US3514669A - High repetition rate strobe light - Google Patents

Description

y 26, 0 J. G. HELMUTH 3,514,669

HIGH REPETITION RATE STROBE LIGHT Filed Jan. 3, 1967 .ZWvewroe (1 7M455 G. HELMUTH United States Patent 3,514,669 HIGH REPETITION RATE STROBE LIGHT James G. Helmuth, Monrovia, Califi, assignor to Chadwick-Helmuth Electronics, Inc., Monrovia, Calif., a corporation of California Filed Jan. 3, 1967, Ser. No. 607,044 Int. Cl. Hb 37/00 US. Cl. 315-241 7 Claims ABSTRACT OF THE DISCLOSURE Improvements in triggering of a particular flasher circuit involve application to one flasher tube electrode of trigger voltage E of a polarity such that tube discharge diodes present high impedance to E and application to a terminal exterior of the tube of trigger voltage E to enhance tube gas ionization, .IE I and {E having such time and magnitude relationship as to result in several benefits.

This invention relates generally to flasher circuits, and more particularly concerns improvements in stroboscopic light and flasher circuits of the type described in my copending application for U.S. Letters Patent, Ser. No. 508,039, entitled Strobe Light, and filed Nov. 16, 1965.

In that application there was disclosed an unusually effective and simple flasher circuit that includes a flash tube, electrical charge storage means connected to discharge through the tube in response to triggered ionization of tube gas, diode means connected to provide a relatively low impedance path for such discharge, and trigger voltage supply means connected to supply to the tube a high trigger voltage of polarity such that the diode means presents a high impedance path to the trigger voltage. The present invention improves upon such a device in that less cooling of the diodes is required; substantially greater light output is obtainable for the same power input to the device; reliable flashing is obtainable at low energy discharge, i.e. short flashes occurring at high flash rates; the required trigger voltage applicable to the tube electrodes to secure flashing is less variable with temperature and aging of the apparatus; and fewer diodes are needed.

Basically, the invention concerns the provision of trigger voltage means including a terminal extending externally of and in such proximity to the tube as to enhance ionization of the gas in the tube in response to trigger voltage application to that external terminal coincidentally with trigger voltage application to the tube internal electrode. As will appear, the trigger voltage means typically includes a source of trigger voltage E applicable to the tube internal electrode and E applicable to the external terminal, wherein E and E both increase to flash initiating values characterized in that the absolute value of E is at least twice the absolute value of E In this regard, E is normally negative and applied to the tube cathode, while E may be positive or negative.

3,514,669: Patented May 26, 1970 As will appear, an unusually advantageous trigger voltage means includes transformer secondary winding sources of trigger voltage E applicable to the tube cathode and E applicable to the external terminal, and transformer primary winding structure coupled to the secondary winding sources and adapted to receive trigger pulses.

These and other objects and advantages of the invention, as well as the details of illustrative embodiments, will be more fully understood from the following detailed description of the drawings, in which:

FIG. 1 is a circuit diagram showing one preferred form of flasher circuit incorporating the invention;

FIG. 2 is a section showing use of the flash tube as a point source of light with a reflector; and

FIG. 3 is like FIG. 2, but showing the addition of a focussing lens; and

FIG. 4 is a graph showing changes of E and E The flasher circuit of FIG. 1 shows one form of flash tube 10 containing gas subject to ionization in response to application across the tube of a predetermined voltage differential. A typical usable tube is identified by the designation X- a product of PEK Laboratory, Sunnyvale, Calif. Connected to anode side 11 of the tube is one form of electrical charge storage means to discharge current through the tube in response to gas ionization. Also provided are diode means 12 connected to the opposite, i.e. cathode, side 13 of the tube to provide a relatively low impedance path for the discharge. Trigger voltage supply means is also connected to tube side 13 to apply to the tube a relatively high trigger voltage E of a polarity such that the diode means presents a relatively high impedance path thereto. Typically, the diode means may comprise silicon junction diodes 14 connected as shown between point 15 and common terminal or ground 16 for presenting high impedance to negative trigger voltage.

More specifically and as described in said copending application referred to above, the charge storage means connected to tube 11 may include multiple storage capacitors 17 and 18, the former connected with inductance elements 19 to form one segment of a delay line and the latter capacitors connected with inductance elements 20 to form another segment of the delay line. Means is also provided to optionally charge different of the capacitors to effect control of flash intensity and flash rate upon capacitor discharge through tube 10. For example, such means may include a transformer 21; a full wave rectifier bridge 22 taking input voltage from the transformer, rectified DC output at 23 being filtered at inductance 24, resistance 24a and capacitance 25 and supplied via diode 26 to terminal 27 of SPDT switch 28. When switch arm 29 engages terminal 30, only capacitors 18 are subjected to charging, since diode connected between inductance 19 and 20 blocks charging of capacitors 17. On the other hand, when switch arm 29 engages terminal 31, all capacitors 17 and 18 are charged. The former mode is characterized by fast flash rates and lower flash intensity, whereas the latter mode is characterized by slower flash a 3 rates and higher flash intensity or power. The delay line reduces peak currents delivered to the flash tube upon capacitor discharge.

Switch arm 29 is ganged at 32 with another SPDT switch arm 33 operable to connect diflerent taps 34 and 35 of transformer secondary alb with the input terminal 36 of the rectifier bridge. Thus, higher voltage is applied to terminal 36 during operation in slower flash, higher flash intensity (and duration) mode. The transformer primary 21a is suitably connected at 37 with AC source current via on-off switch 38.

Turning now to the trigger voltage supply means, it may typically include a trigger charge storage capacitor 40, a pulse transformer 41 having a low voltage primary winding 42 connected in series with the capacitor and a high voltage secondary winding 43 connected with the trigger input side 13 of tube 10, together with means to trigger the discharge of the capacitor 40. The latter means may typically and advantageously comprise a silicon controlled rectifier or SCR 44 connected in series with capacitor 40, B++ voltage being supplied at junction 45 to charge capacitor 40. Such voltage may be obtained from tap 46 of power transformer secondary winding 21b, as indicated. That voltage may also be applied to terminal 30 of switch 28 so as to assure a desirably high voltage charge on the capacitors 18 at the time of the first flash.

The SCR 44 has a control or switching input terminal 47 to receive amplified trigger input signals. Various pulse input points are indicated at 48-50, whereas a sine wave input point appears at 51. Pulse inputs are suitably amplified at 52 and applied to SCR terminal 47. Collector voltage for transistors 70 and 71 is obtained from point 72 in voltage divider that includes resistors 73, 74 and 75. A source of controllable frequency stroboscopic pulses is indicated generally by clock 53. The sine wave input point 51 is connected in series with a normally non-conducting neon bulb 54. The latter becomes conductive during the negative portion of the sine wave trigger input signal, and a corresponding pulse is applied to the amplifier input at 55 via path 56.

The trigger voltage supply means also includes a terminal (as for example loop 101) extending externally of and in such close proximity to the tube as to enhance ionization of the tube gas in response to application of trigger voltage E to that terminal coincidentally with application of trigger voltage E to the tube electrode 13. As seen in FIG. 4, E and E increase to tube flash initiating levels at time t characterized in that the absolute value of E i.e. IE' I, is at least about twice the absolute value of E i.e. IE I. Further, whereas E is negative at flash initiation, E may be positive or negative at flash initiation. These relationships result in the improvements in operation discussed in the introduction. Typically, at t, E is about 12,000 volts whereas E is between 5,000 and 7,000 volts.

The trigger voltage supply means also includes another pulse transformer 102 having a low voltage primary winding 103 connected in series with capacitor 40 and in parallel with primary winding 42, with polarities as indicated. Transformer 102 also includes a high voltage secondary winding 104 connected with terminal loop 101 wrapped closely about tube 10 as indicated, to supply E to the loop. As a result of applying both E and E the gas in the tube ionizes at a much lower A. to /s) level of voltage E than would be required in the absence Of E'T.

The use of silicon diodes is of particular advantage since the hold off (back) impedance can be very large and conducting (forward) impedance very small and switching from one state to the other very rapid. In this regard, the point source has a much lower conducting impedance than a conventional flash tube, which requires a much lower series impedance. As stated earlier, the number of diodes required is reduced significantly in view of the dual trigger voltage relationships.

Also, diode means 12 prevents reverse conduction of flash tube should the characteristics of the tube and circuit cause the discharge capacitors to end with a negative voltage. Reverse conduction of flash tube tends to degrade operation of the tube due to electrode abuse.

When the voltage across tube 10 falls sufliciently, the tube deionizes and the storage capacitors recharge. Likewise, the SCR 44 is switched oil by a drop off in the output of amplifier 52, after capacitor 40 discharges, so that capacitor 40 then recharges. Diode 59 prevents any ringing from reaching the SCR 44.

A blower 60 has a motor connected in a circuit path from common terminal 16 to the rectifier bridge terminal 61, so that average charging current for the discharge or storage capacitors is drawn through the blower causing it to run at a rate proportional to the power input to tube 10. The blower fan cooling air discharge cools the tube 10. Meter 63 also indicates average power by reading the voltage across the blower motor circuit. Cooling requirements are minimized in view of the improvements of the invention.

'FIG. 2 shows the flash tube 10 in the form of a point source of light contained within and spaced from parabolic reflector 65 to yield a nearly collimated light beam 66. A typical source 10 may be rounded and about 1 mm. in diameter, the associated reflector having a focal length of .4 inch and a 3 /2 inch diameter. The ionizable gas in the lamp is typically above 8 atmospheres pressure. FIG. 3 shows the same structure as in FIG. 2, and adds a lens 67 in front of the point source 10. The lens sharply focuses the light from the reflector, generating a small spot at 68, almost all light from source 10 is utilized in FIG. 3.

I claim:

1. In a flasher circuit, a flash tube containing electrodes and gas subject to ionization, electrical charge storage means connected to discharge through the tube in response to said ionization, diode means connected to one tube electrode to provide a relatively low impedance path for said discharge, and trigger voltage supply means including a connection to apply to said one tube electrode a trigger voltage of a polarity such that the diode means presents a relatively high impedance path thereto, said trigger voltage means including a terminal extending externally of and in such proximity to the tube as to enhance ionization of the gas in the tube in response to trigger voltage application to said terminal coincidentally with trigger voltage application to said tube electrode, said charge storage means being connected with another tube electrode and including storage capacitor means, and means to charge said capacitor means to effect control of flash intensity created by capacitor discharge through the flash tube, inductance connected to said capacitor means to provide a delay line, said trigger voltage means comprising a trigger charge storage capacitor, a transformer having primary winding means connected with the trigger capacitor and secondary winding means connected with said one tube electrode and with said terminal and sized to produce a voltage E applicable to said one electrode and a voltage E' applicable to said terminal and wherein E and E increase to flash initiating levels characterized in that IE' I is substantially greater than [E and means to trigger the discharge of the trigger capacitor and including a gate controlled rectifier connected in series with the trigger capacitor and having a control terminal, a trigger signal input connection, an amplifier connected between said input connection and said control terminal, and a source of input trigger signals.

2. The combination of claim 1, wherein E and E increase to flash initiating levels characterized in that IE I is at least about twice 3. The combination of claim 1, wherein E is negative and E is positive or negative.

4. The combination of claim 1, in which said diode means and trigger voltage supply means are connected with the tube cathode, and said charge storage means is connected with the tube anode, thediode means presenting said high impedance to negative trigger voltage.

5. The combination of claim 4, in which said storage capacitor means includes multiple storage capacitors and 5 said charge storage means includes means to optionally charge different of said capacitors to effect control of flash intensity created by capacitor discharge through the flash tube.

6. The combination of claim 4, in which said diode means comprises series connected silicon diodes.

7. The combination of claim 1 wherein the tube forms a light source zone the overall cross dimension of which is less than 4 millimeters.

References Cited UNITED STATES PATENTS 10 JOHN W. HUCKERT, Primary Examiner B. ESTRIN, Assistant Examiner US. 01. X.R. 7

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