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參數(shù)資料
| 型號： | ALD1000U |
| 英文描述： | IC-SM-PROG LINE DRIVER |
| 中文描述： | 集成電路釤PROG線路驅(qū)動(dòng)器 |
| 文件頁數(shù)： | 11/14頁 |
| 文件大小： | 209K |
| 代理商： | ALD1000U |
11
ALD1000
FIGURE 4. Simplified Block Diagram of a 20ma Current
Loop. The IA is in a Gain of 5 to Match the 1V
Full Scale Shunt Signal to the 5V Full Scale
Input Signal.
50
12.5k
Load
ALD1000
IA
XTR
C
E
5V FS
Signal
+
–
Here the input signal affects loop stability. A 10V full scale
input signal would require an IA gain of 10. A lower input
signal, 5V as shown in Figure 4, allows the IA gain to be
reduced to 5. This results in a lower loop gain and increased
phase margin.
Note that it is possible to reduce the IA gain to less than 1
by using a voltage divider at the IA output.
VOLTAGE FEEDBACK AND THE
INSTRUMENTATION AMPLIFIERS
The instrumentation amplifiers can be used for remote
sensing in a voltage feedback loop as illustrated in Figure 5.
Here the instrumentation amplifier tends to reject small
ground potential differences between the source and load.
The voltage loop, however, is more sensitive to reactive load
impedance than the current loop. The ALD1000 emitter
resistor and compensation capacitor need to be selected for
the specific load conditions. Voltage feedback may not be
appropriate for variable load conditions.
FIGURE 5. Simplified Block Diagram of the ALD1000 in
Voltage Feedback.
Load
ALD1000
XTR
C
E
10V
Signal
+
–
C
COMP
R
COMP
USING THE ALD1000 WITH
EXTERNAL DRIVE TRANSISTORS
Power dissipated by the internal driver stage affects the
built-in instrumentation amplifiers compromising their ac-
curacy. External transistors reduce the internal power
dissapation.
The external transistors are configured as current sources. A
PNP transistor delivers positive current. An NPN supplies
the negative drive. Either or both can be used. For example
a 4ma to 20ma current loop may only require a PNP
transistor since negative current drive is not required. See
Figure 9.
Degeneration resistors are required (refer to R
1
and R
2
in
Figure 6). The value of the degeneration resistors will affect
stability, load sharing with the internal driver devices, and
the current limit value. These issues are covered in more
detail below.
EXTERNAL TRANSISTORS AND THE CURRENT
LIMIT VALUE
The ALD1000 contains circuitry to prevent damage to the
internal components due to excess current. When using the
internal driver stage by itself, current to the load is limited
to about 20ma at room temperature. When using external
drivers, the current limit depends, approximately, on the
load sharing ratio between the internal and external transis-
tors. Figure 6 illustrates the circuit relationship between the
current limit circuitry and external drive transistors.
THE DEGENERATION RESISTORS
The degeneration resistors, R
1
and R
2
in Figure 6, control the
load sharing between the internal and external transistors.
Choose the resistor values by measuring load current, cur-
rent through the external transistor, and calculating the
current being supplied by the internal drive.
LOOP STABILITY AND THE DEGENERATION
RESISTORS
Loop stability depends on loop gain. Because the degenera-
tion resistors affect the voltage to current ratio of the loop
the value of these resistors also affect loop gain and thus
stability. Smaller resistor values will increase loop gain. It
may be necessary to compensate for this by adjusting the
value of the XTR gain resistor connected to the E Pin, R
4
in
Figure 6.
EXTERNAL TRANSISTORS AND OUTPUT
VOLTAGE SWING
The output voltage swing must be limited within the input
range of the instrumentation amplifiers. The 100
resistor
shown in Figure 6 limits output swing under high current
conditions. Resistor R
3
performs this function with external
transistors. R
3
must be sized to limit output swing, at the
expected full load, within the input range of the instrumen-
tation amplifiers. Refer to the section on the instrumentation
amplifiers for further information.
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| ALD-105 | 制造商:Panasonic 功能描述:Bulk |
| ALD105T | 制造商:Panasonic Electric Works 功能描述: |
| ALD105W | 功能描述:通用繼電器 1 Form A 3A 277VAC 3A 30VDC 5V RoHS:否 制造商:Omron Electronics 觸點(diǎn)形式:1 Form A (SPST-NO) 觸點(diǎn)電流額定值:150 A 線圈電壓:24 VDC 線圈電阻:144 Ohms 線圈電流:167 mA 切換電壓:400 V 安裝風(fēng)格:Chassis 觸點(diǎn)材料: |
| ALD106 | 功能描述:通用繼電器 RELAY POWER SLIM 3A 6VDC PCB RoHS:否 制造商:Omron Electronics 觸點(diǎn)形式:1 Form A (SPST-NO) 觸點(diǎn)電流額定值:150 A 線圈電壓:24 VDC 線圈電阻:144 Ohms 線圈電流:167 mA 切換電壓:400 V 安裝風(fēng)格:Chassis 觸點(diǎn)材料: |
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