Tektronix 323, Instruction Manual

Page: 56 / 170

Circuit Description— Type 3 2 3
ing the presence of a charging pulse. See Fig. 3-10 (H)
and (I).
During TRICKLE CHARGE operation, R633 provides cur­
rent to R630. This increases the voltage at the base of
Q634 and decreases the current through R639. With less
drive, Q621 provides less drive current to Q620, which de­
creases the drive current to Q617. The current that Q617
delivers to the battery is thereby reduced to a trickle charge
rate. See Fig. 3-11 (A).
When the Power Pack is being charged and the Oscil­
loscope POWER switch is turned on, the base of Q634 is
driven negative between charging current pulses.
This
occurs because the battery reverses current flow through
R615 while it supplies the Oscilloscope with power. The
net result is that the average charge on C636 tends to de­
crease, providing more drive to Q634. This permits more
current to flow through Q617, keeping the average charge
on C636 at its previous value by supplying the battery
with additional current to make up for that being drained
between half cycles. See Fig. 3-11 (B).
Fig. 3 -1 1 . V o lta g e across R615 d u rin g (A ) TRICKLE CHG o p eratio n
w ith Oscilloscope OFF, and (B ) FULL CHG o p eratio n w ith O scil­
loscope O N and INTENSITY a t maximum brightness setting.