Electric source circuit for telephone sets

An output voltage of a first diode deriving out an office line voltage, and an output voltage of a second diode deriving out the voltage of a back-up battery are combined and then smoothed by a smoothing capacitor. The smoothed voltage is supplied to a control circuit. A voltage limiting circuit is connected to the input side of the first limiter for limiting the upper limit of the smoothed voltage. A switch circuit is provided which is rendered conductive at the time of talking and the at the time of sending out a dial pulse for combining the office line voltage with the combined voltage. A voltage limiting circuit is also provided which is enabled only at the time of talking and at the time of sending out a dial pulse for limiting the upper limit of the combined voltage.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electric source circuit for a telephone set 
having a control circuit for accessing a dial transmission circuit, 
effecting key input reception from a dial key pad, setting of the state of 
a talking line, etc., and more particularly an electric source circuit 
provided with a battery acting as a back-up power source for memory means 
for storing control data of the control circuit. 
2. Description of the Prior Art 
Various types of multifunction electric button telephone apparatus 
utilizing microprocessors have recently been developed. In these telephone 
sets, obtaining an electric source for driving the microprocessor, 
presents a problem. Since an appropriate electric source capable of stably 
supplying power to such electronic button telephone apparatus is not yet 
available, a commercial power source has been exclusively used. However, 
where a commercial power source is used, it is necessary to use connecting 
lines for connecting the telephone sets to the commercial power source. 
Moreover, circuit means for stepping down the voltage of the commercial 
source to the driving voltage of the microprocessor and for rectifying the 
commercial AC voltage requires a large amount of space which prevents 
miniaturization of the entire apparatus and increases the cost of 
manufacturing. 
For this reason, a telephone apparatus has been proposed in which office 
line current is used and a battery is provided acting as a back-up source 
for the memory means or the like of the apparatus. In such a telephone 
apparatus, however, there is a problem of how to minimize the degradation 
or consumption of the back-up battery so as to lengthen its effective 
life. 
Among the reasons that cause shortening of the effective life of the 
back-up battery are the leakage of the battery while speech is not made 
(idle time) and consumption of the battery caused by the drop of the 
office line voltage. The leakage of the back-up battery during idle time 
is mainly caused by the current flowing through a Zener diode constituting 
a voltage limiting circuit which is provided for the purpose of 
stabilizing the source voltage. More particularly, the Zener diode is 
connected to a line where the output of the back-up battery and the output 
of the office line voltage flow so that the output battery of the back-up 
voltage is constantly applied across the Zener diode. Although the 
operating voltage of the Zener diode is generally set to be slightly 
higher than the output voltage of the back-up battery, a small current 
flows through the Zener diode even in a range lower than the operating or 
yielding voltage of the Zener diode. Thus, this small current is one of 
the causes that rapidly consume the back-up battery. 
Usually the office line voltage is derived out through a plurality of 
diodes and transistors. However, a diode has a forward voltage drop of 
about 0.7 V and a transistor has a voltage drop of about 0.01 V-0.3 V. 
Moreover, the office line voltage often decreases to about 3 V due to the 
connection state of other telephone sets. In such a case, it becomes 
impossible to drive a microprocessor or the like with the office line 
voltage. For this reason, provision of the back-up battery is essential. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a novel electric source 
circuit capable of lengthening the operating life of a back-up battery by 
minimizing as far as possible the consumption thereof. 
According to this invention, there is provided a source circuit for a 
telephone set comprising first diode means deriving out an office line 
voltage; a back-up battery; second diode means for deriving out an output 
voltage of the back-up battery; a smoothing capacitor connected to a line 
supplied with the outputs of the first and second diode means for 
smoothing a combined output voltage of the first and second diode means; a 
voltage limiting circuit connected to the input side of the first diode 
means, for preventing the combined output voltage from exceeding a 
predetermined definite voltage; and means for supplying the smoothed 
voltage to a control circuit which controls a dial pulse sending out 
operation and a talking operation, the smoothed voltage acting as a source 
voltage for the control circuit. 
According to a modified embodiment of this invention, there is provided a 
source circuit for a telephone set comprising a back-up battery; first 
circuit means including a first diode for deriving out an office line 
voltage, a second diode for deriving out the voltage of the back-up 
battery and first smoothing means for smoothing a combined voltage of the 
output voltages of the first and second diodes; second circuit means 
including a third diode for deriving out the office line voltage; a fourth 
diode for deriving out the output voltage of the back-up battery, and a 
second smoothing means for smoothing a combined voltage of the output 
voltages of the third and fourth diodes; a Zener diode connected to the 
input sides of the first and third diodes and acting as a voltage limiter; 
a current limiting circuit connected to the input side of the fourth diode 
of the second circuit means; a control circuit including memory means and 
a control unit; means for supplying the output of the first circuit means 
to the memory means, and means for supplying the output of the second 
circuit means to the control unit. 
According to still further embodiment of this invention, there is provided 
a source circuit for a telephone set comprising a back-up battery; a first 
diode for deriving out an office line voltage; a second diode for deriving 
out the output voltage of the back-up battery; a smoothing capacitor 
connected to a line supplied with the outputs of the first and second 
diodes for smoothing a combined voltage of the output voltages of the 
first and second diodes; a current limiting circuit connected to the input 
side of the second diode for limiting current flowing through the second 
diode; a negative voltage forming circuit for forming a negative source 
voltage from a combined voltage of the output voltages of the first and 
second diodes; a control circuit including a control unit and memory 
means; means for supplying the combined voltage to the control unit; and 
means for supplying the output of the negative voltage forming circuit to 
the memory means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the general construction of an office source type telephone 
set (telephone set using a office line current as an electric source) 
having a control circuit including a microprocessor. The telephone set 
comprises office line terminals 1 and 2 and a hook switch 3 which is 
thrown to a paging circuit 4, as shown in FIG. 1, in a paging signal 
waiting state, so as to send the paging signal to a paging circuit 4 upon 
receipt of the paging signal to cause a sounder or loudspeaker to generate 
a paging tone. On the other hand, at the time of transmitting a dial 
signal and at the time of talking, the hook switch 3 is thrown to the side 
of a diode bridge circuit 6 so that a talking signal from a telephone set 
of a calling party is sent to a telephone set circuit 8 via the diode 
bridge circuit 6 and a dial pulse transmitting circuit 7. The telephone 
set circuit 8 sends the received talking signal to a handset 9 or 
reception monitor loudspeaker 10 to be produced as a voice. A control 
circuit 11 is provided for controlling the dial signal transmitting 
operation and the talking operation. The control circuit 11 is supplied 
with the output of a hook switch contact 12 interlocked with the hook 
switch 3 and the output of a dial key pad 13 for controlling the sending 
out of the dial pulse, the operation of the telephone set circuit 8 at the 
time of talking, switching between the transeiver 9 and the reception 
monitor loudspeaker 10 and for preventing excessively loud tone at the 
time of transmitting the dial pulse. 
FIG. 2 shows the construction of a prior art source circuit for operating 
the control circuit 11. As shown, the output of the diode bridge circuit 6 
is connected to a first diode 21 through a resistor 20 for deriving out 
the office source voltage at the time of talking. The output of the diode 
bridge circuit 6 is also supplied to the dial pulse transmitting circuit 
7, and its output is supplied to a second diode 23 via a resistor 22 so as 
to derive out the office source voltage via the dial pulse transmitting 
circuit 7 at the time of transmitting the dial pulse and during talking. 
The office source voltages thus derived out are combined on the output 
sides of the diodes 21 and 23 and the combined voltage is smoothed with a 
smoothing capacitor 24 and its magnitude is limited to a constant value by 
a Zener diode 25, whereby the constant voltage is supplied to the control 
circuit 11. In this case, for providing a back-up voltage to memory means, 
not shown, in the control circuit 11, the output voltage of a back-up 
battery 26 is also combined with the output voltages of the diodes 21 and 
23 via a diode 27. 
In another prior art source circuit shown in FIG. 3 a constant current 
circuit is constituted by diodes 17 and 18 and a transistor 31, and the 
output of the constant current circuit is derived out through a diode 21 
and its output is combined with the output of a backup battery 26 via a a 
diode 27. The combined voltage is smoothed by a smoothing capacitor 24 and 
maintained at a constant value by a Zener diode 25. The voltage thus 
obtained is supplied to the control circuit 11 as a source voltage. 
In the source circuit having a construction just described, since the 
voltage of the back-up battery 26 is normally impressed across the Zener 
diode 25 provided for the purpose of maintaining the office source voltage 
at a constant value, even when the voltage of the battery 26 is higher 
than the operating voltage of the Zener diode, a small current would flow 
through the Zener diode 25 from the battery 26 in a region below the 
operating point of the Zener diode, whereby the battery is rapidly 
consumed. 
The embodiment of this invention shown in FIG. 4 is different from the 
prior art circuit shown in FIG. 2 in that independent Zener diodes 25A and 
25B acting as voltage limiters that present the office source voltage from 
exceeding a definite voltage are connected to the input sides of the 
diodes 21 and 23 respectively. With this connection, the output of the 
back-up battery 26 becomes opposite to the forward direction of diodes 21 
and 23 so that there is no fear that the current of the battery leaks 
through Zener diodes 25A and 25B, thus preventing unwanted consumption of 
battery 26. A DC voltage of 48 V-100 V is applied to a wire 26a connected 
to resistor 20 at the initial time of line connection and at the time of 
sending out the dial pulse, while a DC voltage of 24 V-10 V is applied to 
a wire 27 connected to resistor 22 at the time of talking. However, since 
independent Zener diodes 25A and 25B are connected to the input sides of 
diodes 21 and 23, it is possible to limit the leakage of the office source 
in regions below the operating points of respective Zener diodes. Other 
circuit elements shown in FIG. 4 identical to those shown in FIG. 2 are 
designated by the same reference characters. 
Another embodiment of this invention shown in FIG. 5 is different from the 
prior art circuit shown in FIG. 3 in that Zener diode 25 which has been 
connected to the output side of diode 21 is connected to the input side of 
diode 21 and, at the time of sending out the dial pulse, the office source 
voltage is derived out through a transistor 30 and then combined with the 
output of diode 21 via a resistor 32. Furthermore, for the purpose of 
limiting the office source voltage to a definite value, a second Zener 
diode 36 is connected to the junction between resistor 32 and diode 21 and 
the second Zener diode 36 is rendered operative by a transistor 33 only at 
the time of sending out the dial pulse and at the time of talking. In this 
case, a transistor 30 is turned ON by a transistor 33 at the time of 
sending out the dial pulse and at the time of talking. Reference numerals 
31, 34, 35, 38 and 39 show resistors connected as shown. 
With this construction, in a path including the diode 21, a voltage drop of 
only about 0.7 V occurs, and in a path including the transistor 30, a 
voltage drop is only 0.2 V. For this reason, it is not only possible to 
decrease loss of the office source voltage but also to supply a stable 
source voltage to the control circuit 11. In the prior art circuit shown 
in FIG. 3, the output voltage of the back-up battery 26 is always 
impressed across the Zener diode 25, whereas in this embodiment, the 
battery voltage is blocked by diode 21. Moreover, since the second Zener 
diode 36 also operates only at the time of sending out the dial pulse and 
at the time of talking, the voltage of the back-up battery 26 would not be 
constantly applied across the Zener diode 36. For this reason, a small 
current from battery 26 does not flow through the Zener diodes 25 and 36 
in regions belows the operating points thereof, thereby decreasing 
consumption of the battery 26. 
The Zener diode 36 may be connected to the emitter electrode of transistor 
30. 
FIG. 6 shows still another embodiment of this invention which is 
constructed to limit consumption of the back-up battery and to improve the 
noise-proof characteristic of the memory means of the control circuit 11. 
In this embodiment, the source voltages for a control unit 111 of the 
control circuit 11 and a memory unit 110 are separately derived out. More 
particularly, the negative office source voltage is derived out by a first 
pair of diodes 21 and 23 with their cathode electrodes connected to the 
office line and smoothed by a capacitor 33. The smoothed voltage is then 
supplied to the control unit 111. In the same manner, the negative office 
source voltage is derived out by a second pair of diodes 30 and 31 with 
their cathode electrode connected to the office line, smoothed by a 
capacitor 34 and then supplied to the memory unit 110. The negative 
voltage of the back-up battery 26 is applied to the anode electrodes of 
diodes 30 and 31 via a resistor 35 and a diode 32. The negative voltage of 
the battery 26 is also applied to the anode electrodes of the diodes 21 
and 23 though a current limiting circuit 28 via diode 29. The current 
limiting circuit 28 is made up of resistors 280 and 281, a Zener diode 
282, a diode 283, a transistor 284, and a smoothing capacitor 285 and the 
Zener voltage or the operating voltage of the Zener diode 282 determines 
the value of the limited current. 35 shows a current limiting resistor for 
preventing latch up of the memory unit 110. 
The Zener diodes 25A and 25B acting as voltage limiters are connected to 
the input or anode sides of diodes 21 and 23 respectively. 
Since this embodiment is constructed to derive out the negative office 
source voltage, the transistor of the dial pulse transmitting circuit 7 
has a polarily opposite to those of FIGS. 4 and 5. 
In this embodiment, since the output polarity of the back-up battery 26 is 
opposite to the forward direction 
of the diodes 21, 23, 30 and 31, there is no leakage of the battery 26 
through Zener diodes 25A and 25B, thus preventing consumption of the 
battery. A DC voltage of 48 V-100 V is applied to wire 36 connected to 
resistor 20 at the time of initial connection of the office line and at 
the time of sending out the dial pulse, while a DC voltage of 24 V-10 V is 
applied to line 27 connected to resistor 22 but since independent Zener 
diodes 25A and 25B are connected to the input sides of diodes 21, 23, 30 
and 31 respectively, it is possible to minimize the leakage of the office 
source in regions below the operating points of the Zener diodes 25A and 
25B. 
Moreover, since the control circuit 11 is fed with power from a negative 
source with its ground potential maintained at a high potential, the chip 
enable signal CE and the read/write signal R/W of the memory unit 110 are 
shifted to an inoperative side at the time of generating external noise 
(that is a CE terminal becomes "H" level to select a chip, while a R/W 
terminal becomes "H" level to assume R side), thereby improving the noise 
resistant characteristic. Moreover, since the source voltage systems of 
the control unit 111 and the memory unit 110 are separate, even when the 
source voltage for the control unit 111 becomes the same or lower than the 
voltage necessary for the memory unit 110, the operation thereof would not 
be adversely effected. Consequently, the memory unit can hold such data as 
abbreviated dial numbers or the like without destructing them. In 
addition, since the current supplied to the control unit 111 from the 
battery 26 is limited to an order of several microamperes by the current 
limiting circuit 28, it is possible to further minimize abnormal 
consumption of the battery 26 (about several 100 .mu.A to several mA) 
As above described, since a Zener diode is used for the current limiting 
circuit and the leakage current in the forward direction of the Zener 
diode is smaller than that of an ordinary diode, the current consumption 
can be limited to an order of only several microamperes. 
In a still further embodiment of this invention shown in FIG. 7, a positive 
source voltage is supplied to the control unit 111, a negative source 
voltage is supplied to the memory unit 110, and the office source voltage 
is directly derived out from the input side of the diode bridge circuit 6 
for eliminating the effect of voltage drop caused thereby. 
More particularly, the positive office source voltage is derived out 
through resistor 20, Zener diode 25 and a first diode 21, and the positive 
office source voltage is also directly derived out through diodes 40 and 
41 connected to the input side of the diode bridge circuit 6, the derived 
out voltage is combined with the output voltage of the diode 21 through a 
transistor 42 and a resistor 43. After limiting the combined voltage to a 
definite voltage with a Zener diode 45, the definite voltage is supplied 
to the control unit 111 as a source voltage. The output voltage of the 
back-up battery 26 is supplied to a second diode 47 via a current limiting 
circuit constituted by a diode 46, a Zener diode 48, a transistor 49 and a 
resistor 50, and the output voltage of the back-up battery 26 is also 
supplied to the control unit 111. Diodes 51 and 52 and a resistor 53 are 
serially connected between the negative terminal of the battery and the 
ground, and a negative potential is derived out from the junction between 
the diodes 51 and 52. After being smoothed by a capacitor 54, the derived 
out voltage is supplied to the memory unit 110 as a source voltage. 
A transistor 42 is turned ON when transistor 44 is turned ON at the time of 
sending out the dial pulse. A Zener diode 45 is connected to the ground 
via a transistor 46 which is turned ON when the dial pulse is sent out. 
Consequently, the office source voltage is derived out through diodes 40 
and 41 only at the time of sending out the dial pulse and limited to the 
definite voltage by the Zener diode 45, and the output of this Zener diode 
is combined with the output of diode 21. 
With the construction shown in FIG. 7, since the office source voltage is 
derived out also from the input side of the diode bridge circuit 6, a 
decrease in the source voltage corresponding to the voltage drop of the 
diode bridge circuit can be efficiently compensated for. Moreover, since 
the memory unit 110 is operated by the negative source voltage, upon 
occurrence of an external noise, the chip enabling signal CE and the 
read/write signal R/W of the memory unit 110 would not be shifted to 
inoperative side. Accordingly, the memory unit can hold such data as 
compressed dial numbers without destruction. Moreover, since Zener diode 
25 acting as a voltage limiter is connected to the input side of diode, 
the consumption of the battery 26 can be suppressed. 
In the foregoing embodiments, although the office source voltage was 
derived out at the time of sending out the dial pulse, if desired such 
construction can be eliminated.