JPS6338593Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a telephone set that transmits a dial tone to the handset after off-hook and after the power supply voltage reaches the operation guaranteed voltage of the control circuit.

Generally, the telephone communication circuit of a telephone is formed by turning on the telephone switch due to the off-hook, so the dial tone can be heard immediately after the off-hook, and the user who confirms the dial tone immediately performs the dialing operation.

However, in telephones using a central power supply system, depending on the central line resistance value, the rise of the voltage of the telephone's internal power supply generated from the central power supply is delayed, and the time period during which a voltage lower than the guaranteed operation voltage of the control circuit is supplied to the control circuit is delayed. becomes longer. In this case, in a control circuit using a semiconductor, the operation of the control circuit becomes unstable and is not guaranteed during a period when the supplied voltage is below the guaranteed operation voltage, so even if the dial tone can be heard for a while after off-hook. , accurate dialing signals may not be sent.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a telephone that can send an accurate dialing signal after the user performs a dialing operation after hearing a dial tone.

In order to achieve such an object, the present invention short-circuits the communication circuit so that dial tone is not sent to the handset when the voltage of the internal power supply of the telephone is lower than the operation guaranteed voltage of the control circuit. The present invention will be described in detail below with reference to drawings showing embodiments.

The figure is a circuit diagram showing an embodiment of the telephone according to the present invention, and shows the main parts of the public telephone. In the figure, a billing signal receiving circuit 1, a diode bridge 2, a dial impulse sending and forced disconnection circuit 3, a dial shunt circuit 4, a telephone call circuit 5, a power supply circuit 6, a control circuit 7, a telephone switch HS and a central office line terminal L1, L2 constitutes a public telephone circuit. The oscillation circuit 8, the conversion circuit 9 that converts the signal generated by the oscillation circuit 8 into a DC voltage, and the determination circuit 10 that determines the level of the DC voltage output from the conversion circuit 9 constitute a reset circuit. .

Further, the dial shunt circuit 4 includes a transistor 41, a resistor 42, a capacitor 43, and an FET 44 as an element that short-circuits the receiver when turned on.
It is made up of. The FET 44 exhibits a conductive state when no bias voltage is supplied, and exhibits a non-conductive state when the bias voltage reaches a predetermined level. Also, the transistor 41
constitutes a circuit that maintains the FET 44 in a non-conductive state based on the output of the control circuit 7 after the power supply voltage reaches the operation guaranteed voltage of the control circuit 7. It is composed of a high resistance 61, diodes 62 to 64, Zener diodes 65 and 66, and capacitors 67 and 68, and generates a backup power source for the RAM and a power source for operating other circuits from the local power source.

The control circuit 7 includes RAM71, CPU72, and ROM7
3, and the CPU 72 has a reset terminal 72.
When a "0" level signal is supplied to a, reset control is performed. The oscillation circuit 8 also has a capacitor 8
0,81, inverter 82-86, resistor 87,8
8. It is composed of a crystal oscillator 89, and when the power supply voltage _VDD , which is the internal power supply of the telephone, is supplied, it generates a signal with a frequency determined by the crystal oscillator 89, and the amplitude of the signal is determined by the supplied power supply voltage _VDD . corresponds to a value.

The conversion circuit 9 includes capacitors 90, 91 and a resistor 9.
2, 93, diodes 94, 95, and the judgment circuit 10 is of the depletion type.
It consists of a FET 101, Schmitt trigger type inverters 102 and 103, and a resistor 104. Then, the conversion circuit 9 converts the FET 10 after the power supply voltage V _DD reaches the operation guaranteed voltage of the control circuit 7.
The constants are selected to generate a DC voltage that turns FET 101 off and turns FET 101 on at all other times.

The operation of the circuit configured in this way is as follows. When off-hook, a DC loop is formed by the hook switch HS, and the capacitors 67 and 68
is charged. In this case, capacitor 67 is trickle charged during on-hook, so there is no change in voltage, but capacitor 68 is discharged during on-hook, so its terminal voltage, that is, the power supply voltage.
The voltage that becomes V _DD increases with time. When this voltage is supplied as a power supply, the oscillation circuit 8 starts oscillating, and the amplitude of the oscillation output increases as the power supply voltage V _DD increases. The oscillation output generated by the oscillation circuit 8 is converted by the conversion circuit 9 into a DC voltage proportional to its amplitude, and the oscillation output is converted to a DC voltage proportional to the amplitude of the oscillation output, and the judgment circuit 10
is supplied to the FET 101. As mentioned above, the conversion circuit 9 generates a DC voltage that turns on the FET 101 when the power supply voltage V _DD is below the operation guaranteed voltage of the control circuit 7, so the input terminal of the inverter 102 becomes "0" level. This signal is inverted by inverters 102 and 103, respectively, and the CPU 7
A "0" level signal is supplied to the second reset terminal 72a, and the CPU 72 is reset-controlled. on the other hand,
When the power is turned on, bias voltage is not supplied to the control electrode of FET44, so FET44
is in a conductive state. For this reason, the communication circuit 5
Since it is shorted by FET 44, no dial tone is heard on the handset. but,
After the power supply voltage reaches the operation guaranteed voltage of the control circuit 7, the transistor 41 outputs a signal that maintains the FET 44 in a non-conductive state based on the output of the control circuit 7. As a result, the bias voltage supplied to the FET 44 exceeds a predetermined value, and the FET 44 becomes non-conductive. Therefore, after this, the short circuit of the communication circuit 5 caused by the FET 44 is released, and the dial tone can be heard from the receiver.

Although the above embodiments have been described with respect to public telephones, the present invention is not limited to this, and can be similarly used as long as the transmission of signals is prohibited until the power supply voltage reaches a predetermined voltage.

As explained above, in the telephone according to the present invention, the dial tone can be heard after the power supply voltage reaches the operation guaranteed voltage of the control circuit, so the control circuit accurately transmits the dial signal accompanying the dial operation. This has the effect of allowing control such as transmission.

[Brief explanation of drawings]

The figure is a circuit diagram of a telephone showing an embodiment of the present invention. 4... Dial shunt circuit, 5... Call circuit, 6... Power supply circuit, 7... Control circuit, 8... Oscillation circuit, 9... Conversion circuit, 10... Judgment circuit, 4
4...FET.

Claims (1)

[Scope of utility model registration request] In a telephone that supplies the power supply voltage to the control circuit using the call loop current from the station, when the bias voltage is not supplied to the control electrode, it shows a conductive state and short-circuits the handset, and when the bias voltage reaches a predetermined level. A switching element that becomes non-conductive to release the short circuit in the handset, and a circuit that maintains the switching element in a non-conductive state based on the output of the control circuit after the power supply voltage reaches the operation guaranteed voltage of the control circuit. . A telephone set, characterized in that the handset is short-circuited until the power supply voltage reaches a guaranteed operation voltage of the control circuit.