Abstract:
A passive infrared (PIR) wall switch is operable in a two-wire circuit to control power to a load. The PIR wall switch can include one or more PIR sensors with a low current two stage amplifier-filter. The PIR sensor(s) monitor infrared (IR) radiation. The amplifier can provide a pulse signal when an IR radiation level has changed. Power for control circuitry of the PIR switch may be derived from a ground leakage type power supply, which can supply phase line wire leakage current to ground of less than 0.5 milliampere.

Description:
[0001]     This application claims the benefit of the filing date of a provisional application having Ser. No. 60/591,274, which was filed on Jul. 27, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates generally to passive infrared (PIR) switches.  
         [0004]     2. Description of the Prior Art  
         [0005]     A passive infrared (PIR) occupancy switch is a device that can be used to replace a single-pole-single-throw (SPST) switch including standard mechanical wall switches found in many homes and businesses. The PIR switch detects infrared energy due to motion in an area. Control circuitry in the PIR switch operates to open or close contacts of a relay to disconnect or connect power to a load, such as a lighting circuit, based on the level of infrared energy detected.  
         [0006]     The PIR switch can be used in a two-wire system. That is, power can be received from a phase line and can be coupled through the relay contacts to a phase load line. A neutral (or return) wire may not be available. When the switching relay contacts are closed, the phase line and phase load lines are connected to provide power to the load. There is no voltage between the phase and the load lines. Thus, power between the phase line and phase load lines is not available to drive the PIR control circuitry when the relay contacts are closed because the relay contacts short circuit the control circuitry.  
         [0007]     Power for the control circuitry can be provided between the phase line wire and ground. Safety considerations can limit the amount of current that may be drawn between the phase line wire and ground. Two-wire electrical control devices, other than PIRs, that switch power across a load when energized may have similar power considerations. That is, when the switched contacts are in a low impedance state as occurs when the relay contacts are closed, the voltage across the device drops from an alternating current (AC) line voltage to almost zero. Thus, when the control device is ON (energized), no power is available to drive the switching control circuitry.  
         [0008]     One solution utilizes a technique whereby a small amount of current is purposely leaked to ground to drive the control circuitry when power is switched to the load. The switching control circuitry, if designed to draw only a small amount of current (compared to the load circuitry), can derive the power it needs to operate from this ground leakage current. When leakage current is used to operate switching/control circuitry, Underwriters Laboratory (UL) requires that the current not exceed a value of 0.5 milliampere (mA) (500 microamperes (μA)). Circuits which satisfy this limitation can be difficult to implement.  
         [0009]     U.S. Pat. No. 5,786,644 (&#39;644) assigned to Leviton Manufacturing Co., Inc., assignee of the present disclosure, discloses the use of an energy storage means such as a capacitor which uses ground leakage current to operate switching control circuitry of a passive infrared switch. Referring to FIG. 1 of &#39;644, there is shown a two wire sensor 10 which includes switching means 18 settable to one of a high (e.g., open circuit) and a low (e.g., short circuit) impedance state in response to a switching signal from a PIR control 16 for connecting/disconnecting a source of AC power to/from an electrical load 22 such as a light. The switching means 18 is located in a main conduction path which provides power between the AC source and the load. The switching means is connected between a first leg of the AC source and a first terminal of the electrical load. The second terminal of the electrical load is connected to a second leg of the AC source. An energy storage means 14 for storing an electrical charge is electrically coupled to the first leg of the AC source and to the first terminal of the electrical load. A charge control means 12 is connected between the switching means and the energy storage means to regulate the voltage across the energy storage means and, therefore, the current flowing therein. When the contact in the switching means 18 is open, that is, in a non-conductive state, substantially no power is delivered to the load and substantially all of the AC source voltage appears across the circuit 10 because it has a relatively high impedance relative to the load 22. At this time leakage current is provided to and is stored in the energy storage device. When the contacts are closed, the power required to drive the PIR control circuit is obtained from the energy storage means. Circuitry for controlling the switching means is coupled across the energy storage means 14 and responds to detection (or sensing) of the monitored condition by generating the switching signal.  
       SUMMARY OF THE DISCLOSURE  
       [0010]     Techniques and methods are disclosed for a passive infrared (PIR) wall switch that is operable in a two-wire circuit to control power to a load. The PIR wall switch can include one or more PIR sensors with a low current two stage amplifier-filter. The PIR sensor(s) monitor infrared (IR) radiation. The amplifier can provide a pulse signal when an IR radiation level has changed, for example, because of motion in a surrounding area. Power for control circuitry of the PIR switch may be derived from a ground leakage type power supply, which can supply phase wire leakage current to ground of less than 0.5 milliampere.  
         [0011]     The passive infrared switch can be used in a two wire system and includes a relay switch coupled to control the flow of power to a load. A passive infrared control circuit can be coupled to operate the relay switch upon detecting a change of infrared radiation. A power supply is coupled to supply a current not greater than 0.5 mA to the passive infrared control circuit.  
         [0012]     Some of the implementations of the disclosed techniques may include one or more of the following advantages. The PIR wall switch can continue to operate in a two-wire system that supplies phase current to a load wire when the switch is energized (closed). The PIR switch can use a power supply, which supplies a current no greater than 0.5 mA to the PIR circuitry, which may be drawn from the phase wire to ground. The 0.5 mA limit can avoid a potentially hazardous condition.  
         [0013]     The above-stated and other advantages of the invention will become apparent from the following detailed description when taken with the accompanying drawing. It will be understood, however, that the drawing is for the purpose of illustration and is not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of a preferred embodiment of the invention when taken in conjunction with the following drawings wherein like parts are represented by similar reference numbers.  
         [0015]      FIG. 1  is a functional block diagram of a prior art PIR occupancy sensor which utilizes a rechargeable energy storage device to operate the switching circuit;  
         [0016]      FIG. 2  is a functional block diagram of a PIR wall switch for use in a two wire system which has a ground leakage current type power supply;  
         [0017]      FIG. 3  is a schematic diagram of a ground leakage current type of power supply for use with the PIR wall switch of  FIG. 2  to operate the switching circuit; and  
         [0018]      FIG. 4  is a schematic diagram of a modification of the ground leakage current type of power supply of  FIG. 3  which provides a zero crossing signal output. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Referring to  FIG. 2 , there is shown a functional block diagram of a PIR wall switch for use in a two wire system which has a ground leakage current type power supply which provides a leakage current of no greater than the 0.5 mA for operating the PIR control. The wall switch  30  includes a switching device  32 , a PIR control circuit  34  and a ground leakage current type power supply circuit  36 . The wall switch can have three terminals  38 ,  40 ,  42 . Terminal  38  is connected to the phase conductor  44  of an AC power source and terminal  40  is connected to the neutral conductor  46  of the AC power source. A load, such as a lamp  48 , is connected to output terminal  42 , which can have two conductors and is connected through at least one set of contacts in a switching device such as relay switch  32  to the phase and neutral conductors  44 ,  46 . The state of switching device  32  (conducting or non-conducting) controls the flow of power to the load  48  and is controlled by the PIR control circuit  34 . Thus, switching device  32  can be selectively set to either of two states, conducting (ON or low impedance) or non-conducting, (OFF or “high impedance”) states which correspond to the closed or open contact states of the device. Relay switch  32  can be a conventional latching type relay which consumes pulse power only during switching periods and consumes no power at other times.  
         [0020]     PIR control circuit  34 , is electrically coupled by conductor  50  to control the operation of relay switch  32  and is connected to the AC power terminals  38 ,  40 . The PIR control circuit monitors an area for a predetermined condition and generates a signal when the predetermined condition occurs. The sensor of the PIR control circuit can be preferably a passive infrared (PIR) control sensor to provide an occupancy sensing function. The sensor comprises conventional circuitry well known to those skilled in the art and the state of the relay switch is defined by the sensor in accordance with the amount of infrared energy detected by the PIR.  
         [0021]     When the contact in relay switch  32  is in its open state, (that is, a non-conductive state), substantially no power is delivered to the load  48 . A majority of the AC source voltage on conductors  44 ,  46  appears across the contacts  38 ,  40  of the wall switch  30  while the relay switch  32  is non-conductive because it has a relatively high impedance relative to the load  48 . However, current is provided both to the ground leakage type of power supply  36  and the PIR control circuit  34  by conductor  51 , which is coupled to terminals  38 ,  40 .  
         [0022]     The ground leakage type of power supply  36  has input terminals connected to the phase conductor  44  by terminal  38  and the neutral conductor  46  by terminal  40  of the wall switch. A terminal  56  of the ground leakage type of power supply  36  is connected to provide power to the PIR control circuit  34 , and terminal  58  of the ground leakage type power supply is connected to the building ground which can be the system ground or reference point for the switch circuitry. Ground leakage type of power supply  36  is more fully disclosed in  FIGS. 3 and 4 .  
         [0023]     Referring to  FIG. 3 , there is shown a ground leakage type power supply which has a leakage current which does not exceed 0.5 mA for use in the two wire (that is, no neutral) system herein disclosed. The ground leakage type of power supply shown here is disclosed as a Constant Current Supply Over A Wide Range Of Input Voltages in U.S. Pat. No. 6,031,750 which is assigned to Leviton Manufacturing Co., Inc., the assignee of the instant application, and is incorporated herein in its entirety by reference. The ground leakage type power supply shown in  FIG. 3  can supply a constant current of 0.5 mA for different input voltage levels which can vary from about 102 to 230 or more volts. An AC source is coupled to ground leakage type power supply  36  by phase input terminal  38  and neutral input terminal  40 . The AC line voltage is fed to a bridge  60  including diodes  62 ,  64 ,  66  and  68  to produce a DC voltage signal. The anode of diode  62  can be coupled to the cathode of diode  68  and the AC conductor  44 . A resistor R 24  can be in conductor  44  to save some lost current in low current applications. The use of resistor R 24  is optional. The cathode of diode  62  is coupled to the cathode of diode  64  and to a conductor  70 . The anode of diode  64  is coupled to the cathode of diode  66  and by conductor  45  and terminal  40  to the conductor  46  ( FIG. 2 ). The anode of diode  66  is coupled to the anode of diode  68  and to a circuit ground terminal  72 .  
         [0024]     The DC level on conductor  70  is applied to two resistors R 25  and R 26  coupled in series to limit the current applied to the circuit and bias the base B of a transistor Q 1 . The base B of transistor Q 1  also is connected to the cathode of a zener diode Z 1 . Transistor Q 1  acts as an emitter follower and the emitter E of transistor Q 1  is connected to the base B of a transistor Q 2 . Collectors C of transistors Q 1  and Q 2  are connected to conductor  70 . The output at emitter E of transistor Q 2  is coupled to a resistor R 27 . The transistors Q 1  and Q 2  are connected as a Darlington amplifier or cascaded emitter followers. Resistors R 25  and R 26  limit the voltage applied to zener diode Z 1  to prevent burnout and limit current to the load. The output to the emitter E of transistor Q 2  is applied to a first end of the output resistor R 27  and a second end of resistor R 27  is connected to the cathode of a zener diode Z 2  and to ground  58  through a bypass capacitor C 29 . The use of the bypass capacitor C 29  is optional. The anode of zener diode Z 2  is coupled to the circuit ground  58 .  
         [0025]     The ground leakage type power supply  36  regulates the current through the resistor R 27 . The zener diode Z 1  and the base B to emitter E voltage drop of transistors Q 1  and Q 2  determines the voltage across R 27 . The voltage on terminal  56  from the emitter E of transistor Q 2  to ground  58  will be fixed.  
         [0026]     As the input voltage at terminals  38  and  42  by conductors  44  and  46  to the bridge  60  increases above voltage Ve 2 , the extra voltage will be dropped across the collector C to emitter E of transistor Q 2 , this is voltage Vce 2 . Therefore, the same current will flow through resistor R 27  for input voltages in the range of 102 to 400 volts. This allows the use of one terminal for phase power input and one terminal for the AC neutral to the ground leakage type power supply  36 . The voltage applied to resistor R 27  and which is on terminal  56  is used as an input to the PIR control circuit to power the Control circuitry. The ground leakage type power supply  36  limits the supply current to the PIR control circuit to 0.5 ma.  
         [0027]     To limit the leakage current to this level, current is leaked from the input conductor  44  to the neutral line  45  or circuit ground, which can be the building ground. Ground point  58  is the system ground or reference point for the switchable circuitry. The acceptable level of leakage current is 0.5 mA and the ground leakage type power supply limits the current regardless of the load applied to it.  
         [0028]     Referring to  FIG. 4 , there is shown a modification of the ground leakage type of power supply of  FIG. 3  having a zero crossing signal output which is obtained by connecting to terminal  42  of conductor  45  a resistor R  28  having a high value of resistance, which can be connected from terminal  42  to the anode of diode D 1 . The zero crossing signal is read between terminal  42  and a ground terminal  72 . The cathode of the diode D 1  is connected to the regulated operating voltage at a regulated DC voltage taken from zener diode Z 2 . A system ground is available at terminal  74 .  
         [0029]     While there have been shown and described and pointed out the fundamental features of the invention as applied to the preferred embodiment, as is presently contemplated for carrying them out, it will be understood that various omissions and substitutions and changes in the form and details of the device described and illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention.