GB2262998A

GB2262998A - Power supply for proximity switch integrated circuit

Info

Publication number: GB2262998A
Application number: GB9127571A
Authority: GB
Inventors: Douglas William Hudson Calder; Arthur James Bizley
Original assignee: Square D Co
Current assignee: Schneider Electric USA Inc
Priority date: 1991-12-31
Filing date: 1991-12-31
Publication date: 1993-07-07
Anticipated expiration: 2011-12-31
Also published as: GB9127571D0; GB2262998B; WO1993013469A1; EP0619893A4; GB2262998A8; EP0619893A1

Abstract

There is disclosed a two wire AC power supply for proximity switch integrated circuits. A problem has existed with previous power supplies in that such have been implemented using discrete devices, which take up valuable room on any printed wiring assembly. This invention therefore 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 power supply preferably comprises a bridge rectifier (BR1), a voltage regulator (Z1, R1, M1), a thyristor (SCR), a diode (D1), a storage capacitor (CVS), a comparator, and an AND gate, wherein at least the comparator and the AND gate are provided within the integrated circuit.

Description

IMPROVEMENTS IN AND RELATING TO PROXIMITY SWITCHES This invention relates to proximity switches or sensors and in particular to a two wire AC power supply for proximity switch integrated circuits.

Accordingly, one aspect of the present invention provides a two wire AC power supply for a proximity switch integrated circuit comprising 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, the other 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, wherein, 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 circuitry may be implemented in bipolar transistor technology, or in any other suitable transistor technology.

Preferably, the comparator comprises a PNP differential pair Q1, Q2 powered via a further current source Q7, Q8, the first input of the comparator being connected to means for dividi.ng down the input voltage QD1, R1, R2 and D2, the divided down voltage being applied to the base of the transistor Q1, 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 Q1, 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.

Preferably, the constant current circuit comprises two NPN transistors QCC1, QCC2 connected in parallel, and further connected between their collectors and bases in parallel with a resistor R1OOUA, the emitters being connected to a parallel arrangement comprising a resistor R250QUA connected in parallel between the base to emitter 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 QCC1 and QCC2.

d Preferably, 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 QDARS 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 QSOMA which is connected in series with a resistor RTHUR2, the collector of the other transistor Q5OMA further being connected to the base of the transistor QDARfl.

Preferably the base current to transistor QDAR 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.

According to 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.

Preferably, the integrated circuit of the power supply is integrated with that of the proximity switch.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings which are: 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; Figs. 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; Figs. 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; Figs. 5 (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. 6: a schematic circuit diagram of a comparator for use in the integrated circuit of Fig. 1; and Fig. 7: a schematic circuit diagram of a constant current switch circuit for use in the integrated circuit of Fig. 1.

Referring to Fig. 1 there is shown a block schematic diagram of an embodiment of an integrated circuit (IC), generally designated 5, for use in a power supply according to the present invention.

The external environment of the IC 5 is shown in Fig. 2 which shows a schematic circuit diagram of a power supply using the IC 5 within a sensor (i.e. proximity switch) 10. Fig. 2 further shows how the sensor 10 is serially connected to a load ZL across an AC power supply.

Referring to Fig. 2 the power supply comprises a full wave bridge rectifier BR1, the output of which is connected across a conventional voltage regulator comprising a resistorRl, nchannel MOSFET M1 and zener diode Z1. 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 S1, 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.

Connected to pin VT externally of the IC 5 is the anode of a diode D1, the cathode of the diode D1 being connected to an external pin VS of the IC 5 from whence the main IC supply voltage VS may be derived, the cathode of the diode D1 further being connected to one end of a storage capacitor CVS, the other end of the storage capacitor cvs being connected to ground. The storage capacitor cVS may be of the value of around 10 gF.

The cathode of the diode Di is further connected to a resistor RO which is itself connected to an anode of an LED, the cathode of the LED being connected to an external pin OPLED of the XC 5.

External pin QSCR1 of the IC 5 is connected between the cathode of the diode D1 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 BRi.

In the OFF state of the switch/sensor, the bridge BR1 provides full wave rectification of the AC supply, the output of the bridge BR1 being across VO and ground, as shown in Fig. 2.

The full wave rectified signal is shown in Fig. 3(a). The rectified voltage developed is regulated to a suitable level for the IC 5 by the regulator comprising components, Z1, R1 and N1, the regulated voltage VS being supplied to the IC 5 via a pin CCIN.

In this state the logical operation of the circuitry is such that QSCR1 and QSCR2 are inactive and the SCR is not triggered, and the only leakage current drawn from the supply is that which is required to bias the regulator and supply the internal circuits of the IC 5.

The current flowing into pin CCIN flows through the current limiting circuit CC and the external diode D1 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 tip 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.

Since, in the OFF state, the SCR is not active at any time during the AC cycle, the rectified and smoothed voltage VS is maintained at a satisfactory level indefinitely, as can be seen from Fig. 3(b). As can be seen from Fig. 3(c), the current IT through the SCR is effectively zero in this state.

In the ON state, i.e. when the target is in such a position to energise the output signal from the front end of a sensor, the current limiting circuit CC is by-passed by the switch S1. This allows storage capacitor CVS to charge at a rate which is fixed primarily by the value of the load impedance ZL.

The operation of the circuitry can in this instance be described with reference to Figs. 4 and 5. At a zero current/zero voltage cross-over point of the rectified AC wave form, 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 maces the two outputs of the sensor a low impedance circuit to the AC power supply. As can be seen from Fig. 1, the output of the comparator is ANDed via an AND gate with the signal from the front end of the sensor.In this way, the thyristor SCR is only integrated 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.

When the gate of the SCR is activated, and the power supply becomes low impedance, the voltage VO collapses to almost zero, and the storage capacitor cv5 is relied upon to power the IC 5 and LEDs till the next zero current cross-over point when the SCR extinguishes.

After the next cross-over point the cycle desribed above repeats itself. It should, of course, be noted, as can be seen from Fig. 4(b) that the supply voltage VS must at all times stay above the minimum operating level for the IC 5 which is approximately 4.5 volts in this case.

The rest of the timing diagrams as shown in Figs. 4 and 5 are apparent in view of the foregoing description and shall not be described in any more detail herein.

Fig. 6 shows the detail of the comparator circuit used in the present embodiment. As can be seen from Fig. 6, the comparator circuit comprises a PNP differential pair of transistors Q1 and Q2 powered from a current source comprising transistors Q7 and Q8. The input signal VT to one input of the compator is divided down by a combination of the transistor QD1, resistor R1, resistor R2 and transistor QDS. The reference voltage input to the other input of the comparator is provided by the combination of resistors R1, R4 and R5 and transistors Q5 and i6. Transistors Q3 and Q4 form a differential to single-ended converter, and the comparator output DRVEC is developed at the collector of transistor Q6 using a current source comprising a transistor Q9.

In this embodiment, the signal BIAS is the reference voltage provided by a simple IC network of the IC 5, while VS and V35V5, 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 resistors QCC1, QCC2, Q2500UA and resistor R2500UA and THUR1 and RiOOUA between external pins CCIN and VT of the IC 5.

In parallel with the constant current circuit is a switch, i.e. a switchable high-current path, comprising transistors QDARL, QSW, Q5AMA and resistors RSAT, RWDARL, RQSW, R50M 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, QD1, QD2 and diode D1. Note that the signals V3V5 and BIAS have the same meaning as in the comparator circuit.

The remaining blocs shown in Fig. 1, i.e. buffer, LED driver and AC are all simple Darlington driver arrangements as known in the art, and shall therefore not be discussed in any more detail herein.

It should be appreciated that the electronic circuitry associated with a proximity switch operating in two wire applications has until now been implemented using discrete devices which take up valuable room on the printed wiring assembly. This places 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 associated (ASIC) 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.

An embodiment of'the invention has hereinbefore been described. It should, however, be appreciated that the embodiment disclosed is in no way meant to limit the scope of the invention and that other embodiments and variations on the disclosed embodiment may be envisaged.

Finally, it should be appreciated that an important advantage of the present invention is that it enables smaller size and lower cost t-wo wire 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.

Claims

f 1. A two wire AC power supply for a proximity switch integrated circuit comprising 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, the other 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, wherein, the comparator and the AND gate are provided within the integrated circuit.
2. A two wire AC power supply as claimed in Claim 1, wherein a current limiting circuit is connected in parallel with a switch which is 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.
3. A two wire AC power supply as claimed in either of Claims 1 or 2 wherein the integrated circuit is implemented in bipolar transistor technology.
4. A two wire AC power supply a8 claimed in Claim 3, wherein the comparator comprises a PNP differential pair comprising first and second transistors (Q1, 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, R1, R2 and D2), the divided down voltage being applied to the base of the first transistor (Q1), 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 teing derived from the integrated circuit, the collectors of the differential pair (Q1, Q2) being connected to a differential to single-ended converter (Q3, Q4) an output from the comparator being developed at the collector of a third 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.
5. A two wire AC power supply as claimed in either of Claims 3 or 4, wherein the constant current circuit comprises fourth and fifth NPN transistors (QCC1, QCC2) connected in parallel, and further connected between their collectors and bases in parallel with a resistor( R1OOUA), the emitters being connected to a parallel arrangement comprising a second resistor (R2500UA) connected in parallel between the base to emitter of a sixth NPN transistor (Q2500UA) which is connected in series with a third resistor RTHUR1, the collector of the sixth transistor (Q2500UA) being connected to the bases of the fourth and fifth NPN transistors (QCC1) and (QCC2).
6. A two wire AC power supply as claimed in any of claims 3 to 5, wherein the switch connected in parallel with the constant current circuit comprises a fourth resistor (RSAT) connected to the collector of a seventh transistor (QDARL) having a fifth resistor (RODARL) connected between its base and emitter, the emitter of the transistor (QDARL) being connected to the base of an eighth transistor (QSW), the eighth transistor (QSW) having a fifth resistor (RQSW) connected between its base and emitter, the emitter of the eighth'transistor (QSW) further being connected to a parallel arrangement comprising a sixth resistor (SOMA) and the base to emitter junction of a ninth transistor (Q5OMA) which is connected in series with a seventh resistor 4RTHUR2), the collector of the ninth transistor (Q50MA) further being connected to the base of the transistor (QDARL).
7. A two wire AC power supply as claimed in Claim 6, wherein the base current to the seventh 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.
8. An integrated circuit for use in a two wire AC power supply for a proximity switch.
9. An integrated circuit as claimed in Claim 8, wherein the integrated circuit of the power supply is integrated with that of the proximity switch.
10. A two wire AC power supply for a proximity switch integrated circuit as hereinbefore described with reference to the accompanying drawings.
11. An integrated circuit for use in a two wire AC power supply for a proximity switch, as hereinbefore described with reference to the accompanying drawings

11. An integrated circuit for use in a two wire AC power supply for a proximity switch, as hereinbefore described with reference to the accompanying drawings.

AlrlONMENTS TO ThE CLAMS HAVE BEEN FLED AS FOLLOWS

1. 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.

2. A two wire AC power supply as claimed in claim 1 comprising 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, wherein, the comparator and the AND gate are provided within the integrated circuit.

3. A two wire AC power supply as claimed in claim 2, wherein a current limiting circuit is connected in parallel with a switch which is 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.

4. A two wire AC power supply as claimed in either of claims Z or 3, wherein the integrated circuit is implemented in bipolar transistor technology.

5. A two wire AC power supply as claimed in claim 4, wherein the comparator comprises a PNP differential pair comprising first and second transistors (Q1, 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, Ri, R2, QD2), the divided down voltage being applied to the base of the first transistor (Q1), 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 (Q1, Q2) being connected to a differential to single-ended converter (Q3 Q4) an output from the comparator being developed at the collector of a third 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.

6. A two wire AC power supply as claimed in claim 3, wherein the constant current circuit comprises fourth and fifth NPN transistors (QCC1 QCC2) connected in parallel and further connected between their collectors and bases in parallel with a resistor (R1OOUA), the emitters being connected to a parallel arrangement comprising a second resistor (R2500UA) connected in parallel between the base to emitter junction of a sixth NPN transistor (Q2500UA) which is connected in series with a third resistor (RTHUR1), the collector of the sixth transistor (Q2500UA) being connected to the bases of the fourth and fifth NPN transistors (QCC1, QCC2).

7. A two wire AC power supply as claimed in claim 3, wherein the switch connected in parallel with the constant current circuit comprises a fourth resistor (RSAT) connected to the collector of a seventh transistor (QDARL) having a fifth resistor (RODARL) connected between its base and emitter, the emitter of the seventh transistor (QDARL) being connected to the base of an eighth transistor (QSW), the eighth transistor (QSW) having a sixth resistor (RQSW) connected between its base and emitter, the emitter of the eighth transistor (QSW) further being connected to a parallel arrangement comprising a seventh resistor (RSOMA) and the base to emitter junction of a ninth transistor (Q5OMA) which is connected in series with an eighth resistor (RTHUR2), the collector of the ninth transistor (Q5 OMA) further being connected to the base of the seventh transistor (QDARL).

8. A two wire AC power supply as claimed in claim 7, wherein the base current to the seventh 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.

9. A proximity switch integrated circuit, wherein at least some circuitry associated with a two wire AC power supply for the proximity switch is provided within the integrated circuit.

10. A two wire AC power supply for a proximity switch integrated circuit as hereinbefore described with reference to the accompanying drawings.