GB2372842A

GB2372842A - Voltage regulator using a field effect transistor

Info

Publication number: GB2372842A
Application number: GB0126102A
Authority: GB
Inventors: Eric Beattie
Original assignee: EDINBURGH COMM Ltd
Current assignee: EDINBURGH COMM Ltd
Priority date: 2000-11-01
Filing date: 2001-10-31
Publication date: 2002-09-04
Also published as: GB0126102D0; WO2002037824A1; AU2002214128A1; GB0026778D0

Abstract

A regulator circuit suitable for supplying a telephone line, e.g. in an alarm monitoring arrangement, has a series FET 11 controlled by a zener diode 14 connected to the circuit output. Diode 14 is coupled to the gate of FET 11 by a bipolar transistor 13. The circuit draws a low quiescent current and is insensitive to input voltage variations.

Description

1. REGULATOR AND A METHOD OF REGULATING

The present invention relates to a regulator and to a method of regulation.

Typically, a conventional regulator comprises a bridge rectifier, a zener diode and a PNP transistor. Thus, there must be sufficient current not only to bias the diode but to supply the transistor. However telephone lines typically provide only 25 amp available for the whole unit.

Also, in telephone lines, the voltage variation is typically between 7 and l 92 volts, well outside the normal maximum of 40 volts for conventional regulators. Is Furthermore, the zoner voltage varies with input current supplied via the resistor. Thus the regulator will have a slightly varying output voltage depending on the input voltage and hence the current through the resistor.

For all these reasons, conventional regulators cannot be used in practice on to telephone lines and PSTN distribution systems.

According to the present invention, there is provided regulator apparatus comprising means to provide a regulated output at a predetermined voltage range independent of the input voltage at the apparatus, the apparatus :5 comprising FET transistor means located with the drain of the FET on the positive of the input voltage.

Preferably, the apparatus comprises means to place the input voltage via a bridge rectifier or a blocking diode being a zener diode with a reference so voltage derived from the output voltage.

_ _.? - -..

. : f ^ À Preferably, the FET is able to withstand more than 192V between its drain and source, advantageously the FET has a drain/source characteristic of 240V. A resistor may be provided on the gate of the FET, and the source of the FET means may comprise the regulated output.

The apparatus may have means to limit the regulated output, e.g. a zener lo diode, biased by a resistor. There may be provided a zener diode and resistor combination to supply a feedback voltage to control the regulator.

Preferably, the apparatus has a bipolar transistor with a low quiescent current, the emitter of the bipolar transistor being connected as the 15 reference, and the base of the bipolar transistor is connected to the feedback voltage reference point, and the collector of the bipolar transistor is connected to the junction of the FET means and the resistor.

In this way, apparatus of the invention may provide regulation of a so telephone line.

Preferably, the apparatus comprises capacitor means to desensitize the circuit to input voltage fluctuations.

:5 Preferably, the apparatus comprises means to power a unit for connection in an alarm monitoring system.

Preferably, the apparatus also provides means to power a telephone answering unit.

(a - - - ' A a, Àe The present invention also provides an alarm monitoring system including regulator apparatus according to the present invention.

Regulator apparatus of the present invention as described herein may 5 provide the following advantages: À The provision of a regulated supply for widely varying voltage inputs; À The provision of a regulated supply from a telephone line; À Effective powering of stand-alone devices from telephone lines or PSTN distribution systems.

The present invention also provides a method of regulating a supply providing a regulated output at a predetermined voltage range independent of the input voltage at the apparatus, the method comprising providing FET transistor means located with the drain of the PET on the positive of the 15 input voltage.

Preferably the method comprises providing a zoner diode with a reference voltage derived from the output voltage.

so Preferably the method comprises powering a unit on a telephone line.

The invention is applicable to: À Telephone answering machines; Memory back-up units; 25 À Hand-held computer equipment; À Mobile telephones.

The alarm monitoring system of the present invention is suited to warn of any difficulty or danger which occurs in the home e.g. a break-in to the

r ? _ C premises, a fire, a medical emergency, an assault on a person, any temporary or prolonged incapacity, essentially any situation in which an occupant wishes to summon help or assistance.

5 While the present invention is primarily described in relation to use in a domestic house, it is equally applicable to use in other applications, for example in hospitals, schools, factories, offices or any industrial or commercial multi-occupancy buildings.

lo In order that the present invention may more readily be understood, a description is now given, by way of example only, reference being made to

the accompanying drawings in which: Figure 1 is a block circuit diagram of a conventional regulator; 15 Figure 2 is a block circuit diagram of a regulator embodying the present invention; Figure 3 is a block schematic drawing of an alarm monitoring system incorporating the regulator of the present invention; Figure 4 is a handset of the system of Figure 3; and so Figure 5 is an answering machine incorporating a regulator of the present invention.

Conventional regulator 1 as shown in Figure 1 (e.g. for power supplies) generally cannot have a potential of greater than 40 volts applied to its input terminals. This is of no use in a telephone circuit, as the voltage on the line (defined by terminals 2, 3) can be as low as 7 volts, and as high as 192 volts. Notwithstanding this, normal supplies have other drawbacks when trying to supply regulated power to an associated circuit when only limited input power is available. This increasingly common problem is accentuated so when working with the PSTN. It is a regulatory requirement that when a

r _, rat {' " " t ? circuit is in its quiescent mode (the normal mode) it must draw no more than 25!1 amps from the PSTN.

A normal regulator 1 must take enough current through a ground current 5 resistor 4 not only to bias a zoner diode 5, but also to supply the PNP regulator transistor 6. Even using a very high current gain or HFE transistor, this current is several magnitudes more than the 25,u amps available for the whole circuit.

lo This problem is further compounded by the fact that the zener voltage varies with input current supplied via resistor 4. This means the regulator l will have a slightly varying output voltage depending on the input voltage and hence current through the resistor 1.

Is The regulator lO of Figure 2 overcomes all these problems as follows. The zener reference voltage is derived from the output voltage. A 240V FET 11 replaces the PNP transistor to overcome the input voltage problem, and to avoid the problem of bipolar HFE variance. FET's are voltagecontrolled devices, and hence no current is required to operate them.

As the input voltage is increased to the circuit, the resistor R1 (12) will freely pull-up the voltage on the gate of FET 11 until stopped by the collector of the NPN transistor 13 whose only special feature is a low quiescent or "dark current".

No matter what the turn on voltage of the FET 11 is, its source eventually rises to the zener diode voltage. At this point, the anode of diode 14 also starts to rise, and this in turn causes the base of the NPN transistor 13 to rise. A point is reached when the current flowing into the base of transistor

- i.: : 13 will be sufficient to cause its collector to hold the rise of R1 (12). This in turn stops the rise of the base and hence the source of FET 11.

A state of equilibrium now exists. Capacitor C1 (15) and C2 (16) simply s decouple the output as with any regulator circuit. Resistor R3 (18) can now be varied (or the zener changed) to alter the output voltage as required.

Capacitor C3 (17) serves to desensitise the circuit to input voltage fluctuations (this is normally described as a gyrator circuit and is the lo transistor equivalent of an inductor).

As the circuit 10 requires virtually no bias current to operate, the quiescent current of the entire regulator circuit is almost entirely defined by resistor R1 (12) and the FET pull-up. With an input of, e.g., 15 volts with the Is output set to 5 volts, the quiescent of the circuit is only 1,u amp.

Figure 3 shows schematically an alarm monitor system 20 of the present invention having, in a domestic house 21, a telephone receiver unit 22 and telephone line 23. An alarm handset unit 24 is permanently connected, via so a two-way connector plugged into the telephone line 23 such that, when alarm button 25 is pressed, an alarm call is made via the telephone line to a call cenke 26 which is permanently manned by a number of operators 27 who have access to a databank 28 of subscriber information. The alarm call to call centre 26 comprises a signal in the V.23 modem format with as appropriate data content and it includes a serial number identifying the actual handset 24.

Reception of the alarm call at call cenke 26 causes compiler 29 to locate within, and then output from, database 28 all the relevant subscriber so information (SI) and pass it on to an operator 27.

_ À r -,, AL

À:: i' ' Thus, when an alarm call is received by an operator 27, simultaneously the operator is provided with the following information from databank 28: À Address of house 21; 5 À Location of alarm handset 24 (as there may be more than one handset 24 in a house) within house 21; À The name(s), age(s) and medical condition or medical information of the occupant(s) as registered with the call centre; À The telephone number of the house 21; lo À The telephone number of the nearest Police station; À The telephone number of any contact; À The telephone number of the nearest Ambulance call-out; À The telephone number of the nearest Fire Station centre call-out; À A security number or code pre-agreed with the subscriber.

Is À A history of the subscriber's use of the service and of previous calls.

The operator immediately telephones the house 21 using the centre telephone number provided by the databank 28. If the telephone call is answered, the operator 27 asks for the security number or code given so corresponding to that which is on the databank; if this is correctly given, then the operator asks if any further assistance is required. If the security number or code given differs, or if no security number or code is given, then the operator immediately telephones the nearest Police station.

25 If the telephone call is not answered, within a predetermined time period (e.g. 30 seconds), the operator 27 immediately telephones the nearest Police station (perhaps also the Ambulance call-out centre andlor the Fire Station call-out centre) and advises that the call has not been answered.

it.... r _ _. In this way, as soon as an alarm call is received at the alarm call monitor centre, an immediate appropriate response is made.

Figure 4 shows the front face of the alarm handset 24 which has alarm s button 25 designated by a circular area shown in red and forming a slightly raised domed portion as compared to the flat surrounding region 30. When slight pressure is applied to button 25 e.g. by a human finger, there is a responsive physical depression and audible click, thereby giving a positive feedback that switching has been achieved.

Handset 24 has a transparent circular portion 31 though which there can be seen a light-emitting diode 32 which is illuminated when handset is plugged into the telephone system. Region 30 is impregnated with fluorescent material so that the front face of handset 24 can be seen in the dark.

Handset 24 has two lateral walls 33 and 34 on either side of the long side edges of region 30, being bridged by a third wall 35, the three walls forming a U-shape with button 25 located at its apex, the height of walls 33 and 34 increasing towards button 25. In this way, the front face of handset 24 is to shaped so that a person is able to readily and quickly locate the button area 25 by touch alone (e.g. in the dark or in a smoky atmosphere) having little or no familiarity with the design of the handset.

Figure 5 shows schematically a telephone answering machine 40 :5 comprising a message read-out unit 41 and a message record unit 42, both powered by a power supply unit 43 incorporating a regulator of the present invention. Power unit 43 is connected to telephone lines 44, 45 and thereby provides a so continual regulated power supply derived from the telephone lines.

to À À: . - t * In a variant, handset 24 is incorporated in a telephone answering machine 40. 5 The handset 24 may have a wire-less link e.g. by infra-red, ultra-sonic, radio-frequency or optical signals, to a base unit connected to the telephone system, for example allowing the handset to be worn by the subscriber or to be carried around the house 21. Information on such location can be included in the SI data.

lo The regulator 1 can be used to power directly electronic equipment for example as described hereinbefore, and/or it can be used to power storage units e.g. capacitors or batteries which are used to power electronic units.

The circuit of regulator 1 can be utilised in a wide variety of other 15 applications including mobile telephoning applications, memory back-up applications, hand-held or portable computers.

Claims

r À À À. -r -. s CLAIMS

1. Regulator apparatus comprising means to provide a regulated output at a predetermined voltage range independent of the input voltage at the 5 apparatus, the apparatus comprising FET transistor means located with the drain of the FET on the positive of the input voltage.

2. The apparatus of Claim 1 comprising means to place the input

voltage via a bridge rectifier.

3. The apparatus of Claim 1 or 2 comprising means to place the input voltage via a blocking diode.

4. The apparatus according to Claim 3 comprising a zener diode with a Is reference voltage derived from the output voltage.

5. The apparatus according to any preceding claim wherein the FET is able to withstand more than 1 92V between its drain and source.

20

6. The apparatus according to Claim 5 wherein the FET has a drain/source characteristic of 240V.

7. The apparatus according to Claim I or 2 comprising a resistor on the gate of the FET.

8. The apparatus according to any preceding claim wherein the source of the FET means comprises the regulated output.

9. The apparatus according to Claim 8 comprising means to limit the so regulated output.

f À : _..

10. The apparatus according to Claim 9 wherein the limit means comprises a zoner diode.

5

1l. The apparatus according to Claim 10 wherein the zener diode is biased by a resistor.

12. The apparatus according to any preceding claim comprising a zoner diode and resistor combination to supply a feedback voltage to control the lo regulator.

13. The apparatus according Claim 12 comprising a bipolar transistor with a low quiescent current.

15

14. The apparatus according to Claim 13 wherein the emitter of the bipolar transistor is connected as the reference.

15. The apparatus according to Claim 13 or 14 wherein the base of the bipolar transistor is connected to the feedback voltage reference point.

16. The apparatus according to any of Claims 13 to 15 wherein the collector of the bipolar transistor is connected to the junction of the FET means and the resistor.

25

17. The apparatus according to any preceding claim comprising means to limit the rate of voltage change on the PET control voltage.

18. The apparatus according to Claim 17 comprising capacitor means to desensitise the circuit to input voltage fluctuations.

_ - ',, 5

if, '

19. The apparatus according to Claim 18 comprising a capacitor located between VSS and the gate of the FET.

20. The apparatus according to any preceding claim further comprising 5 means to power a unit on a telephone line.

21. The apparatus according to any preceding claim further comprising means to power a unit for connection in an alarm monitoring system.

lo

22. The apparatus according to any of Claim 1 to 20 further comprising means to power a telephone answering unit.

23. An alarm monitoring system including regulator apparatus according to any of Claims 1 to 21 or23.

24. A telephone answering unit including regulator apparatus according to any of Claims 1 to 20 or 22.

25. A method of regulating a supply providing a regulated output at a so predetermined voltage range independent of the input voltage at the apparatus, the method comprising FET transistor means located with the drain of the FET on the positive of the input voltage.

26. The method according to Claim 25 comprising providing a zoner :5 diode with a reference voltage derived from the output voltage.

27. The method according to Claim 25 or 26 comprising providing a resistor on the gate of the FET.