US3646359A

US3646359A - Flasher circuit with outage indication

Info

Publication number: US3646359A
Application number: US35496A
Authority: US
Inventors: John F Bolinger
Original assignee: Meridian Industries Inc
Current assignee: Meridian Industries Inc
Priority date: 1970-05-07
Filing date: 1970-05-07
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28

Abstract

A flasher circuit has a power transistor controlling a circuit with a load therein; a multivibrator produces a timed pulse signal applied to the power transistor for turning the power transistor ''''on''''; and additional current sensing means coupled to the load and sensitive to a reduction in the current flow therethrough, due to an outage, is operatively connected to the multivibrator for eliminating the timed occurrence of said signal.

Description

United States Patent Bolinger 1 Feb. 29, 1972 [54] FLASHER CIRCUIT WITH OUTAGE 2,994,013 7/1961 Skellett ..331/113 X INDICATION 3,217,207 11/1965 Webb ..317/33 B 3,253,186 5/1966 Rogers et a1. ..331/1l3 X 1 lnvemofl John s" Mlchlsan Y 3,408,540 10/1968 Nield et al. ....317/14s.s B 7 Assigneez di -h fl Inc. southfield 3,551,744 12/1970 Keller et ....3l7/333 R Primary Examiner-Johns. Heyman [2 Filedi y 1970 Attorney-McGlyma, Reising, Milton 8!. Ethington, Martin J Adelman, Allen M. Krass, Owen E. Perry, Thomas N. Young [21] Appl. No.. 35,496 and Stanley C Thorpe [52] US. Cl ..307/202, 307/240, 307/246, [57] ABSTRACT [5| 1 Int Cl 307/247 307/252 331/113 A flasher circuit has a power transistor controlling a circuit [58] Fieid J with a load therein; a multivibrator produces a timed pulse 331/62 3l5/209 5 5 R 3 signal applied to the power transistor for turning the power 148 5 R 5 transistor on; and additional current sensing means coupled to the load and sensitive to a reduction in the current flow therethrough, due to an outage, is operatively connected to [56] References Cited the multivibrator for eliminating the timed occurrence of said UNITED STATES PATENTS Signal- 2,832,900 4/1958 Ford ..307/202 X 8 Claims, 1 Drawing Figure PAIENTEDFEB29 I972 INVENTOR. Jim ffiofz'zzgez BY v M fM ATTORNEYS FLASI'IER CIRCUIT WITH OUTAGE INDICATION BACKGROUND OF THE INVENTION Heretofore various circuits have been proposed for use as flasher circuits. However, such flasher circuits have been, and often still are, susceptible to the occurrence of a particular lamp or bulb, within the overall load, becoming burned out. Such occurrences can become dangerous where, for example, the flasher circuit is employed as a directional turn indicator on motor vehicles or an emergency flashing system as on school buses or the like, because the vehicle operator may not have knowledge that a particular lamp or bulb is burned out and is assuming that all pedestrians as well as other vehicles are aware that he is signaling his particular intent to perform a particular vehicular maneuver.

Accordingly, the invention as herein disclosed and described is directly concerned with the solution of the above as well as other related problems.

SUMMARY OF THE INVENTION According to the invention, a switching circuit comprises electrical load means, a load circuit containing said electrical load means, first load switching means in circuit with said load circuit, second means for cyclically producing a control signal for causing said first switching means to be at times rendered conductive, and additional means responsive to the occurrence of an outage condition in said load means and being effective in response thereto to prevent the said cyclic production of said control signal.

Various general and specific objects and advantages of the invention will become apparent when reference is made to the following detailed description considered in conjunction with the drawings.

DESCRIPTION OF THE DRAWINGS The single drawing is a schematic wiring diagram of a flasher circuit employing the invention disclosed herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greater detail, the singe drawing illustrates a flasher circuit comprised of a first conductor 12 having an end 14 suited for connection to a suitable source of electrical potential 16 and a second conductor 26 which leads to ground as at 28.

A signal producing portion 30 of the circuit 10 is illustrated as comprising oscillator means composed of

transistors

32 and 34. Transistor 32 has its collector electrode 36 connected in series with a resistor 38 leading to conductor 12 while its emitter electrode 40 is connected to conductor 26. Transistor 34 similarly has its collector electrode 42 connected, in series with a resistor 44, to conductor 12 while its emitter electrode 46 is connected, via conductor 48, to the base electrode 50 of a third transistor 52 which, in turn, has its emitter electrode 54 connected to conductor 26 via conductor means 27.

Base electrode 56 of transistor 32 is electrically connected, viaconductor S7, in series with one end of a resistor 58 which has its other end adapted for connection to conductor 12 as through a switch 20. Similarly, base electrode 60 of transistor 34 is electrically connected, via conductor 62, in series with one end of a resistor 64 which has its other end connected to conductor 12.

A first capacitor 66 has one end or side connected to a point electrically between resistor 38 and collector electrode 36 and the other end or side connected to conductor 62. A second capacitor 68 similarly has one side connected to a point electrically between resistor 44 and collector electrode 42 of transistor 34 while its other side is connected to conductor 57. Additionally, capacitors 70 and 71 may be provided so as to have their respective one sides connected to conductors 57 and 62 while their respective other sides are connected to ground through conductor 26.

The collector electrode 72 of transistor 52 is connected to a voltage divider network comprised of conductors 74, 76 and 78 between which are serially connected resistors 80 and 82. Conductor 78 is connected to conductor 12 while the base electrode 84 of a fourth transistor 86 is connected to a point generally between resistors 80 and 82 as at 88 on conductor 76. Transistor 86, which may be considered as a switching transistor, has its emitter electrode 90 connected to conductor 12 as by means of a conductor 92 while the collector electrode 94 thereof is connected, via conductor 96, to the base terminal 98 of a power or load switching transistor 100 the collector 102 of which is connected to conductor 12 by means of conductor 104. A conductor 106, connected at one end to the emitter 108 of transistor 100, has its other end connected to one end of coil means 110 the other end of which is connected to a conductor 112 leading to related electrical load means 114 which, in turn, is connected to ground as at 116. As shown, a resistor 118 has its opposite ends connected to conductors 96 and 106 while resistor 120 has its opposite ends respectively connected to conductors 48 and 26.

The circuit 10 may also include short protection means comprised of a shutdown transistor 122 having its emitter 124 connected, through a resistor 126, to conductor 12 while its collector 128 is connected, through a resistor 130, to ground as by conductor 26. The base electrode 132 of transistor 122 is connected, as by a conductor 134 and resistor 136 in series therewith, to conductor 74 as at 138.

A silicon-controlled rectifier (SCR) 140 has its anode connected, via conductor 142, to conductor 48, as at 144, while its cathode is connected by means of a conductor 146,- which may include a diode 148 serially arranged therewith, to conductor 106 as at 150. The gate electrode 152 of SCR 140 is connected through a resistor 154 to conductor 156 leading between collector 128 and resistor 130.

Generally, in order to make an SCR conductive, forwardly, it is necessary to apply a voltage across the anode to cathode terminals of the SCR (making the anode positive, with respect to the cathode) and at the same time apply a voltage (or current flow) to the gate-to-cathode circuit by making the gate positive, with respect to the cathode. Of course, if after the SCR is made conductive, current flow from the anode to cathode is interrupted, the SCR will again go into its nonconductive state.

7 In addition to the above, a diode 158 may be connected to conductor 106, as at 160, and to conductor 26, as at 162. Such a diode 158 has been found to be desirable where the particular circuit employed exhibited high inductance whenever the load was turned off. The provision of such means as diode 158 serves to reduce such circuit-created high inductance at load turnoff.

Further, it has been found that a zener diode 164 and diodes 166 and 168 are preferably serially provided in conductor means 27 when the associated short protection means disclosed herein is employed. Diodes 170 and 172 respectively connected in the base circuits of

transistors

32 and 34, although not essential to the practice of the invention, are nevertheless preferred in order to serve as voltage limiters for such transistors. In this connection, resistor 174, in series with conductor 12, may also be employed as a means of reducing the line voltage to the oscillator or multivibrator section 30. Capacitors 70, 71 and 73 are primarily provided as a means of noisesuppression in order to prevent

transistors

32, 34 and 52 from going into conduction as a result of stray signals.

OPERATION OF THE INVENTION In view of the above, it can be seen that each of transistors, 32, 34, 52 and 100 are of the NPN type while transistors 86 and 122 are of the PNP type. Accordingly, during normal conduction, in the NPN type, the emitter will be negative with respect to both the collector and base while the collector is positive with respect to both the emitter and base. In the PNP type, normal operation or conduction is achieved when the emitter is positive with respect to both the collector and base while the collector is negative with respect to both the emitter and base.

Further,

transistors

32 and 34 comprise a multivibrator the operation of which is generally as follows. First, for ease of presentation, let it be assumed that switch is nonexistant and that resistor 58 is connected to conductor 12; further, assuming that a related control switch 175 is closed, let it be assumed that transistor 32 has just switched on, creating current flow through the emitter-collector circuit 40, 36, and that transistor 34 has switched off or to its nonconducting state. It can be seen that at this particular instant capacitor 66 was fully charged and that the side thereof connected to resistor 64 was negative with respect to the other side of capacitor 66 which is connected to resistor 38 and collector 36. The circuit through emitter-collector circuit 36, 40 is completed to ground 28 as by conductor 26. At this time capacitor 68 will be discharged.

Capacitor 66 now starts charging toward the opposite polarity through resistor 64 by virtue of being essentially connected to conductor 26 when transistor 32 is conducting and the emitter-collector circuit thereof is completed. It can also be seen that because of the charge existing on capacitor 66, at the instant that transistor 32 went into conduction, and its connection to base electrode 60 of transistor 34 via conductor 62, the emitter-base electrodes of transistor 34 are reverse biased (the base being negative with respect to emitter 46) thereby keeping transistor 34 in an off or nonconducting state. At this same time, capacitor 68 will start to charge essentially through the emitter-base circuit of transistor 32 and resistor 44. This charging current holds transistor 32 conductive or hard-on; further, even when charging of capacitor 68 is completed, the transistor 32 will remain conductive by virtue of the base current provided by resistor 58.

As the potential across capacitor 66, holding transistor 34 off, is reduced, a condition is finally attained where the capacitor 66 voltage can no longer maintain transistor 34 in the nonconducting state. As transistor 34 starts to become conductive, by virtue of a biasing current through resistor 64, the collector to emitter voltage thereof drops and the charged capacitor 68 now starts to discharge through the emitter-base circuit of transistor 32, resulting in a reverse bias driving transistor 32 into nonconduction.

When transistor 32 is thusly driven into nonconduction, the voltage across its emitter 40 and collector 36 increases causing capacitor 66 to again start charging through the emitterbase circuit of conductive transistor 34.

In this new state (transistor 34 being conductive) capacitor 68 starts to charge toward the opposite polarity through resistor 58 by virtue of being connected to conductor 26 through the conducting transistor 34. When transistor 34 was switched into conduction, capacitor 68 was negatively charged on its side connected to conductor 57, with respect to its side connected between resistor 44 and collector 42. Further, the polarity on capacitor 68, at the time of switching transistor 34 on, produces a reverse bias on transistor 32.

During the time that transistor 34 is conducting capacitor 66 is being charged so that its end or side connected to resistor 64 and conductor 62 will become negative with respect to its side connected between resistor 38 and collector 36. Such charging of the capacitor 66 is the consequence of the base current flow through transistor 34 which also serves to hold the transistor 34 in its on or conductive state. It should be apparent that transistor 32 is also maintained conductive for some period after capacitor 66 has been fully charged because of the base bias provided by resistor 64.

However, as capacitor 68 continues to discharge and the voltage thereacross approaches zero, the voltage holding transistor 32 in a nonconducting state decreases and transistor 32 starts to again become conductive. This initiates the regenerative cycle which results in the rapid tum on of transistor 32 and tumoff of transistor 34 as well as the subsequent rapid tumoff of transistor 32 and tum on" of transistor 34. In this

arrangement resistors

38 and 44 serve to respectively limit the collector currents of

transistors

32 and 34 while resistor 64 and capacitor 66 combine to determine the off" or nonconducting time of transistor 34 and, similarly, resistor 58 and capacitor 68 combine to determine the off or nonconducting time of transistor 32.

It can be seen that when transistor 34 is in its conducting state, the emitter-base circuit of transistor 52 is biased into conduction thereby completing the circuit through the emitter 54 and collector 72 of transistor 52. When transistor 52 is thusly driven into conduction, a circuit is completed through conductors 78, 76 and 74, collector electrode 72, emitter 54 and conductor means 27 causing a voltage drop to occur across resistor 82 thereby causing point 88 and base 84 to be negative with respect to emitter which is exposed to plus potential of conductor 12. Consequently switching transistor 86 is turned on completing a circuit through the emitter 90 and collector 94 thereby, through conductor 96, placing the base electrode 98 of load or power transistor 100 effectively at the plus potential of conductor 12. The emitter 108 is, in turn, at negative potential of ground 116. Accordingly, with emitter 108 negative with respect to base 98, transistor 100 is turned on completing the load circuit comprised of conductors 104, collector 102, emitter 108, conductor 106, coil 110 and conductor 112 so as to energize the electrical load means 114. As should be apparent, the diagrammatically depicted load means 114 may in fact be comprised of, for example, one or a plurality of lamps or bulbs and, as is often the case, some of such bulbs could be located within the interior of the vehicular passenger compartment, as operator signal readouts, while others could be located externally of the vehicle as indicators to pedestrians and vehicular traffic.

In view of the preceding, it can be seen that, in the embodiment disclosed, every time that oscillator or multivibrator transistor 34 is turned on the buffer transistor 52, switching transistor 86 and load transistor 100 are likewise turned on." The contrary is, of course, true; that is, whenever transistor 34 is in its off or nonconductive state, transistors 52, 86 and 100 are also in their off or nonconductive state.

Now, considering the short protection means, it will be remembered that in order to make the SCR 140 conductive, both the anode and gate thereof have to be made positive with respect to the cathode. Accordingly, it can be seen that whenever the shutdown transistor 122 is off or in a nonconductive state, the circuit described by conductor 176, resistor 126, conductor 178, conductor 156 and resistor is open by virtue of no conduction through the emitter-collector circuit of transistor 122. Consequently, the gate electrode 152 of SCR will be at negative or ground potential by virtue of its connection to conductor 156.

However, it will be noted that each time transistor 52 goes into conduction base 132 of transistor 122 is effectively brought to ground potential as at point 138 thereby causing transistor 122 to become conductive thereby completing the circuit through conductors 176, 178 and 156. Gate 152 is therefore made positive by virtue of resistors 126 and 130 acting as a voltage divider. However, SCR 140 does not go into conduction because its cathode is effectively at positive potential by virtue of its connection to conductor 106 as at which, because of transistor 100 being on, is at the plus potential of conductor 12.

Now, let it be assumed that a short has occurred in the load 114 and that transistor 34 has just turned on" which, as explained above, causes the transistor 122 to be simultaneously turned on. Therefore, gate 152 of SCR 140 is made positive and the cathode of SCR 140, by virtue of the short in the load 114, is placed effectively at ground potential. Further, with transistor 34 being on the anode of SCR 140 is at same plus value relative to its cathode. This, of course, as previously explained, causes SCR 140 to become conductive completing a circuit from point 144 through conductors 142, 146 and 112.

When the SCR- thereby becomes conductive, the forward bias on the base-emitter circuit of transistor 52 is eliminated or so reduced as to prevent transistor 52 from going to conduction which, in turn, prevents transistors 86 and 100 from being turned on" thereby eliminating the possibility of damage to the load transistor 100 as a consequence of such a short in the load.

As was previously stated, it has been found advantageous to provide means such as the zener diode 164. That is, when SCR 140 is made conductive, a voltage drop, in the order of possibly 1.0 volts, will occur across the SCR 140. However, this voltage drop would also appear across the base-emitter diode of the transistor 52 and would be sufficient to cause the transistor 52 to become conductive. Accordingly, by including the zener diode 164 in the emitter circuit of transistor 52 such possible tum-on" of the transistor will be positively prevented until the potential across the base-emitterzener becomes of a value distinctly in excess of the voltage drop across SCR 140 when in its conducting state.

Having described the operation of the signal producing section 30 and the nonnal load switching operation as well as the function and operation of the related short protection means, the remaining circuitry and operation of the related outage indication means will now be considered.

The concern with the occurrence of shorts arises because of the loss of effective resistance in the load circuit; in contrast, with the occurrence of an outage condition, at least some portion of the electrical load is, for example, burned out and therefore such portion appears as an open switch in the cir cuit. Y

The operation of the circuitry remains the same as previously described except that now switch is again considered as being in the location illustrated, and operatively connected, as by means 180, to coil 110. (Switch 20 and winding 110 may, in fact, comprise a reed-type switch wherein member 20 is moved, without benefit of mechanical connections, to open and closed positions in response to the generation of an associated magnetic field.)

Switch 20 can be considered as a normally open switch in the sense that it will be open, as shown, whenever there is either no current flow through coil 110 orcurrent flow below a predetermined value.

Accordingly, when the associated master switch 175 is closed current will not be pennitted to flow through resistor 58 because of the open switch 20; however, as previously described, current flow through resistor 64 causes transistor 34 to be turned on" thereby causing transistors 52, 86 and 100 to be also driven into conduction. If the load 114 is nor mal (no outage present) the current flow through winding 110 will be sufiicient to cause switch 20 to become closed thereby permitting the oscillator or multivibrator to function normally, as previously described, causing the transistor 34 to be cyclically energized.

However, should one or more of the individual loads 1140,

114b, or ll4c (if in fact the load 114 is comprised of a plurali-' ty of loads) create an outage as by becoming burned out, the efiective resistance of the electrical load means will increase thereby reducing the magnitude of the current flow therethrough as well as through the winding or field generating means 110. Therefore, if the winding or field generating means 110 is so constructed or calculated as to develop sufficient force or energy to close switch 20 only when all of the electrical loads in the load means 114 are normal, it-can be seen then that upon the occurrence of an outage in the load means, the current therethrough will diminish to a value less than a predetermined minimum value resulting in switch 20 again becoming opened and remaining open.

When this happens, the base circuit of transistor 32 loses its forward bias and therefore remains in a nonconductive state while transistor 34 becomes continuously forwardly biased through resistor 64 thereby remaining "on or in its conductive state. As a consequence of transistor 34 being held on the remaining transistors 52, 86 and 100 are also held on thereby serving to keep the normal electrical loads (the ones which have not burned out) in a continuously energized state which would indicate to the vehicle operator that an outage had occurred. A resistor 182 arranged in parallel with capaci' tor 68 serves as a bleed resistor permitting the capacitor 68 to be discharged therethrough whenever switch 20 is opened.

In view of the preceding, it should be apparent that functional equivalents could be substituted for the various sections of the circuitry as well as components or elements contained therein. Also, as should be apparent, the circuitry disclosed could be practical employing NPN transistors for those that are shown as PNP and vice versa where appropriate polarity changes are made as is well known in the art.

Although only one embodiment of the invention has been disclosed and described, it should be apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims.

I claim:

1. A flasher circuit of the type adapted to intermittently energize a signal lamp load from a voltage source including an oscillator for producing intermittent control signal impulses, a switching device adapted to be switched between on and off conditions in response to said control signal impulses to connect and disconnect the load and the voltage source, the improvement comprising control means connected in circuit with said load and effective to change from a first condition to a second condition when the magnitude of the current through the load decreases below a predetermined value, said control means being efiective in said second condition to hold said switching device in said on condition whereby a decrease of said current below said predetennined value causes the remaining signal lamps to be continuously energized from said voltage source to indicate the outage of one of said signal lamps.

2. The invention as defined in claim 1 wherein said control means is a current-responsive device having an input circuit connected with said load circuit and an output circuit operatively connected with said switching device.

3. The invention as defined in claim 2 wherein said control means comprises a relay having an energizing winding in said load circuit and having switch contacts operatively connected with said switching device.

4. The invention as defined in claim 3 wherein said oscillator is a multivibrator comprising a pair of cross-coupled transistors and the switch contacts of said relay are connected in the input circuit of one of said transistors.

5. A flasher circuit for automotive vehicles and adapted to intermittently energize a load circuit including signal lamps from a voltage source, an oscillator for producing intermittent control signal impulses, a switching device connected with the oscillator and adapted to be switched between on and off conditions in response to the intermittent control signal impulses to connect and disconnect the load circuit and the voltage source, .first control means having an input connected across the load and having an output connected to the switching device, said first control means being adapted to change from a first conductive state to a second conductive state when the voltage across the input thereof decreases below a predetermined value and being efiective in said second conductive state to hold said switching device in said off condition to deenergize the load in the event of a short circuit, second control means having an input connected with the load circuit and an output operatively connected with said switching device, said second control means being adapted to change from a first conductive state to a second conductive state when an open circuit occurs in one of the signal lamps and the current through said load decreases below a predetermined value, said second control means being effective in the second conductive state to hold said switching device in the on condition and continuously energize the remaining signal lamps in the load circuit.

6. The invention as defined in claim 5 wherein said first control means is a voltage-responsive device and said second control means is a current responsive device.

tor is a multivibrator comprising a pair of crosscoupled transistors and the switch contacts of said relay are connected to the input of one of said transistors to hold the multivibrator in one stable state when the contacts are closed.

Claims

1. A flasher circuit of the type adapted to intermittently energize a signal lamp load from a voltage source including an oscillator for producing intermittent control signal impulses, a switching device adapted to be switched between on and off conditions in response to said control signal impulses to connect and disconnect the load and the voltage source, the improvement comprising control means connected in circuit with said load and effective to change from a first condition to a second condition when the magnitude of the current through the load decreases below a predetermined value, said control means being effective in said second condition to hold said switching device in said on condition whereby a decrease of said current below said predetermined value causes the remaining signal lamps to be continuously energized from said voltage source to indicate the outage of onE of said signal lamps.

5. A flasher circuit for automotive vehicles and adapted to intermittently energize a load circuit including signal lamps from a voltage source, an oscillator for producing intermittent control signal impulses, a switching device connected with the oscillator and adapted to be switched between on and off conditions in response to the intermittent control signal impulses to connect and disconnect the load circuit and the voltage source, first control means having an input connected across the load and having an output connected to the switching device, said first control means being adapted to change from a first conductive state to a second conductive state when the voltage across the input thereof decreases below a predetermined value and being effective in said second conductive state to hold said switching device in said off condition to deenergize the load in the event of a short circuit, second control means having an input connected with the load circuit and an output operatively connected with said switching device, said second control means being adapted to change from a first conductive state to a second conductive state when an open circuit occurs in one of the signal lamps and the current through said load decreases below a predetermined value, said second control means being effective in the second conductive state to hold said switching device in the on condition and continuously energize the remaining signal lamps in the load circuit.

7. The invention as defined in claim 6 wherein said current responsive device is a relay having an energizing winding in circuit with the load and having switch contacts operatively connected with the switching device.

8. The invention as defined in claim 7 wherein said oscillator is a multivibrator comprising a pair of cross-coupled transistors and the switch contacts of said relay are connected to the input of one of said transistors to hold the multivibrator in one stable state when the contacts are closed.