Abstract:
A semiconductor based relay is provided for selectively coupling differing periodic power sources to loads through semiconductor switches provided therein while selectively using such power sources to also contribute to the operation of the relay circuitry, each in a different manner, in conjunction with selection signals.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 09/303,149, filed Apr. 30, 1999 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to solid state relays and, more particularly, to solid state relays used in traffic signal light control systems. 
     Intersecting vehicle thoroughfares often have provided at their intersections standards supporting vehicle traffic control signal lights with one light of each color on each standard visible across the intersection from each of the thoroughfares. These signal lights are typically operated under the control of a control system, including the timing controller and the conflict monitor, housed in a control system cabinet provided in the vicinity of the intersection. The control system and the signal lights are typically operated using alternating current obtained from a commercial electrical power distribution system. 
     The green, red and yellow signal lights usually used at an intersection, under the direction of the control system, are typically operated to be continuously switched on for selected short time intervals, or are otherwise operated in a switched on-switched off, or flashing, sequence over other selected time intervals. The control system accomplishes such operation of the signal lights through generating signals in the timing controller to close and open load switches that control the supply of alternating currents through a flash transfer relay to the signal lights in those situations in which the signal lights are to be continuously switched on during selected intervals. The flash transfer relay is placed in a first switching state by the conflict monitor during times including those selected intervals that enables the load switches to be effective in selecting those intervals for delivery of alternating current to the lights. In those intervals in which the signal lights are to flash, the conflict monitor directs this condition through the flash transfer relay by changing the relay to another, or second, switching state. 
     The flash transfer relays provided in typical traffic signal light control systems have traditionally been electromagnetic devices using the presence or the absence of current in a coil to create or end magnetic fields to open or close electrical contacts. These contacts, in the absence of contamination, or other electrical conductivity limiting effects, tend to have very small voltage drops there across during times they are closed and carrying substantial electrical currents therethrough. Thus, they dissipate relatively little electrical power during the carrying of substantial electrical currents therethrough. On the other hand, such contacts suffer from impact recoil so that they rapidly open and close following the first making contact in a switch closing thereby leading to “chattering”, and there are discharges between the contacts as they come close to one another leading to “arcing” which causes corrosion and erosion of those contacts. Such contacts, of course, are already subject to contamination from external sources if they are not in a sealed enclosure. In addition, such behavior often leads to the generation of unwanted electrical noise in the circuits connected thereto and in circuits located nearby. 
     Because of these deficiencies in electromechanical relays, solid state relays have been developed as substitutes in some situations. Such relays use power semiconductor devices which can operate as switches to switch on and off relatively large currents, and can withstand relatively large voltages thereover when switched off. The use of such semiconductor device switches avoids the presence of any moving parts which can wear out, and avoids the use of contacts which are subject to erosion, corrosion and contamination, and thereby also avoids contact chattering and the undue generation of electrical noise. However, such power semiconductor switches do have a relatively large voltage drop there across even when switched on to conduct current therethrough and, thus, these devices are subject to significant electrical energy dissipation. 
     The use of a solid state relay for flash transfer relays in traffic signal light control systems of typical design is difficult because of the electrical signals available to operate the flash transfer relay. In typical control systems of the past, electromechanical relays were used which merely need to have an alternating current supply provided to the coil thereof whenever relay contacts therein are to be actuated, and removed therefrom when those relay contacts are to no longer be actuated. Thus, such a selectively provided alternating current supply serves as the operating signal for switching the flash transfer relay between switching states thereof. 
     In some typical traffic signal light control systems, such signal operation control alternating current is always supplied when the signal lights are to be switched on continuously over selected intervals, and this alternating current is removed when the signal lights are to flash (a “energized”“energized” system). Other typical signal light control systems are operated in the opposite manner with the signal operation control alternating current being supplied only during instances in which the signal lights are to be flashing, and otherwise not provided when the signal lights are to be switched continuously on over selected intervals (an“deenergized” system). 
     However, in either type of system, in those situations in which the signal operation control alternating current is not being provided to the flash transfer relay, that relay may not be receiving any electrical power which can be continuously used to operate the circuitry therein which controls the selection of the corresponding switching state thereof. Thus, there is a desire for a solid state relay which can operate as a flash transfer relay in a traffic signal light control system of a typical design. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a semiconductor based relay for selectively coupling differing periodic power sources to loads through semiconductor switches provided therein while selectively using such power sources to also contribute to the operation of the relay circuitry, each in a different manner, in conjunction with selection signals. Such selection signals are provided by a control system which is typically a traffic signal light control system that provides these signals to operate controlled switches for use with the relay serving as a flash transfer relay therein, and with the loads being signal lights. No other sources of electrical energization are typically provided to the flash transfer relay in the control system. 
     Suitable semiconductor switches are triads activated by bilateral switches. Optical isolation between the bilateral switches and the rest of the relay switching controller is provided. The periodic power source outputs are typically converted to constant polarity waveforms in contributing to the operation of the relay circuitry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an electrical schematic diagram of a circuit embodying the present invention, 
     FIG. 2 shows an electrical schematic drawing of an alternative circuit embodying the present invention 
     FIG. 3 shows an electrical schematic drawing of another alternative circuit embodying the present invention; and 
     FIG. 4 shows an electrical schematic drawing of a further alternative circuit embodying the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an electrical schematic diagram of a semiconductor device based, or solid state, relay  10 , within the dashed line enclosure, serving as a flash transfer relay in a traffic signal light control system (this control system being only partly shown in that figure) of an otherwise typical design as used for conventional control systems offered in the commercial marketplace. Control signals to flash transfer relay  10  select the switching status, or state, of that relay so that the traffic signal lights,  11  and  12 , controlled in part thereby are, in one switching state, enabled to be continuously on over time intervals selected by the timing controller load switches or, in another switching state, are operated in an on off alternating sequence, i.e. “flashing” those lights. Control signal lights  11  and  12  may be, for instance, both red colored lights on a standard installed at an intersection, with one of them being observable by people in vehicles or by pedestrians traveling along one street or thoroughfare crossing that intersection. The remaining light would visible along the other street crossing that intersection. 
     The traffic signal light control system for these lights is typically supplied electrical energy from a commercial source providing voltages and currents therefrom in the form of single phase sinusoidal waveforms characterized by a selected frequency and amplitude, i.e. alternating currents. One typical commercial source provides an approximately constant amplitude voltage single phase sinusoidal waveform with a frequency of 60 Hz and an amplitude of about 115 volts rms. In the portion of the traffic signal light control system shown in FIG. 1, such an electrical energy source would have a neutral conductor correspondingly connected to a zero voltage reference terminal,  13 , of relay  10  and a phase conductor correspondingly connected to a phase or “hot” terminal,  14 . 
     Three switches,  15 ,  16  and  17 , are provided in the other portions of the traffic signal lights control system outside of relay  10  with one side of each connected to “hot” terminal  14 . These switches are schematically shown in FIG.  1 . Switch  15  is provided to control operation of relay  10 , and switches  16  and  17  are provided to control continuously on operation of lights  11  and  12  through power switches in relay  10  so as to have this control effectively enabled by relay  10 . 
     Switch  15  is the “flash/automatic” switch which determines the switching state of relay  10 , and so whether lights  11  and  12  are enabled to operate in a continuously on condition over selected time intervals or to operate in a flashing condition. The signal for opening and closing switch  15  is provided from the remaining portions of the control system on a terminal,  18 , specifically, the conflict monitor. 
     Switches  16  and  17  are the “load switches” indicated above which are switched, in those situations in which lights  11  and  12  are to be operated continuously on or off over selected time intervals, to set just what the intervals are during which these off or continuously on light operations occur. A control signal from the remaining portions of the control system for controlling the opening and closing of switch  16  appears on a terminal,  19 , and a control signal from the remaining portions of the control system for controlling the opening and closing of switch  17  appears on a further terminal,  20 . Control signals on terminals  19  and  20  are specifically provided by the timing controller. 
     Thus, the control signals provided on terminals  19  and  20  from the remaining portions of the control system to open and close switches  16  and  17 , respectively, determine if electrical energy is supplied from “hot” terminal  14  to lights  11  and  12  when permitted by the then current switching state of relay  10 . Relay  10  enables any such supplying of electrical energy to lights  11  and  12  because switches  16  and  17  are connected to lights  11  and  12  only through relay  10 . That is, lights  11  and  12  are electrically connected to a pair of relay power output terminals,  21  and  22 , and switches  16  and  17  are electrically connected to a pair of corresponding relay power input terminals,  23  and  24 , respectively. Hence, switches  16  and  17 , during those times they are switched on, provide electrical energy to lights  11  and  12  to keep them continuously lit only in those situations in which relay  10  is in a switching state in which power input terminal  23  is conductively connected to power output terminal  21  and power input terminal  24  is conductively connected to power output terminal  22  in relay  10 . 
     “Hot” terminal  14 , in addition to being connected to switches  15 ,  16  and  17 , is also connected to a power frequency converter,  25 , again located in other portions of the traffic signal light control system than is relay  10 . Frequency converter  25 , commonly referred to as a “flasher”, is also connected to reference terminal  13 . Flasher  25  provides a sinusoidal waveform at an output thereof,  26 , to serve as an electrical energy source for operating lights  11  and  12  during flashing operations. This is accomplished by flasher output  26  being electrically connected to one of two further relay power input terminals,  27  and  28 , shown electrically connected together in FIG.  1  through the provision of an external “jumper” interconnection,  29 , so that flasher output  26  is connected to both. 
     Flasher  25  is also used to serve as the electrical energy source for operating other circuitry in relay  10  to thereby overcome the unavailability of an electrical energization supply for this purpose at the location of the flash transfer relay in conventional traffic signal lights control systems. This unavailability, as described above, is the result of commercially offered control systems being designed to accommodate electromechanical relays for use as flash transfer relays which require only the presence or absence of electrical energy in the coil thereof as provided through switch  15  to be placed in an appropriate switching state. Flasher  25  continuously provides typically “on-of” periods of equal duration of a 60 Hz sinusoidal voltage waveform at output  26  thereof having an “on-off” frequency of just 1 Hz and again having an amplitude of about 115 volts rms during “on” periods. 
     Electrical energy in a constant polarity form for operating circuitry in relay  10  is obtained from flasher  25  by half-wave rectifying the sinusoidal power output waveform provided at output  26  thereof. This rectification is provided by a diode,  30 , having its anode connected to flasher output  26  and its cathode connected to a series string of components including a pair of current limiting resistors,  31  and  32 , a voltage reducing Zener diode,  33 , having a breakdown voltage of  51  volts, and an output voltage determination Zener diode,  34 . 
     Resistor  31  is connected between the cathode of diode  30  and the cathode of Zener diode  33 , with resistor  32  connected between the anode of Zener diode  33  and the cathode of Zener diode  34 . The anode of Zener diode  34  is connected to reference terminal  13 . An electrolytic capacitor,  35 , is connected from the junction of the anode of Zener diode  33  and resistor  32  to reference terminal  13  to aid in reducing the voltage variations due to half-wave rectification, i.e. to reduce voltage fluctuations across resistor  32  and output determination Zener diode  34 . Thus, a constant polarity relatively constant magnitude voltage of approximately 3.3 volts, the typical breakdown voltage value for output determination Zener diode  34 , is provided at a junction interconnection,  36 , of resistor  32  and Zener diode  34  as the relay electrical energization operating voltage supplied to portions of the remaining switching control circuitry of relay  10  for operating those circuit portions. 
     An npn bipolar phototransistor,  37 , in a transistor output optoisolator,  38 , (typical commercial part: Motorola, Inc. part MOC8113) has its emitter connected to reference terminal  13  and its collector electrically connected through a load resistor,  39 , to relay operating voltage interconnection  36 . A further npn bipolar transistor,  40 , has its base connected to the collector of phototransistor  36  and its emitter connected to reference terminal  13 . Transistor  40  has its collector electrically connected through a load resistor,  41 , to relay operating voltage interconnection  36 . 
     In addition, the collector of transistor  40  is connected to relay operation power interconnection  36  along two further electrical interconnection paths. In the first of these paths, interconnection  36  has the anode of a light-emitting diode,  42 , connected thereto with the cathode of that diode connected through a current limiting resistor,  43 , to the collector of transistor  40 . Light-emitting diode  42  is in a zero voltage crossing, bilateral switch output optoisolator,  44 , (typical commercial part: Motorola, Inc. part MOC3063) in which there is also provided an optically activated silicon bilateral switch,  45 , having incorporated therewith a zero-crossing control circuit,  46 , (shown in block form only) to cause optically operated bilateral switch  45  to break down within a few volts of zero volts occurring across the main contacts thereof. 
     In the second further interconnection path between interconnection  36  and the collector of transistor  40 , there is a further light-emitting diode,  47 , having its anode connected to interconnection  36  and its cathode connected through a further current limiting load resistor,  48 , to the collector of transistor  40 . Light emitting diode  47  is part of a further zero voltage crossing, bilateral switch output optoisolator,  49 , like optoisolator  44 , and which also contains an optically activated silicon bilateral switch,  50 , along with again a zero-crossing control circuit,  51 , shown only in block form. Thus, by switching transistor  40  into an “on” condition, current is drawn through light emitting diodes  42  and  47  along with their series load resistors, and further current is drawn through load resistor  41  all passing through the collector and emitter of transistor  40  to reach reference terminal  13  to which the emitter of transistor  40  is connected. The current drawn through light emitting diodes  42  and  47  is sufficient to cause them to emit light enough to switch on corresponding bilateral switches  45  and  50 . 
     Bilateral switch  45  of optoisolator  44  is connected at a main terminal thereof in series with a current limiting resistor,  52 , which resistor is connected at its opposite end to relay power output terminal  21 , and to a main terminal of a triac,  53 , (typical commercial part: Motorola, Inc. part MAC224A8). Bilateral switch  45  is connected at its other main terminal to the gate of triac  53 . A further resistor,  54 , is connected between the gate of triac  53  and power input terminal  27  to thereby be connected to the other main terminal of triac  53  which is electrically connected to relay power input  27 . Resistor  54  shunts and supplies current to the gate of triac  53 , depending on the polarity of the voltage between the main terminals of that triac, to thereby delay the switching of triac  53  into the on condition with either polarity of voltages applied across the main terminals thereof. A “snubber” circuit can be further supplied across these main terminals, as is well known, to control the increases of voltage across, and current through, triac  53 . 
     Similarly, bilateral switch  50  of optoisolator  49  is connected at a main terminal thereof in series with a current limiting resistor,  55 , which resistor is connected at its opposite end to relay power output terminal  22 , and to a main terminal of a triac,  56 . Bilateral switch  50  is connected at its other main terminal to the gate of triac  56 . A further resistor,  57 , is connected between the gate of triac  56  and power input terminal  28  to thereby be connected to the other main terminal of triac  56 . Resistor  57  too shunts and supplies current to the gate of triac  56 , depending on the polarity of the voltage between the main terminals of that triac, to thereby delay the switching of triac  56  into the on condition with either polarity of voltages applied there across. A “snubber” circuit can again be used with triac  56  if desired. 
     This operating circuitry connected to relay operation power interconnection  36 , and the associated bilateral switches and triads coupled thereto, are operated under the direction of signals provided from the remaining portions of the control system on terminal  18  controlling the opening and closing of switch  15 . Control signals provided on terminal  18  to open and close switch  15  determine whether relay  10  is in a switching state allowing continuously on operation of lights  11  and  12  for intervals determined by load switches  16  and  17 , or is in an alternate switching state allowing flashing operation of lights  11  and  12 . In a so-called “deenergized” system type of traffic signal lights control system, switch  15  is opened to permit continuous operation of lights  11  and  12  and closed to permit flashing operation of those lights. In a “energized” system type of signal traffic lights control system, just the opposite arrangement is provided with switch  15  being closed to permit continuous operation of lights  11  and  12  and opened to permit flashing operation of those lights. FIG. 1 shows connecting relay  10  into the remainder of the control system in a manner suited for operation in a “energized” system type of traffic signal lights control system. 
     The closure of switch  15  by a control signal on terminal  18  results in providing a constant polarity voltage signal to direct the operation of the circuitry connected to the relay operation power interconnection  36  just described, and to direct the operation of certain other circuitry to be described below. The opening of switch  15  by control signals on terminal  18  leads to no such constant polarity voltage signal being supplied to such circuitry. 
     Thus, closure of switch  15  results in the connection of “hot” terminal  14  to another half-wave rectifying arrangement. This rectification is provided by a diode,  60 , having its anode connected to the side of switch  15  opposite that to which terminal  14  is connected. The cathode of diode  60  is connected to a series string of components including a pair of current limiting resistors,  61  and  62 , a voltage reducing Zener diode,  63 , having a breakdown voltage of 51 volts, and an output voltage determination Zener diode,  64 . 
     Resistor  61  is connected between the cathode of diode  60  and the cathode of Zener diode  63 , with resistor  62  connected between the anode of Zener diode  63  and the cathode of Zener diode  64 . The anode of Zener diode  64  is connected to reference terminal  13 . An electrolytic capacitor,  65 , is connected from the junction of the anode of Zener diode  63  and resistor  62  to reference terminal  13  to aid in reducing the voltage variations due to half-wave rectification, i.e. to reduce voltage fluctuations across resistor  62  and output determination Zener diode  64 . Thus, a constant polarity relatively constant magnitude voltage of approximately 6.2 volts, the typical breakdown voltage value for output determination Zener diode  64 , is provided at a junction interconnection,  66 , of resistor  62  and Zener diode  64  as a constant polarity signal voltage for directing the switching operations of the switching control circuitry of relay  10 . 
     This constant polarity signal voltage, when present due to the closure of switch  15 , is provided across three different light-emitting diode and resistor series combinations all connected to reference terminal  13 . The first of these has a light-emitting diode,  67 , in optoisolator  38 , with its anode electrically connected to signal interconnection  66  and its cathode electrically connected to a current limiting resistor,  68 , having its other end connected to reference terminal  13 . Thus, the closure of switch  15  results in a current be drawn through diode  67  causing it to emit light to switch on phototransistor  37 . 
     In the absence of voltage on interconnection  66  due to switch  15  being open, phototransistor  37  is switched off resulting in bipolar transistor  40  being switched on because the current in resistor  39  is shunted into the base of transistor  40 . As a further result, current is drawn through light-emitting diodes  42  and  47  allowing the voltage on output  26  of flasher  25  to break over bilateral switches  45  and  50  so as to provide currents to and from the gates of triads  53  and  56  depending on the polarity of that voltage. Such currents switch on triads  53  and  56  in each polarity segment of the flasher output voltage supplied thereto on relay power input terminals  27  and  28 . Lights  11  and  12  then flash on and off with the frequency of the output voltage waveform of flasher  25  as suitable for a energized system. Closure of switch  15  results in a constant polarity voltage being provided on signal voltage interconnection  66  to switch on phototransistor  37  through light-emitting diode  67 , and switch off bipolar transistor  40 . Thus, no current is drawn through light-emitting diodes  42  and  47  so that bilateral switches  45  and  50  can no longer break over due to the flasher output voltage waveform on relay power inputs  27  and  28  thereby leaving triads  53  and  56  in the off condition. 
     The second of the light-emitting diode and resistor series combinations between voltage signal interconnection  66  and terminal  13  has a light-emitting diode  69 , in a zero voltage crossing, bilateral switch output optoisolator,  70 , like optoisolator  44 , with diode  69  having its anode electrically connected to signal interconnection  66  and its cathode electrically connected to a current limiting resistor,  71 , that has its other end connected to terminal  13 . Optoisolator  70  also contains an optically activated silicon bilateral switch,  72 , along again with a zero-crossing control circuit,  73 , shown only in block form. 
     Similarly, the third of the light-emitting diode and resistor series combinations between voltage signal interconnection  66  and terminal  13  has a light-emitting diode  74 , in a zero voltage crossing, bilateral switch output optoisolator,  75 , like optoisolator  44 , with diode  74  having its anode electrically connected to signal interconnection  66  and its cathode electrically connected to a current limiting resistor,  76 , that has its other end connected to terminal  13 . Optoisolator  75  also contains an optically activated silicon bilateral switch,  77 , along again with a zero-crossing control circuit,  78 , once more shown only in block form. 
     Bilateral switch  72  of optoisolator  70  is connected at a main terminal thereof in series with a current limiting resistor,  79 , which resistor is connected at its opposite end to relay power output terminal  21 , and to a main terminal of a triac,  80 . Bilateral switch  72  is connected at its other main terminal to the gate of triac  80 . A further resistor, 81 , is connected between the gate of triac  80  and power input terminal  23  to thereby be connected to the other main terminal of triac  80  which is electrically connected to relay power input  23 . Resistor  81  shunts and supplies current to the gate of triac  80 , depending on the polarity of the voltage between the main terminals of that triac, to thereby delay the switching of triac  80  into the on condition with either polarity of voltages applied across the main terminals thereof. 
     Similarly, bilateral switch  77  of optoisolator  75  is connected at a main terminal thereof in series with a current limiting resistor,  82 , which resistor is connected at its opposite end to relay power output terminal  22 , and to a main terminal of a triac,  83 . Bilateral switch  77  is connected at its other main terminal to the gate of triac  83 . A further resistor,  84 , is connected between the gate of triac  83  and power input terminal  24  to thereby be connected to the other main terminal of triac  83 . Resistor  84  too shunts and supplies current to the gate of triac  83 , depending on the polarity of the voltage between the main terminals of that triac, to thereby delay the switching of triac  83  into the on condition with either polarity of voltages applied there across. “Snubber” circuits can also be used with triacs  80  and  83  as desired. 
     In the absence of voltage on interconnection  66  due to switch  15  being open, no current is drawn through light-emitting diodes  69  and  74  so that bilateral switches  72  and  77  can not break over in the presence of any voltages provided thereto on relay power inputs  23  and  24  through load switches  16  and  17 , respectively, to thus leave triacs  80  and  83  in the off condition. Closure of switch  15  results in voltage on signal voltage interconnection  66  so that current is drawn through light-emitting diodes  69  and  74  allowing any output voltages provided through load switches  16  and  17  on relay power inputs  23  and  24  to break over bilateral switches  72  and  77 , respectively, so as to provide currents to and from the gates of triacs  80  and  83  depending on the polarity of that voltage. Any such currents, resulting from the closure of load switches  16  and  17 , switch on triacs  80  and  83  in each polarity segment of the voltage supplied thereto on relay power input terminals  23  and  23  through load switches  16  and  17 . 
     FIG. 2 is an electrical schematic diagram showing the connecting into the remainder of the control system of a flash transfer relay,  10 ′, within the dashed line enclosure, of essentially the solid state relay type nature described above but in a manner suited for operation in an “deenergized” system type of traffic signal lights control system. In general, relay  10 ′ is constructed like, and operates like, relay  10  of FIG.  1 . Components shown in FIG. 2 that are essentially the same as the corresponding ones shown in FIG. 1 have the same numerical designations in each figure. Relay  10 ′ also operates with the same kinds of electrical energization and with the same kinds of control signals though the control signal provided on terminal  18  in FIG. 2 will be the complement of that provided on terminal  18  in FIG. 1 because of being an “deenergized” system type rather than a “energized” system type. 
     Relay  10  of FIG. 1, in being for control systems of the “energized” system type, has lights  11  and  12  flashing on and off in the absence of voltage on voltage signal interconnection  66  because of switch  15  being open. Since, in this situation, triacs  53  and  56  are switched on, i.e. “normally closed” with switch  15  open, output  26  of flasher  25  is connected to the relay power input terminals connected to these triacs, or terminals  27  and  28 . Triacs  80  and  83  are switched off in this situation, i.e. are “normally open” with switch  15  open, and they are connected through relay power input terminals  23  and  24  to load switches  16  and  17 , respectively, so that switch  15  must be closed for lights  11  and  12  to be lit continuously by any closures of load switches  16  and  17 . 
     On the other hand, relay  10 ′ of FIG. 2, in being for control systems of the “deenergized” system type, has lights  11  and  12  flashing on and off in the presence of voltage on voltage signal interconnection  66  because of switch  15  being closed. Since, in this situation, triacs  80  and  83  are switched on, i.e. “normally closed” with switch  15  closed (though still “normally open” in the conventional sense with no signal applied, i.e. with switch  15  open), output  26  of flasher  25  is connected to one of the relay power input terminals connected to these triacs, or terminals  23  and  24 , with an external “jumper” interconnection,  29 ′, connecting them together rather than being connected to relay power input terminals  27  and  28 . Triacs  53  and  56  are switched off in this situation of switch  15  closed, i.e. are “normally open” with switch  15  closed (though still “normally closed” in the conventional sense with no signal applied, i.e. with switch  15  open), and they are connected through relay power input terminals  27  and  28  to load switches  16  and  17 , respectively, rather than to relay power input terminals  23  and  24  so that switch  15  must be opened for lights  11  and  12  to be lit continuously by any closures of load switches  16  and  17 . 
     FIG. 3 is an electrical schematic diagram showing the connecting into the remainder of the control system of a flash transfer relay,  10 ″, within the dashed line enclosure, of essentially the solid state relay type nature described above in connection with FIG. 1 as an alternative thereto, and again connected in a manner suited for operation in a “energized” system type of traffic signal lights control system. In general, relay  10 ″ operates like relay  10  of FIG. 1 but is instead constructed using bridge rectifiers for alternating current rectification. Components shown in FIG. 3 that are essentially the same as the corresponding ones shown in FIG. 1 have the same numerical designations in each figure. Relay  10 ″ also operates with the same kinds of electrical energization and with the same kinds of control signals as are used in the system of FIG.  1 . 
     “Hot” terminal  14  here, in addition to being connected to switches  15 ,  16  and  17 , is also again connected to power frequency converter  25  located in other portions of the traffic signal light control system than is relay  10 ″. Frequency converter  25  is, as before, also connected to reference terminal  13 . Flasher  25  provides a sinusoidal waveform at output  26  thereof to serve as an electrical energy source for operating lights  11  and  12  during flashing operations. That is, flasher  25  continuously provides typically “on-off” periods of equal duration of a 60 Hz sinusoidal voltage waveform at output  26  thereof having an “on-off” frequency of just 1 Hz and again having an amplitude of about 115 volts rms during “on” periods. Again, this is accomplished by flasher output  26  being electrically connected to one of relay power input terminals  27  and  28  also shown electrically connected together in FIG.  3  through the provision of external “jumper” interconnection  29  so that flasher output  26  is connected to both. In system  10 ″, however, flasher  25  is not used as an electrical energy source for operating other circuitry to relay  10 ″. Instead, all electrical energy is obtained from “hot” terminal  14  after suitable switching and rectification. As before, lights  11  and  12  are electrically connected to corresponding relay power output terminals  21  and  22 , respectively, and switches  16  and  17  are electrically connected to corresponding relay power input terminals  23  and  24 , respectively. 
     This operating circuitry of relay  10 ″ is operated under the direction of signals provided from the remaining portions of the control system on terminal  18  controlling the opening and closing of switch  15 . Control signals provided on terminal  18  to open and close switch  15  determine whether relay  10 ″ is in a switching state allowing continuously on operation of lights  11  and  12  for intervals determined by load switches  16  and  17 , or is in an alternate switching state allowing flashing operation of lights  11  and  12 . In this “energized” system type of signal traffic lights control system, switch  15  is closed to permit continuous operation of lights  11  and  12  and opened to permit flashing operation of those lights. 
     The closure of switch  15  by a control signal on terminal  18  results in providing a constant polarity voltage signal to direct the operation of the circuitry coupled thereto. The opening of switch  15  by control signals on terminal  18  leads to no such constant polarity voltage signal being supplied to such circuitry. 
     Thus, closure of switch  15  results in the electrical connection of “hot” terminal  14  to a full-wave rectifying arrangement. This rectification is provided by a diode bridge rectifier,  90 , having the cathode of a diode,  91 , and the anode of a diode,  92 , electrically connected to the side of switch  15  opposite that to which terminal  14  is connected to form the alternating current input terminal. The cathode of diode  92  is electrically connected to the cathode of another diode,  93 , to form the more positive constant polarity voltage terminal of the bridge rectifier. The anode of diode  91  is electrically connected to the anode of a final diode,  94 , in the bridge to form the more negative constant polarity voltage bridge terminal. A last connection in the bridge has the cathode of diode  94  electrically connected to the anode of diode  93  and to ground reference terminal  13 . 
     The more positive constant polarity voltage terminal of bridge rectifier  90  is electrically connected through a current limiting resistor,  95 , to a ripple reducing, noise limiting capacitor,  96 , having its other side electrically connected to the more negative constant polarity voltage terminal of bridge rectifier  90 . Capacitor  96  is also electrically connected across the input terminals of an input controlled, optically isolated, two pole switch,  100 , (typical commercial part: C. P. Clare Corporation part LCC110) each of which inputs is electrically connected to a corresponding one of the opposite sides of a light-emitting diode,  101 , in optically isolated two pole switch  100 . Diode  101  has its anode electrically connected to the junction of resistor  95  and capacitor  96  and its cathode electrically connected to the other side of capacitor  96  and so to the more negative constant polarity voltage terminal of bridge rectifier  90 . Thus, the closure of switch  15  results in a current being drawn through diode  101  causing it to emit light in optically isolated two pole switch  100 . 
     This light, when emitted by diode  101 , impinges on an integrated array of photovoltaic cells in circuitry electrically connected to the gates of each of two pairs of light responding metal-oxide-semiconductor field-effect transistors (MOSFET&#39;s),  102  and  103 , that provide the two pole switching function in response to current through the diode, the MOSFET&#39;s in each pair being n-channel devices having their channel regions connected electrically in series with one another. Thus, MOSFET pair  102  are each depletion mode devices and the series connected channels thereof are electrically connected between two single pole switch terminals,  104  and  105 , of two pole switch  100  to form a normally closed single pole switch therebetween in the absence of emitted light from diode  101  which switch opens upon such emission. MOSFET pair  103  are enhancement mode devices and the series connected channels thereof are electrically connected between two single pole switch terminals,  106  and  107 , of switch  100  to form a normally open single pole switch therebetween in the absence of such light which switch closes upon such emission. 
     Controlled switch  100  output terminal  104  is electrically connected to the more negative constant polarity voltage bridge terminals of two further diode bridge rectifiers,  110  and  120 , each operating like diode bridge rectifier  90  with the same diode configuration. Thus, the diodes in bridge rectifiers  110  and  120  are designated as in bridge rectifier  90  except prime marks are added to the designations of the first ( 91 ′,  92 ′,  93 ′ and  94 ′) and double prime marks are added to the designations of the second ( 91 ″,  92 ″,  93 ″ and  94 ″). The alternating input terminals of bridge rectifiers  110  and  120  are each electrically connected to output  26  of flasher  25  with that of rectifier  120  being so connected through jumper  29 . The ground reference terminals of bridge rectifiers  110  and  120  are again electrically connected to reference terminal  13 . 
     The more positive constant polarity voltage terminal of bridge rectifier  110  is electrically connected through a current limiting resistor,  111 , to a ripple reducing, noise limiting capacitor,  112 , having its other side electrically connected to controlled switch  100  single pole switch terminal  105 , and so to the more negative constant polarity voltage terminal of bridge rectifier  110  through single pole switch  102 . Capacitor  112  is also electrically connected across the input terminals of zero voltage crossing, bilateral switch output optoisolator  44  (here, typically commercial part: Toshiba, Inc. part TLP3063) each of which inputs is electrically connected to a corresponding one of the opposite sides of light-emitting diode  42 . Light emitting diode  42  is in optoisolator  44  again with optically activated silicon bilateral switch  45  having incorporated therewith zero-crossing control circuit  46  to cause optically operated bilateral switch  45  to break down within a few volts of zero volts occurring across the main contacts thereof Diode  42  has its anode electrically connected to the junction of resistor  111  and capacitor  112  and its cathode electrically connected to the other side of capacitor  112 , and so to single pole switch terminal  105  and the more negative constant polarity voltage terminal of bridge rectifier  110  through single pole switch  102 . 
     Similarly, the more positive constant polarity voltage terminal of bridge rectifier  120  is electrically connected through a current limiting resistor,  121 , to a ripple reducing, noise limiting capacitor,  122 , having its other side electrically connected to controlled switch  100  single pole switch terminal  105 , and so to the more negative constant polarity voltage terminal of bridge rectifier  120  through single pole switch  102 . Capacitor  122  is also electrically connected across the input terminals of zero voltage crossing, bilateral switch output optoisolator  49 , like optoisolator  44 , each of which inputs is electrically connected to a corresponding one of the opposite sides of light-emitting diode  47 . Light emitting diode  47  is in optoisolator  49  again with optically activated silicon bilateral switch  50  having incorporated therewith zero-crossing control circuit  51  to cause optically operated bilateral switch  50  to break down within a few volts of zero volts occurring across the main contacts thereof. Diode  47  has its anode electrically connected to the junction of resistor  121  and capacitor  122  and its cathode electrically connected to the other side of capacitor  122 , and so to single pole switch terminal  105  and the more negative constant polarity voltage terminal of bridge rectifier  120  through single pole switch  102 . The current drawn through light-emitting diodes  42  and  47  is again sufficient to cause them to emit light enough to switch on corresponding bilateral switches  45  and  50 . 
     In a similar arrangement, controlled switch  100  output terminal  106  is electrically connected to the more negative constant polarity voltage bridge terminals of two further diode bridge rectifiers,  130  and  140 , each operating like diode bridge rectifier  90  with the same diode configuration. Thus, the diodes in bridge rectifiers  130  and  140  are again designated as in bridge rectifier  90  except triple prime marks are added to the designations of the first ( 91 ′″,  92 ′″,  93 ′″ and  94 ′″) and equivalent quadruple prime marks are added to the designations of the second ( 91   iv ,  92   iv ,  93   iv  and  94   iv ). The alternating input terminals of bridge rectifiers  130  and  140  are each electrically connected to a corresponding one of relay power output terminals  23  and  24 . The reference terminals of bridge rectifiers  130  and  140  are again electrically connected to reference terminal  13 . 
     The more positive constant polarity voltage terminal of bridge rectifier  130  is electrically connected through a current limiting resistor,  131 , to a ripple reducing, noise limiting capacitor,  132 , having its other side electrically connected to controlled switch  100  single pole switch terminal  107 , and so to the more negative constant polarity voltage terminal of bridge rectifier  130  through single pole switch  103 . Capacitor  132  is also electrically connected across the input terminals of zero voltage crossing, bilateral switch output optoisolator  70 , like optoisolator  44 , each of which inputs is electrically connected to a corresponding one of the opposite sides of light-emitting diode  69 . Light emitting diode  69  is in optoisolator  70  again with optically activated silicon bilateral switch  72  having incorporated therewith zero-crossing control circuit  73  to cause optically operated bilateral switch  72  to break down within a few volts of zero volts occurring across the main contacts thereof. Diode  69  has its anode electrically connected to the junction of resistor  131  and capacitor  132  and its cathode electrically connected to the other side of capacitor  132 , and so to single pole switch terminal  107  and the more negative constant polarity voltage terminal of bridge rectifier  130  through single pole switch  103 . 
     Similarly, the more positive constant polarity voltage terminal of bridge rectifier  140  is electrically connected through a current limiting resistor,  141 , to a ripple reducing, noise limiting capacitor,  142 , having its other side electrically connected to controlled switch  100  single pole switch terminal  107 , and so to the more negative constant polarity voltage terminal of bridge rectifier  140  through single pole switch  103 . Capacitor  142  is also electrically connected across the input terminals of zero voltage crossing, bilateral switch output optoisolator  75 , like optoisolator  44 , each of which inputs is electrically connected to a corresponding one of the opposite sides of light-emitting diode  74 . Light emitting diode  74  is in optoisolator  75  again with optically activated silicon bilateral switch  77  having incorporated therewith zero-crossing control circuit  78  to cause optically operated bilateral switch  77  to break down within a few volts of zero volts occurring across the main contacts thereof. Diode  74  has its anode electrically connected to the junction of resistor  141  and capacitor  142  and its cathode electrically connected to the other side of capacitor  142 , and so to single pole switch terminal  107  and the more negative constant polarity voltage terminal of bridge rectifier  140  through single pole switch  103 . The current drawn through light-emitting diodes  69  and  74  is again sufficient to cause them to emit light enough to switch on corresponding bilateral switches  72  and  77 . 
     When switch  15  is in the open position so that there is no direct current from bridge  90  through diode  101 , controlled switch  100  has internal switches  102  and  103  in their energized states, i.e. in their normal states in the absence of impinging light. In this situation, as indicated above, switch  102  will be closed in its normally closed state, and switch  103  will be open in its normally open state thereby allowing no significant current to be established therethrough. Switch  102  being closed, however, and having the more negative constant polarity voltage terminals of bridge rectifiers  110  and  120  each connected to single pole switch terminal  105 , effectively connects them also to single pole switch terminal  104  so that current can flow in two further electrical interconnection paths. 
     In the first of these paths, direct current flows from the more positive constant polarity voltage terminal of bridge rectifier  110  through resistor  111 , capacitor  112 , and diode  42  to the more negative constant polarity voltage terminal of bridge rectifier  110  through switch  102 . Thereby, capacitor  112  is charged and the voltage applied across light emitting diode  42  is stabilized. 
     In the second further interconnection path, direct current flows from the more positive constant polarity voltage terminal of bridge rectifier  120  through resistor  121 , capacitor  122 , and diode  47  to the more negative constant polarity voltage terminal of bridge rectifier  120  through switch  102 . Thereby, capacitor  122  is charged and the voltage applied across light emitting diode  47  is stabilized 
     The remainders of the circuits connected to optoisolators  44  and  49  involving triacs  53  and  56  operate as described above in connection with FIG.  1 . In the presence of current being drawn through light-emitting diodes  42  and  47  due to switch  15  being open, the output voltage provided through flasher  25  in the closed condition on relay power inputs  27  and  28  can break over bilateral switches  45  and  50 , respectively, so as to provide currents to and from the gates of triacs  53  and  56  depending on the polarity of that voltage. Such voltages switch on triacs  53  and  56  in each polarity segment of the voltage supplied thereto on relay power input terminals  27  and  28  through flasher  25  allowing current to be drawn through lamps  11  and  12 . 
     Also, a small fraction of any such currents will be used to also cause coinciding light emission in a corresponding one of a pair of output indicator light emitting diodes,  124  and  125 , each having its cathode electrically connected to reference terminal  13 . In association with the switching on of lamp  11 , voltage at relay power output terminal  21  is half-wave rectified by a diode,  126 , having its anode electrically connected thereto, and the current drawn therethrough, and through diode  124 , is limited by a resistor,  127 , which is electrically connected in series between the cathode of diode  126  and the anode of diode  124 . In association with the switching on of lamp  12 , voltage at relay power terminal  22  is half-wave rectified by diode  128 , having its anode electrically connected thereto, and the current drawn therethrough, and through diode  125 , is limited by a resistor,  129 , which is electrically connected in series between the cathode of diode  128  and the anode of diode  125 . 
     When switch  15  is alternatively in the closed position so that there is direct current from bridge  90  through diode  101 , controlled switch  100  has internal switches  102  and  103  in their deenergized states, i.e. in states opposite their normal states in the absence of impinging light. In this situation, as indicated above, switch  102  will be open as opposed to its normally closed state, thereby allowing no significant current to be established therethrough, and switch  103  will be closed as opposed to its normally open state. Switch  103  being closed, however, and having the more negative constant polarity voltage terminals of bridge rectifiers  130  and  140  each connected to single pole switch terminal  107 , effectively connects them also to single pole switch terminal  106  so that current can flow in two further electrical interconnection paths if load switches  16  and  17  are also closed to provide alternating voltage to the alternating current inputs of bridge rectifiers  130  and  140  as well as relay power output terminals  23  and  24 . 
     In the first of these paths, direct current flows from the more positive constant polarity voltage terminal of bridge rectifier  130  through resistor  131 , capacitor  132 , and diode  69  to the more negative constant polarity voltage terminal of bridge rectifier  130  through switch  103 . Thereby, capacitor  132  is charged and the voltage applied across light emitting diode  69  is stabilized. 
     In the second further interconnection path, direct current flows from the more positive constant polarity voltage terminal of bridge rectifier  140  through resistor  141 , capacitor  142 , and diode  74  to the more negative constant polarity voltage terminal of bridge rectifier  140  through switch  103 . Thereby, capacitor  132  is charged and the voltage applied across light emitting diode  74  is stabilized. 
     The remainders of the circuits connected to optoisolators  70  and  75  involving triacs  80  and  83  also operate as described above in connection with FIG.  1 . In the presence of current being drawn through light-emitting diodes  69  and  74  due to switch  15  being closed, the output voltage provided through load switches  16  and  17  in the “on” on relay power inputs  23  and  24  can break over bilateral switches  72  and  77 , respectively, so as to provide currents to and from the gates of triacs  80  and  83  depending on the polarity of that voltage. Such voltages switch on triacs  80  and  83  in each polarity segment of the voltage supplied thereto on relay power input terminals  23  and  24  through load switches  16  and  17 , respectively, allowing current to be drawn through lamps  11  and  12 . 
     Again, a small fraction of any such currents will be used to also cause light emission in the corresponding one of output indicator light emitting diodes  124  and  125  coinciding with switching on of the corresponding one of lamps  11  and  12 . Output indicator light emitting diodes  124  and  125  are located to be exposed visually to the exterior of the enclosure for relay  10 ″ so that an observer can receive indications of when lamps  11  and  12  have been switched on without having to observe them directly. 
     FIG. 4 is an electrical schematic diagram showing the connecting into the remainder of the control system of a flash transfer relay,  10 ′″, within the dashed line enclosure, of essentially the solid state relay type nature described above in connection with FIG. 3 but in a manner suited for operation in an “deenergized” system type of traffic signal lights control system. In general, relay  10 ′″ is constructed like, and operates like, relay  10 ″ of FIG.  3 . Components shown in FIG. 4 that are essentially the same as the corresponding ones shown in FIG. 3 have the same numerical designations in each figure. Relay  10 ′″ also operates with the same kinds of electrical energization and with the same kinds of control signals though the control signal provided on terminal  18  in FIG. 4 will be the complement of that provided on terminal  18  in FIG. 3 because of being an “deenergized” system type rather than a “energized” system type. 
     Relay  10 ″ of FIG. 3, in being for control systems of the “energized” system type, has lights  11  and  12  flashing on and off in the absence of a conductive path through single pole switch  103  because of switch  15  being open. Since, in this situation, triacs  53  and  56  are switched on, i.e. “normally closed” with switch  15  open, output  26  of flasher  25  is connected to the relay power input terminals connected to these triacs, or terminals  27  and  28 . Triacs  80  and  83  are switched off in this situation, i.e. are “normally open” with switch  15  open, and they are connected through relay power input terminals  23  and  24  to load switches  16  and  17 , respectively, so that switch  15  must be closed for lights  11  and  12  to be lit continuously by any closures of load switches  16  and  17 . 
     On the other hand, relay  10 ′″ of FIG. 4, in being for control systems of the “deenergized” system type, has lights  11  and  12  flashing on and off in the presence of a conductive path through single pole switch  103  because of switch  15  being closed. Since, in this situation, triacs  80  and  83  are switched on, i.e. “normally closed” with switch  15  closed (though still “normally open” in the conventional sense with no signal applied, i.e. with switch  15  open), output  26  of flasher  25  is connected to one of the relay power input terminals connected to these triacs, or terminals  23  and  24 , with an external “jumper” interconnection,  29 ′, connecting them together rather than being connected to relay power input terminals  27  and  28 . Triacs  53  and  56  are switched off in this situation of switch  15  closed, i.e. are “normally open” with switch  15  closed (though still “normally closed” in the conventional sense with no signal applied, i.e. with switch  15  open), and they are connected through relay power input terminals  27  and  28  to load switches  16  and  17 , respectively, rather than to relay power input terminals  23  and  24  so that switch  15  must be opened for lights  11  and  12  to be lit continuously by any closures of load switches  16  and  17 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.