Specifications

CA1 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 58
being a pulse which is used for the flyback generation.
At the collector of Q505 is a waveform with a positive going flyback pulse, effectively this device is
connected as a class A output with R512, D502, R501, R503 and R508 as its collector load. This
waveform is fed directly to the base of Q504 the first of the two output transistors. This is a PNP transistor
connected as an emitter follower providing unity voltage gain and high ( Hfe ) current gain.
Further up the ladder on the Collector load of Q505 ( junction of R503 & R501 ) is the feed to the base
of the second output transistor Q502. Again this device is connected as an emitter follower providing the
necessary current gain to fulfil the push pull action of this output stage. The two emitters of these devices
are connected together by R504 and R505 two fusible resistors of low values which provide crossover
cushioning and the necessary fusing action should something fail in the output.
Q509 is used for flyback boost switching. During the scanning period of the waveform Q503 and therefore
Q510 are turned on, this results in Q509 being turned off.
Whilst this situation prevails the capacitors Q504 and 501 are able to charge from the +10V rail being
connected at the negative plates to the -10V rail via D509 and Q510 ( presently saturated ). When the
waveform completes scan and enters into the positive going flyback pulse ( at Q505 ) the current through
the collector load of Q505 falls dramatically, as a result of this the voltage across R503 falls turning off
Q503 and Q510, the base of Q509 is now pulled up by R502 this saturates Q509 effectively connecting
the lower plate of C514 to the +10V rail. As these two capacitors are already charged to 20V this enables
the cathode of D501 to rise momentarily to +30v ( +10V and +20V ), this enables a large flyback pulse to
be fed to the scan coils, at the end of which the capacitors are discharged.
Frame Scanning Coils
Figure 51 : CA1 Vertical Scanning Coils Circuit