Television receiver isolated input for external equipment - uses line transformer as isolating transformer for receiver circuits

摘要

The television receiver isolated input circuit allows the safe connection of auxiliary units such as video tape recorders whose chassis must not normally be connected with that of the receiver. The mains supply (4) feeds only a part of the receiver circuits i.e. stabilisation (13) and line deflection circuit comprising a phase comparator (14), oscillator (15) driver and output stages (16) (1). The output transistor is connected to the primary of the line transformer (2). Synchronisation is via a transistor and isolation transformer (18). The remaining DC supplies for the receiver circuits are taken from the secondary of the line transformer (8) and rectifiers (21-24). these serve the video and I.F. amplifiers, frame deflection, video output and audio circuits. The external auxiliary equipment (11) can then be connected to any of these stages in safety.