Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 22
top of this capacitor will be in excess of 160V peak. The start point of the two waveforms on the cathode
of D507 ( 60V peak ) and the anode ( 160V peak ) will occur at the same time, but the cathode will turn off
sooner ( determined by the modulating input signal of Q506 ). This being the case, the signal on the anode
of D507 will be modulated with amplitude variations on each line pulse, and these variations will vary
depending upon the point at which they occur in the parabola. The resultant waveform on the top of C610
will be a line pulse signal, modulated with the controlling parabola. This now meets our above criteria of
changing the charge on C610 to vary the width of the picture during the frame scan.
Figure 23 : Idealised East/west Pulse Waveforms
As the east/west output circuit only requires power during the pulse part of its operation, it is possible to
reduce the power dissipated by the circuit by using the circuit based around Q507. At initial start up, no
voltage will be present in the east/west output circuit ( because the line has not started up ), so the +18V
supply from the chopper stage is used to charge up C520. When the collector of Q506 goes high, it will
turn on Q507 so that voltage can be supplied from C520. As the line stage starts up, the charge on C520
needs to be replenished quickly and this is done from the line output transformer itself ( pin 6 ) via D516
and D519. D517 and D518 along with the +18V supply ensure that the voltage on the collector of Q507
does not exceed fifty four volts at any time.
D509 protects the collector emitter junction of Q507 should the pulses on the top of C610 become
excessive.
A feed back circuit comprising of D508, R529, C517 and R523 provides negative feed back from the output
of the driver stage. This is to prevent the circuit from oscillating, drawing too much current and causing
damage to Q506 and Q507.