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参数资料
| 型号： | AN-242 |
| 厂商： | National Semiconductor Corporation |
| 英文描述： | LJT 18C 18#20 SKT RECP |
| 中文描述： | 应用新的精密运算放大器 |
| 文件页数： | 9/16页 |
| 文件大小： | 267K |
| 代理商： | AN-242 |
The input resistor, R6, serves two functions. First, it protects
the op amp input in the event of overload. Second, it insures
that an overload will not give a false meter indication until it
exceeds a couple hundred volts.
Since the reference is bootstrapped to the input, this circuit
is easily converted into a linear, direct-reading ohmmeter. A
resistor from the top of D1 to the input establishes the mea-
surement current so that the voltage drop is proportional to
the resistance connected across the input.
R1
e
R3; R2
e
R4
I
OUT
e
R2 V
IN
R1 R5
TL/H/7479–17
Figure 15. Output resistance of this voltage/current
converter depends both on high value feed-
back resistors and their matching.
current sources
The classical op amp circuit for voltage-to-current conver-
sion is shown inFigure 15. It is presented here because the
output resistance is determined by both the matching and
the value of the feedback resistors. With the LM11, these
resistors can be raised while preserving DC stability.
While the circuit in Figure 15 can provide bipolar operation,
better performance can be obtained with fewer problems if
a unipolar output is acceptable. A complete, battery-pow-
ered current source suitable for laboratory use is given in
Figure 16 to illustrate this approach. The op amp regulates
the voltage across the range resistors at a level determined
by the voltage on the arm of the calibrated potentiometer,
R3. The voltage on the range resistors is established by the
current through Q2 and Q3, which is delivered to the output.
The reference diode, D1, determines basic accuracy. Q1 is
included to insure that the LM11 inputs are kept within the
common-mode range with diminishing battery voltage. A
light-emitting diode, D2, is used to indicate output satura-
tion. However, this indication cannot be relied upon for out-
put-current settings below about 20 nA unless the value of
R6 is increased. The reason is that very low currents can be
supplied to the range resistors through R6 without develop-
ing enough voltage drop to turn on the diode.
If the LED illuminates with the output open, there is suffi-
cient battery voltage to operate the circuit. But a battery-test
switch is also provided. It is connected to the base of the op
amp output stage and forces the output toward V
.
*
calibrate range
2
select for I
CBO
s
100 pA
TL/H/7479–18
Figure 16. Precision current source has 10 nA to 10 mA ranges with output compliance of 30V to
b
5V. Output current
is fully adjustable on each range with a calibrated, ten-turn potentiometer. Error light indicates output
saturation.
9
相关PDF资料 |
PDF描述 |
|---|---|
| AN-40 | Application Note 40 |
| AN-5002 | LJT 18C 18#20 SKT WALL RECP |
| AN-5025 | Applications Using the GTLP10B320 |
| AN-5026 | Circular Connector; No. of Contacts:19; Series:MS27656; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:15-19 RoHS Compliant: No |
| AN-5031 | GTLP Power Configuration |
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