A speech amplifier associated with a LED

摘要

The invention relates to a transmit amplifier for a telephone set without self supply, comprising a LED (1) having an anode connected to a first positive terminal (A) of the telephone line and means for determining the ratio between the line current (IL) and the line voltage (VL). The LED (1) is supplied with a constant current and this current is derived when the voltage (VL) across the terminals (A, B) of the line becomes lower than a predetermined value (Vs1). $$