Parallel phone blocker. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Thyristor parallel telephone blocker. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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Another version of the 1x2 parallel phone blocker is shown in the figure below.

When the subscriber of the first device picks up the phone, a line voltage of 1 V is applied to the anode of the thyristor VS 60. The voltage on the control electrode of the thyristor is less by the voltage drop across the zener diode VD 1. The thyristor opens, and TA 1 is connected to the line. If after that the second subscriber picks up the phone, a residual line voltage of 2-5 V will be applied to the thyristor VS15, which is less than the opening voltage of the zener diode VD3, and, accordingly, the thyristor VS2 remains locked. TA2 will be disabled until then. until the first party hangs up the handset. Diodes VD2 and VD4 are designed to pass the negative half-cycle of the AC voltage of the inductor call.

The disadvantage of the scheme is as follows: picking up the handset on one of the devices at the time when the second one is dialing, leads to dialing interference (phones are switched). The disadvantage is compensated by the simplicity of the circuit design and the possibility of placing circuit elements in a telephone socket.

Thyristor parallel telephone blocker

Schematic diagram of a parallel telephone blocker

Publication: cxem.net

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