Abstract: A dialer circuit equipped with built-in dialer memories for auto-redial or abbreviated-dial telephone communication and operable to send out a DTMF signal or a pulse signal to a telephone circuit based on a key input signal. A battery voltage is supplied to the dialer memories from a back-up battery, while a supply voltage is supplied to the other function circuits from a telephone circuit line. A voltage level converter means is located between the dialer memories and the other function circuits and eliminates production of through current resulting from the difference between the back-up battery voltage and the line voltage.

Abstract: A dialer circuit comprising a microcomputer for controlling the dialing of a telephone. This dialer circuit is capable of storing a telephone number and transmitting a signal concerning this telephone number to a telephone circuit according to a given command. The dialer circuit is equipped with a means for detecting the ON state or the OFF state of a hook switch; upon detection of the state of the hook switch, the dialer circuit performs a resetting of the entire system except a memory in which the telephone number is stored. The result is that when operating the hook switch, it is possible to automatically reset only the system, thus effectively preventing any reckless driving of the system.

Abstract: A side tone preventive circuit for telephones which prevents the output of the transmitter on the speaker's side from being transmitted to the receiver on the same side. The balance of the impedance bridge in a bridge circuit for separating a transmission signal and a reception signal is automatically adjusted in accordance with the circuit impedance at the location at which a telephone is installed. An impedance measuring circuit measures the impedance of the telephone circuit, and a balance adjustment circuit the impedance of which is adjustable is provided in the bridge circuit. The impedance of the telephone circuit is measured at the time of installation of a telephone, and the impedance of the balance adjustment circuit is adjusted in correspondence with the result of measurement. Thus, the impedance balance of the bridge circuit is adjusted in correspondence with the circuit impedance, thereby effectively preventing a side tone.

Abstract: This disclosure dipicts a circuit for power supply comprising: a first constant-output-current circuit (16) for generating a constant-current-output in response to a non-inverted output current from a comparator (4) for comparing an input signal voltage with a reference voltage; and a second constant-output-current circuit (18) for flowing a superfluous current to a lower potential side in response to an inverted output current from the comparator (4), the second constant-output-current circuit (18) including a plurality of NPN type transistors.