Tektronix 7834

Theory of Operation-7834
Capacitor C1243 charges
through CR1244 to the peak volt-
age across the primary of
T1310 . If this voltage exceeds a
safe level, VR1246 conducts to
trigger SCR 01248 into its
forward-conduction state .
Capacitor C1243 then discharges
through C1249,
R1249, R1248, and 01248 into the base-
emitter junction of
01246 . 01246 turns on, short-circuits
the base-drive
winding of T1230 and stops the Inverter
switching action
. Since CR1249 becomes forward biased
when
01248 is triggered on, C1242 in the Start
Network is
prevented
from charging to the breakdown voltage
of
CR1238, thus preventing the Inverter from starting
. Tran-
sistors 01248 and 01246 continue to
conduct until the dis-
charge current of C1243
through R 1248 drops below the
3- 54
holding current of 01248 . After 01248
returns to its
forward-blocking state, CR1249
continues
to
inhibit the
Inverter Start Network while C1243
charges through
R1247 and R1210 in the Inverter
Start Network . When the
voltage on C1243 is sufficient to
fire CR1238, the Inverter
will start .
Inverter Control
The Inverter
Control stage, made up of
primarily U1275,
provides
pre-regulation and fault protection
functions . For
pre-regulation purposes, U1275
varies the hold-off time
(Tb, in Fig . 3-4113) of the Inverter
switching transistors .
T1310
(1676-16) 1988-66
Figure 3-41 . (A) Representation of Inverter stage . Idealized
waveforms of (B) total inverter current, It, (C) voltage of
CR1234 and CR1241,
and
(D) voltage across primary .