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參數(shù)資料
| 型號： | AN-242 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LJT 18C 18#20 SKT RECP |
| 中文描述： | 應(yīng)用新的精密運算放大器 |
| 文件頁數(shù)： | 7/16頁 |
| 文件大小： | 267K |
| 代理商： | AN-242 |
The complete meter circuit in Figure 12 uses a different
scheme. A floating supply is available so that the power
ground and the signal ground can be separated with R12. At
full-scale, the meter current plus the measured current flow
through this resistor, establishing the degeneration. This
method has the advantage of allowing even-value range re-
sistors on the lower ranges but increases degeneration as
the measured current approaches the meter current.
Bias-current compensation is used to increase the meter
sensitivity so there are two zeroing adjustments; current bal-
ancing, that is best done on the most sensitive range where
it is needed, and voltage balancing that should be done with
the inputs shorted on a range below 100
m
A, where the
degeneration is minimal.
With separate grounds, error could be made dependent on
offset current. This would eliminate bias-current compensa-
tion at the expense of more complicated range switching.
The op amp input has internal, back-to-back diodes across
it, so R6 is added to limit current with overloads. This type of
protection does not affect operation and is recommended
whenever more than 10 mA is available to the inputs. The
output buffers are added so that input overloads cannot
drag down the op amp output on the least-sensitive range,
giving a false meter indication. These would not be required
if the maximum input current did not approach the output
current limit of the op amp.
TL/H/7479–14
Figure 12. Current meter ranges from 100 pA to 3 mA, full-scale. Voltage across input is 100
m
V at lower ranges rising
to 3 mV at 3 mA. Buffers on op amp are to remove ambiguity with high-current overload. Output can also
drive DVM or DPM.
7
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PDF描述 |
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| AN-40 | Application Note 40 |
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| 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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