| 摘要 |
In using a transistorised microphone in telephone sets which is de-activated during dialling and is connected to the speech wires only after the dialling, the difficulty arises that, due to the different electronic components of a microphone of this type, a stable voltage condition of the type which prevails when a call is in progress is reached by this microphone only after a delay. At the beginning of the connection to the speech wires, the microphone concerned is still in a high-impedance state, which leads to an undesirable temporary excess voltage between the speech wires. To reduce this excess voltage or render it harmless, the invention proposes that the reversing pulse for the bistable changeover relay which initiates the connection of the microphone to the speech wires by de-energising this relay also acts on the electronic pulse contact in such a way that the latter transfers from the conductive to the blocked condition only when a stable voltage state has been established in the transistorised microphone, so that, up to this time in parallel with the temporarily higher-impedance microphone, a low-impedance current path is produced which effectively suppresses the aforementioned voltage increase.
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