US3113293A

US3113293A - Flashing light systems

Info

Publication number: US3113293A
Application number: US151072A
Authority: US
Inventors: Breese Robert Finley; Albert C Zagotta
Original assignee: Chicago Rock Island and Pacific Railroad Co
Current assignee: Chicago Rock Island and Pacific Railroad Co
Priority date: 1961-11-08
Filing date: 1961-11-08
Publication date: 1963-12-03
Anticipated expiration: 1980-12-03

Description

Dec. 3, 1963 R. F. BREESE EI'AL 3,113,293

FLASHING LIGHT SYSTEMS Filed Nov. 8, 1961 2 Sheets-Sheet 2 INVENTO Eober/ fin/ey Breese BY rf/berf C Faye/fa A TTORNE YS United States Patent 3,113,293 FLASH-KING LIGHT SYSTEMS Robert Finley lireese and Albert C. Zagotta, Chicago, Ill., assiguors to Chicago, Rock Island and Pacific Railroad Company, Chicago, 111., a corporation of Delaware Filed Nov. 8, 1961, Ser. No. 151,072 16 Claims. (Cl. 340-50) This invention relates to flashing light systems and more particularly to systems usable in railroad applications for warning and signalling purposes and on the front or rear of a train or at highway crossings. The systems of this invention are rugged and reliable in operation, can withstand shocks, vibrations and wide temperature changes, and they require minimum lamp replacement and maintenance. At the same time, the systems are very compact, are relatively inexpensive in construction, and are readily installed.

Heretofore, many flashing lights for railroad applica tions have been of the type wherein a lamp or a reflector is mounted for rotational or swinging movement to obtain a flashing effect where observed from a distance. The mechanical drives of such systems have not been entirely satisfactory, and the maintenance costs thereof have been high. Systems have also been used wherein the lamps have been mounted in fixed position, and relays have been used to periodically energize the same, but the contacts of such relays burn out rapidly, to create a safety problem and to require excessive maintenance.

This invention was evolved with the general object of overcoming the disadvantages of such prior art systems. According to this invention, an incandescent lamp is periodically energized by a solid state electronic circuit which is extremely rugged a .d reliable in operation and yet comparatively simple and inexpensive in design.

An important feature of the invention is in the use of silicon controlled rectifiers which have a long life, can withstand severe shocks and vibrations and wide temperature variations, and they have a low internal resistance and can handle large currents. Certain problems, however, are introduced by the use of such rectifiers and further features of the invention relate to circuits for overcoming such problems.

Another important feature relates to the provision of circuit arrangements for minimizing the effect of wide variations in power supply voltage, such as are experienced in railroad operation.

A further feature of the invention relates to a circuit arrangement for energizing a plurality of lamps pointed in different directions, in a manner such as to obtain the same effect as obtained by a swinging lamp or reflector.

These and other objects, features and advantages of the invention will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate preferred embodiments and in which:

FIGURE 1 is a side elevational view of a rear end portion of a railroad observation car, showing the positioning of one form of signalling light in a system of the present invention;

FIGURE 2 is a schematic diagram of a circuit for energizing a light such as the light of FIGURE 1;

FIGURE 3 is a side elevational view of a forward end portion of a railroad locomotive, showing the positioning of a signal light arrangement constructed according to this invention;

FIGURE 4 is a front elevational view, on an enlarged scale, of the signal light on the locomotive of FIGURE 3;

FlGURE 5 is a sectional view taken substantially along line VV of FlGURE 4; and

FEGURE 6 is a schematic diagram of a circuit for energizing the lamp system of FIGURES 35.

Referring to FIGURE 1, reference numeral ltl generally designates a signal light unit shown mounted on the rear end of an observation car 11 of a passenger train. The unit 111 includes a stationary lamp 12 which is periodically energized through the circuit shown in FIGURE 2. A flash repetition rate of approximately 62 flashes per minute is a convenient rate, but much slower or much higher rates may be used.

To periodically energize the lamp 12, one terminal thereof is connected to a circuit point 13 which is connected through a silicon controlled rectifier 14 to a negative bus 15 which is connected to the negative terminal 16 of a power supply 17. The other terminal of the lamp 12 is connected to a circuit point 18 which is connected through a voltage adjustment circuit 19 and a fuse 21 to the positive terminal 21 of the power supply 17. The voltage adjustment circuit 19 serves to maintain the voltage between the bus 15 and the circuit point 13 Within certain limits, as will be described hereinafter.

The silicon controlled rectifier 14 is a PNPN device forming the semi-conductor equivalent of a gas thyratron, and has a control or gate electrode 22 which forms the equivalent of the grid of a gas thyratron. In operation, with a positive voltage applied to the anode relative to the cathode, the flow is blocked until a certain forward breakover voltage is reached. At this point the device goes into a high conduction state and the voltage thereacross drops to one or two volts. In the high conduction state, the current flow is limited only by the external circuit impedance and supply voltage. At anode to cathode voltages less than the breakover voltage, the device can be switched into the high conduction mode by a small pulse applied from the gate electrode to the cathode. Once the device is in the high conduction state, it will continue conduction indefinitely after removal of the gate signal until the anode cur-rent is interrupted or diverted for a short time interval after which the device regains its forward blocking capabilities.

To utilize such properties of the silicon controlled rectifier in periodically energizing the lamp 12, the voltage across the rectifier 14 must not exceed the forward breakover voltage and a positive pulse must be applied to the gate or control electrode 22 of sufficient amplitude as to switch the rectifier 14 into its high conduction state. It is also necessary to provide means for interrupting or diverting current through the rectifier, after the lamp 12 has been energized for the desired flash time duration.

The voltage adjustment circuit 19 limits the voltage between circuit point 18 and the negative bus 15 to thereby limit the maximum voltage across the rectifier 14 and to thereby aid in preventing a voltage exceeding the breakover voltage. In addition, the maximum voltage across the rectifier 14 is limited by a resistor 23 connected in parallel therewith. Resistor 23 also serves a very desirable and important function in maintaining a certain current flow through the lamp 12 to prevent the temperature of the lamp filament from dropping below a certain value. This substantially increases the operating life of the lamp 12.

To periodically apply a positive pulse to the gate or control electrode 22 of the rectifier 14, a pulse generating circuit is provided which comprises a unijunction transistor 24, having a first base electrode 25 connected through a resistor 26 to the negative bus 15', a second base electrode 27 connected through

resistors

28 and 29 to a circuit point 30 and an emitter electrode 31 connected through a timing resistor 32 to the circuit point 30 and through a timing capacitor 33 to the negative bus 15. Circuit point 31) is connected through a resistor 34 to the circuit point 18 so as to be at a positive potential relative to the negative bus 15, the positive potential being maintained constant by a voltage regulator in the form of a Zener diode 35 connected between circuit point 30 and the bus 15. This voltage regulator is very important in obtaining uniform and stable operation of the timing circuitry despite supply voltage variations such as encountered in railroad applications.

In operation, the voltage across timing capacitor 33 gradually increases, through current flow through a timing resistor 32, until it exceeds a voltage approximately equal to the voltage of circuit point 30, multiplied by the ratio of resistance 26 to the total resistance of

resistors

26, 28 and 29. At this point the unijunction transistor 24 conducts heavily to discharge the timing capacitor 33 through the resistor 26 and to develop a positive pulse at the first base electrode 25, whereupon the voltage again starts to build up across the timing capacitor 33. The positive pulse developed at base 25 is applied through a coupling capacitor 36 to the gate electrode of the silicon controlled rectifier 14, a resistor 37 being connected between the gate electrode 22 and the negative bus 15.

When a positive pulse is applied to the gate electrode 22, the silicon controlled rectifier 14 conducts heavily, to energize the lamp 12. To thereafter deenergize the lamp 12, after the desired flash time duration, it is necessary to provide means for interrupting or diverting current through the rectifier. In the circuit of FIGURE 2, such means comprise a second silicon controlled rectifier 38 having a cathode connected to the negative bus and an anode connected through a resistor 39 to the circuit point 18 and through a capacitor 40 to the circuit point 13.

When the rectifier 14 conducts to energize the lamp 12, the circuit point 13 is placed at a potential close to that of the negative bus 15 and the capacitor 49 is gradually charged up through current flow through resistor 39, to a polarity as indicated on the drawing. After the lamp 12 has been energized for the desired duration of time, the rectifier 38 is then rendered conductive to place its anode at a potential close to that of the negative bus 15. Circuit point 13 (and the anode of rectifier 14) are then placed at a potential which is negative relative to that of the bus 15, because of the charge of capacitor 40 and the fact that it is not possible to instantaneously change the charge of a capacitor. Thus current flow through the rectifier 14 is interrupted and another positive pulse must be applied before the rectifier is again rendered conductive. The silicon controlled rectifier 38 in this application (FIGURE 1) should preferably not remain conductive until the rectifier 14 again conducts, and the resistor 35 preferably has a resistance which is high enough to reduce steady state current flow through rectifier 38 to a value less than that required to maintain conduction of the rectifier 38.

A positive pulse is applied to a gate electrode 41 of the rectifier 33 at appropriate times by means of a pulse generating circuit including a unijunction transistor 42 having a first base electrode connected to the negative bus 15 through a resistor 43, a second base electrode connected to the junction between

resistors

28 and 29, and an emitter electrode connected through a timing resistor 44 to the circuit point 30 and through a timing capacitor 45 to the negative bus 15. The first base electrode is also connected through a coupling capacitor 45 to the gate electrode 41 which is connected through a resistor 47 to the negative bus 15.

The operation of this circuit is synchronized with the operation of the circuit of transistor 24. In particular, the connection of the second base of transistor 42 to the junction of

resistors

28 and 29 places it at a higher potential than that of the second base 27 of transistor 24, when both transistors are non-conductive. As a result, the emitter voltage required to trigger transistor 24 is less and it fires first. When transistor 24 fires, the potential of the second base electrode of transistor 42 drops instantaneously and in proper operation, the emitter voltage thereof is then sufficient to cause it to fire instantaneously.

Thus the firing of the

transistors

24 and 42 is simultaneous for all practical purposes. A pair of positive pulses are thus simultaneously applied to the

gates

22 and 41 of the silicon controlled

rectifiers

14 and 38. When the first pair of pulses is applied, the rectifier 14 is rendered conductive. When the next pair of pulses is applied, there is no direct effect on the rectifier 14 since it is already conductive, but the rectifier 38 is rendered conductive to cut off the rectifier 14 through the capacitor 40. When the next following pair of pulses is applied, the silicon controlled rectifier 14 is again rendered conductive, and so on. Thus the lamp 12 is energized periodically at a rate equal to one half the repetition rate of the pulse generating circuits. For example, the pulse generating circuits may be operated at the rate of 124 per minute, to energize the lamp 12 at the rate of 62 fiashes per minute.

As above indicated, the voltage adjustment circuit 19 serves to maintain the voltage between bus 15 and the circuit point 18 within certain limits. It is particularly designed for railroad applications where the supply voltage may be either in a low range of from 32 to 38 volts, or within a high range of from 64 to 76 volts. A resistor 48 is connected between circuit point 18 and the power supply terminal 21 and has two adjustable taps 49 and 5!), tap 49 being connected to the end of the resistor 48 which is connected to the circuit point 18. When the voltage is in the low range, the

taps

49 and 59 are connected together through a normally closed contact 51 of a relay 52 which is connected in series with a resistor 53 between tap 5t and the power supply terminal 16. Tap 50 may then be adjusted to obtain the optimum voltage at circuit point 18. When the voltage reaches the high range, the relay is energized to disconnect the

taps

49 and 50 and to introduce a higher resistance in the circuit. Tap 49 may then be adjusted to obtain optimum output voltage. The relay 52 is of course energized only in response to a voltage in excess of the highest voltage of the low range and lower than the lowest voltage of the high range.

Referring now to FIGURES 3, 4 and 5, reference numeral 55 generally designates a signal light unit mounted on the front end of a railroad locomotive 56, and arranged to produce the same general effect as the sweeping beam produced by a conventional swinging headlight, but with stationary lamps. The illustrated unit 55 comprises a lower lamp 57, an upper lamp 58 spaced above the lamp 57, and two side lamps 59 and 6d disposed in horizontal alignment on opposite sides of the plane of the axes of lamps 57 and 5?. The illustrated lamps 57-61) are sealed beam units mounted in a plate 61 by conventional mounting means. The upper and

lower lamps

57 and 58 are arranged to project beams directly forward from the locomotive, while the

side lamps

59 and 60 are angularly displaced in opposite directions so as to project beams at slight side angles with respect to the directly forward direction.

FIGURE 6 is a schematic diagram of a circuit for energizing the lamps SL619. This circuit operates cyclically to energize the lower lamp 57 and one side lamp 59 during the first half of a cycle and to energize the upper lamp 58 and the other side lamp 60 during the second half of a cycle. To an observer who is approach ing or in the path of the beams, the effect is substantially the same as that produced by the sweeping beam from a conventional swinging headlight.

The circuit of FIGURE 6 is very similar to that of FIGURE 2 and uses many of the same components. For convenience, the same reference numerals, with primes, are applied to those elements or components which are the same. The circuit of FIGURE 6 diiiers from that of FIGURE 2 in that

lamps

57 and 59 are substituted for the lamp 12 of FIGURE 2, while

lamps

58 and 60 are connected in place of the resistor 39. The

lamps

58 and 60 are energized for a complete half cycle whereas as above noted the resistor 39 of FIGURE 2 has a relatively high value so as to starve conduction of the rectifier 38, shortly after it is rendered conductive to cut off the rectifier 14. To limit the voltage across rectifier 38 during periods of non-conduction thereof, a resistor 62 is connected in parallel with the silicon controlled rectifier 3fi. Resistor 62 also maintains the

lamps

58 and 60 in a dimmed condition in which the temperature of the filaments thereof does not drop below a certain value, to thus prolong the operating life of the lamps.

To insure proper operation of the circuit or" FIGURE 6, a capacitor 63 is connected between the positive circuit point 30 and the gate electrode 41' of the rectifier 38' so as to apply a positive signal to the gate electrode 41 and cause conduction of the rectifier 38' when the power supply voltage is initially applied. The capacitor 4%) is then charged up with a polarity as indicated in FIGURE 6. When the first pair of pulses is developed by the triggering circuits, the rectifier 14' is then rendered conductive and through the charge of the capacitor 40', the rectifier 38' is rendered non-conductive. The capacitor 40' is then charged up to a polarity opposite that illustrated, so that when the next pair of positive pulses are developed by the pulse generating circuits, the rectifier 38 is again rendered conductive and the rectifier M will be cut oil. If the capacitor 63 were not provided, an operation might result in which neither rectifier would conduct when the power was initially applied and in which both rectifiers would be placed in conduction in response to the first pair of pulses developed by the pulse generating circuits, to prevent the capacitor 40' from developing any charge and to prevent any commutating action, so that both rectifiers would remain continuously in conduction.

By way of illustrative example and not by way of limitation, the following values or types of components may be used:

Reference numeral: Value or type 12, 57-60 150 or 200 watt, 32 Volt. 14, 14', 38 Transitron type TCR 1010. 38 Transitron type TCRlOOS. 23, 23', 62 ohms, 100 watts. 24, 24', 42, 42' General Electric type 2N49l. 26, 26', 43, 43' 56 ohms, /2 watt. 28, 28' 180 ohms, /2 watt. 29, 29' 150 ohms, /2 watt. 32, 32', 44, 44' 56,000 ohms, /2 watt. 33, 33', 45, 45 10 microfarads, 150 volt. 34, 34 1000 ohms, 10 watt. 35, 35 Transitron type SV2045. 36, 36, 4d, 45 1 microfarad, 150 volt. 37, 37, 4 7, 47 a. 10,000 ohms, /2 watt. 39 2200 ohms, 1 watt. 49, ill 30 microfarads, 150 volt. 48, 48' 10 ohms, 200 watts. 52, 52. Vapor, 32 volt. 53, 53 3000 ohms, 10 watts. 63 2 microfarads, 150 volts.

It will be appreciated that various modifications or additions may be made. For example, additional lamps may be connected in parallel with the illustrated lamps, and additional silicon controlled rectifiers may be connected in parallel with those illustrated to handle higher power.

It will also be appreciated that the systems of this invention may be used in a variety of applications and the term railroad as used herein is intended to include all applications similar to those illustrated.

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.

We claim as our invention:

1. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, a first silicon controlled rectifier having gate and anode electrodes and having a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, means normally operative to maintain said gate electrode at a certain potential relative to said cathode, means for periodically applying a positive pulse signal to said gate electrode to initiate conduction of said rectifier, a capacitor having one terminal connected to said anode electrode, resistance means connected between the other terminal of said cappacitor and said positive terminal to charge said capacitor while said rectifier conducts, a second silicon controlled rectifier having a gate electrode, a cathode electrode connected to said negative terminal and an anode electrode connected to said other terminal of said capacitor, and means for applying a positive pulse to said gate electrode of said second rectifier to interrupt current flow through said first rectifier after it has conducted for a certain length of time.

2. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, a silicon controlled rectifier having gate and anode electrodes and having a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, a unijunction transistor having an emitter and first and second base electrodes, first resistance means connected between said first base electrode and said ne ative terminal, second resistance means connected between said second base electrode and said positive terminal, a timing capacitor connected between said emitter electrodes and said negative terminal, a timing resistor connected between said emitter electrode and said positive terminal for charging said capacitor until said emitter electrode reaches a firing potential at which said transistor conducts to discharge said capacitor and to develop a positive pulse at said first base electrode thereof, coupling means for applying said positive pulse to said gate electrode to initiate conduction of said silicon controlled rectifier, and means for interrupting current flow through said rectifier after it has conducted for a certain length of time following each positive pulse.

3. In a signal light system, a semiconductor device having a pair of main electrodes and a control electrode for controlling conduction between said main electrodes, a lamp having a pair of terminals, means connecting one terminal of said lamp to one of said main electrodes, means for connecting the other terminal of said lamp and the other of said main electrodes to a voltage source, means normally operative to maintain said control electrode at a certain potential relative to the other of said main electrodes, means for periodically applying a signal to said control electrode to cause conduction of said semiconductor device and to thereby energize said lamp, and a resistor connected in parallel with said semiconductor device to reduce the voltage thereacross so as to prevent conduction of said device while said control electrode is at said certain potential and to also maintain said lamp in a dimmed condition.

4. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode electrode connected to said negative terminal, first and second resistance cans respectively connected between said anode electrodes and said positive terminal, at least one of said resist-ance means including a lamp, a commutation capacitor connected between said anode electrodes, first and second unijunction transistors each having emitter and first and second gate electrodes, third and fourth resistance means connected between said first base electrodes and said negative terminal, fifth resistance means connected in series between said second base electrode of said first transistor and said positive terminal, sixth resistance means connected between said second base electrodes, a pair of timing capacitors connected between said emitter electrodes and said negative terminal, a pair of timing resistors connected between said emitter electrodes and said positive terminal to charge said timing capacitors until said emitter electrode of said second transistor reaches a firing potential at which said second transistor conducts to then lower the potential of said second base electrode of said first transistor and initiate firing thereof, thereby to simultaneously discharge said timing capacitors and simultaneously develop a pair of pulses at said first base electrodes, and means for applying said pulses to said gate electrodes to initiate conduction of one rectifier and cut oflf conduction through the other.

5. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, a silicon controlled rectifier having gate and anode electrodes, and a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, means for periodically applying a positive pulse to said gate electrode to render said rectifier conductive, means for internupting current through said rectifier after it has conducted for a certain length of time, and a resistor connected in parallel with said recti fier to limit the voltage thereacross while it is non-com ductive and to maintain said lamp in a dimmed condition.

6. In a railroad flashing light system, negative and positive terminals, means including a series resistor having an adjustable tap for connecting said terminals to a source of voltage which is either in a high range or a low range, a relay arranged to be energized when said voltage is in said high range and having a normally closed contact connecting said tap and one end of said resistor when said relay is deenergized, a silicon controlled rectifier having gate and anode electrodes, and a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, means for periodically applying a positive pulse to said gate electrode to render said rectifier conductive, and means for interrupting current through said rectifier after it has conducted for a certain length of time.

7. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, a first silicon controlled rectifier having gate and anode electrodes and having a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, means normally operative to maintain said gate electrode at a certain potential relative to said cathode, means for periodically applying a positive pulse signal to said gate electrode to initiate conduction of said rectifier, a capacitor having one terminal connected to said anode electrode, resistance means connected between the other terminal of said capacitor and said positive terminal to charge said capacitor while said rectifier conducts, a second silicon controlled rectifier having an emitter electrode, a cathode electrode connected to said negative terminal and an anode electrode connected to said other terminal of said capacitor, and means for applying -a positive pulse to said gate electrode of said second rectifier to interrupt current flow through said first rectifier after it has conducted for a certain length of time, said resistance means having a value high enough to starve said second rectifier of current after it has conducted to cut oli said first rectifier.

8. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, a silicon controlled rectifier having gate and anode electrodes and having a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, a unijunction transistor having an emitter and first and second base electrodes, first resistance means connected between said first base electrode and said negative terminal, a Zener diode having one terminal connected to said negative terminal, second resistance means connecting the other terminal of said diode to said positive terminal, third resistance means connected between said second base electrode and said other terminal of said diode, a timing capacitor connected between said emitter electrode and said negative terminal, a timing resistor connected between said emitter electrode and said positive terminal for charging said capacitor until said emitter electrode reaches a firing potential at which said transistor conducts to discharge said capacitor and to develop a positive pulse at said first base electrode, coupling means for applying said positive pulse to said gate electrode to initiate conduction of said silicon controlled rectifier, and means for interrupting current flow through said rectifier after it has conducted for a certain length of time following each positive pulse.

9. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode electrode connected to said negative terminal, first and second resistance means respectively connected between said anode electrodes and said positive terminal, at least one of said resistance means including a lamp, a commutation capacitor connected between said anode electrodes, first and second unijunction transistors each having emitter and first and second gate electrodes, third and fourth resistance means connected between said first base electrodes and said negative terminal, fifth resistance means connected in series between said second base electrode of said first transistor and said positive terminal, sixth resistance means connected between said second base electrodes, a pair of timing capacitors connected between said emitter electrodes and said negative terminal, a pair of timing resistors connected between said emitter electrodes and said positive terminal to charge said timing capacitors until said emitter electrode of said second transistor reaches a firing potential at which said second transistor conducts to then lower the potential of said second base electrode of said first transistor and initiate firing thereof, thereby to simultaneously discharge said timing capacitors and simultaneously develop a pair of pulses at said first base electrodes, means for applying said pulses to said gate electrodes to initiate conduction of one rectifier and cut off conduction through the other, and a capacitor connected between said positive terminal and the gate electrode of one of said rectifiers to insure conduction thereof upon initial application of supply voltage.

10. In a railroad flashing light system, negative and positive terminals, means including a series resistor having an adjustable tap for connecting said terminals to a source of voltage which is either in a high range or a low range, a relay arranged to be energized when said voltage is in said high range and having a normally closed contact connecting said tap and one end of said resistor when said relay is deenergized, a silicon controlled rectifier having gate and anode electrodes, and a cathode electrode con nected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, means for periodically applying a positive pulse to said gate electrode to render said rectifier conductive, means for interrupting current through said rectifier after it has conducted for a certain length of time, and a resistor connected in parallel with said rectifier to limit the voltage thereacross while it is non-conductive and to maintain said lamp in a dimmed condition.

11. In a railroad flashing light system, negative and positive termianls for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode electrode connected to said negative terminal, first and second lamps respectively connected between said anode electrodes and said positive terminal, a commutating capacitor connected between said anode electrodes, means for periodically applying a pair of synchronized pulses to said gate electrodes to initiate conduction of one rectifier and thereby cut off conduction through the other, and means mounting said lamps to project beams in angularly related directions.

12. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, a first silicon controlled rectifier having gate and anode electrodes and having a cathode electrode connected to said negative terminal, a lamp connected between said anode electrode and said positive terminal, means normally operative to maintain said electrode at a certain potential relative to said cathode, means for periodically applying a positive pulse signal to said gate electrode to initiate conduction of said rectifier, a capacitor having one terminal connected to said anode electrode, resistance means connected between the other terminal of said capacitor and said positive terminal to charge said capacitor while said rectifier conducts, a second silicon controlled rectifier having an emitter electrode, a cathode electrode connected to said negative terminal and an anode electrode connected to said other terminal of said capacitor, and means for applying a positive pulse to said gate electrode of said second rectifier to interrupt current flow through said first rectifier after it has conducted for a certain length of time, said resistance means including a econd larnp.

13. in a railroad flashing light system, negative and positive terminals for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode electrode connected to said negative terminal, first and second resistance means respectively connected between said anode electrodes and said positive terminal, at least one of said resistance means including a lamp, a coinrnutating capacitor connected between said anode electrodes, and means for periodically applying a pair of synchronized positive pulses to said gate electrodes to initiate conduction of one rectifier and to thereby cut ofi conduction through the other.

14. In a railroad flashing light system, negative and positive terminals for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode connected to said negative terminal, first and second lamps respectively conected between said anode electrodes and said positive terminal, a commutating capacitor connected between said anode electrodes, means normally operative to maintain each of said gate electrodes at a certain potential relative to said cathode, means for periodically applying a pair of synchronized pulses to said gate electrodes to initiate conduction of one rectifier and thereby cut oil conduction through the other, and a pair of resistors connected in parallel with said rectifiers to reduce the voltage across each rectifier while it is non-conductive and to also maintain the associated lamp in a dimmed condition.

15. In a railroad flashing light system, negative and postive terminals for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode electrode connected to said negative terminal, first and second resis ance means respectively connected between said anode electrodes and said positive terminal, at least one of said resistance means including a lamp, a coinrnutating capacitor connected between said anode electrodes, means for periodically applying a pair of synchronized positive pulses to said gate electrodes to initiate conduction of one rectifier and to thereby cut off conduction through the other, and a capacitor connected between said positive terminal and the gate electrode of one of said rectifiers to insure conduction thereof upon initial application of supply voltage.

16. In a railroad flashing light system, first and second lamps arranged to project a pair of beams in one direction, third an fourth lamps arranged to project beams at one side and the other of said pair of beams and at opposite angles relative thereto, negative and positive terminals for connection to a voltage source, first and second silicon controlled rectifiers each having gate and anode electrodes, and a cathode electrode connected to s negative terminal, connecting said first and rd larnps betwee said anode electrode of said first rectifier and said positive terminal, means connecting said second and fourth lamps between said anode electrode of said second rectifier and said positive terminal, a commutating capacitor connected between said anode electrodes, and means for periodically applying a pair of synchronized pulses to said gate electrodes to initiate conduction of one rectifier and thereby cut oil conduction through the other.

References Cited in the file of this patent UNITED STATES PATENTS 2,891,195 Srnyth June 16, 1959 3,002,127 Grontlrowski Sept. 26, 1961 3,024,386 Chauvineau Mar. 6, 1962

Claims

14. IN A RAILROAD FLASHING LIGHT SYSTEM, NEGATIVE AND POSITIVE TERMINALS FOR CONNECTION TO A VOLTAGE SOURCE, FIRST AND SECOND SILICON CONTROLLED RECTIFIERS EACH HAVING GATE AND ANODE ELECTRODES, AND A CATHODE CONNECTED TO SAID NEGATIVE TERMINAL, FIRST AND SECOND LAMPS RESPECTIVELY CONNECTED BETWEEN SAID ANODE ELECTRODES AND SAID POSITIVE TERMINAL, A COMMUTATING CAPACITOR CONNECTED BETWEEN SAID ANODE ELECTRODES, MEANS NORMALLY OPERATIVE TO MAINTAIN EACH OF SAID GATE ELECTRODES AT A CERTAIN POTENTIAL RELATIVE TO SAID CATHODE, MEANS FOR PERIODICALLY APPLYING A PAIR OF SYNCHRONIZED PULSES TO SAID GATE ELECTRODES TO INITIATE CONDUCTION OF ONE RECTIFIER AND THEREBY CUT OFF CONDUCTION THROUGH THE OTHER, AND A PAIR OF RESISTORS CONNECTED IN PARALLEL WITH SAID RECTIFIERS TO REDUCE THE VOLTAGE ACROSS EACH RECTIFIER WHILE IT IS NON-CONDUCTIVE AND TO ALSO MAINTAIN THE ASSOCIATED LAMP IN A DIMMED CONDITION.