TRANSMISSION AMPLIFIER FOR TELEPHONE SET THAT DOES NOT HAVE ITS OWN POWER SUPPLY

摘要

PROBLEM TO BE SOLVED: To supply constant current to LED and to hold constant illuminance by providing a means for guiding current flowing in LED for a sound transmission amplifier. SOLUTION: The anode of LED 1 is connected to the positive terminal A of a telephone line and a cathode is connected to the sound transmission amplifier 11. They are connected in series. The Sound transmission amplifier 11 is provided with a means for deciding a ratio between line current and line voltage and an NPN transistor T3 as a means for guiding current flowing in LED 1 when voltage between the terminals A and B becomes lower than a previously decided value. The transistor T3 is controlled by the sound transmission amplifier 11 and it shunts LED 1 when the voltage of the telephone line becomes lower than the previously decide value.