Pulse-dialing-telephone
The TP5700 or TP5710 can reduce the number of components required to build a pulse-dialing telephone. The typical current source can be eliminated by utilizing the VREG1 output to power a TP50982A low-voltage (1.7 V) pulse dialer through a blocking diode. A low forward-voltage drop diode, such as a Schottky type, is essential because VREG1 operates in its nonregulated mode, and its output voltage may drop to 2 V under a 20-mA loop. Additionally, a 100 µF decoupling capacitor is necessary to maintain the pulse dialer supply voltage during dialing. This capacitor will take approximately one second to charge when the telephone is first connected to the line; however, once charged, the 20 MΩ resistor, which is required to retain the last-number dialed memory, will keep the capacitor charged. Partial muting can be achieved by directly connecting the N-channel open-drain mute output of the pulse dialer to the RCV in pin on the speech circuit. A fully muted pulse dialer design necessitates the use of a shunt-mode dialer, such as the TP50981A or TP50985A.
The TP5700 and TP5710 integrated circuits are designed to simplify the construction of pulse-dialing telephones by minimizing the number of external components required. By leveraging the VREG1 output, these circuits can power a TP50982A low-voltage pulse dialer directly, bypassing the need for a traditional current source. This configuration is particularly advantageous in reducing overall circuit complexity and enhancing reliability.
The use of a blocking diode is critical in this setup, as it prevents reverse current flow that could potentially damage the pulse dialer. The selection of a Schottky diode is recommended due to its low forward voltage drop, which is essential to ensure that the pulse dialer receives adequate voltage even when VREG1 operates in a nonregulated mode. In conditions where the loop current is 20 mA, the output voltage may decrease to 2 V, making the choice of the diode crucial for maintaining functionality.
A 100 µF decoupling capacitor is incorporated into the design to stabilize the supply voltage during dialing operations. Upon initial connection to the telephone line, this capacitor requires about one second to charge, ensuring that the pulse dialer operates correctly. Once charged, the capacitor is kept at the necessary voltage level by a 20 MΩ resistor, which serves to retain the last-number dialed memory, thereby enhancing user experience by allowing quick redialing.
For muting functionality, the design permits partial muting by connecting the N-channel open-drain mute output of the pulse dialer to the RCV in pin of the speech circuit. This connection allows for effective muting of the dialing sound during operation. For applications requiring complete muting, the integration of a shunt-mode dialer, such as the TP50981A or TP50985A, is recommended to ensure that all dialing sounds are fully suppressed, providing a quieter user experience. This comprehensive approach to pulse-dialing telephone design illustrates the efficiency and effectiveness of the TP5700 and TP5710 circuits in modern telecommunication applications.The TP5700 or TP5710 can reduce the number of components required to build a pulse-dialing telephone, as shown. The usual current source can be eliminated by using the VREGl output to power a TP50982A low-voltage (1.
7 V) pulse dialer via a blocking diode. A low forward-voltage drop diode such as a Schottky type is necessary because VREGl is used in its nonregulated mode and its output voltage might fall to 2 V on a 20-mA loop. A 100-I"F decoupling capacitor is required to hold up the pulse dialer supply voltage during dialing. This capacitor will take about one second to charge up when the telephone is first connected to the line, but thereafter, the 20-MO resistor, required to retain the last-number dialed memory, will keep this capacitor charged.
Partial muting is obtained by directly connecting the N -channel opendrain mute output of the pulse dialer to the RCV in pin on the speech circuit. A fully muted pulse dialer design requires the use of a shunt-mode dialer, such as the TP50981A or TP50985A.
🔗 External reference
The TP5700 and TP5710 integrated circuits are designed to simplify the construction of pulse-dialing telephones by minimizing the number of external components required. By leveraging the VREG1 output, these circuits can power a TP50982A low-voltage pulse dialer directly, bypassing the need for a traditional current source. This configuration is particularly advantageous in reducing overall circuit complexity and enhancing reliability.
The use of a blocking diode is critical in this setup, as it prevents reverse current flow that could potentially damage the pulse dialer. The selection of a Schottky diode is recommended due to its low forward voltage drop, which is essential to ensure that the pulse dialer receives adequate voltage even when VREG1 operates in a nonregulated mode. In conditions where the loop current is 20 mA, the output voltage may decrease to 2 V, making the choice of the diode crucial for maintaining functionality.
A 100 µF decoupling capacitor is incorporated into the design to stabilize the supply voltage during dialing operations. Upon initial connection to the telephone line, this capacitor requires about one second to charge, ensuring that the pulse dialer operates correctly. Once charged, the capacitor is kept at the necessary voltage level by a 20 MΩ resistor, which serves to retain the last-number dialed memory, thereby enhancing user experience by allowing quick redialing.
For muting functionality, the design permits partial muting by connecting the N-channel open-drain mute output of the pulse dialer to the RCV in pin of the speech circuit. This connection allows for effective muting of the dialing sound during operation. For applications requiring complete muting, the integration of a shunt-mode dialer, such as the TP50981A or TP50985A, is recommended to ensure that all dialing sounds are fully suppressed, providing a quieter user experience. This comprehensive approach to pulse-dialing telephone design illustrates the efficiency and effectiveness of the TP5700 and TP5710 circuits in modern telecommunication applications.The TP5700 or TP5710 can reduce the number of components required to build a pulse-dialing telephone, as shown. The usual current source can be eliminated by using the VREGl output to power a TP50982A low-voltage (1.
7 V) pulse dialer via a blocking diode. A low forward-voltage drop diode such as a Schottky type is necessary because VREGl is used in its nonregulated mode and its output voltage might fall to 2 V on a 20-mA loop. A 100-I"F decoupling capacitor is required to hold up the pulse dialer supply voltage during dialing. This capacitor will take about one second to charge up when the telephone is first connected to the line, but thereafter, the 20-MO resistor, required to retain the last-number dialed memory, will keep this capacitor charged.
Partial muting is obtained by directly connecting the N -channel opendrain mute output of the pulse dialer to the RCV in pin on the speech circuit. A fully muted pulse dialer design requires the use of a shunt-mode dialer, such as the TP50981A or TP50985A.
🔗 External reference