| 摘要 |
<p>A protection circuit for a telephone having a two wire subscriber line (L1, L2) and an earth line (E) comprises a single surge protection device (2) connected between a bridge rectifier polarity-guard (D1, D2, D3, D4) which is across the subscriber line and the remainder of the telephone circuitry (1, 4) which is connected to the output of the polarity guard. Three diodes (D5, D6, D7) are used to interconnect the earth line and the pair of output lines from the polarity guard to the protection device in such a way as to prevent surges from being fed to the remainder of the telephone circuit, the surge paths including one or two arms of the polarity guard.</p> |
