Tektronix FG 5010 User Manual

7
П
n
C
to conduct . This is immediately reinforced by Q1341 , so the
circuit
quickly changes
state . The
collector of
Q1341 pulls
positive on pin 1 , establishing that point at the upper switch
ing
potential .
Now , the two
Schmitt
trigger
transistors have
switched states , and so have Q1341 and Q1342 . This ac
tion reverses the condition of the Transistor Bridge , so it is
now operating in the up - current mode , and the triangle wave
is
rising .
If
up or down current
is applied , the
current flow through
R1344 - R1343 changes , and the voltage at pin 1 rises or
falls commensurate to the change in current . The down
shrink current is applied all the time ; thus , when Q1341 is
conducting
to apply the
up -
shrink current , that
current
is
stronger
in order
to
cancel the
down -
shrink
current . The
shrink
-
current principle is
discussed in
more detail
later in
this
section
.
Transistor Q1233 receives the SCHFEAT signal from
Diagram 14. This signal is low whenever triggered , burst , or
gated modes are selected , and the starting point is above
85 ° on the triangle . The current provides the necessary cur
rent boost to raise the switching potential of the Schmitt
trigger above the level that noise spikes might cause the
loop
to free
- run .
The
output of the
Level
Detector
is
signal is
applied
to the
Bridge
Buffer
.
square
wave .
The
Bridge
Buffer
The
Bridge Buffer circuit
receives
the differential
- drive
squarewave
output
from the
Level
Detector
, and
applies
it
to the HF Square Wave Buffer and the Transistor Bridge .
The buffer consists of unity - gain amplifiers Q1440 and
Q1441 . These two transistors , unlike the others in the
switching circuits , are kept operating in the linear region by
the bias set by CR1330 and CR1440 . The current through
R1446 and R1445 , the buffer emitter resistors , is set by
Schottky diode
CR1440
. Compensation
for the
V
drop
of
Q1440 and Q1441 is provided by CR1330 .
BE
The Bridge Buffer operates as a signal splitter , in that the
emitter and collector excursions are essentially equal . Drive
current from these elements control the Transistor Bridge .
Differential drive from the buffer is also provided to the
HF Square Wave Buffer . Zener diode VR1450 reduces pow
er dissipation through the buffer stage .
Theory
of
Operation - FG
5010
Transistor
Bridge
UP
This circuit switches the charge currents in and out of the
Loop Capacitor circuit . Charge currents up and IDN are ap
plied to the emitters of differential pairs Q1432 and Q1430
( up ) , and to Q1343 and Q1340 ( DN ) . These pairs are
switched asymmetrically , so only one of the two currents is
connected to the capacitor circuit at a time .
Switching of the conduction states of the bridge is con
trolled by the Bridge Buffer circuit . This circuit , upon receiv
ing
a change
in level from the
Level
Detector , drives one
section of the bridge from saturation to cutoff , and the other
section vice - versa .
HF
Square
Wave
Buffer
This circuit translates the signals from the Bridge Buffer
into ECL levels , which are applied to the Squarewave Selec
tor circuits depicted on Diagram 14 .
Differential drive from the Bridge Buffer is applied to the
base
inputs of
transistor array
U1315B
. This
is a differential
pair
that is
supplied
by a
current sink .
Zener
diode VR1351
sets the operating point and standing current of the stage .
Triangle
Selector
Through control
of relays K1131
and K1231
, the CPU
selects either the low - frequency triangle wave from the
Loop 2 circuits or the high - frequency triangle wave from the
Triangle Buffer ,
one of which
is then applied
to the Sine
Shaper circuits . The second section of K1231 connects a
75 termination resistance to the output of the Triangle
Buffer , when the low - frequency triangles are used , to main
tain a constant load impedance on the circuit .
13
SHRINK
CONTROL
Introduction
The Shrink Control consists of five major circuits : Shrink
Control
Amplifier , Up
Shrink
Current Source ,
Down
Shrink
Current
Source ,
Relay Drivers , and
the Digital Control
Cir
cuits . The last circuit is discussed in the Digital Control sec
tion at the beginning of the Loop 1 description .
Refer to Fig . 4-6 , which is a simplified diagram of the
Shrink Control Amplifier and the two current sources . The
4-13

Tektronix FG 5010 Specifications

General

Brand	Tektronix
Model	FG 5010
Category	Portable Generator
Language	English