Method and Apparatus for Saving Energy

This invention relates to a method and apparatus for saving the energy of a power source and more particularly to regulating circuits for allowing DC or battery powered lamps to be efficiently operated at a desired, constant output light level over a wide range of source voltages without the need for replacing the power source.

One form of direct current powered lamp is the conventional hazard warning lamp that may be controlled to flash on and off to signal a hazard to a motorist or pedestrian. A timing device is conventionally employed with these flashing lamps to control the duration of the flash to some preselected, fixed time interval which is typically 100 milliseconds. A major cost in the use of battery operated flashers is the cost of replacing the battery which is employed for powering these hazard warning lights. It has been found that when a battery is new its voltage is high so that the luminous flux output of the lamp is greater than required. This excessive generation of luminous flux from the lamp is wasteful of the battery power and contributes to the degeneration of the battery voltage at a faster rate than necessary. As the battery voltage decreases with use, a point is reached when the luminous flux output of the lamp is at the desired preselected light level. Any further use of the battery beyond this voltage level results in a reduction of luminous flux output. In present day battery powered warning systems this occurs at about 75-80 percent of the rated battery voltage or the battery voltage at the time of installation of a new battery. It is then necessary to replace such a battery even though its full power capabilities have not been expended. Any attempt to operate at lower battery voltages by using lamps of a lower voltage rating has resulted in accelerating the initial waste of power and also lowers the lamp filament life.

The present invention provides a relatively inexpensive regulation method and regulation circuits for DC or battery powered lamps to maintain a constant luminous flux output from the lamp over a substantial range of voltages of the source to extend the life of the battery for substantially longer periods of time than it was heretofore thought possible. In accordance with the teachings of the present invention, battery powered lamps may be used until about 50 percent of the rated voltage of the battery is reached as contrasted with the present day battery lives of 75-80 percent of the new battery voltage. This represents a substantial increase in battery life than that possible with present day systems. While increasing the battery life, the method and apparatus of the present invention prevents excessive power dissipation when the initial or rated voltage is delivered from the battery. The regulating system of the present invention prevents the wasting of energy when the battery is new or the voltage is high by switching the battery on and off to the lamp at a controlled duty cycle to maintain a constant flux output from the lamp. When the voltage is less than the rated voltage of the battery or the power source, the regulator increases the duty cycle to compensate for the reduced voltage to maintain the desired light output from the lamp. In addition, the regulating system of the present invention allows a lower voltage rated lamp to be employed than the rated voltage output for the power source without excessive energy dissipation so that the battery can be used until the voltage reaches approximately 50 percent of its initial voltage level. For example, a 6-volt lamp can be used with a 12-volt supply thereby yielding a significant increase in battery life not heretofore thought possible. The luminous light flux from the lamp is controlled by the regulating systems of the present invention by varying the duty cycle at which the lamp is switched on and off in response to a feedback signal from the energized lamp representative of a lamp operating parameter which may be either lamp voltage or lamp resistance.

From a method standpoint, the method of the present invention maintains a luminous flux output of a DC powered lamp substantially constant with variations in the voltage output of the power source through the steps of sensing the lamp parameter to be controlled and providing a feedback signal proportional to the value sensed. This lamp feedback signal is compared with a reference signal proportioned to maintain the luminous flux output of the lamp at a preselected constant level and providing a comparison output signal representative of any deviations between the feed back signal and the reference signal. The comparison output signal is employed for switching the power source to the lamp on and off at a duty cycle proportioned relative to the magnitude of the comparison output signal to maintain a substantially constant flux output from the lamp over a relatively wide range of voltage variations in the source.

In a specific apparatus embodiment of the present invention, a regulating system for a DC powered lamp comprises a bridge circuit having impedance means of preselected impedance value arranged in three legs of the bridge circuit and a lamp to be regulated connected as the fourth leg of the bridge circuit. The value of the impedance means in each of the three legs of the bridge circuit are proportioned relative to the impedance of the lamp undergoing regulation to provide a balanced bridge circuit condition when the energized lamp produces a preselected luminous flux output. The error amplifying means has its input circuit connected to the pair of junctions between each pair of legs of the bridge circuit for detecting the deviations in impedance exhibit by the lamp and provides an amplifier error output signal in accordance with the sensed deviations. The regulation system includes an alternating current signal generating means providing an output signal having a preselected wave shape and exhibiting reversals in direction regularly and continuously. Comparison means are coupled to be responsive to the output signals from the signal generating means and the error amplifying means for providing lamp regulating output signal pulses during the time intervals one of the input signals has a greater instantaneous voltage magnitude than the other signal. The source of DC voltage or the battery is coupled between the other pair of junctions of the legs of the bridge circuit for powering the bridge circuit. Electrical switching circuit means is coupled to be responsive to the lamp regulating output signal pulses from the comparison means and is coupled between the power source and the bridge circuit for coupling the power source to the bridge circuit in accordance with the reception of a regulating signal pulse and for decoupling the power source from the bridge circuit in the absence of a regulating signal pulse.

These and other features of the present invention may be more fully appreciated when considered in the light of the following specification and drawings, in which:

FIG. 1 is a general block diagram of the energy saving system concept embodying the present invention;

FIG. 2A is a graphical representation of a typical output signal from the AC signal generator and a typical output signal from the error amplifier for the system illustrated in FIG. 1;

FIG. 2B is a graphical representation of the regulating output signal pulses derived from the comparison means of the system of FIG. 1;

FIG. 3 is a schematic-block diagram of one embodiment of the regulating system of FIG. 1;

FIG. 4 is a schematic-block diagram of another embodiment of the regulating system of FIG. 1;

FIG. 5 is a graphical illustration of the RMS voltage of a lamp with varying battery voltages when the regulating system of FIG. 4 is employed therewith;

FIG. 6 is a schematic-block diagram of a balanced bridge circuit embodiment of the regulating system illustrated in FIG. 1;

FIG. 7 is a schematic diagram of a complete regulating system utilizing the bridge circuit arrangement illustrated in FIG. 6;

FIG. 8 is a schematic diagram of the basic embodiment of FIG. 1 wherein the lamp feedback is error-corrected by summing it with battery voltage in a desired proportion;

FIG. 9 is a block diagram of another embodiment of the duty cycle control for the energy saving system concept of FIG. 1;

FIG. 10 is a block diagram of a duty cycle lamp control circuit based on sensing the power applied to the lamp;

FIG. 11 is a block diagram of a lamp regulating circuit wherein the feedback signal is based on sensing the luminous flux generated by the lamp.

Now referring to the drawings, and with particular reference to FIG. 1, the basic concept of the invention utilized in the implementation of its various embodiments will be described in detail. An important aspect in the implementation of the invention is the means for supplying a feedback signal to the regulating system for maintaining a constant luminous flux output from the regulated lamp. The various embodiments of the invention illustrated in FIGS. 3, 4 and 6 all embody the basic concept illustrated in FIG. 1 but implement the means for supplying the feedback signal by different means. The feedback signal utilized in the regulating system for the lamp undergoing regulation represents a lamp electrical operating parameter for signalling the actual voltage applied to the lamp from the power source of a battery. This electrical lamp operating parameter may be either the lamp voltage or the lamp resistance. The embodiments illustrated in FIGS. 3, 4 and 8 provide a lamp voltage feedback signal while the embodiments of FIGS. 1, 6 and 7 employ a lamp resistance feedback signal. With the derivation of the desired feedback signal representative of the lamp electrical operating parameter, the luminous flux output of the lamp undergoing regulation is controlled by varying the duty cycle at which the power is switched on and off to the lamp in response to the feedback signal.

As illustrated in FIG. 1, the lamp 10 undergoing regulation is connected to a DC voltage source 11 by means of an electronic switching circuit 12 connected to control the coupling and decoupling of the DC voltage source to the lamp 10. One terminal of the lamp 10, as well as one terminal of the DC voltage source 11 is connected directly to ground. An error amplifier 13 which may be an operational amplifier has one of its inputs connected to a reference source 14 for comparison with the feedback signal which is representative of the lamp electrical operating parameter. The feedback signal is provided by the lead wire 15 connected between the battery side of the lamp 10 to the negative terminal of the error amplifier 13. The reference source 14 is connected to the positive terminal of the error amplifer 13. The difference between the feedback signal and the reference source signal is amplified in the error amplifier 13. The error amplifier 13 provides a DC signal of a varying magnitude in accordance with the deviations of the feedback signal derived from the lead wire 15, as can be appreciated from examining FIG. 2A. The output signal from the error amplifier 13 is applied to the positive input terminal of the comparator 16. The negative terminal of the comparator 16 is coupled to an AC signal generator 17. The output signal from the AC signal generator normally has a triangular wave shape although it could be sinusoidal. A typical sinusodial wave shape is illustrated in FIG. 1 as the generator output signal, while a triangular shaped signal is illustrated in FIG. 2A. The comparator 16 compares the input signals from the signal generator 17 and the error amplifier 13 and produces a lamp regulating output pulse during the time intervals one of the input signals has a greater instantaneous voltage magnitude than the other input signal thereto. These regulating output pulses from the comparator 16 are applied to the switching circuit 12 for rendering the circuit conductive thereby coupling the power source 11 to the lamp 10. In the absence of a regulating output pulse, the circuit 12 is rendered non-conductive and the lamp 10 is de-energized.

The output signal from the AC signal generator 17 establishes the switching rate that the power source 11 is switched on and off to the lamp. The choice of frequency for the output signal from the signal generator 17 is governed by the thermal time constant exhibited by the lamp 10 so that the switching rate will be fast compared to the thermal time constant but yet slow enough to avoid undue switching losses. Stated differently, the rate the voltage to the lamps is switched on and off should be selected so that the lamp filament does not change temperature appreciably during either the time interval the lamp is energized or de-energized so as to effect the light output of the lamp. A typical switching frequency would be 2 kiloHertz. The regulating pulses are illustrated in FIG. 2B along with their relationship to the signals illustrated in FIG. 2A and thereby graphically illustrate the function of the comparator 16 with regard to turning the switch 12 on and off. In terms of the triangular wave shape illustrated in FIG. 2A, it will be noted that during the initial time interval beginning with time 0 that the error amplifier 13 has an output signal which is at a higher instantaneous voltage level for a preselected time period than the instantaneous voltage level of the AC signal generator 17 output signal and thereby results in the production of a regulating pulse from the comparator 16. The regulating pulse will have a time period corresponding to the time interval during which the error amplifier 13 has an output signal exceeding the magnitude of the voltage of the output signal from the signal generator 17. After this time interval, the triangular wave signal has a magnitude greater than the signal from the error amplifier 13 for a preselected time period during which time period no regulating pulse is derived from the comparator 16 until the signal generator output signal drops to a voltage level below the level of the voltage of the signal from the error amplifier 13 and the sequence continues; see FIG. 2B. The regulating pulses 12 from the comparator 16 applied to the switching circuit 12 are effective for rendering the switching circuit 12 conductive and nonconductive in accordance with the presence or absence of the switching pulses respectively.

The system of the present invention allows the lamps used in present day hazard warning systems to be regulated and one such 6-volt lamp that has been employed is the General Electric 1949 miniature lamp. The use of the G. E. lamp permits a 12-volt DC voltage source to be utilized therewith and thereby results in a significant increase in battery and lamp life when the regulating circuits are implemented in accordance with the teachings of the present invention. From the above description, it should be appreciated that the lamp 10 is regulated to provide the desired constant luminous flux output from the lamp 10 while the DC voltage source 11 degenerates from its rated voltage source to a value about 50 percent of its initial voltage.

One of the important considerations in implementing the concept of the present invention is the consideration of the means for deriving the feedback signal representative of the lamp operating parameter for coupling to the error amplifier 13. A number of methods have been developed and are disclosed hereinafter for producing this desired feedback signal. One method of generating the desired feedback signal is by monitoring lamp voltage. A problem associated with this method is the difference between average voltage and the root mean square, RMS, voltage for a rectangular wave form of voltage such as encountered with a switching regulator. Light output from a lamp is a function of RMS voltage which for a switched voltage is equal to peak voltage times the square root of the duty cycle or as expressed mathematically by Equation 1:

The average most easily sensed and controlled is the average voltage which is equal to peak voltage times the duty cycle as represented in Equation 2:

Controlling the average voltage to the lamp, however, gives a considerable error in luminous flux output from the lamp.

In FIG. 3, one method of overcoming the duty cycle problem without resorting to an RMS sensing circuit but permitting the use of the average battery voltage is illustrated. In the embodiment illustrated in FIG. 3, an electrical filter is used to filter the pulses derived from the switching circuit 12 for energizing the lamp 10 to thereby couple direct current onto the lamp 10 when it is energized and thereby avoid the duty cycle problem. The electrical filter as illustrated in FIG. 3 comprises the inductor 30 arranged in series circuit with the output from the switching circuit 12 and the power terminal of filament 10.sub.f for the lamp 10. The other element of the electrical filter is the capacitor 31 connected between the lamp side of the inductor 30 and ground potential. On the switching circuit end of the inductor 30, or the end opposite capacitor 31, there is connected a diode 32 having its anode electrode directly connected to ground potential. The filter removes the alternating current from the pulse wave form and thereby causes a direct current to flow through the filament 10.sub.f for the lamp 10 and avoid the problems associated with employing the average voltage applied to the lamp for regulation purposes.

It will be understood that the remaining portion of the system illustrated in FIG. 3 conforms to the system illustrated in FIG. 1. For this purpose, the reference source 14 generally represented in FIG. 1 comprises a reference source 14E. The voltage provided by the source 14E has been proportioned so that the desired luminous flux will be generated by the lamp 10 when the voltage of the source is within preselected voltage range. The voltage provided by the source 14E is compared with the voltage applied across the lamp 10 by means of the feedback signal provided by the lead wire 33 coupled between the output end of the filter and the input terminal of the error amplifier 13. Accordingly, the feedback signal applied to the error amplifier 13 by means of the lead wire 33 is also a direct current signal representative of lamp voltage.

In FIG. 4 there is illustrated yet another method of avoiding the aforementioned average voltage feedback problem when the feedback signal represents average voltage across the lamp rather than the RMS value. The second method utilizes a signal representative of the average voltage feedback applied across the lamp summed with feedback signals representative of the battery voltage which approximately cancels the error resulting from using average voltage instead of RMS voltage. This circuit arrangement is illustrated in FIG. 4, where resistors R.sub.A -40 and R.sub.B -41 represent attenuation ratios that are calculated from those formulas 3 and 4 wherein:

and

In the formulas (3) and (4), E.sub.max represents the maximum voltage and E.sub.min the minimum voltage at which the lamp is designed to operate. The error resulting from using this approximation is about plus or minus 3 percent for duty cycles ranging from 25 percent to 100 percent.

The voltage signal E.sub.A, the voltage source, and the signal E.sub.B, the voltage across the lamp 10 are summed in a proportion determined by the attentuation ratios A and B at the terminal ST and compared with the reference voltage source signal provided by the source 14E. Accordingly, the output signal from the error amplifier 13 is corrected or compensated in terms of the summation of these voltage signals to provide the necessary error correction permitting the use of the average voltage instead of the RMS voltage. As in the previous embodiment, the remaining portions of the system illustrated in FIG. 4 operate the same as the basic concept illustrated in FIG. 1.

In FIG. 5, there is graphically illustrated the normalized RMS voltage applied to the lamp 10 with respect to the battery voltage for a regulating system of the type employing the feedback arrangement illustrated in FIG. 4. From this it will be noted that the variations in the RMS voltage applied to the lamp 10 varies very little while the battery varies over a relatively large range. The luminous flux output of the lamp 10 varies approximately .+-.3 percent for battery voltages that vary from 6.5 to 13 volts.

Another method of providing a feedback signal from the lamp without employing a voltage feedback signal is illustrated in FIG. 6. In this arrangement, the feedback signal is a signal representative of the lamp resistance R.sub.L of the lamp 10. In this arrangement, the lamp 10 is arranged in one leg of a balanced bridge circuit 60 for providing the input signals to the error amplifier 13. The bridge 60 comprises three impedance elements arranged in individual legs of the bridge with the lamp 10 arranged in the other leg. The impedance values of the elements arranged in the various legs of the bridge circuit 60 are proportioned relative to the impedance value exhibited by the lamp 10 to provide the balanced bridge condition when the lamp 10 provides the desired luminous flux output. Accordingly, as the lamp resistance R.sub.L varies, the deviations from the balanced condition of the bridge are signalled to the error amplifier 13. The advantage of using the bridge circuit arrangement of FIG. 6 is that the bridge circuit functions both as a reference source and as a feedback source for the associated regulating system. Specifically, the bridge can be readily defined by means of the lamp 10 and three resistive impedance elements. As illustrated in FIG. 6, for example, the two lower legs of the bridge circuit 60 include a resistor 61 in the left-hand leg of the bridge having a resistive impedance value of 100 ohms with a resistor 62 arranged in the opposing leg having a resistive impedance value of 1 ohm. The common junction of the resistive elements 61 and 62 are each connected directly to ground. The lamp 10 is coupled in the upper portion of the bridge circuit 60, as illustrated in FIG. 6, with the lamp connected in series circuit relationship with the resistive element 62 and the power source 11. In the remaining leg of the bridge circuit 60 there is provided a resistor 63 having one terminal connected to the source 11 in common with the lamp 10 and in series circuit relationship with the resistive element 61. The impedance value of the resistive element 63 can be proportioned to be 100 times the resistive value exhibited by the filament of the lamp 10 when emitting the desired luminous flux, or as illustrated in FIG. 6, 100 R.sub.L for defining a balanced condition. The common junction 60J of the bridge circuit 60 is connected directly to receive the pulses from the switching circuit 12. The intermediate junctions of the bridge circuit 60 are the junctions 60-IR and 60-IL and are coupled directly to the individual inputs for the error amplifier 13. The junction 60-IR is identified as the junction between the lamp 10 and the resistor 62. The junction 60-IL is the junction between the resistor 63 and the resistor 61. As in the previous two embodiments, the remaining portion of the regulating system including the bridge circuit arrangement of FIG. 6 operates as discussed in conjunction with FIG. 1.

Now referring to FIG. 7, the complete schematic circuit diagram of the regulator for the lamp 10 in accordance with the bridge feedback technique of FIG. 6 will be described in detail. In this instance, the lamp 10 comprises a commercially available lamp that is employed in present day hazard warning lights and may be a General Electric Model 1949 miniature lamp. This type of lamp is rated for 6-volt operation and 0.125 amps of current. When the General Electric lamp is utilized in the bridge circuit 60, the resistor 63 may have a value of 5.04 kilo ohms to provide a balanced bridge condition with the resistors 61 and 62. For this purpose, the resistor 61 will have 100 ohms of resistance while the resistor 62 will have 1 ohm of resistive impedance.

The AC signal generator 17, illustrated in FIG. 7, is a triangular wave generator 17 and comprises an operational amplifier 170 which may be selected from the type commercially available from the National Semiconductor Company of Santa Clara, Calif., and identified as one of its LM124 series quad operational amplifiers. The series of operational amplifiers also includes Models LM224 and LM324. The output circuit of the operational amplifier 170 is coupled in series circuit relationship with the resistor 17R and a parallel output capacitor 17C connected between ground voltage level and the output side of the resistor 17R. The triangular wave is generated through the use of the National Semiconductor operational amplifier by the circuit elements illustrated in FIG. 7 functioning to alternately charge and discharge the output capacitor 17C to continuously generate an output wave form that approximates a triangular configuration. For this purpose, the capacity of the output capacitor 17C may be two nanofarads. The positive (+) input terminal for the amplifier 170 is connected by means of a resistive element 17I to ground level. A feedback resistor 17FB is coupled between the output terminal and the positive input terminal. The negative (-) input terminal for the element 170 is coupled directly to the output end of resistor 17R.

The error amplifier 13 as implemented in the regulating circuit of FIG. 7 may also be selected from the National Semiconductor series of operational amplifiers of either the LM124, LM224 or LM324 types. For the purpose of detecting a signal appearing across the bridge circuit 60 at the junctions 60-IL and 60-IR, the operational amplifier of the LM124 series may be one-fourth of the quad operational amplifier normally provided in an integrated circuit package. The LM124 series of operational amplifiers consist of four independent, high gain, internally frequency compensated operational amplifiers designed specifically to operate from a single power supply over a wide range of voltages. This particular operational amplifier series has been selected for use in the regulating system of the present invention since it has common mode capability extending down to its negative supply voltage which is ground in this application. This is of particular value in regulating circuits of the present invention since the inputs to the error amplifier 13 will go to ground level or to 0 volts when the switching circuit 12 renders the lamp 10 de-energized. The utilization of such commercially available operational amplifiers allows the considerable saving in circuit complexity since no additional offsetting or switching components are required.

The comparator 16 may also be a National Semiconductor operational amplifier of the same LM124 series as the signal generator amplifier 17 and the error amplifier 13 described hereinabove. The amplifier element 160 has its negative (-) input terminal coupled to directly receive the triangular wave output signal from the generator 17. The positive (+) input terminal is coupled to the output terminal of the error amplifier by means of series resistor 16I proportioned to have a relatively high resistance value. A feedback resistor 16FB is coupled between the output terminal of the element 160 and the positive input terminal. The output signals from the comparator 16 are the regulating pulses applied to the switching circuit 12.

The switching circuit 12, as illustrated in FIG. 7, comprises three transistor circuits arranged in a switching configuration to receive the output signal from the comparator 16 for controlling the coupling and decoupling of the power source 11 to the lamp 10. For this purpose, three transistors Q2, Q3 and Q4 are employed. The transistor Q2 is coupled to the power source 11 with its emitter electrode connected to the positive terminal of the source 11 and its collector electrode connected in common with the collector electrode for the transistor Q3 to the input junction 60J of the bridge circuit 60. The base electrode for the transistor Q2 is connected directly to the emitter electrode transistor Q3. The base electrode for the transistor Q3 is coupled to a dropping resistor 70 to the collector electrode for the transistor Q4. The emitter electrode for the transistor Q4 is coupled directly to reference potential or to the negative terminal of source 11. The base electrode for the transistor Q4 is connected to the output terminal of the comparator 16 through a resistor 71. In addition, a resistor 73 is connected between the base electrode for the transistor Q3 and the positive terminal of the source 11 in common with the emitter electrode for the transistor Q2. In this switching arrangement, the circuit 12 normally maintains the lamp 10 in a de-energized condition until the regulation pulses are provided from the comparator 16. Upon receipt of a regulating pulse, the switching circuits 12 are rendered conductive to switchably couple the pulses through the bridge circuit 60 for energizing the lamp 10 for the duration of the time of the regulating pulse. In this configuration of switching transistors the transistor Q2 may be a 2N5193 transistor, while the transistors Q3 and Q4 may be 2N3906 and 2N3904 transistors respectively.

When the lamp 10 is employed as a hazard warning lamp and utilized in a blinking condition or intermittently energized and de-energized in accordance with the present day hazard warning cycles, a timing circuit for controlling the flash intervals is normally provided for the lamp. The timing circuit 75 is illustrated in FIG. 7 as coupled between the power source 11 and the regulating circuits for controlling the coupling and decoupling of the source 11 to the regulating circuits. The lamp flash timing circuit 75 may also be constructed of commercially available integrated circuits and, as illustrated in FIG. 7, the flashing timing circuit 75 comprises an integrated circuit element 75A which may consist of an RCA monostable/astable multivibrator Model CD 4047. As illustrated, the element 75A is connected in an astable multivibrator free-running mode. The output pulses are derived from pin 13 of element 75A and coupled to the counter element 75B. The counter element 75B may be a Motorola Model 140173 decade counter/divider integrated circuit for defining the timing cycle for flashing the lamp 10 on and off. It will be recognized by those skilled in the art that the element 75A provides the pulses to be counted to the element 75B and these pulses are counted by the decade counter/divider for providing an output signal at preselected time intervals for energizing the lamp 10 in accordance with the desired flash rate. For this purpose, the output of the element 75B of the circuit 75 is coupled to a switching transistor Q1. The transistor Q1 is coupled between the positive terminal of the power source and the positive input terminal of the element 170 of the triangular wave generator 17T. As illustrated in FIG. 7, the collector electrode for the transistor Q1 is coupled directly to the positive terminal of the source 11 while the emitter electrode is connected by means of a resistor 76 to the positive input terminal of the amplifier 170 and the positive supply terminal of the LM124. For the flashing time intervals defined by the timing circuit 75, the transistor Q1 is rendered conductive in response to the output pulses from the counter 75B and in this condition the power from the source 11 is supplied to the remaining circuit elements of the regulating circuit. When the power to the regulating circuit is removed, the lamp 10 will become de-energized. It should be recognized at this point that when it is desired to have the lamp continuously energized rather than to be flashed on and off in a warning mode, the flash timing circuit 75 may be omitted.

With the above circuitry in mind, and with reference to the graphical illustrations of FIG. 2, the operation of the complete regulating system can be briefly summarized. Assuming, for the present, that the flash timing circuit circuit 75 is not included in the regulating circuit and that power is continuously supplied to the remaining elements of the system for causing the lamp to continually emit light rays, it will be noted that the lamp 10 will be regulated as a result of the signals derived from the bridge junctions 60-IL and 60-IR of the bridge circuit 60 for applying signals to the inputs to the error amplifier 13. The error signal from the amplifier 13 is coupled as one input to the comparator 16 along with the triangular wave signal from the triangular wave generator 17T. These signals are illustrated in FIG. 2A. The output from the comparator 16 corresponds to the pulse regulating signals illustrated in FIG. 2B. Accordingly, with the application of power to the regulating circuit, the error amplifier 13 will provide an output signal and the triangular wave signal will be generated by generator 17T. As time progresses, the output signals will appear as illustrated in FIG. 2A with the magnitude of the output signal from the error amplifier 13 increasing with decreases in battery or source voltage. The regulating pulses will be generated from the comparator 16 as illustrated in FIG. 2B. These regulating pulses are applied to the switching circuits 12 for rendering the lamp 10 conductive during the time intervals that the regulating pulses are provided from the comparator 16 and accordingly de-energized when the regulating pulses are absent from the comparator 16. As the voltage from the power source 11 degenerates from its initial rated, new battery condition, a signal representing this voltage degeneration is coupled into the error amplifier 13 as a result of the bridge 60 becoming unbalanced. The unbalanced condition of the bridge results due to the decreased voltage across the lamp 10 from its initial condition. The error signal from the amplifier 13 will deviate from its initial magnitude in accordance with the graphical representations in FIG. 2A and cause the time duration of the regulating pulses derived from the comparator 16 to be increased. Accordingly, with the decreases in voltage applied to the lamp 10, the circuit 60 maintains the lamp filament 10.sub.f energized for longer periods of time to maintain bridge balance and allow the same amount of luminous flux to be omitted from the lamp 10. This operation is continuous until a duty cycle at 100 percent voltage level is reached. Further operation causes the lamp to emit luminous flux outputs below the desired flux level or the constant level of flux maintained up until the voltage drops below the preselected level. This voltage level is approximately 50 percent of the initial voltage of the battery thereby permitting the battery to be utilized for a substantially longer period of time than heretofore thought possible. It will also be recognized that the source 11 is proportioned to provide an initial voltage of 12 volts to the lamp 10 which is selected to be a 6-volt lamp of the 1949 Model General Electric type. The regulating circuit configuration illustrated in FIG. 7 allows a lamp 10 of a reduced voltage rating to be employed with the 12-volt battery source thereby permitting a significant increase in battery life when the regulating circuit of the present invention is employed.

It should now be recognized that when the lamp 10 is employed in a hazard warning light system and it is desired to flash the lamp on and off, that the lamp timing circuit 75 is included with the regulating system. When the timing circuit 75 is employed, the lamp regulating system will operate as described above except that the lamp will only be energized during certain flash intervals and which intervals are controlled by the timing circuit 75. Under these conditions the transistor Q1 switching circuit will be periodically rendered conductive for powering the regulating system and allow the regulating circuitry to be operative for pulsing the lamp 10 as described hereinabove during the energized periods for the lamp 10.

Now referring to FIG. 8, the schematic circuit diagram of a complete regulating system utilizing the basic voltage sensing regulating technique illustrated in FIGS. 3 and 4 will be described. This regulating system is generally the same from a circuit configuration as illustrated and described in conjunction with FIG. 7. In this arrangement, however, a lamp 10 is not employed in a bridge circuit but in lieu thereof, one of the input terminals of the error amplifier 13 is coupled to a reference voltage source 14E rather than one of the junctions of the bridge circuit 60. As illustrated in FIG. 8, a voltage feedback signal is derived for representing the voltage applied to the lamp 10. This feedback signal is derived through the lead wire 80 coupled to the power side of the lamp 10 in common with the output circuit from the switching circuit 12 through a voltage dividing network coupled to the negative terminal of the source 11. The voltage dividing network comprises the series voltage dropping resistors 81 and 82. The resistive values are proportioned relative to the lamp voltage to provide the desired voltage signal at the junction between the resistors 81 and 82 or the junction 13I. The junction 13I is connected to the negative input terminal of the error amplifier 13.

The reference voltage source 14E provides an accurate DC voltage reference to the error amplifier. In this arrangement, the output circuit of the operational amplifier A4 is arranged for providing the voltage to the positive terminal to the error amplifier 13. An input to the error amplifier 13 from battery voltage through resistor R3 is used to compensate for the difference between RMS and average voltage as previously discussed hereinabove. With these modifications, the general operation of the regulating circuit of FIG. 8 is essentially identical to operation of the system of FIG. 7. The deviations from the desired voltage applied to the lamp 10 are signalled by the amplifier 13 by means of the voltage feedback signals applied through the conductor 80 to the negative input terminal of the amplifier 13.

Now referring to FIG. 9, another embodiment of the invention will be disclosed. This regulating system is basically the same system as disclosed hereinabove but differs in that the pulses applied to the switching circuit 12 are produced at a preselected variable rate and having a fixed time duration to maintain a constant luminous flux output from the lamp 10. The duty cycle control circuit in this embodiment comprises a voltage controlled oscillator 101 and a monostable multivibrator 102. As in the previous embodiments, the duty cycle control circuit is coupled to be responsive to the output signal from the error amplifier 13. The feedback signal representative of a lamp electrical operating parameter is coupled to one input of the error amplifier 13 and is denoted by the feedback signal generator illustrated as a block 103. This signal may be a voltage signal representative of the voltage applied to the lamp 10 or any other of the techniques for feedback disclosed herein for sensing a lamp operating parameter. A lead wire 104 is coupled directly to the power side of the lamp 10, as illustrated in FIG. 9, for deriving a voltage feedback signal. Similarly, the reference voltage source 14E is coupled to the other input of the error amplifier 13. The output signal from the error amplifier 13 provides a difference signal representative of the difference between the reference voltage signal and the actual voltage applied to the lamp 10. This error voltage signal is utilized to control the oscillator 101 so that the frequency of the output signal from the oscillator varies in accordance with the magnitude of the output signal from the error amplifier 13. The frequency of the output signal from the oscillator 101 increases with the sensed decreases in the voltage applied to the lamp. This effectively varies the switching rate of the switching circuit 12. The output signal from the oscillator 101, then, controls the monostable multivibrator 102. The monostable multivibrator 102 is coupled to be responsive to the oscillator signal so as to provide output pulses of a fixed time duration whenever the output signal from the oscillator 101 has a preselected voltage level. Accordingly, with the increases in the frequency of the output signal from the oscillator 101, the repetition rate of the pulse generated by the multivibrator 102 will increase so as to produce the necessary variable duty cycle at the switching circuit 12 for switching the power from the source 11 to the lamp 10 to produce the desired result. In this fashion, the lamp 10 is controlled to maintain substantially constant luminous flux output therefrom. It will be recognized to those skilled in the art that the voltage controlled oscillator 101 and the monostable multivibrator 102 employed with this system are well known and commercially available elements. It will also be recognized that it is within the scope of the concept of this invention that the duty cycle control as embodied in FIG. 9 may be utilized with any of the other feedback circuit arrangements disclosed herein.

Now referring to FIG. 10, another embodiment of the regulating system for the lamp will be described wherein the feedback signal is utilized for controlling the luminous output from the lamp 10 based on monitoring the electrical power applied to the lamp. To this end, the lamp 10 is arranged in the same general fashion as disclosed above with DC voltage source 11 coupled to the lamp 10 by means of switching circuit 12. A voltage signal is derived from the lamp circuit by means of the lead wire 105 coupled to the power side of the lamp 10 as illustrated in FIG. 10. A current feedback signal is similarly obtained through the provision of a current sampling resistor 106 coupled in a series circuit relationship with the common side of the lamp 10 or the grounded side as illustrated in FIG. 10. The current sampling resistor 106 may have a small resistance value compared to the lamp resistance value so that the voltage developed across the resistor 106 is an insignificant portion of the applied voltage so as not to effect the integrity of the lamp operation or voltage feedback signal. The voltage developed across the resistor 106 is small and therefore should be amplified by means such as the amplifier 107 to provide a signal representative of the current flowing through the lamp 10. The amplifier 107 is coupled to the lamp side of the resistor 106 and to one of the inputs of an electrical multiplier circuit 108. The output of the amplifying circuit 107 is electrically combined with the voltage feedback signal appearing on the lead wire 105.

The block 108 represents an electrical multiplier which multiplies the current and feedback signals to provide an output signal on the lead wire 109 representative of the power applied to the lamp. Electrical power P is the product of voltage and current: P=E.times.I. This power output signal on the lead wire 109 is coupled as one input signal to the error amplifier 13. The reference source 110 provides, on its output lead wire 111, a constant voltage indicative of the desired power applied to the lamp for maintaining constant luminous flux output from the lamp 10. As the power to the lamp 10 varies in accordance with the decreases in voltage from the source 11, the signal on the lead wire 109 will decrease and produce a difference signal of increasing amplitude at its output for controlling the duty cycle control circuit 112. The duty cycle control circuit 112 may be the same circuit disclosed in conjunction with FIG. 9 or any of the other above disclosed circuits for controlling the switching circuit 12 for switching the power to the lamp 10 on and off at the desired rates for regulating the luminous flux output from the lamp 10 to maintain it constant.

Now referring to FIG. 11, an embodiment of the lamp regulating circuit is illustrated wherein the feedback signal representative of the lamp operating parameter is provided by a light sensor for sensing the luminous flux produced by the lamp 10. The light sensor is identified in FIG. 11 as the element 113, which may be a photodetector arranged adjacent the lamp 10 for receiving the light rays therefrom. The light sensor 113 may be any conventional photoelectric element that is responsive to the light rays impinging thereon from the lamp 10 and producing an electrical output signal in response to the light rays. It will be recognized by those skilled in the art that the output signal from the sensor 113 will produce an electrical output signal based on the intensity of the light rays impinging thereon. The electrical signal will have electrical characteristics depending upon the type of photoelectric cell selected for this purpose. Assuming that a voltage signal is provided from the light sensor 113, the voltage signal is applied to the amplifying circuit 114 for amplification and this amplified voltage signal is applied as one input signal to the amplifier 13. As in the previous embodiments, the other input signal to the error amplifier 13 is provided by the reference source 14E. The difference signal generated by the error amplifier 13 is applied to the duty cycle control element 112 for controlling the switching rate of the switching circuit 12 as in the previous embodiments.