A26 Blanking Assembly, 05340-60037; Power Supplies - HP 5340A Operating And Service Manual

4-265. A26 BLANKING ASSEMBLY, 05340-60037

4-266. The Blanking Assembly (Figure 8-32) is controlled by logic circuits on A25 and controls
the +175V supply to the display tube(s) that require blanking thus suppressing insignificant
zeroes. For example, with a TTL low on the emitter of Q5, Q5 conducts to turn on QlO which in
turn supplies +175V to the display tube. Similarly the other four tubes are controlled.

4-267. POWER SUPPLIES

4-268. The power supplies include Time Base Power Supply A33 (part of Option OOl), +5 Volt
Regulator A32, +15 Volt Regulator A29, -15 Volt and +175 Volt Regulator A28, and
lator A31. Since the power supplies use similar regulator IC's and circuit arrangements, the
simplest will be described first and the applicable circuit theory will suffice for the remaining
regulator units.
4-269. A33 Time Base Power Supply Assembly, 05340-60039, (Part of Option 001)
4-270. The Time Base Power Supply (Figure 8-35) provides +21 volts unregulated a t approxi-
mately 100 mA and +I1 volts regulated power
The +21 volt supply consists of full-wave rectifier A33CR1, A33CR2, and A33Cl. The regulated
volt supply is made up of A33CR3, A33CR4, A33C2, A33U1, and associated circuitry.
4-271. The regulator consists of a current source, voltage reference amplifier, error amplifier,
current limiter, and series pass transistor. The current source, Zener diode, and voltage reference
amplifier provide a constant 7.2 volt reference output (Vref) for the noninverting input of the
difference amplifier. Th'e inverting input of the difference amplifier senses the power supply
output voltage through vOltage divider A33R7, A33R8, and A33R9 (see schematic for A33).
voltage decreases, the voldage
drives the error amplifi'er output more positive which biases the series pass transistor to decrease
its impedance. When the impedance of the series pass transistor decreases, the output voltage
tends to increase to regulate the output.
at approximately 25 mA to optional oscillator A18.
at A33R8
and the inverting input
Model 5340A
Theory of Operation
-
Volt Regu-
(Ul 2)
pin also decreases. This
4-51