Telephone ringer isolator
US4021617A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 12, 1976 |
| Grant date | May 3, 1977 |
| Priority date | — |
| Expiry date | Jan 12, 1996 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M19/02
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A telephone ringer isolator for isolating ringers and extending ringing range on a multiparty telephone line or for range extension only on single party lines is disclosed. The circuit includes a detector circuit for detecting the direct current superimposed on an alternating current ringing signal. A pair of biasing circuits for transistors are enabled by a properly poled ringing signal appearing between tip and ring conductors. When the transistors are enabled, a capacitor is charged to trigger a silicon-controlled rectifier. When thus fired, the silicon-controlled rectifier enables a diode bridge gate to connect the ringer between one side of the telephone circuit and ground potential. Isolation between the input and output terminals is provided by the high collector resistance of the gating transistors.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.