
Theory of Operation
Detailed Circuit Description
4
4-29
Op amp U606B senses the -400V supply and forces the autobias to the minimum bias
condition when the
±
400V supplies are turned off. Transistor Q606 forces the minimum
bias condition when the window comparator is activated.
High Voltage Amplifier Feedback
4-51.
Feedback for the High Voltage Amplifier is provided by R606, R607, and R608 from the
output signal MVOUT. This means that the high voltage signal transformers are driven
open loop by the High Voltage Amplifier. Feedback for amplitude leveling is provided
on the High Voltage Sense Assembly (A6).
The turns ratio of the hf transformer is less than the other transformers. Resistor R608
compensates for the difference in turns ratio so the overall gain of the High Voltage
Amplifier, plus the signal transformers, is -100 independent of frequency range. Resistor
R608 is switched in by K601 only in standby mode and in hf operation.
Signal Transformers
4-52.
Three transformers cover the four frequency ranges as shown in Table 4-2. The lf
transformer is a C-core. The mf and hf transformers are toroids. All three signal
transformers are located in the transformer box on the left side of the instrument when
viewed from the front.
Table 4-2. Signal Transformer Usage
FREQUENCY
RANGE
TRANSFORMER
TURNS RATIO
HIGH VOLTAGE
AMPLIFIER
OUTPUT(MVOUT)
HIGH VOLTAGE
TRANSFORMER
OUTPUT
40 Hz to 120 Hz
LF (Series)
1:5.5
40 to 200V
220 to 1100V
120 Hz to 3.4 kHz
LF (Parallel)
1:5.5
40 to 200V
220 to 1100V
3.4 kHz to 30 kHz
MF
1:5.5
40 to 200V
220 to 1100V
30 kHz to 100 kHz
H F
1:4.5
49 to 167V
220 to 750V
Four control lines: HFPD, MFPD, LFPD, and VLFPD, control the frequency ranges. The
control lines are generated on the High Voltage Sense assembly. These lines control
relays K601 to K604, which direct the High Voltage Amplifier output to the primary of
the appropriate transformer and switch in feedback resistor R608 to compensate for the
hf transformer turns ratio. Relay K604 switches the primary windings of the lf
transformer into a series connected configuration for 40 to 120 Hz operation, and into a
parallel connected configuration for 120 Hz to 3.5 kHz operation.
Relays on the Interconnect assembly (A1) switch the secondary transformer windings.
These Interconnect relays are driven by the same control lines as the High Voltage
Amplifier assembly. These lines originate from latch/driver U157 on the High Voltage
Sense assembly (A6).
Temperature Monitoring
4-53.
The temperature monitoring circuit estimates the junction temperature of the power
MOSFETs by measuring the temperature of one of the high voltage heat sinks and
adding a calculated temperature rise from heat sink to junction, based on the current in
the +400V supply.
The heat sink temperature is sensed with a stud-mounted thermistor mounted into the P-
channel heat sink #2 via connector J603. Its negative temperature coefficient is linearized
Summary of Contents for 5725A
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Page 133: ...List of Replaceable Parts 8 8 7 aq25f tif Figure 8 1 Final Assembly cont...
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Page 141: ...List of Replaceable Parts 8 8 15 5725A 1611 aq36f eps Figure 8 2 A1 Interconnect PCA...
Page 145: ...List of Replaceable Parts 8 8 19 5725A 1650 aq37f eps Figure 8 3 A2 Current Amplifier PCA...
Page 149: ...List of Replaceable Parts 8 8 23 5725A 1661 aq38f eps Figure 8 4 A3 High Voltage Amplifier PCA...
Page 153: ...List of Replaceable Parts 8 8 27 5725A 1631 aq39f eps Figure 8 5 A4 Power Supply PCA...
Page 155: ...List of Replaceable Parts 8 8 29 5725A 1650 aq40f eps Figure 8 6 A5 Digital PCA...
Page 159: ...List of Replaceable Parts 8 8 33 5725A 1601 aq41f eps Figure 8 7 A6 High Voltage Sense PCA...
Page 161: ...List of Replaceable Parts 8 8 35 aq32f tif Figure 8 8 A12 Transformer Enclosure Assembly...
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Page 169: ...Schematic Diagrams 9 3 9 Figure 9 1 A1 Interconnect PCA 5725A 1611 aq48f eps...
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Page 171: ...Schematic Diagrams 9 5 9 Figure 9 1 A1 Interconnect PCA cont...
Page 172: ...5725A Instruction Manual 9 6 Figure 9 2 A2 Current Amplifier PCA 5725A 1650 aq52f eps...
Page 173: ...Schematic Diagrams 9 7 9 Figure 9 2 A2 Current Amplifier PCA cont...
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Page 176: ...5725A Instruction Manual 9 10 Figure 9 3 A3 High Voltage Amplifier PCA 5725A 1661 aq56f eps...
Page 177: ...Schematic Diagrams 9 11 9 Figure 9 3 A3 High Voltage Amplifier PCA cont...
Page 178: ...5725A Instruction Manual 9 12 Figure 9 3 A3 High Voltage Amplifier PCA cont...
Page 179: ...Schematic Diagrams 9 13 9 Figure 9 4 A4 Power Supply PCA 5725A 1631 aq59f eps...
Page 180: ...5725A Instruction Manual 9 14 Figure 9 4 A4 Power Supply PCA cont...
Page 181: ...Schematic Diagrams 9 15 9 Figure 9 4 A4 Power Supply PCA cont...
Page 183: ...Schematic Diagrams 9 17 9 Figure 9 5 A5 Digital PCA cont...
Page 185: ...Schematic Diagrams 9 19 9 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 186: ...5725A Instruction Manual 9 20 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 187: ...Schematic Diagrams 9 21 9 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 188: ...5725A Instruction Manual 9 22 Figure 9 6 A6 High Voltage Sense PCA cont...
Page 189: ...Schematic Diagrams 9 9 23 aq45f eps Figure 9 7 A12 Transformer Enclosure Assembly...
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