IE41749B1 - Circuit arrangement for tellephone subset - Google Patents

Abstract

1521468 Powering substations STANDARD TELEPHONES & CABLES Ltd 7 Oct 1975 [11 Oct 1974] 44059/74 Heading H4K In a circuit arrangement for a batteryless telephone instrument and including a full wave rectifying arrangement D1-4 adapted to power the instrument from the line, a capacitor C3 maintains power to the circuit during the break periods of outpulsing. The digits of a dialled call code, entered, e.g. at a key block, are transferred to a logic control circuit (not shown) where they are transformed into a pulse stream corresponding to the code. This stream is supplied (at the "Output Drive" terminal) to an arrangement, e.g. an outpulsing relay OPR, for effecting loop disconnect signalling. A clock generator provides timing information (over the "Clock Drive" leads) to the control circuit, which is reset at the start of each call. A transistor outpulsing circuit (TR21-23) may replace the outpulsing relay, Fig. 2 (not shown).

Description

This invention relates to circuit arrangements for use in telephone subsets employing loop disconnect signalling, and in particular to a batteryless telephone circuit operated from the line power and having means for maintaining power to the circuit during the break periods of . outpulsing.

U.K. Specification No. 1,426,585 describes and claims a circuit arrangement for energising an electric decadic push button dial circuit, via a telephone transmission circuit, which arrangement includes a transistor switching circuit arranged to cause a power supply capacitor to be charged . via the transmission circuit and responsive to operation of said dial circuit to cause said dial circuit to draw power from said capacitor during break periods and from the transmission circuit during make periods of the dialled pulses.

According to one object of the present invention there is provided a circuit . arrangement for a batteryless telephone instrument, including a full wave rectifying power supply adapted to power the instrument from the line and having - 2 41749 means including a resevoir capacitor for maintaining power to the circuit during the break periods of outpulsing, a logic control circuit for storing the digits of a dialled call code and for generating a pulse stream corresponding to the call code, means responsive to said pulse stream for efffecting loop . disconnect signalling to the exchange, a clock generator for providing timing information to the logic control circuit, and means for resetting the logic control circuit at the start of each call.

According to another aspect of the invention there is further provided a circuit arrangement for a batteryless telephone circuit of the type in which an · array of push-buttons is employed to set up calls, including a full wave rectifying power supply adapted to power the circuit from the line and having capacitive storage means for maintaining power to the circuit during the break periods of outpulsing, a logic control circuit adapted to store the digits of a call code entered via the pushbutton array and to generate an impulse stream corresponding . to the call code, an output stage for transmitting loop disconnect signals to the exchange in .response to the impulse stream, a clock generator for providing timing information to the logic control circuit so as to control the rate of impulsing, a reset circuit for setting the logic control circuit to zero at the start of each call and at the termination of outpulsing, and means including . a bistable off normal relay for connecting the circuit to the line during outpulsing and for disconnecting the circuit from the line at the termination of outpulsing.

The term dialling as used herein is understood to include selection of a telephone call code via a pushbutton keyblock.

Embodiments of the invention will now be described with reference to the . accompanying drawings' in which Figure 1 shows a circuit arrangement for a batteryless telephone subset; and to Figures 2a to 2c of the accompanying drawings which show an alternative circuit arrangement of the type shown in Figure 1. - 3 41749 Referring to Figure 1, power is taken from the telephone line L via a diode bridge Dl to D4 which protects the circuit against reversals of line voltage. The output from the bridge is fed to a delayed charging circuit comprising transistors TRI, TR2, TR3 and TR4, Zener diode ZDl and . capacitor C3. This arrangement provides an almost instantaneous four volt supply to the telephone circuit when the line is connected, but allows capacitor C3 to charge from the surplus line current so as to store energy to maintain operation during the break periods of outpulsing. Transistor TR4 is switched by the output drive to provide a discharge path from . capacitor C3 to the circuitry during the break periods. The1 power supply may also advantageously include spark quench and transient protection arrangements.

The clock circuit includes an oscillator and a clock drive arrangement.

The oscillator is of a conventional L/C type whose frequency is determined by . the tuning of transformer Tl and capacitor C7. The oscillator output is rectified by transistors TRI3 and TRI5 to charge capacitor CIO. The current pulses which flow in transistors TR13 and TR15 charge the input capacitance of the logic control unit which are then discharged during the following half cycle by transistors TR12 and TRK which are driven from the opposite phase . of the oscillator output. Pulses of less than half a cycle in duration and in antiphase are generated. The output voltage of the capacitor CIO is employed to feed the data and reset inputs of the logic unit.

The output from capacitor CIO also provides a feed to charge capacitor Cll thus giving a delay following the start of clock drive pulses until a trigger . circuit including transistors TR17 and TR18 switches. The output of the trigger circuit is inverted and fed to the reset input of the logic unit by transistors TR19 and TR20 which provide the sharp reset pulse required. At the end of outpulsing transistor TR16 turns on to discharge capacitor Cll thus providing a sharp 'off' pulse and an enforced delay before further data can be entered - 4 41749 as capacitor Cl 1 needs to be recharged. This prevents spurious operation due to possible data input during the reset clear-down sequence.

The off normal relay employed with the circuit arrangement is a bistable relay, advantageously of the dry reed type, and driyen from a . bridge circuit formed by transistors TR5, TR6, TR7, TR8 and TR9. When the first digit of a call code is dialled, e.g. when the first button of a push-button keyblock is depressed, transistors TR5 and TR9 switch on to operate the relay and hold transistors TR6, TR7 AND TR8 off. The off normal output is low at this time but after a short delay, generally 15ms, . it changes to high causing transistors TR5 and TR9 to turn off. The relay does not change over, but all the bridge transistors are held off while the off-norma1 output is high.

At the end of outpulsing the off-normal output goes low causing transistors TR6, TR7 and TR8 to turn on thus operating the relay to its opposite or · transmission position to disconnect the dialling circuitry from the line.

If the off-normal relay becomes incorrectly positioned during transmission it is immediately reset via transistors TR6, TR7 and TR8 as the strobe contacts of the dialling unit or key-block will be open and the off-normal output is its low condition.

. The output pulse stream from the logic unit corresponding to the stored digits of a dialled call is fed to a buffer stage formed by transistor TRIO.

The collector output of the transistor is used to operate an impulse relay to feed loop disconnect signals via the line to the exchange.

The logic control unit employed with the arrangement may advantageously , be of the commercially available HOS type. The logic unit receives data - 5 41749 corresponding to dialled digits» stores the data, and provides outpulse signals at the correct repetition rate for loop disconnect signalling. For clarity the logic unit has been omitted from the drawing and only the various terminal connections to the unit have been shown.

. Figures 2a, 2b and 2c together show an alternative circuit for a batteryless telephone subset; the interconnections between the Figures are via points A, B, C, D, E and F. The circuit differs from that of Figure 1 in three main points. The outpulsing relay of Figure 1 is replaced by a three transistor circuit to provide solid state outpulsing to the line; a second off-normal . relay is provided to perform the receiver shorting function of the mask contacts of the rotary dial: and the common bar switching requirements of the keyblock are reduced to one make-before-break changeover function, the strobe make contact being dispensed with. The operation of the circuit is similar to that of Figure 1 except for the following features.

THE OUTPULSING CIRCUIT This circuit includes a high current, high voltage switching transitor TR21 which is arranged in the incoming telephone line circuit and performs the actual outpulsing function. It is driven by transitor TR23 via transistor TR22, both of which are high voltage types. During the make periods of outpulsing the logic zo output is low so that transistor TR23 is held on. Transistor TR22 is therefore also on thus switching transistor TR21 on to complete the loop of the line circuit. TR21 operates in its saturated mode during this period and thus introduces only a small voltage drop to the circuitry.

In order to provide adequate base current for transistor TR21 transistor TR22 !5 must be allowed to pass sufficient collector current. In the circuit shown in Figure 2 this current is utilized to operate the additional off-normal relay 0NR1. - 6 41749 When the logic output goes to high to signal a break period transistor TR23 is switched off thus switching off transistors TR22 and TR21 to break the line loop circuit. Zener diode ZD1 limits the inductive voltage spike developed across transistor TR21 and provides surge protection during the . break periods of outpulsing. Diode D7 provides a path for additional collector current for transistor TR22 under high line current conditions when transistor TR22 would not be fully saturated.

OFF-NORMAL RELAY As previously described this monostable relay ONR1 operates as soon i« as the circuit is powered when a keyblock button is operated. It is held operated during the break periods of outpulsing, when transistor TR22 is switched off via resistor R33 and diode D6 from the main storage capacitor C3. The contacts of this relay are used to short-circuit the telephone receiver during outpulsing, the relay remaining on after the termination of outpulsing for j5 a period determined by its drop-off characteristic and the discharge rate of the storage capacitors.

''COMMON INPUT FROM KEYBLOCK In this circuit the common or “strobe input from the keyblock is generated by diodes connected to the data contacts as opposed to a separate •’° common bar switch. This change results in the need for transistors TR4 and TRIO to ensure that, during the initial keyblock button depression when the off-normal relay is passing operate current, transistor TRIG is held off to allow a resent signal to be generated by the trigger circuit formed by transistors TR17, TR18, TR19 and TR2O. Resistor R34 is included to provide quenching of the relay coil e.m.f. during switching. - 7 41749 OTHER CHANGES Slight changes are made in the method of powering the clock driven circuit which is now via diode D5 during make periods of outpulsing and diode D20 during break periods.

Clamping of the two clock inputs to the logic circuit is achieved by diodes D21 and D22 which prevent the inputs from going more positive than the rail, since these diodes are connected to the junction of D23 and R45. In the clock drive oscillator circuit, the centre tap of the transformer secondary winding is now connected to the negative supply to increase efficiency and i0 resistor between the bases of TR13 and TRIS, and CIO is dispensed with.

The logic circuit employed in both the embodiments may advantageously be the type AY-5-9100 produced by General Instrument Microelectronics Limited.

This circuit is available in an 18 pin DIL package, the prior connections being shown in the embodiment of Figs. 2a to 2c. Other logic units may of course be employed with consequent minor adjustments to the associates circuitry.

Claims (4)

1. A circuit arrangement for a batteryless telephone instrument, including a full wave rectifying power supply adapted to power the instrument from the line and having means including a reservoir capacitor for maintaining 5 power to the circuit during the break periods of out-pulsing, a logic control circuit for storing the digits of a dialled call code and for generating A pulse stream corresponding to the call code, means responsive to said pulse stream for effecting loop disconnect signalling to the exchange, a clock generator for providing timing information to the logic control circuit, and means for resetting 10 the logic control circuit at the start of each call.

2. A circuit arrangement for a batteryless telephone circuit of the type in which an array of pushbuttons is employed to set up calls, including a full wave rectifying power supply adapted to power the circuit from the line and having capacitive storage means for maintaining power to the circuit during the break 15 periods of outpulsing a logic control circuit adapted to store the digits of a call code entered via the pushbutton array and to generate an impulse stream corresponding to the call code, an output stage for transmitting loop disconnect signals to the exchange in response to the impulse stream, a clock generator for providing timing information to the logic control circuit so as to control 20 the rate of impulsing, a reset circuit for setting the logic control circuit to zero at the start of each call and at the termination of outpulsing, and means including a bistable off normal relay for connecting the circuit to the line during outpulsing and for disconnecting the circuit from the line at the termination of outpulsing. 25

3. A circuit arrangement for a batteryless telephone substantially as described herein with reference to Fig. 1 or to Fig. 2a to 2c of the accompanying drawings. - 9 41749

4. A batteryless telephone when fitted with a circuit arrangement as claimed in claim 1, 2 or 3.