Tektronix 7140 Instruction Manual page 114

Theory of Operation-7104
3- 68
T1310
X1676-16) 2314-21
Figure 3-24 . (A) Representation of Inverter stage. Idealized waveforms of (B) total inverter current, I (C) voltage of CR1234 and
CR1241, and (D) voltage across primary.
Pin 15 is the voltage sensing (E Sense) poinf of the Pre-
current changes direction . The pulse width holds off the
Regulator circuit. Zero volts at pin 15 indicates proper
Inverter by turning on transistor Q1252 through pin 9 of
regulation . Zener diode VR1288 provides a stable reference
U1275, thus shorting out the base drive to 01234 and
voltage for the sensing-divider resistors R1292, R1293,
01240. The pulse width, and therefore hold-off, is con-
R1295, R1286 and R1287. Resistor R1293 in this divider
trolled by a ramp at pin 12 . If the voltage at the E Sense
adjusts the ratio of the divider to adjust the output of the
input, pin 15, is too low, the ramp is not allowed to rise very
+108 volt supply . Outputs of the other supplies are then set
high and the pulse width and hold-off are short. As the E
by the turns ratio of T1310.
Sense voltage rises, the ramp is allowed to rise to a higher
voltage level, increasing 'the hold-off time .
Integrated circuit U1 1 275 regulates the Inverter by varying
the hold-off time of the switching transistors, 01234 and
Fault Protection
01240. A variable pulse-width monostable multivibrator in The fault-protection portions of U1275 provide protection
U1275 is triggered at pins 10 and 11 wheneverthe Inverter
for the power-supply components from damage due to
ADD NOV 1985