Patent GB-1483363-A (GB)
Title: Circuit for incorporation into a vertical deflection signal generator for a television
IPC: H03K4/69
Filed: 1974-07-15
Abstract: 1483363 Vertical time base circuits; oscillators SGS-ATES COMPONENTI ELETTRONICI SpA 15 July 1974 [13 July 1973] 31219/74 Heading H3T Vertical deflection apparatus comprises an integrated circuit including an oscillator supplying pulses preferably of short duration relative to the flyback-time and having external timing components, a synchronizing circuit for the oscillator adapted to receive pulses whether they are positive or negative, a ramp generator controlled by the oscillator pulses and having external components for controlling slope, amplitude and corrections of parabolic or exponential type and a power amplifier for supplying the trace current and controlled by the ramp generator during the sweep, the flyback being initiated by an oscillator pulse and maintained by the flyback current there being provided protection circuits for a driver stage for the power amplifier and for one of the series connected output stages. The oscillator section 0 + 0 1  comprises a comparator amplifier Q12, Q9, Q10, Q13, Q19 and Q20 receiving at the base of Q12 a ramp generated by charging a capacitor C101 (lower left) through resistors 105, 106 via terminal 12 from a stabilized voltage source derived from Q26. When the ramp voltage reaches a reference voltage at the right hand base derived from point F the conductive condition of the comparator changes over rendering a transistor Q31 conducting. This in turn renders both a transistor Q18 conducting rapidly to discharge the capacitor and a transistor Q21 which lowers the reference voltage at point F so that the capacitor discharges to this voltage whereupon the conductive condition of the transistors is restored and a ramp recommences. Synchronizing is effected by pulses at terminal 8 (lower left), whether they be positive or negative, by the circuit designated 0 2 . Transistors Q14 and Q23 lower the potential at point H and thus trigger the flyback. Pulses occurring during the flyback have no effect on the circuit since that part of the reference voltage supply is already shorted by transistor Q21. The ramp generator comprises external capacitors C102 and C103 (lower left) which are charged through terminal 7 from a current mirror comprising transistors Q6, Q7, Q8, the input to the current mirror being controlled via terminal 7 by resistors R101 and R102. Resistors R102 control the slope and amplitude. A resistor 104 (lower left) which controls the charging current to C102 provides exponential correction and resistor R107 controls parabolic correction. The output stage PA 1  receives its input from terminal 1 (lower centre) via capacitor C104, resistor 109, the terminal 10 and a pre-amplifier stage comprising transistors Q41, Q36, Q37 and Q42. The output from this amplifier is applied to transistor Q46 which, via transistor Q45, drives the upper stages Q52 and Q55 and lower stages Q38 and Q56 of a quasi-complementary output amplifier connected via terminal 4 to deflection coils Vv. Negative D.C. feedback is provided from the lower end of the deflection coils via resistors R111 and R110 to the base of transistor Q41 of the pre-amplifier stage where it is compared with a reference voltage applied from a stabilized source to the base of the right hand transistor Q42. A.C. feedback is derived from the lower end of a capacitor C106 connected in series with the deflection coils, the feedback being passed via a resistor R113 to the input of the amplifier where it is compared with the ramp input voltage applied to the same transistor via R109. The flyback is initiated by a pulse from the pulse generator derived from the output transistor Q31 (centre left) of the generator and delivered via a diode transistor Q60 (lower centre) to the base of a transistor Q47 which switches off the output transistor Q56. The voltage at the upper end of the deflection coils rises rapidly carrying with it the emitter of a multi-collector transistor Q39 which thus switches on. The upper collector acts via transistor Q47 to maintain the output transistor Q56 off after the end of the pulse from the pulse generator and until transistor Q39 becomes non-conducting again as a result of the reduction of the flyback voltage across the coils at the end of the flyback. The middle collector of transistor Q39 acts via Q49 to cut off Q51 so that flyback current flowing through diode D53 has a path through diode D54 which the cut off of transistor Q51 allows to conduct. During the second part of the flyback the flyback current reverses and accordingly the diode D54 is shunted by a reversely connected transistor Q57 which is rendered conducting during the flyback by the lowest emitter of transistor Q39. Protection is provided for the pre-driver transistor Q46 (lower centre) during the flyback when the voltage at terminal 5 rises to twice the supply voltage, the protection being effected by a transistor Q45 in series with Q46 which is normally held on by a current mirror circuit Q32, Q33 but which, when the rising voltage at the upper terminal of the deflection coil during the flyback renders the base-emitter path of Q38 conducting, comes out of saturation and thus shields transistor Q46 from this high voltage. Further protection for Q46 during the flyback is effected by a transistor Q48 which is rendered conducting during the flyback by the oscillator pulse and so earths the base of Q46. Protection of output transistor Q56 during the flyback is effected by the application of the cut-off pulse to its base as described above. The necessary bias between the bases of the input transistors Q52 and Q38 of the output stage is provided by a transistor combination Q40, Q58, Q59.