Tektronix 2445, Инструкция по эксплуатации

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Theory o f Operation—2445 Service
As the Prereguiator power supply turns on, capacitor
C l034 charges from the +5-V reference level toward
ground potential through R1034 and R1037. As it does,
the voltage at pin 4 (one input o f Dead-Time Comparator
U1) w ill pass through the positive-peak value of the t r i­
angular waveform on the other input of the Dead-Time
Comparator. The comparator w ill then begin outputting
narrow pulses that become progressively wider as the
voltage on pin 4 settles to zero volts. These pulses drive
switching transistor Q1050, and their slow progression from
narrow to wide causes the various secondary supplies to
gradually build up to their final operating levels. The slow
buildup prevents a turn-on current surge that would cause
the current-lim it circuitry to shut down the supply.
During the startup, capacitor Cl 072 acts as a substantia!
load, and a relatively large current w ill flow in the windings
o f T1050 for the first few cycles of Preregulator switching.
These strong current pulses ensure that storage capacitor
C l066 becomes charged sufficiently to start the Inverter
Drive circuit. Once the Inverter Drive stage is operating,
the normal switching current through T1050 maintains
the required charge on C1066. (The Inverter Drive power
supply is discussed later in this description.)
Dead-Time Comparator U1 is referenced at approxi­
mately 0.1 V above the ground level at pin 4 (established
when C1034 becomes fu lly charged) and outputs a narrow.
3-42
Figure 3-12. Simplified schematic of control network.