JPS6156909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coin insertion reminder display circuit for a public telephone.

Public telephones allow calls to be made for a time determined by the amount of money inserted, and a display is displayed before the call time has elapsed to notify the caller that the time is about to end and to remind them to insert additional money. There is a method that lights up.

In the past, it was easy to light up such a display in public telephones that charge the rectified output of a commercial power supply and use it as a control power source for the telephone circuit by increasing the output current capacity of the power supply. In public telephones of the type that charge a capacitor or battery with direct current to serve as a control power source, the current consumption of the display device is large, so the electric charge charged in the capacitor or battery is quickly consumed, making it difficult to realize this method. .

The present invention is a public telephone of a type in which control power for the telephone circuit is taken out from the above-mentioned telephone line, and in which a display for prompting coin insertion can be easily turned on without adversely affecting the control power. The purpose is to provide a charging reminder display circuit.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an embodiment of the present invention, in which 1 is a switch installed in a telephone office, 2 is a public telephone, and 3 is a telephone exchange installed in a telephone office.
is the communication circuit of the public telephone 2, and L1 and L2 are connection terminals. When the communication circuit 3 is in operation, the DC power supply in the exchange 1 supplies direct current to the communication lines m and n via the connection terminals L1 and L2. Supplied. 4 is a voltage forming circuit that takes out a predetermined DC voltage from the communication lines m and n, and includes diode bridges D 1 to D ₄ and a diode bridge to allow current to flow in the same direction even when the polarity of the DC power supply inside the exchange ₁ changes. A constant voltage diode ZD inserted between D ₁ to _{D 4} and the communication circuit 3,
Consisting of a capacitor C1 connected in parallel to the constant voltage diode ZD to prevent noise caused in the communication circuit 3, the constant voltage diode
A predetermined low DC voltage that does not inhibit the operation of the exchange 1 can be obtained between both ends of the ZD.

Reference numeral 5 denotes a control power supply unit for the public telephone 2, which receives the low DC voltage extracted from the telephone line by the voltage forming circuit 4 and converts it into a control power supply necessary for the public telephone 2. In the embodiment shown in FIG. 1, the control power supply unit 5 includes a DC transistor Tr1, which is an oscillation control element, an oscillation transformer T, diode bridges _D5 to _D8 , a diode _D9 , and a resistor R1.
A capacitor C2 is used to accumulate the outputs of the -DC converter and the DC-DC converter, and a charging voltage V obtained by boosting the voltage supplied from the voltage forming circuit 4 several times is obtained in the capacitor C2.

DP is a display, and R2 is a current limiting resistor, which is connected to both ends of a constant voltage diode ZD via a transistor Tr2.

Reference numeral 6 denotes a control circuit which controls the blinking of the display DP based on the coin insertion reminder signal and cuts off the voltage supply from the voltage forming circuit 4 to the control power supply section 5 when the display DP is turned on. It has a sending circuit 61, a clock circuit 62 that outputs a plurality of clock signals, a NAND circuit 63, a resistor R3, a photocoupler PC, and a transistor Tr2.The photocoupler PC is intermittently operated at a duty ratio determined by the clock signal when outputting the coin insertion reminder signal. It operates according to
In response to this, transistor Tr2 is also turned on intermittently to light up the display DP intermittently, and while transistor Tr2 is on, transistor Tr1 of the DC-DC converter is turned off to stop the oscillation operation. The power supply to the DC-DC converter is cut off.

FIG. 2 shows the output a of the money insertion reminder signal sending circuit 61, the outputs b and c of the clock circuit 62, the output d of the NAND circuit 63, and the DC-
The waveforms of the collector voltage e of the transistor Tr1 and the charging voltage f of the capacitor C2 of the DC converter are shown.

The operation will be explained in detail below with reference to FIG.

Assuming that the coin insertion reminder is not being performed before the end of the call time of the public phone, the output a of the coin insertion reminder signal sending circuit 61 is not generated and is held at "L", and the output d of the NAND circuit 63 is It is “H”. Therefore, the photocoupler PC does not operate and the output of the photocoupler PC does not supply the base current of the transistor Tr2, so the transistor Tr2
remains off. Therefore, the display DP does not light up. On the other hand, in the control power supply unit 5, the DC voltage of the voltage forming circuit 4 is applied, and the base current is supplied to the transistor Tr1 via the resistor R1 and the diode _D9 , and the transistor Tr1 is turned on, but the resistor R
Since the base current that was flowing through Tr1 immediately stops flowing, the transistor Tr1 is turned off. When the transistor Tr1 is turned off, it starts supplying the base current through the resistor R1 again. In this way, the transistor Tr1 repeats the on-off operation,
This oscillation voltage is taken out to the secondary side, rectified by diode bridges _D5 to _D8 , and charged to the capacitor C2, so that the charging voltage f remains constant. The diode _D9 is connected between the resistor R1 and the base of the transistor Tr1, and the voltage between the anode of the diode _D9 and the emitter of the transistor Tr1 when the transistor Tr2 is off is equal to the voltage between the emitter of the transistor Tr2 when the transistor Tr2 is on. - Since the purpose is to make the voltage higher than the collector voltage, the same operation can be obtained by using a Zener diode instead of the diode _D9 .

Next, when the output a of the money insertion reminder signal sending circuit 61 is generated at time t, this reminder signal and the outputs b and c of the clock circuit 62, which have a period ratio of 1:4, all become "H". Only when the output d of the NAND circuit 63 becomes “L”, the photocoupler
When PC operates, the output of photocoupler PC supplies base current to transistor Tr2, turning on transistor Tr2. When the transistor Tr2 is turned on, the voltage across the constant voltage diode ZD is applied to the display device DP via the resistor R2, and the display device DP lights up. On the other hand, when transistor Tr2 is turned on, the anode of diode _D9 and the transistor
The potential between the emitters of Tr1 drops and the diode
Since _D9 is turned off and no base current is supplied to the transistor Tr1, the transistor Tr1 is turned off and the oscillation operation of the transistor Tr1 is stopped.
Therefore, no output is generated on the secondary side of the transformer T.
The charging voltage f of capacitor C2 begins to decrease. However, the output d of the NAND circuit 63 becomes "H" when either one is "L" due to the period of the clock signals b and c, so the transistor Tr2 is turned off, the display DP disappears, and the oscillation operation is restarted, and the capacitor C2 The voltage f immediately recovers. In this way, when the money insertion reminder signal is output, the clock signal b
and c, the voltage taken out to the voltage forming circuit 4 is distributed and supplied to the control power supply unit 5 side and the display device DP side in a time-sharing manner, and the display device DP is displayed by blinking brightly due to the communication current. become. By appropriately setting the duty ratio, even if the charging voltage f of the capacitor C2 of the control power supply section 5 drops slightly during lighting, it immediately recovers and is hardly affected. Note that if a battery is used instead of the capacitor C2, fluctuations in the charging voltage f will be further reduced. In addition, the phototransistor of the photocoupler PC is Darlington connected to the transistor Tr2 and has a large current amplification degree, so the current driven by the NAND circuit 63 is very small and is sufficient for this reason. It also requires less power supply.

It goes without saying that the configuration of the circuit in the above embodiment can be modified in various ways without departing from the spirit of the present invention. For example, when the control circuit 6 is used as the control power supply section 5 to turn on the display device DP, the voltage forming circuit is used. A converter using another oscillation type may be used instead of the DC-DC converter described above, as long as it is configured so that the power supply from the communication circuit 3 side and the control circuit 4 can be cut off. We have explained the case where a photocoupler PC is used to isolate the ground of the photocoupler PC in terms of direct current and to improve insulation from the communication line, but instead of the phototransistor of the photocoupler PC, a PNP transistor is used and its base current is passed through the resistor R3. A circuit connected electrically to the communication line may be used, and by setting the outputs b and c of the clock circuit 62, the blinking period of the display 62 can be arbitrarily changed.

Since the present invention is configured as described above, it is possible to make the display DP brightly illuminated in order to remind the user to insert money by directly passing a communication current to the display device DP in a type of public telephone that draws the control power for the telephone circuit from the communication line. Become. In addition, the voltage forming circuit 4 that was used for the control power supply section 5 is used as an indicator.
Since it is switched and used for DP by the control circuit 6, there is no need to add a device for extracting direct current, such as a Zener diode or a capacitor, to the communication line, and the number of circuit components can be reduced.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a time chart showing waveforms of various parts of the circuit of FIG. DESCRIPTION OF SYMBOLS 1... Switchboard, 2... Public telephone, 3... Call circuit, 4... Voltage formation circuit, 5... Control power supply unit,
6...Control circuit, ZD... Constant voltage diode, C
2... Capacitor, Tr1, Tr2... Transistor, DP... Display, PC... Photocoupler, 61
. . . Money insertion reminder signal sending circuit, 62 . . . Clock circuit, 63 . . . NAND circuit.

Claims (1)

[Scope of Claims] 1. A voltage forming circuit that extracts a predetermined DC voltage from a telephone line, a control power supply section of a telephone circuit that is powered by the output voltage of the voltage forming circuit, and a control power supply section to which the output voltage of the voltage forming circuit is applied. and a control circuit that controls blinking of the display based on a coin insertion reminder signal and cuts off voltage supply to the control power supply when the display is lit. Money input reminder display circuit. 2. A coin insertion reminder display circuit for a public telephone according to claim 1, wherein the control circuit lights up the display intermittently at a duty ratio determined by a clock signal when outputting the money insertion reminder signal. 3. The control power supply section comprises a DC-DC converter, and the operation of the oscillation control element of the DC-DC converter is stopped by the control circuit when the indicator is turned on. A coin insertion reminder display circuit for a public phone set forth in item 2.