TV receiver synchronisation circuit for line deflection - has control voltage path coupled to fixed DC voltage via switch, on failure of line sync. pulses, by generated switching voltage

摘要

The synchronising circuit has a phase control stage (4), fed from line synchronising pulses and an oscillator (6). There is a control voltage path with a low pass filter (5) between the phase control stage and the oscillator. The control voltage path is coupled to a fixed adjustable d.c. voltage (Ubc) via a switch (9). A switching voltage (11) is generated on failure of the line synchronising pulses (Z). The d.c. voltage actuates the control of the VCO to the rated line frequency. The switching voltage is pref. derived from a mute circuit, detecting the failure of the line synchronising pulses. The switching voltage may be applied to a base of a transistor, whose output circuit contains a resistance network (R1, P1, R2). ADVANTAGE - No frequency deviation of the line oscillator, on synchronising signal defect, without complicated circuitry.