Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 18
Line output circuit description
To enable enough emf to be generated by the line stage in this 59/66cm chassis, it is necessary to provide
a high HT voltage of 150VDC. This is fed into the line output transformer, T601, at pin 2 as shown in the
diagram below, note that there is no feed resistor into the transformer.
Figure 17 : Line Output Circuit
From the collector of the drive transistor, Q601, the line drive signal is fed into the base of Q602. This is
a square wave signal that turns on for 26uS and off for 38uS.
When Q602 is turned on, current will start to flow in the primary winding of T601 ( pins 2 to 3 ), this is point
t1 in the current waveform shown on the next page. This current flow will continue to increase until Q602
is turned off some 26uS later, at which point the current in the primary winding will start to decay, point
t2. The time taken for this current to decay is determined by the time constant of the primary winding and
C608 ( for the purpose of this explanation the bottom end of C608 and D603 can be considered to be
ground and C610/D604 ignored ). This charging current is supplied from the HT reservoir capacitor,
C720, which will effectively connect pin 2 of the transformer to ground ( for ac purposes ).
At the point where the current starts to drive negative, t3, the clamp diode, D603 will start to conduct and
thus stops the current going negative. The result of this is that C608 becomes a DC voltage source, which
will discharge via the primary winding and C720, i.e. the current will start to increase again until it reaches
point t4. This is were there is no energy left in C608 and the primary winding. At this point, 38uS after
Q602 has turned off, Q602 will be turned on again and the cycle repeats.