US3414878A - Traffic signal lamp control circuit - Google Patents

Description

United States Patent 3,414,878 TRAFFIC SIGNAL LAMP CONTROL CIRCUIT Barry L. Smith, Rochester, N.Y., assignor to General Signal Corporation, a corporation of New York Filed Dec. 17, 1965, Ser. No. 514,500 6 Claims. (Cl. 340-41) ABSTRACT OF THE DISCLOSURE Apparatus for controlling traflic governing lamps having a gate controlled bi-directional static switch associated with each lamp for conducting alternating current to the lamp, and control circuitry for selectively determining the desired lamp by energization of its associated gate circuit.

This invention relates to circuits for controlling the energization of traffic signal lamps from a traffic signal controller, and more particularly relates to a solid-state electronic control circuitry for selectively energizing such traffic signal lamps with alternating current.

In keeping with present day trends towards control of traffic signals with solid state electronic devices, it becomes desirable to utilize such devices to directly energize and deenergize the signal lamps. However, such solid state devices must be capable of supplying the full-rated load current required by the lamps, in order to achieve reliable and successful operation. In addition, the usual source of alternating current power should be directly applicable to the signal lamps in a manner that simplifies their selective energization. Also, such control of the lamps should be in a suitable manner to minimize its effect upon radio or television reception.

In the past, silicon controlled rectifiers have been employed to operate trafiic signals as disclosed, for example, in the N. A. Bolton et al. Patent No. 3,251,030, filed May 24, 1963 and issued May 10, 1966. Although successful operation of traffic signals may be achieved with silicon controlled rectifier circuits as disclosed, such circuits do not readily lend themselves to connection with the traffic signal lamps. Such a system inherently requires a power rectifier at each traffic signal location which makes such a system expensive.

The present invention proposes to employ the recently developed gate controlled semi-conductor switch, some times known as a bidirectional triode thyristor, and at other times known as a gate controlled bidirectional switch. In the electronic trade, it is termed a Triac which is capable of switching large amounts of alternating current power in response to minimal amounts of control power. A detailed description of the Triac may be found in an article entitled Bi-Directional Static Switch Simplifies AC Control, appearing on pages 75-76 of the March 1964 issue of Control Engineering published by The Ruben H. Donnelley Corp. of New York, NY.

The present invention proposes that each trafiic signal will be controlled directly by a Triac which in turn can be individually controlled through its gate circuit in accordance with the desired selective energization of the associated signal lamp. It is proposed that such control be effected in a manner which will allow the making and breaking of sizable amounts of power but at such times in the alternating current cycles as will minimize any external effects on radio or television reception.

Accordingly, one object of the invention is to provide electronic solid state switching means for energizing and deenergizing the lamps of a traffic signal with alternating current.

Another object is to provide solid state electronic switching means for operating the lamps in a manner which permits the use of a grounded common power con- 3,414,878 Patented Dec. 3, 1968 nection to one terminal of each of the lamps in the signal.

Another object is to provide means for operating the lamps of a traffic signal directly from Triacs which will be turned on during a relatively low current flow for each half cycle of alternating current and which will be turned oft near the end of each half cycle.

Another object of the invention is to provide simple solid state electronic means operable on relatively low values of direct current for controlling the selective energization of the signal lamps by their respective solid state switching means.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawing, and in part pointed out as the description of the invention progresses.

In accordance with an embodiment of this invention in a system for the control of traffic governing lamps, a trafiic signal cont-roller designates several time intervals for each traffic cycle. A gate controlled bi-directional static switch for each of the lamps normally renders its lamp deenergized but is capable of being gated to supply alternating current to its lamp. Gate control means for each of the static switches, and circuit means controlled by the controller for rendering the gate control means for the several switches selectively effective at the beginning of each half cycle of alternating current to cause the static switch associated with the selected gate control means to be conductive for the remainder of that half cycle, whereby each lamp is repeatedly energized. for successive half cycles of alternating current as long as the circuit means energizes the selected gate control means.

In describing the invention in detail, reference will be made to a single figure of drawings which is in part a schematic diagram and in part a block diagram of the invention.

For the purpose of simplifying the illustration and facilitating the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed. The drawings have been made more with the purpose in mind of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable sources of direct current; and the circuits with which these symbols are used always have current flowing in the same direction. In some instances the negative terminal of such sources is not shown, but it is assumed to be grounded.

In a similar manner, the spmbol (+)AC is used to designate one terminal of the usual commercial alternating current power supply and the other terminal thereof ()AC is assumed to be ground or connected to a common lead.

Turning now to the single figure of drawing, there is shown a traffic signal controller 7. Such controller 7 may be of any suitable type for designating the different intervals in the signal phases of operation useful at the particular highway intersection where such signals are located. For example, the controller may be of the well known mechanical type for timing the application of energy to successive terminals for giving the sequence of operation of the signals through its different phases. On the other hand, such traffic controller may be of the electronic type where a single counter is operated through its different steps and is timed with respect to each step so as to give the periods during which the different signals should be operated. Such an electronic controller is shown, for example, in the above mentioned Patent No. 3,251,030 of N. A. Bolton et al.

In particular, the trafiic signal controller 7 is assumed to apply energy for appropriate times to the output terminals desi nated 1 through 6. The controller is considered to be of the two-phase type with each phase including four periods of time constituting a complete cycle. More specifically, each phase is considered to have a green and walk period, a green period, a caution period, and a red period. The red period for the phase A is assumed to coincide with the active periods for phase B; and the red period for phase B is assumed to coincide with the active periods for phase A. The active periods are designated by the application of from a suitable source connected to the tralfic signal controller in turn to the terminals 1, 2, 3, 4, and 6. The time that such energy is applied to each terminal is measured so that each signal period will be appropriate for the intersection to which it is applied. For example, the green time may be short or it may be long for each phase. The caution time may be relatively short near the end of the active periods for any particular phase; and the lengths of the cycles may be changed to suit traffic conditions.

In considering the detailed operation of the phases A and B circuits located within the dotted rectangles desig nated 8 and 10, it will immediately be pointed out that there is no positive control for the red signal of either phase coming from the traflic signal controller, because the absence of the green or caution signal controls for any phase will automatically cause the red signal for that phase to be displayed. A similar control is provided for the Dont Walk signal lamp 14 in that it is on whenever the Walk lamp 12 is not on. All of this will be cle scribed in greater detail hereinafter.

The phase A circuits 8 are directly associated with the phase A" lamps 9. It is assumed that the phase B circuits 10 are identical to the phase A circuits 8. Similarly, the phase B lamps 11 are assumed to be identical to the phase A lamps 9.

Both the phase A circuits 8 and the phase B circuits 10 are controlled by common apparatus including an SCR, an NPNI, diodes D11, D12, D13, D14, and transformer T. Associated with these devices are resistors R8, R9, R10, R11, R12 and R13. The control is effected over buses 25 and 26 as explained in detail later.

Alternating current supplied from (+)AC is fed over bus 27 to each of the several Triac devices Q1, Q2, Q3, Q4 and Q5 as well as similar devices in the phase B circuits. Such (+)AC is supplied to the so-called heat sink terminal of each Triac; whereas the output terminal of each Triac is connected directly to its respective lamp, such as lamps 12, 13, 14, and 16. The gate of each of the Triacs Ql-QS is controlled by its respective transformer T1, T2, T3, T4 and T5. These transformers are relatively simple iron powder transformers which have inputs from the respective capacitors C1, C2, C3, C4 and C5. The respective inputs are also controlled by diodes D1, D2, D3, D4 and D5. The energy which is supplied to these respective circuits is fed to the common bus 26 which connects with the anode of the SCR; and such energy returns via diode D14 and bus to the lower terminals of the respective capacitors C1C5.

Normally, the NPNl is conducting by reason of the positive energy supplied from through resistor R10 to the base of the transistor NPNl. The output current flows from through resistors R11 and R12 through the collector and emitter of transistor NPNl to ground. The capacitor C6 is charged through resistor R11, diode D14, transistor NPNI, to the voltage appearing across the resistor R12. With the transistor NPNI conducting, the gate of the SCR is maintained near ground through resistor R13.

Let us now assume that the traflic signal controller is initiated and applies energy to the terminal 1, for example. This positive energy is applied to the upper terminal of capacitor C1 through resistor R1, and the other side of the capacitor C1 is connected to the bus 25 and thence to ground through transistor NPNl. This causes a positive charge to build up on the capacitor C1 which cannot leak off through the diode D1 because the SCR is non-conductive.

The transformer T is of the torroid type having a care characteristic causing the flux to quickly shift from one direction of flux to the other at about ten degrees into each half cycle. When this shift in flux takes place, it causes a positive current to flow in its secondary winding through either the diode D11 or D12 depending upon the particular polarity of the half cycle, through diode D13 and resistor R9. This flow of current puts a negative pulse on the base of the transistor NPNl causing it to be non-conductive. This non-conductivity of NPNI causes the left side of the capacitor C6 to place a positive voltage on the gate of the SCR and renders it conductive. The positive charge from the uper terminal of capacitor C1 then discharges through the diode D1, primary winding of transformer T1, anode of SCR, through the diode D14, to the lower side of the capacitor C1, via the bus 25.

This momentary pulse of 7 or 8 microseconds from capacitor C1 occurs at approximately ten degrees into the half cycle then being applied to the bus 27 and induces a momentary pulse in the secondary of transformer T1 applied directly to the gate for Triac Q1. This point in the half cycle is the point at which sufficient current will flow through the Triac Q1 for maintaining it conductive nearly to the end of that half cycle. When the current reaches a certain limited value near the end of the half cycle, the Triac ceases conduction and the current drops to zero.

However, it should be noted that immediately following the conduction of such pulse through the SCR, the transistor NPNl restores to its normal condition of conductivity because of the cessation of the pulse applied to it from the secondary winding of the transformer T. Thus, the capacitor C1 can then begin charging and continues to charge through the remainder of that half cycle and up to the ten degree point in the next half cycle of alternating current at which time another pulse is supplied from the transformer T so as to allow the capacitor C1 to again discharge and again render the Triac A1 conductive in a similar manner.

In this way so long as positive energy is applied to the terminal 1 of the traffic signal controller the capacitor C1 through its associated circuits supplies a pulse for rendering its associated Triac A1 conductive for the ensuing half cycle. This means that the current is turned on while it is still at a relatively low value while rising, and is turned off at a slightly lower value while decreasing for each succeeding half cycle. In this way the application of positive energy to the terminal 1 causes the Walk lamp 12 to be energized.

Also, the positive energy applied to the terminal 1 is applied through diode D6, resistor R2 to the capacitor C2 which also supplies a discharge current pulse through its transformer T2 to render its associated Triac Q2 conductive for each succeeding half cycle in a similar manner as explained for Triac Q1. Diode 15 is provided to prevent back feed to terminal 2 and related circuits.

It will be noted that the positive energy applied to terminal 1 is also applied through diode D7 through the resistor R6 to the base of the transistor NPN2. This renders such transistor NPN2 conductive and in effect connects the upper terminal capacitor C3 to ground, so that it cannot become charged. Since there is no charge on the capacitor C3, it cannot discharge when the SCR becomes conductive and thus the Dont Walk signal 14 remains dark.

In a similar fashion the application of positive energy to the terminal 1 flows through diode D8 and resistor R7 to the base of NPN3 to render it conductive. This also connects the upper terminal of capacitor C5 to ground so that such capacitor cannot become charged. Thus, it cannot discharge through its transformer T5 for each half cycle when the SCR becomes conductive, and for this reason the Red signal 16 remains dark.

However, when the traffic controller has appropriately timed out the interval for the Green and Walk signals to arrive at the time that the green alone should be i1- luminated, energy is then applied to the terminal 2. This positive energy is supplied through resistor R2 to the capacitor C2, so that it is alternately charged and discharged as previously explained for each of the succeeding half cycles. This causes the green lamp 13 to be energized. However, under this circumstance the diode D6 prevents positive energy from the terminal 2 from reaching the capacitor C1. For this reason, the Triac Q1 is not rendered conductive and the Walk lamp 12 is extinguished.

Also, the removal of the positive energy from the terminal 1 removes the energy which flowed through diode D7 and resistor R6 to the base of transistor NPN2, and this renders such transistor non-conductive. This then allows the capacitor C3 to be charged through resistor R3 and to be discharged through diode D3, transformer T3, bus 26, SCR, diode D14, bus 25, to the lower terminal of capacitor C3. This causes the Dont Walk lamp 14 to be illuminated.

The application of the positive energy on the terminal 2 also supplies energy through the diode D9, through the resistor R7, to the transistor NPN3, causing it to continue to be conductive and withhold the red lamp 16 from being illuminated.

The timing out of the traffic signal controller for the period requiring the green alone to be energized along with the Dont Walk signal 14 then causes the positive energy from to be applied to the terminal 3. This causes the capacitor C4 to become charged and to be discharged through the SCR via the diode D4, transformer T4, bus 26, SCR, diode D14, bus 25, to the lower terminal of the capacitor C4. This of course energizes the gate of Triac Q4 and causes the yellow lamp to be illuminated.

Concurrently the positive energy on the terminal 3 flows through diode D10, resistor R7, to the base of the transistor NPN3. This in effect grounds the upper terminal of the capacitor C5 so that the red lamp is still maintained unilluminated.

When the traffic signal controller times out the period for the yellow signal, it is then effective to apply positive energy from to terminals 4, 5 and 6 in turn so that the phase B circuits operate in exactly the same way as described for the phase A circuits. It will be noted that throughout the time that positive energy is removed from the terminals 1, 2 and 3, the transistors NPN2 and NPN3 become non-conductive and the capacitors C3 and C5 charge and discharge for each half cycle to cause the Triacs Q3 and Q5 to be conductive and illuminate the Dont Walk signal 14 and the red signal 16. In other words, when the phase B circuits are operating to cause proceed indications to be displayed with regard to the phase B lamps, the phase A no-movement lamps continue to be illuminated throughout that period.

In connection with the transfer of the positive energy from terminal to terminal by the tratfic signal controller 7, there is assumed to be no interruption of the energy as it is being transferred between terminals 1, 2 and 3 and between terminals 4, 5 and 6. However, there may well be a desired interruption of the positive energy between terminals 3 and 4, and between terminals 6 and 1. Such interruption of energy would result in the energization of all of the red lamps for both phases A and B. If desired, a separate timed interval can be provided by the trafiic signal controller following the time interval for terminal 3, and also another separate time interval can be provided following the time interval for terminal 6. These separate timed intervals, of suitable length, can be employed to provide any desired length energization of all the red lamps for both phases A and B.

Although the traffic signal controller 7 is only shown as having two phases A and B, it is to be understood that any desired number of phases can be employed. In fact, additional phases may be added to the two phases shown without changing the equipment already shown. This addition of phases would only require additional controller units and additional lamp control units with the continuation of buses 25, 26 and 27. This then makes this type of traffic signal control organization readily adaptable to extensions and additions as may be required by practice.

With the organization above described, a very small amount of power is required for the control functions. For example, three to six milliamperes of control current is approximately all that is required for the control of each individual lamp.

It is also noted that resistor R8 is connected in series with the primary winding of the transformer T to limit the current therein during the times that the flux in the transformer core is at saturation.

Having thus described one form of a traffic signal lamp control circuit as one specific embodiment of the present application, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present. invention.

What -I claim is:

1. In a system for the control of trafific governing lamps, a trafiic signal controller for designating the several time intervals for each cycle, a gate controlled bi-directional static switch for each of said lamps normally rendering its said lamp deenergized but capable of being gated to supply an alternating current to its said lamp, gate control means for each of said switches, and circuit means controlled by said controller for rendering said gate control means for the several switches selectively effective, said circuit means momentarily rendering said selected gate control means effective at the beginning of each half cycle of the alternating current to cause said switch associated with said selected gate control means to be conductive for the remainder of that half cycle, whereby each lamp is repeatedly energized for successive half cycles of the alternating current as long as said circuit means energizes said selected gate control means.

2. In a system according to claim 1 a plurality of gate controlled bi-directional static switches each having its gate control circuit adapted for momentary energization by said circuit means, and wherein each said gate control means is controlled by a master circuit means for efiecting said momentary energization of said selected switches at the beginningof each half cycle of alternating current.

3. In a system according to claim 2, wherein means normally render gate control means active for a particular lamp, and other means render said means inactive when another gate control means is rendered effective by said controller, whereby a more restrictive indication is normally given whenever the controller does not render an associated less restrictive indication effective.

4. In a system according to claim 2, a plurality of capacitor discharge circuits, each associated with one of said gates, said circuit means governed by said controller for selectively rendering said capacitor discharge circuits effective, and said master circuit means controlled by said alternating current momentarily rendering all of said effective capacitor discharge circuits active at the beginning of each half cycle causing their respective gates to be momentarily operated, each of said switches rendered momentarily active at the beginning of a half cycle remaining conductive for the remainder of that half cycle, whereby each lamp is repeatedly energized for successive half cycles so long as said controller selectively renders active its capacitor discharge circuit.

5. In a system according to claim 4, wherein a capacitor is provided for each of said switches and is normally charged when said controller is designating its respective switch, and wherein each said respective gate control means includes an impulse transformer having a secondary winding connected to the gate of said respective switch and a primary winding with one terminal connected to a first terminal of said respective capacitor and another terminal connected to a common lead, and switching means controlled by said alternating current for momentarily connecting said transformer primary across said respective capacitor at the beginning of each half cycle, whereby said charged capacitors discharge through their respective primary transformer winding and said transformer secondary generates a pulse momentarily gating said respective switch.

6. The system of claim 5 wherein the switching means comprises:

(a) a saturable switching transformer energized by said alternating current; (b) unidirectional current devices connecting to opposing ends of said transformer secondary for gen- 5 erating pulses of the same polarity on respective alternate cycles; (0) transistor switching means changing conduction state relative to each generated pulse; and (d) silicon controlled rectifier means connecting between said common lead and the said terminal of said respective capacitor responsive to the change in conductance state of said transistor switching means for connecting said impulse transformer primary across said respective capacitor.

References Cited UNITED STATES PATENTS 3,175,184 3/1965 Shelar 340-41 20 THOMAS B. HABECKER, Primary Examiner.

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