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SECTION III
Model 4277A
EXTERNAL DC BIAS OPERATION (<±40V)
1
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1
DC POWER
SUPPLY
AC Bypass
Capociror
To
make
capacitance
measurements
using
externally supplied dc bias voltages up tp ±40V,
connect a dc voltage source to EXT INPUT/INT
MONITOR connector on the rear panel as shov^n
in the diagram.
CAUTION
DO
NOT
APPLY
GREATER
THAN
±40V TO THE 4277A'S EXT INPUT/INT
MONITOR
CONNECTOR.
IF
THE
APPLIED VOLTAGE EXCEEDS ±40V,
THE 4277A MAY BE DAMAGED.
CAUTION
BE SURE THE CORRECT FUSE (HP
P/N 2110-0011) IS INSTALLED IN THE
DC
BIAS
FUSE
HOLDER
ON
THE
REAR PANEL.
PROCEDURE:
1. Set DC BIAS select switch on rear panel to
EXT.
2. Connect the test fixture or test leads to
the UNKNOWN terminals of the 4277A.
3. Turn on the instruments.
4. Set the 4277A's controls as described in
steps 5 through 7 of Figure 3-20. Set the
DISPLAY A function to "C" measurement
mode.
5. Perform OPEN and SHORT Zero Offset
Adjustments as described in paragraph 3-51.
6. Connect a sample to the test fixture or
test leads.
CAUTION
DO NOT SHORT THE HIGH AND LOW
TERMINALS.
CAUTION
WHEN A POSITIVE BIAS VOLTAGE IS
USED, THE POSITIVE TERMINAL OF
ELECTROLYTIC CAPACITORS MUST
BE
CONNECTED
TO
THE
INSTRUMENT'S
HIGH
TERMINAL.
WHEN
USING
A
NEGATIVE
BIAS
VOLTAGE,
CONNECT
THE
CAPACITOR'S NEGATIVE TERMINAL
TO
THE
INSTRUMENT'S
HIGH
TERMINAL.
7. Set the external dc voltage source to the
desired output voltage.
8. Read the measured values.
Wait until the
applied dc bias across the sample becomes
stable.
9. Reset the external voltage source to OV.
10. Remove the sample from test fixture or
test leads.
Use a stable do voltage source.
To
make
stable
measurements,
connect
an
ac
bypass
capacitor
(approximately 1 yF) between positive
terminal and negative terminal of the
external dc voltage source.
Figure 3-23. External DC Bias (Sheet 1 of 4).
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