Theory of Operation
Analog Section Detailed Circuit Description 2
2-51
2-92. Switch Matrix Operation
:
2
.
2V DC Range
Refer to Figure 2-11 for the following discussion. The dc 2.2V range circuit consists of
the dc 2.2V attenuator and a dc 2.2V range amplifier as outlined on sheet 3 of the Switch
Matrix schematic. This circuit contains a CA3096 transistor array IC (U19A-E),
transistor Q4, FETs Q12 and Q13, resistors R20, R23-R30, and R32, relays K1 and K2,
part of the resistor network 4R07, and a dc amplifier heated hybrid.
The resistor network is bonded to the hybrid and this entire assembly is called the 5700A-
4HR1 (HR1) on the schematic. Transistor Q3 drives the heater resistor on the hybrid. The
heater control circuit adjusts the base voltage of Q3 to deliver the correct power to the
heater resistor to maintain thermal control. Transistor Q8 protects the hybrid in case Q3
fails.
To produce the dc 2.2V range, the DAC assembly (A11) is set to the 11V range. DAC
OUT HI and DAC SENSE HI are connected to pin 10 of the resistor network by relay
K1, and DAC LO is connected to pin 9 by relay K2. The network divides the voltage by
five. The divided voltage from pin 8 is connected to the input (pin 11) of the dc amplifier
hybrid.
This temperature-controlled amplifier is used as a buffer amplifier. The output of the
buffer amplifier (pin 18) drives the 2.2V range high current output stage consisting of
U19, Q4, R25-R30, R32, and CR7-CR9. This circuit enables the 2.2V range to support
50 mA of current with current limiting. FETs Q12 and Q13 provide localized feedback
for the precision dc amplifier during unusual conditions, such as a short circuit at the
OUTPUT binding posts or when this range is in standby.
Line 2.2V OUT is connected to INT OUT HI through relays K27 and K30 on the Switch
Matrix. Line INT OUT HI is connected to the OUTPUT HI binding post through relay
K1 on the motherboard. Line 2.2V SENSE is connected to INT SENSE HI through relays
K25 and K26 on the Switch Matrix. Motherboard relays K2 and K3 switch INT SENSE
HI to the SENSE HI binding post during external sensing, or to OUTPUT/SENSE HI
during internal sensing.
Line PA COM is connected to the OUTPUT LO binding post through relays K11 and
K10. Switch Matrix relays K14 and K15 connect R COM to the SENSE LO binding post
during external sensing, or OUTPUT/SENSE LO during internal sensing.
To Next Page
Loading...
Need help?
General
