Transistorized Flasher Circuit

Abstract

A transistorized flasher circuit having a set of normally closed relay contacts in series with a lamp load across a voltage source. The relay contacts are periodically opened and closed to flash the load by an oscillator which includes a relay coil which controls the relay contacts and includes the emitter and collector electrodes of a transistor connected in series. The base electrode of the transistor is connected between a capacitor and a resistor which are in series across the source. A discharge path is provided for the capacitor when the relay coil is energized. The transistor is turned on to energize the coil when the capacitor is charged and is turned off to deenergize the coil when the capacitor is discharged, whereby the source is periodically connected directly to the lamp load for flashing the lamps as the capacitor is periodically charged and discharged.

Parent Case Text

This application is a substitute for the application SN 130,157 filed Aug. 8, 1961, now abandoned.

Description

This invention relates to a transistorized flasher circuit and more particularly to flasher circuits of the type suitable for use in vehicle signal light circuits.

Many types of flashers have been proposed to produce a periodic current for use in blinking turn signals lamps and other warning lamps for vehicles. Usually such flashers are sensitive to load conditions so that a change of flasher frequency occurs whenever the circuit load changes thereby necessitating a different flasher design for each type of signal system, and further, any particular signal circuit utilizing such a flasher must be limited to a single load magnitude.

The present invention contemplates a flasher which is not affected by load changes and hence is universal in its application, and further permits a change of load within any particular signal system.

The invention is carried out by providing an improved low frequency transistorized relaxation oscillator wherein means within the circuit not only assist in the oscillation function, but also cause periodic energization of the output terminal of the flasher.

The above and other advantages are made more apparent from the following specification taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts and wherein:

FIG. 1 is a schematic diagram of a transistorized flasher according to the invention; and

FIG. 2 is a schematic diagram of another embodiment of a flasher and associated warning signal circuitry according to the invention.

Referring now to FIG. 1, a flasher 10 comprises a transistor 12 having emitter 14, collector 16, and base terminals 18. The emitter 14 is connected through a relay coil 20, positive input terminal 21, and manually operated switch 22 to the positive terminal 24 of a power supply such as a battery 26 while the collector 16 is connected directly to the negative input terminal 27 of the flasher and to the negative terminal 28 of the power supply 26 which may be grounded. The transistor base 18 is connected through a variable base resistor 30 to the negative input terminal 27. A capacitor 32 is connected between the positive input terminal 21 and the transistor base 18. A switching armature 34 controlled by the relay coil 20 is also connected to the positive terminal 21 and is normally closed with respect to a first contact 36 which in turn is connected to the flasher output terminal 38. When the relay coil 20 is energized, the armature 34 is moved from the first contact and closes with a second contact 40 which is connected through a variable discharge-controlling resistor 42 to the transistor base 18. A small capacitor 44 is connected between the second contact 40 and the negative input terminal 27. The purpose of this capacitor 44 is to provide a small discharge upon operation of the armature 34 to clean the second contact 40 and the associated armature contact area.

In operation, when the manual switch 22 is initially closed the capacitor 32 is not charged and hence the full power supply potential appears across the base resistor 30 thereby biasing the transistor 12 to cut off so that no current will flow through the emitter-collector circuit. However, as current flows through the capacitor 32 the voltage across the base resistor 30 gradually decreases so that the emitter-base current through the transistor 12 increases, and hence the emitter-collector current increases. When the emitter current flowing through the relay coil 20 becomes large enough to pull in the relay armature 34, the armature 34 will move from the first contact 36 to the second contact 40 thereby removing the battery voltage from the output terminal 38 and at the same time providing a discharge path for the capacitor through the armature 34, the second contact 40, and the variable resistor 42. Obviously this current flow causes the voltage across the capacitor 32 to decrease and the voltage across the base resistor 30 to increase. Eventually the voltage across the base resistor 30 will increase to the point where the emitter current is diminished to a value insufficient to hold in the relay armature, and then the armature 34 will return to the first contact 36 to reenergize the outlet terminal 38 and to initiate another cycle of the flasher.

The time required to charge the capacitor 32 sufficiently to cause the relay armature 34 to pull in is, of course, a function of the size of the capacitor 32 and of the base resistor 30. Accordingly, this period may be adjusted by varying the magnitude of the base resistor 30. Similarly, the time required to cause the relay to drop out is adjustable by varying the magnitude of the discharge-controlling resistor 42. It follows that the total oscillation period of the flasher is a function of the sizes of both resistors.

It has been found that when an RCA 2N408 transistor and a 12 volt power supply are used, then suitable values for the other components to produce a flash rate of 1 or 2 cycles per second are 100 microfarads for the capacitor 32, 410 ohms for the relay coil 20, and nominal values of 5,000 ohms, and 27,000 ohms for the two resistors 42 and 30, respectively.

Among the advantages of the flasher of this invention is that variations in load conditions of circuits associated with the load terminal have no effect on flasher operation, since the oscillation function of the flasher circuitry is entirely independent of the load terminal. Another advantage is that inherent voltage regulation is provided in that any transients due to opening or closing of contacts will not be applied directly to the emitter 14 but rather will be initially applied across the coil 20.

A specific example of an application of a flasher of the type described is illustrated in FIG. 2 wherein a slightly modified flasher is used. The circuit of FIG. 2 is a vehicle warning light circuit similar to that described in out copending application U. S. Serial No. 130,158, now U. S. Pat. No. 3,213,418, filed Aug. 8, 1961, for "Turn Signal and Warning System", and assigned to the assignee of the present invention. A turn signal system comprises two banks of switches each controlled by a relay coil 56, 56'. When the switches 50, 50' are in the position shown, a brake switch 58 energizes the brake light circuit 60 and causes illumination of the combined stop and turn lamps 62, 62' by way of rear turn signal switches 53, 53'.

When the left turn signal actuating push button switch 64 is manually closed momentarily, the left relay coil 56 will be energized by current flowing from the battery 66 through an ignition switch 68, a manual cancel switch 70 and through the left turn signal switch 64, and the relay coil 56 to ground to pull down the left bank of switches 50. The closing of the left holding switch 51 permits current flow therethrough and through a connecting line 72 to the flasher 10'. In addition, current will flow from the connecting line 72 through the right holding switch 51', and through an auxiliary line 74 to the left relay coil 56 thereby establishing a holding circuit for the left relay coil 56. The flasher 10' is somewhat similar to the flasher 10 described above in FIG. 1 but differs in that two relay armatures 34' and 35' and three associated output contacts 36', 40', and 41' are used and the base resistor regulates both the charging and discharging of the capacitor 32'. When the relay coil 20' is not energized, the first armature 34' is closed with the contact 36' which is connected to the front turn circuit 76 thereby lighting the left front turn lamp 78 through the closed left front turn switch 52. When the relay coil 20' is energized, the first armature 34' closes with contact 40' connected with the rear turn circuit 80 permitting current to flow through the left rear turn switch 53 and the left rear lamp 62. At the same time, however, the second armature 35' is closed with contact 41' permitting current to flow through the left pilot switch 54, the left pilot lamp 82, and the left front turn lamp 78 to ground. While the current is sufficient to illuminate the high resistance pilot lamp 82, it will not illuminate the turn lamp 78. In order for the flasher 10' to operate it is necessary to provide a capacitor discharge circuit, and this is accomplished by connecting the base resistor with the contact 40'. Since the transistor base is then grounded through the left rear lamp 62, burnout of that lamp will cause the flasher to stop operating, and hence, the pilot lamp 82 will not light. However, if only the left front lamp 78 burns out, then the flasher operation will not be impaired, but the pilot lamp 82 will not light since it is grounded through the left front lamp 78. Accordingly, the circuit provides a positive indication of any lamp failure. Since the turn signal circuit is symmetrical, the right turn signal may be operated in exactly the same way as that described for the left turn signal.

In certain cases it is desirable to flash both right and left sets of turn signal lamps 62, 78 and 62', 78' simultaneously to provide an emergency warning signal. Referring again to FIG. 2, if the emergency flash switch 84 is closed with its associated contacts 86, 86', then both right and left relay coils 56, 56' will be energized and both banks of switches 50, 50' will be pulled down. The flasher will operate to flash both sets of turn signal lamps 62, 78 and 62', 78' at the same flashing rate used to flash a single set of lamps, since the flasher is insensitive to load conditions except when indicating the complete failure of a rear lamp. In the case of the emergency signal, even the burnout of one rear lamp 62 or 62' will not impair the operation of the flasher 10' since the remaining lamp will provide a ground for the transistor base circuit.

It will thus be readily seen that the present invention provides an improved flasher and permits the use of warning signal circuits which are not practical for use with previous flashers.

It is not intended to limit the scope of the invention to the circuits described herein, but rather it is to be limited only by the following claims:

Claims

We claim:

1. A flasher comprising a transistor having an emitter, a collector, and a base, a relay coil in series with said emitter, capacitor means associated with said transistor for controlling the current therethrough, an input terminal connected with said relay coil, an output terminal, a resistor connected to said base, and a relay armature connected to said input terminal and alternately connectable to said output terminal and said resistor.

2. A flasher comprising a transistor having an emitter, a collector, and a base, a relay coil in series with said emitter, a capacitor connected between said coil and base, an input terminal connected with said relay coil, an output terminal, a first resistor connected to said base, a relay armature connected to said input terminal and alternately connectable to said output terminal and said resistor, and a second resistor connected between said base and said collector.

3. A flasher comprising a transistor having an emitter, a collector, and a base, a relay coil in series with said emitter, an input terminal connected with said relay coil, a capacitor connected between said input terminal and base, an output terminal, a resistor connected to said base, and a relay armature connected to said input terminal and alternately connectable to said output terminal and said resistor.

4. A flasher comprising input and output terminals, a transistor having an emitter, a collector, and a base, the emitter being connected with said input terminal, a capacitor connected between said input terminal and said base, means responsive to the voltage across the capacitor for controlling emitter current, and relay means energized by emitter current for effecting charging and discharging of said capacitor and for effecting periodic energization of said output terminal.

5. A warning light circuit including at least one lamp and a flasher, said flasher comprising input and output terminals, a transistor having an emitter, a collector, and a base, the emitter being connected with said input terminal, a capacitor connected between said input terminal and said base, biasing means responsive to the voltage across the capacitor for controlling emitter current, and relay means responsive to emitter current to effect charging and discharging of said capacitor and periodic energization of said output terminal.

6. A warning light circuit including at least one warning lamp, a flasher, and a power source, said flasher having a transistor having an emitter, a collector, and a base, a capacitor connected between said power source and said base, a resistor connected to said base, a capacitor charging path including said resistor and said lamp, a capacitor discharge path including said resistor, and means responsive to emitter current for effecting charging and discharging of said capacitor.

7. A warning light circuit including at least one warning lamp, a flasher, and a power source, said flasher having a transistor having an emitter, a collector, and a base, a capacitor connected between said power source and said base, a resistor connected to said base, a capacitor charging path including said resistor and said lamp, a capacitor discharge path including said resistor, and relay means in series with said emitter and responsive to emitter current for effecting charging and discharging of said capacitor.

8. A warning light circuit including at least one warning lamp, a flasher, and a power source, said flasher having a transistor having an emitter, a collector, and a base, a capacitor connected between said power source and said base, a resistor connected to said base, a capacitor-charging path including said resistor and said lamp, a capacitor discharge path including said resistor, a base bias means including said resistor, and means responsive to emitter current for effecting charging and discharging of said capacitor.

9. A signal circuit including several lamps, a flasher, and a voltage source, said flasher including a capacitor, a transistor controlled by said capacitor, a switch means operated by said transistor, said switch means normally connecting the voltage source to at least one of said lamps and alternately connecting the voltage source to other of said lamps, a capacitor discharge path controlled by said switch means, and a capacitor charge path including one of said lamps.

10. A flasher having input, output and common terminals adapted to receive a direct voltage across the input and common terminals and to develop a periodic voltage between the output and common terminals, a transistor having input, output and common electrodes, a relay including a coil and an armature movable between first and second contacts, the armature being connected to the input terminal, the coil being connected between the input and common terminals through the output and common electrodes of the transistor, a resistor connected between the input electrode and the common terminal, a capacitor connected between the input terminal and the input electrode whereby charging current for the condenser biases the transistor to one conductive condition, the first contact being connected to the output terminal and the second contact being connected to the input electrode whereby the condenser is discharged and the transistor is biased to its other conductive condition.

11. In an electronic switching circuit: a source of direct current and a switch in series; a transistor connected as an emitter follower with a relay in the emitter circuit; and a charging circuit connected across the battery and switch comprising a load, charging resistor, and charging capacitor, the junction of the charging resistor and charging capacitor being connected to the base of the transistor; said relay having a normally open contact adapted when closed to connect the battery voltage across the lamp load; the closing of the relay contact allowing the charging capacitor to discharge through the charging resistor.

12. An electronic switching circuit comprising: a battery and switch in series; a transistor, a series combination of a relay, the transistor emitter, and the transistor collector in that order connected across the battery and switch; a second series combination of a load and a normally open contact in said relay connected across the battery and switch; and a third series combination of a capacitor and a resistor connected across the relay contact, the junction point of the resistor and capacitor being connected to the base of the transistor.

13. In an electronic switching circuit: a source of direct current, a load, resistance means and a capacitor connected in series; a relay and the collector and emitter electrodes of a transistor connected across said source, said relay being connected to the emitter of the transistor; the junction point of the resistor and capacitor being connected to the base electrode of said transistor; and a normally open contact in said relay adapted to complete a circuit when said relay is energized to place substantially the full potential of said source across said load.

14. In an electronic switching circuit: a source of direct current and a switch in series; a transistor; a relay connected to the emitter electrode of said transistor, said transistor having its collector and emitter circuit including said relay connected across said source and switch; a load, said relay having a normally open contact connected in series with said load, said load and relay contact being connected across said source and switch in parallel with said transistor collector-emitter circuit; and means connecting said load, the base electrode of said transistor and said source to alter the potential at said base electrode when said switch is closed thereby causing current flowing through said collector-emitter circuit to energize said relay and complete a circuit through said source, switch, load and relay contact.

15. A circuit as defined in claim 14, wherein said potential altering means comprises a resistor and capacitor connected in series between said load and source, the junction point of said resistor and capacitor being connected to said base electrode.

16. A flasher comprising a transistor having an emitter, a collector, and a base; a first input terminal, a relay coil connected between the input terminal and the emitter, a second input terminal connected to the collector, the input terminals being adapted to be connected across a source of energy, a timing capacitor connected between the first input terminal and the base, a relay armature actuated by the relay coil connected to the first input terminal and cooperating with alternately engageable contacts, a timing resistor connected between one said contact and the base, and an output terminal connected to the other said contact.