US2842721A - Control circuit - Google Patents

Description

C. E. ATKINS CONTROL CIRCUIT July 8, 1958 Filed June 2, 1954 FTE. N

ATTORN EYS United States CNTROL CIRCUHT Carl E. Atkins, Bloomfield, N. l., assigner to 'Kung-Sol Electric Inc., Newark, N. 3., a corporation of Belaware Application dune 2, 1954, Serial No. 433,959

liti Claims. (Ci. 3l7--13t) The present invention relates to light responsive co trol circuits and more particularly although not enclusively to circuits for control of the dimming switch automobile headlamps. The circuit of the present invention while basically that disclosed and claimed in my copending application, Serial No. 411,208, filed February 1.8, 1954, comprises an improvement over such circuit in a number ofimportant respects.

The present circuit like that of my said copending application comprises in general a photo-electric tube, preferably a diode, which when subjected to light causes inif crease in current through an electronic multi-element tube, an oscillatory circuit coupled to the electronic tube and so connected in the circuit as to be quiescent except when light is incident on the photocathode of the photoelectric tube and a relay control tube connected to the oscillatory circuit to receive controlling pulses therefrom when the photoelectric tube is subjected to light. The relay control tube is normally conductive to hold energized in its plate circuit a sensitive relay which upon release of its armature closes contacts controlling the circuit of a power relay. Positive pulses delivered by the oscillatory circuit when light of a given intensity is incident on the photocathode of the photoelectric tube drive negative the grid of the relay control tube by virtue of the self-rectit'ying properties of the cathode grid circuit of the relay control tube to cause release of the sensitive relay and consequent operation of the dimming switch by the power relay. To prevent return to the high beam conditions when an approaching car dirns its headiights the circuit includes means for increasing the sensitivity to incident light after release of the sensitive relay.

One feature of the present invention comprises irnproved means for insuring rapid return of the circuit to normal conditions when the light intensity falls below a predetermined value, such means being eiective even after flooding of the photocathode with light of high intensity. The multi-electrode electronic tube which l will designate as the electrometer tube for it functions as such has its control grid connected to the photccathode ot' the photoelectric tube. Under no light or low light conditions the grid and the inherent capacity associated therewith become negatively charged by virtue of reception of electrons from the cathode of the electrometer tube. Consequently, when the photoelectric tube becomes co-nductive the current through the electrometer tube is increased and a control voltage is delivered to the oscillatory circuit to initiate oscillation thereof. in the circuit of the said copending application the electrometer tube operates as a cathode follower, the signal to the oscillatory circuit being taken from the junction of a cathode resistor with the cathode of the electrometer tube. As the return to normal conditions .requires negative charging of the control grid of that tube the presence of the cathode resistor in its circuit introduces an element of delay when thephotoelectric tube has passed a relatively large current due to excess light on the photocathode thereof. ln the circuit ot the present invention e estatal Patented lIuly 8, 1958 the signal from the multi-electrode tube is taken from the i anode rather than from the cathode and the cathode is grounded. This permits electrons to llow from the cathode to the grid directly from the ground rather than through a cathode resistor, insuring thereby a. quick recovery of the circuit. Quicker recovery in the new circuit is also obtained by a novel circuit connection to the screen grid which takes advantage of a screen grid current to depress the screen potential and hold it low during the period of negative charging of the control grid following cessation of light.

Another feature of the invention comprises improved means for coupling the electrometer tube controlled by the photoelectric tube to the oscillatory circuit which obviates critical adjustments of circuit constants and insures more stable operation of the circuit. This improvement has been effected in part by the taking of the signal from the anode of the electrometer tube and in part by the provision between the oscillatory circuit and the electrorneter tube of phase inverting and amplifying means. The oscillatory circuit is a multi-vibrator normally prevented from oscillation by the application of positive potential to the cathode of the iirst triode thereof, a cathode resistor being connected between that cathode and ground. With the phase inverting and amplifying means in the circuit, variations in value of the cathode resistor of the multi-vibrator circuit as for example, as a result of change in temperature, will not affect overall operation of the circuit.

A further feature of the invention comprises improved coupling between the multi-vibrator circuit and the relay control tube that insures delivery to the relay control tube of relatively larger control pulses. In the said copending application the signal to the control grid of the relay control tube was taken from the anode of the first half of the multi-vibrator circuit which half includes the cathode resistor in its circuit. In the circuit of the present invention larger control pulses are obtained by taking the signal from the anode of the second half of the multivibrator circuit, the cathode of which is grounded.

Still another and important feature of the present invention is a novel circuit arrangement whereby pulses appearing at the anode of the relay control tube are utilized for increasing the bias of the control grid during the presence of a signal.

Other features of the invention, including improved means for rendering operation of the electrometer tube insensitive to battery voltage uctuation will become apparent as the description proceeds.

For a better understanding of the invention and of the novel features thereof reference may be had to the accompanying drawing of which the single figure is a schematic diagram of the preferred embodiment thereof.

The circuit shown in the drawing is adapted for control of the dimming switch of automobile headlamps. The car carried battery of say twelve volts is indicated diagrammatically at 2, the power relay at 4 and the sensitive relay for control of the power relay at 6. The photoelectric tube 8 is positioned for reception by the photocathode oi' light from approaching cars.v The anode of tube 8 is grounded and its photocathode is connected to the control grid of a tetrode itl. Tube 1G, the electrometer tube, may be a 6AK6 but preferably is one speciically designed to reduce leakage between terminals of electrodes which are at different potentials. A tube of this general type is illustrated in Fig. 4 of my copending application Serial No.1326,809, led December l0, 1952, Patent No. 2,730,629, wherein is shown a triode, the control grid of which is brought out to a separate terminal. In tube lt), as in the tube of the said application, the control grid is brought out to a separate terminal as indicated diagrammatically in the drawing by the lbracket l2. The cathode of the electrorneter tube is grounded. The anode of that tube is connected through a dropping resistor iid to a line i6 which is connected through a filter comprising a resistor and loy-pass capacitor i9 to aline Ztl of regulated potential, preferably about eight volts. The potential of line Ztl is regulated by connection to the low voltage side of a ballast lamp 22 connected in series with an adjustable resistor across the battery 7.. Line 2l) through a resistor Z5 supplies the current for the cathode heater or" tube itl. m e screen grid circuit, as hereinafter described, is ccl.....ected to the line i6 of regulated and filtered voltage. Even with substantially regulated voltage thus applied to cathode, screen grid and anode of the tube some undesired change of anode potential may occur with change in bat-- tery voltage because of incomplete .compensation for the change in cathode emission. To avoid such undesired changes in anode potential, a second dropping resistor 26 of relatively high ohmage, is provided between the anode and the positive side of battery Z. By proper selection of the magnitude of this resistor, which thus introduces a potential correction direct from the source, substantially complete stability of the circuit with change in battery voltage is insured.

The screen grid of the electrometer tube is connected through two series-connected resistors 27 and 26 to the line 16 and the junction of resistors 27 and 2d is connected through an adjustable resistor 3l) comprising the hc-ld control of the circuit and a resistor 32 to ground, A capacitor 34, the purpose of which will become apparent as the description proceeds, is connected between the screen grid of the electrometer tube and ground. To provide increase in sensitivity after dimming of the headlamps, the junction of resistors 27 and 23 is connected through an adjusable resistor 36 to the front contact associated with the grounded armature 38 of relay 6. Adjustment of resistor 36 controls the light level at which the dimming switch will be operated and adjustment of resistor 30 controls the light level at which high beam conditions will be restored.

Before describing the remainder of the circuit the operation of the elcctrorneter tube will tirst be described. Under no light conditions the tube will pass a relatively small current. Electrons from the cathode will pass to the control grid and negatively charge that grid and the inherent capacity associated therewith. The potential on the screen grid will be positive and at some value less than eight volts by virtue of the potential drop across resistor 2S. The potential drop across resistor 27 will be substantially negligible. The potential at the anode of the tube will be roughly two volts if the value of resistor i4- is high, say 4.7 meg. When light falls on the photocathode of the tube 8 electrons from the control grid will leak off through the tube S reducing the negative potential of the grid and causing increased current through the electrometer tube. The potential of the auode will thus decrease to say one-half volt due to conduction through the tube and the consequent increase in potential drop across resistors ld and 26. lf the intensity of the light has high the grid will tatie substantial current and this screen current due to the potential drop across resistor 27 lowers the potential of the screen and of the ungrounded side of the capacitor 3a'. When the light is suddenly remove from the photocathode the screen grid will not return to its normal positive potential until the capacitor has regained its full charge. Thus the screen grid potential will reins-.iu for an appreciable time, permitting the control grid to regain its negative charge and during such time preventing substantial conduction by the electrometer tube.

The anode of the -electrometer tube is connected to the No. l grid of a phase inverter and amplier tube lshown as a pentode. The tube di) could be, for example, a 6BJ6. The cathode of: tube dil is maintained at positive potential, say about one and one-half volts, by virtue '4 of a connection to the junction of resistors 42 and 41% connected in series between the line 16 and ground. The No. 2 or screen grid of tube itl is maintained at the poial of line le and the No. 3 grid is tied to the anode i. ch latter is connected to line t6 through a potential t opping resistor 46 of thc order of 68K. The anode of tube is connected through series-connected re` tl to ground and the junction of these reted to the control grid SZ of the .first half ie triode 5d connected as a multi-vibrator. The cathode associated with this control grid is maintained at a positive potential by virtue of a connection to the junction of a pair of resistors 56 and 5S connected in series between line lr6 and ground. The anode 66 associed with 52 is connected to the line i6 through a potential dropping resistor 62 of about 15K and is connected through capacitor 64 to the control grid 66 of the second haltc of the tube 5ft. The cathode associated with grid 66 is grounded and the anode 6d of the second half of the` tube is connected to line i6 through a potential dropping resistor '76 of say 15K and through a capacitor 72 to control grid 52. The anode 63 is also connected through a capacitor '74 with the control grid of a relay control tube 76.

Tube '76 is a tetrode of the space charge grid type. Its cathode is grounded and its No. l grid maintained at a positive potential by direct connection to line 20. The anode of tube '76 is connected through the winding of relay 6 directly to the positive terminal of battery 2. In the absence of a signal, tube 76 is .conducting to maintain relay 6 energized with its armature 3S grounding the dimming circuit of the screen grid of the electrometer tube. When the current through tube '76 decreases to a predetermined value relay 6 releases, closing the circuit of the power relay 4 through the back contact of the relay armature Preferably to avoid damage to the relay contacts from the inductive surge through the power relay, a resistor '78 is connected between the low potential side of the power relay and the positive terminal of the battery 2.

The control grid (grid No. 2) of the relay control tube 76 is provided with a bias resistor Sil of say 3.3 meg., one end of which is grounded and the other end of which is connected to the control grid through a resistor 82 of say 150K.. Before describing the additional circuit elements associated with the control grid of the relay control tube which are provided to increase the bias during the presence of a signal, the overall operation of the circuit without such additional elements will be described. When, as the result of incident light of a given intensity the potential at the anode of the electrometer tube falls as heretofore described, current through the phase inverter and amplier tube 4t) will be reduced and consequently the potential applied to the control grid 52 of the first half of the multi-vibrator will be increased and will override the bias provided by the positive potential on the cathode thereof. The rst half of the multi-vibrator which had heretofore not been conducting will now conduct as the grid potential corresponds to that required for triggering the circuit. When the rst half of the multi-vibrator conducts, a negative pulse is transmitted through capacitor 64 to control grid 66 to reduce the current through that half of the tube 54. Consequently, a positive pulse is impressed upon grid 52 through condenser 72 and upon the control grid of the relay control tube through capacitor 74. The potential of grid 66 then rises as capacitor 64 discharges through resistor 67. When the threshold potential is reached by grid 66 conduction by the second half of the tube 54 is -resumed with resultant application of a negative pulse to grid 52 to block conduction by that half of the tube. If light is still incident on the photocathode the cycle repeats and the vibrator continues to transmit positive pulses to the control grid of the relay control tube.

When positive pulses are impressed on'the control grid `of the relay control tube, as above described,7the`cur-rentv through the tube is rst momentarily increased and elec` trons flow to the grid to charge the capacitor 74. As grid resistor 80 is large, these electrons cannot leak off rapidly and hence tend to drive the grid negative, thus lowering the grid potential and correspondingly reducing the current through the relay 6, finally causing release of the relay and energization of the power relay 4. When the relay 6 releases the circuit through resistor 36 is opened increasing the potential of the screen grid of the electrometer tube and thereby increasing the sensitivity of the circuit to insure that high beam conditions will not be restored until the intensity of the incident light drops to a predetermined value.

The means now to be described insure that the grid bias of the relay control tube will be increased during the presence of a signal. The junction of resistors 80 and 82 is connected through a diode 84, shown as a crystal diode, and a capacitor 86 to the anode of the relay control tube 76, the anode of the diode being connected to the junction of the resistors. A resistor 88 of say 330K is connected between the cathode of the diode and ground and a capacitor 90 of say .005 microfarad is connected across bias resistor Si). When signals are impressed upon the control grid of the relay control tube negative voltage Li' pulses will appear at the anode 4of the tube. These negative pulses are applied through the capacit-or 86 to the cathode of the diode S4. The potential at the anode of the diode will thus be ldriven to the lowest potential occurring during each such pulse .and capacitor 90 will be charged to such low potential. Thus during the presence of signals additional negative potential is automatically applied to the control grid of the output tube. When the signals cease, discharge of capacitor 90 through re sistor 80 restores normal grid bias. The purpose of resistor 52 is to prevent application of the signals from the oscillator directly to the diode S4.

The invention has now been described with reference to a single embodiment thereof and with specific reference to the control of the dimming switch of automobile headlamps. lt will be apparent, however, that the invention in its broadest aspects is not limited to such speciiic application. Obviously also, although certain numerical values for the various constants of the circuit have been suggested the invention is not limited to such selected constants and various changes could be made in parts of the circuit without departing from the spirit of the invention or the scope of the accompanying claims. For example, although the hold control has been shown as being in the screen circuit of the electrorneter tube adjustment for this purpose could be provided at the control grid of the rst half of the multivibrator circuit if desired. Also, although the diode in the grid bias circuit of the relay control tube has been indicated as of the crystal type, an electronic tube could Other modifications will occur be substituted therefor. to those skilled in the art.

The following is claimed:

l. A light responsive circuit comprising in combination a photoelectric tube having a photocathode, an electronic tube having a grounded cathode, a control grid connected to said photocathode, a screen gri-d and an anode, a low voltage source of energizing potential connected to said anode through a dropping resistor, output means adapted to be actuated in response to a predetermined decrease in anode potential resulting from increase in control grid potential consequent to incidence of light on said photocathode and circuit means connected to said screen grid for providing a -positive potential on said screen grid which decreases with increase in conduction of said tube, said last mentioned circuit means including means for delaying return to normal of the screen grid potential during decrease in control grid potential consequent to cessation of light on said photocathode.

amarsi 2. The circuit according to claim l wherein said circuit connected to said screen grid comprises a potential divider connected across said source, a dropping resistor interconnected between a point on said potential divider and said screen grid and a capacitor connected between said screen grid and ground, said capacitor providing said delay means.

3. The circuit according to claim l wherein said circuit connected to said screen grid includes means for adjusting the sensitivity of the circuit to incidence of light on said photocathode.

4. A light responsive circuit comprising in combination a photoelectric tube having a photocathode, an electronic tube having a grounded cathode, a control grid connected to said photocathode, a screen grid and an anode, a low voltage source of energizing potential connected to said anode through a dropping resistor, potential dividing means and a dropping resistor coupling said screen grid to said source, a capacitor connected between said screen grid and ground, a normally energized output electronic tube, an oscillatory circuit, biasing means normally preventing oscillation of said oscillatory circuit, means responsive to decrease in anode potential of said iirst mentioned electronic tube resulting from conduction by said photoelectric tube .under the iniuence of light for overriding said biasing means, and means responsive to oscillation of said oscillatory circuit for reducing the current through said output tube.

5. The circuit according to claim 4 wherein said oscillatory circuit comprises a first and second triode connected as a multi-vibrator, the cathode of the second triode being grounded and the cathode of the irst triode being connected to a point of positive potential providing the biasing means normally preventing oscillation, phase inverting means coupling the anode of said first mentioned tube with the control grid of the lrst triode, and means for impressing pulses appearing at the anode ot the second triode when the multi-vibrator is oscillating upon said out put tube.

6. In a control circuit, the combination comprising a normally energized output tube having a cathode, at least one grid and an anode, a resistor of high resistance interconnecting said grid and cathode, a multivibrator adapted when oscillating to produce control pulses, biasing means normally preventing oscillation of said multivibrator, a capacitor connected between said multi-vibrator and said grid to transmit positive pulses to said grid when the multivibrator is oscillating, photoelectric means for overriding said biasing means to cause oscillation of said multivibrator when light of predetermined intensity is incident on the photosensitive element of said photoelectric means, said grid when pulsed being driven negative by negative charging of said capacitor from said cathode with consequent reduction of current through said tube, and circuit means connected to the anode and responsive to pulsation of potential thereat for increasing the bias on said grid when said grid is pulsed.

7. In a condition responsive circuit, a low voltage source of energizing potential, an asymmetrical multivibrator circuit energized from said source and adapted, when oscillating, to yield positive voltage pulses, condition responsive means for controlling oscillation of said multivibrator circuit, a space charge grid tetrode coupled to said source and having a control grid connected to receive positive pulses from said multivibrator circuit when said multivibrator circuit is oscillating, and means, including a rectifier and lilter connected in series across said tetrode, for augmenting the negative potential appearing between pulses at said grid.

8. The circuit according to claim 7, including a resistor connected between said grid and the junction of said rectilier and lter to prevent application of pulses from said multivibrator circuit to said rectifier.

9. The circuit according to claim 7 wherein said condition responsive means includes an electronic tube having a grounded cathode, a cathode heater, a control grid the potential of which is responsive to the condition, a screen grid and an anode and wherein means are provided for supplying substantially regulated voltage from said source across said heater and through dropping resistors `to said screen grid and anode, and means for increasing the stability of anode potential to iiuctuations in voltage of said source comprising a dropping resistor connected between said source and said anode to compensate for changes in cathode emission with change in regulated voltage.

10. A light responsive circuit comprising in combination a photoelcctrie tube having a photocathode, an electronic tube having a control grid connected to said photocathode, a cathode, a screen grid and anode, a low voltage source of energizing potential and a dropping resistor connected in a series circuit with said anode and cathode, output means adapted to be actuated in response to a predetermined decrease in anode potential resulting from increase in control grid potential consequent to incidence of light on said photocathode and circuit means connected to said` screen grid for providing a positive potenF tial onsaid screen grid which decreases with increase in conduction of said tube, said last mentioned circuit means including a capacitor for delaying return to normal of the screen grid potential dur-ing decrease in control grid per tential Vconsequent to cessation of light on said photocathode.

References Cited in the tile of this patent 'UNITED STATES PATENTS 2,016,147 La Pierre et al Oct. 1, 1935 2,070,640 Ballantine Feb. 16, 1937 2,070,900 Harris Feb. 16, 1937 2,243,071 Crago Ma', 27, 1941 2,430,547 Anderson etal Nov. 11, 1947 2,431,394 Friedman Nov. 25, 1947 2,493,307 Moore et al. Ian. 3, 1950 2,598,420 Onksen May 27, 1952 2,730,629 Atkins Ian. 10, 1956 2,741,725 Thomas Apr. 10, 1956

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