
In accordance with these and many other objects, an embodiment of the present invention comprises a circuit for controlling the energization of a high intensity radiation source or lamp which uses an alternating current po ential source and which does not requi e one or more rather large storage capacitors. This circuit is such that the energization of a starter electrode on the lamp is svnch onized with the connection of the lamp to the alt rnating current potential source. More specifically, the cont ol circuit includes a controlled conduction device or silicon controlled rectifier connected in series with the two main terminals of a xenon lamp across the output 3,497,768 Patented Feb. 24, 1970 ICC terminals of an alternating current potential source. To provide means for pulsing the starter electrode of the lamp, a capacitor normally charged from the potential source is coupled to one winding of a pulse transformer, the other winding of which is coupled to the starter electrode. When the lamp is to be energized, a trigger circuit places the silicon controlled rectifier in a conductive state to connect the main terminals of the lamp directly across the alternating current potential source during a properly poled half cycle of the input potential, and the storage capacitor also discharges through the conductive silicon controlled rectifier and the connected winding of the pulse transformer to apply an ionizing or starting potential to the starter electrode of the lamp. Thus the lamp is energized for approximately one-half cycle of the alternating current input potential to provide a short duration, high intensity source of radiation. The triggering circuit can be actuated manually or in synchronism with the movement of the web or sheet material through the copying machine.
Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which-- FIG. 1 forms a schematic circuit diagram of a control circuit embodying the present invention; and
FIG. 2 illustrates a modified form of the circuit shown in FIG. 1.
Referring now more specifically to FIG. 1 of the draw ings, therein is illustrated a control circuit which embodies the present invention and which is indicated generally as 10. The control circuit 10 provides means for effecting controlled short duration energization of a high intensity radiation source such as a xenon lamp 12 from a conventional alternating current potential source and without requiring the use of storage capacitors of substantial value. The lamp 12 is of conventional construction and includes a pair of main electrodes 14 and 16 and a starter or auxiliary electrode 18.
The circuit 10 is energized from a conventional sixty cycle, volt alternating current source which is connected to primary winding 20A of a step-up transformer 20, the secondary winding 20B of which provides an output potential on the order of 500 volts. The lamp 12 is adapted to be connected directly in series across the secondary 'winding 20B over a circuit including a rectifier or unidirectional conducting device 22, a silicon controlled rectifier or controlled conduction device 24, and another unidirectional conducting device or rectifier 26. The controlled conduction device includes two output electrodes, i.e., the cathode and anode, and a control or gate electrode. The silicon controlled rectifier 24 is normally in a nonconductive state and, when triggered to a conductive state, connects the lamp 12 directly across the alternating current potential source to be energized during a selected positively poled half cycle of the input potential.
In the normal condition of the circuit 10, a small storage capacitor 28 is charged through the rectifier 22 and a resistance element 30 during the positively poled half cycles of the input potential. The capacitor 28 is also connected to the anode of the silicon controlled rectifier 24 through a resistance element 32 which is shunted across the two main terminals 14 and 16 of the lamp 12. Thus, after the capacitor 28 is charged, a positive potential is applied to the anode of the silicon controlled rectifier 28 during both the positive and negative half cycles of the alternating current potential supply.
A one-shot trigger circuit indicated generally as 34 provides a means for energizing the lamp 12 during a single positive-going half cycle of the alternating current input potential. The trigger circuit 34 includes a switch 36 providing a pair of normally closed contacts 36A and a pair of normally open contacts 36B. The switch 36 can be manually operated or in photocopying machines, may be operated under the control of sheet or web material. In the normal position of the switch 36, the closed contacts 36A provide a circuit for discharging a capacitor 38 through a series connected resistance 40. The normally open contacts 36B of the switch 36 are connected to the cathode of the silicon controlled rectifier 24, the gate electrode of which is returned to one side of the secondary winding 20B through a resistance element 42.
When the control circuit is to be actuated to flash or energize the lamp 12, the switch 36 is operated to open the contacts 36A and to close the contacts 363. The closure of the contacts 36B does not have any effect on the circuit 10 during the positive-going half cycles. However, on the first negative-going half cycle occurring following the closure of the contacts 36B, a circuit is completed for charging the capacitor 38 extending from one side of the secondary winding B through a diode 44, the resistance element 40, the capacitor 38, the closed contacts 36B, the control gap between the cathode and gate electrodes of the silicon controlled rectifier 24, the resistance element 42 to the other terminal of the secondary winding 20B. The current flowing over this path to charge the capacitor 38 biases the control gap betwen the gate electrode and the cathode of the silicon controlled rectifier 24 to trigger this rectifier into a conductive condition. Since the upper terminal of the secondary winding 20B is negative with respect to the lower terminal at the time that bias current is applied to the rectifier 24, the diode 22 is reverse biased, and the capacitor 28 provides the holding current for the rectified 24 by discharging through the resistance elements 30 and 32 and the diode 26. The values of the resistance elements 30 and 32 and the capacitor 28 are so chosen that the capacitor 28 will be discharged to the point at which holding current for the rectifier 24 can be sustained for no longer than one half cycle.
On the following positive-going half cycle, conduction through the rectifier 24 is sustained by the potential supplied by the secondary winding 20B, and the main electrodes 14 and 16 of the lamp 12 are connected directly across this secondary winding through the forward biased diodes 22 and 26 and the conductive rectifier 24. The lamp 12, however, is not placed in a conductive or ionized condition until a starting or ionizing pulse is applied to the auxiliary or starter electrode 18, and this start signal is applied by a starter control circuit indicated generally as 46.
In the normal condition of the circuit 10, a relatively low value storage capacitor 48 is charged to a positive potential by the input alternating current supply potential over a circuit including a diode or rectifier 50 and a series connected resistance element 52. The capacitor 48 is connected in parallel with the silicon controlled rectifier 24 and the rectifier or diode 26 over a circuit including a diode or rectifier 54 and a primary winding 56A of a pulse transformer 56. The secondary winding 56B of the pulse transformer 56 is connected to the starter electrode 18.
When the silicon controlled rectifier 24 is placed in a conductive state, the capacitor 48 discharges through the primary winding 56A, the diode or rectifier 54, the silicon controlled rectifier 24, and the diode or rectifier 26 so that a pulse of substantial magnitude, e.g., on the order of 15 kv., is coupled by the secondary winding 56B to the starter electrode 18. The application of this relatively high potential pulse to the starter electrode 18 ionizes the gas, such as xenon, in the lamp 12 and thus flashes the lamp 12 during the positive-going half cycle next following the negative-going half cycle in which the switch 36 was closed. At the end of this half cycle, the lamp 12 is returned to its normal state independent of the operated or released condition of the control switch 36.
More specifically, even though the switch 36 is maintained in an operated state so that the contacts 36B are closed following the positive half cycle during which the lamp 12 was flashed, the reversal in polarity of the alternating current supply potential removes the holding current from the silicon controlled rectifier 24, the capacitors 28 and 48 having been discharged, and the rectifier 24 returns to a nonconductive state. Even though the contacts 36B are held in a closed condition, the time con- 'stants for the charging circuit for the capacitor 38 are so chosen that the capacitor 38 is now fully charged to block current to the gate electrode, and thus the control gap between the cathode and gate electrodes of the rectifier 24 cannot be biased thereafter until the switch 36 has been released to open the contacts 36B and to close the contacts 36A. When the contacts 36A are closed, the capacitor 38 discharges through the resistance element 40.
During the interval following the flashing of the lamp 12, the capacitors 28 and 48 are charged on positive-going half cycles and the control circuit 10 is restored to a normal condition. These capacitors provide only control potentials for the circuit 10, and the current for operating the lamp or radiation source 12 is supplied directly from the alternating current input potential.
FIG. 2 of the drawings illustrates a modified form of the circuit 10 in which the lamp 12 includes the main electrodes 14 and 18 and the secondary winding 56B of the pulse transformer 56 is connected to the electrode 14. When the rectifier 24 is placed in a conductive condition, the pulse developed in the winding 56B is applied across the electrodes 14 and 16 to trigger the lamp into a conductive state. The operation of the circuit 10 connected in the manner shown in FIG. 2 is in other respects similar to the operation of the circuit shown in FIG. 1.
Although the control circuit 10 can be made using component values in ranges suitable for each particular application, as is well known to those in the art, the following table lists component values for one control circuit 10 made in accordance with the present invention:
TABLE Capacitor 28 ,u.fCl 10 Resistance element 30 ohms 330 Resistance element 32 do 87 Capacitor 38 ufd .1 Resistance element 40 ohms Resistance element 42 do 100 Capacitor 48 Mfd .5 Resistance element 52 ohms K Although the present invention has been described with reference to two illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that Will fall Within the spirit and scope of the principles of this invention.
What is claimed and desired to be secured by Letters Patent of the United States is:
1. A control circuit for use with a potential source comprising:
a gaseous discharge lamp provided with electrode means,
a controlled conduction device including a pair of output electrodes and a control electrode,
first circuit means connecting the electrode means of the lamp and the two output electrodes of the device in series across the potential source,
a trigger circuit connected between the potential source and device for applying a bias between the control electrode and one of the output electrodes for placing the device in a conductive state for a predetermined interval, said trigger circuit including bias blocking means for blocking the application of a bias between the control electrode and said one output electrode subsequent to said predetermined interval, thereby to limit the conduction of said controlled conduction device, and
second circuit means connected between one of the output electrodes of the device and the electrode means for energizing the electrode means in response to conduction through the device.
2. A control circuit for use with an alternating current potential source comprising a lamp including two main electrodes and a starter electrode,
a controlled conduction rectifier having two output electrodes and a gate electrode,
first circuit means connecting the two main electrodes of the lamp and the two output electrodes of the rectifier in series across the alternating current potential source,
a trigger circuit connected between the potential source and the rectifier to apply a bias between the gate electrode and one of the output electrodes for placing the rectifier in a conductive state to connect the main terminal of the lamp to the alternating current potential source,
second circuit means including a unidirectional conducting device for connecting the capacitive means to the potential source for charging the capacitive means,
and third circuit means coupled to the starter electrode for applying a start signal to the starter electrode, said third circuit means including means for discharging the capacitive means through the conductive rectifier.
3. A control circuit for energizing a load from an alternating current potential source comprising a gas-filled lamp having a pair of main electrodes and a starter electrode,
a silicon controlled rectifier having a pair of output electrodes and a gate electrode,
first circuit means connecting the two main electrodes of the lamp and the two output electrodes of the rectifier in series across the alternating current potential source,
a trigger circuit connected between the potential source and rectifier to apply a bias between one of the main electrodes and the gate electrode for placing the rectifier in a conductive condition to connect the main terminals of the lamp to the potential source,
a pulse transformer having first and second windings,
second circuit means connecting the first winding of the transformer to the starter electrode,
capactive means charged from the potential source, and third circuit means connecting the capacitive means and the second winding of the pulse transformer across the rectifier so that the capacitive means dis charges through the rectifier and the second winding when the rectifier is placed in a conductive condition so as to place a signal on the starter electrode.
4. The control circuit set forth in claim 3 in which the trigger circuit includes a capacitor and switch means for controlling the connection of the capacitor to the rectifier.
5. The control circuit set forth in claim 3 in which the first circuit means includes a unidirectional conducting device poled in the same direction as the rectifier, and in which a storage capacitor is connected in series with the unidirectional device and in parallel with the lamp and rectifier.
6, A control circuit for controlling the energization of a triggered load by an alternating current potential source comprising a lamp having a pair of main electrodes and a starter electrode,
a normally non-conductive controlled conduction device having a pair of output electrodes,
first circuit means connecting the two main electrodes of the lamp and the two output electrodes of the device in series with the alternating potential source,
a trigger circuit connected to the device and operable to place the device in a conductive condition to connect the lamp to the alternating current potential source, and
a synchronizing circuit connected between the starter electrode of the lamp and the device and responsive to conduction through the device for applying an energizing signal to the starter electrode.
References Cited UNITED STATES PATENTS 3,278,799 10/1966 Gordy 3l5--171 3,416,031 12/1968 Franks et al. 3l5119 JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R.