Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/945—Proximity switches
  • H03K17/95—Proximity switches using a magnetic detector
  • H03K17/951—Measures for supplying operating voltage to the detector circuit

Definitions

• This invention relates to proximity switches or sensors, and in particular to a two wire AC power supply for proximity switch integrated circuits.
• one aspect of the present invention provides a two wire AC power supply for a proximity switch integrated circuit, wherein at least some circuitry associated with the power supply is provided within the integrated circuit.
• the two wire AC power supply comprises a bridge rectifier, an output of which is connected in parallel across a voltage regulator and also in parallel across a thyristor, an output of the regulator being connected in parallel to a diode connected in series to a storage capacitor, the cathode of the diode being connected to the storage capacitor, the output of the regulator further being connected to one input of a comparator, another input of the comparator being held at a constant reference voltage, an output of the comparator being connected to a first input of an AND gate, a second input of the AND gate being connected to an output from the proximity switch indicative of the switch state, an output of the AND gate being connected to a gate of the thyristor, and wherein further, the comparator and the AND gate are provided within the integrated circuit.
• a current limiting circuit connected in parallel with a switch may be provided between the output of the voltage regulator and the anode of the diode, the current limiting circuit and the switch also being provided within the integrated circuit.
• the integrated circuit may be implemented in bipolar transistor technology, or in any other suitable transistor technology.
• the comparator comprises a PNP differential pair Ql, Q2 powered via a further current source Q7, Q8, the first input of the comparator being connected to means for dividing down the input voltage QD1, Rl, R2 and QD2, the divided down voltage being applied to the base of the transistor Ql the second input being connected to further means for dividing down a regulated voltage and for providing hysteresis R3, R4, R5, Q5, Q6 the regulated voltage being derived from the integrated circuit, the collectors of the differential pair Ql, Q2 being connected to a differential to single-ended converter Q3, Q4 an output from the comparator being developed at the collector of a further transistor Q6, the collector of which is connected to a current source Q9, and the base of which is connected to the further dividing down means.
• the constant current circuit comprises two NPN transistors QCCl, QCC2 connected in parallel, and further connected between their collectors and bases in parallel with a resistor R100UA, the emitters being connected to a parallel arrangement comprising a resistor R2500UA connected in parallel between the base to emitter junction of a further NPN transistor Q2500UA which is connected in series with a resistor RTHUR1, the collector of the further transistor Q2500UA being connected to the bases of the two NPN transistors QCCl and QCC2.
• the switch connected in parallel with the constant current circuit comprises a resistor RSAT connected to the collector of a transistor QDARL having a resistor RODARL connected between its base and emitter, the emitter of the transistor QDARL being connected to the base of a transistor QSW, the transistor QSW having a resistor RQSW connected between its base and emitter, the emitter of transistor QSW further being connected to a parallel arrangement comprising a resistor R50MA and the base to emitter junction of another transistor Q50MA which is connected in series with a resistor RTHUR2, the collector of the other transistor Q50MA further being connected to the base of the transistor QDARL.
• the base current to transistor QDARL is provided by a current mirror QM4, QM5, QM6 , QM7, QM8, input current to the mirror being controlled by a signal derived from the proximity switch.
• a second aspect of the present invention there is provided an integrated circuit for use in a two wire AC power supply for a proximity switch.
• the integrated circuit of the power supply is integrated with that of the proximity switch.
• Fig 1 a block schematic diagram of an embodiment of an integrated circuit for use in a power supply for a proximity switch according to the present invention
• Fig 2 a schematic circuit diagram of a power supply using the integrated circuit of Fig 1;
• Fig 3 (a) , (b) , (c) various signal timing diagrams relating to the power supply of Fig 2 when the proximity switch is in an open state;
• Fig 4 (a), (b),(c) various signal timing diagrams relating to the power supply of Fig 2 when the proximity switch is in a closed state;
• Fig 5 (a) , (b) , (c) additional signal timing diagrams relating to the power supply of Fig 2 when the proximity switch is in a closed state;
• Fig 6 a schematic circuit diagram of a comparator for use in the integrated circuit of Fig 1;
• Fig 7 a schematic circuit diagram of a constant current switch circuit for use in the integrated circuit of Fig 1.
• IC integrated circuit
• Fig 2 shows a schematic circuit diagram of a power supply using the IC 5 within a sensor (ie proximity switch) 10.
• Fig 2 further shows how the sensor 10 is serially connected to a load ZL across an AC power supply.
• the power supply comprises a full wave bridge rectifier BRl, the output of which is connected across a conventional voltage regulator comprising a resistor Rl, n- channel MOSFET Ml and zener diode Zl.
• the regulated voltage which may for example be 12V, is supplied to the IC 5 via a pin CCIN.
• the pin CCIN is connected, internally of the IC 5 to a current limiting circuit comprising a current source CC connected in parallel with a switch SI, this parallel arrangement further being connected in parallel with a reverse biassed diode Dd.
• the other end of this parallel arrangement is connected internally of the IC 5 to an external pin VT of the IC 5.
• the storage capacitor CVS may be of a value of around 10 ⁇ F.
• the cathode of the diode is further connected to one end of a resistor Ro the other end being connected to an anode of an LED, the cathode of the LED being connected to an external pin OPLED of the IC 5.
• An external pin QSCR1 of the IC 5 is connected between the cathode of the diode Dl and the storage capacitor CVS.
• An external pin QSCR2 is further connected externally of the IC 5 to resistors R2 and R3 in series.
• Resistor R3 is connected in parallel with a capacitor C, the gate of a thyristor or silicon controlled rectifier SCR further being connected between resistors R2 and R3.
• the SCR itself is connected in parallel across the output from the bridge rectifier BRl.
• the bridge BRl provides full wave rectification of the AC supply.
• the full wave rectified signal is as shown in Fig 3 (a) .
• the rectified voltage developed is regulated to a suitable level for the IC 5 by the regulator comprising components Zl, Rl and Ml, the regulated voltage Vs being supplied to the IC 5 via pin CCIN.
• the current flowing into pin CCIN flows through the current limiting circuit CC and the external diode Dl to VS.
• VS is the main supply rail of the IC 5.
• the purpose of the current limiting circuit CC is to limit the current flow into the storage capacitor CVS at power up when the capacitor CVS is in a discharged state. Without this protection, the switch on current transient drawn from the supply through load ZL would be sufficient to activate the load electrically.
• the current limiting circuit CC is by-passed by the switch SI. This allows storage capacitor CVS to charge at a rate which is fixed primarily by the value of the load impedance ZL.
• the SCR At a zero current/zero voltage cross-over point of the rectified AC waveform, the SCR is off. As the voltage Vo builds up, the reservoir capacitor CVS begins to charge up. When the charge stored on the capacitor CVS has built up to a sufficient level, for example 8 volts, sufficient to independently power the integrated circuit and LEDs for the rest of the AC half- cycle, an internal comparator circuit energises the gate of the SCR. Thus, the low SCR anode to cathode impedance makes the two outputs of the sensor a low impedance circuit to the AC power supply.
• the output of the comparator is ANDed via an AND gate with the signal from the front end of the sensor.
• the thyristor SCR is only activated if the voltage VT has reached a sufficient level and the signal from the front end of the sensor indicates that a target has been detected.
• Fig 6 shows the detail of the comparator circuit used in the present embodiment.
• the comparator circuit comprises a PNP differential pair of transistors Ql and Q2 powered from a current source comprising transistors Q7 and Q8.
• the input signal VT to one input of the comparator inputs is divided down by a combination of a transistor QD1, resistor Rl, resistor R2 and transistor QD2.
• the reference voltage input to the other input of the comparator is provided by the combination of resistors R3, R4 and R5 and transistors Q5 and Q6.
• Transistors Q3 and Q4 form a differential to single-ended converter, and the comparator output DRVAC is developed at the collector of transistor Q6 using a current source comprising a transistor Q9.
• a signal labelled BIAS is the reference voltage provided by a simple IC network of the IC 5, while VS and V3V5, as indicated in Fig 6, are the unstablised and regulated supply rails respectively.
• Fig 7 shows the detailed implementation of a constant current and switch circuit.
• the constant current circuit comprises transistors QCCl, QCC2, Q2500UA and resistors R2500UA and RTHUR1 and R100UA provided between external pins CCIN and VT of the IC 5.
• a switch ie. a switchable high-current path, comprising transistors QDARL, QSW, Q50MA and resistors RSAT, RQDARL, RQSW, R50MA and RTHUR2, this arrangement being internally current limited to approximately 55 mA to prevent excess dissipation.
• This second, low impedance path from CCIN to VT can be turned ON or OFF by controlling the base current to QDARL which is provided by a current mirror comprising transistors QM4, QM5, QM6, QM7, QM8.
• the input current to the current mirror is in turn controlled by a signal from the sensor front end via transistors QM1, QM2, QM3, QB1, QD1, QD2 and diode D2.
• the signals V3V5 and BIAS have the same meaning as in the comparator circuit, shown in Fig 6.
• the electronic circuitry associated with a proximity switch operating in two wire AC applications has until now been implemented using discrete devices, which take up valuable room on the printed wiring assembly. This has placed a limit on the smallest size of product in which a two wire AC function can be included. This problem can be obviated or mitigated by use of the present invention.
• the invention provides this by incorporating into the application specific integrated circuit (ASIC) associated with the proximity switch some or all of the circuitry associated with the power supply, for example the comparator circuitry and ANDing circuitry, as well as the constant current circuitry and switch.
• ASIC application specific integrated circuit
• an important advantage of the present invention is that it enables smaller size and lower cost two wires AC power supplies for proximity switch ICs to be produced, and further enables a two wire AC proximity sensor circuit to be built into a smaller diameter tube than has previously been the case.

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• 1991
  • 1991-12-31 GB GB9127571A patent/GB2262998B/en not_active Expired - Fee Related
• 1992
  • 1992-12-28 WO PCT/US1992/011232 patent/WO1993013469A1/fr not_active Ceased
  • 1992-12-28 EP EP93902772A patent/EP0619893A4/fr not_active Withdrawn

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