- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄358806 > LM117 (意法半導體) CAP .047UF 100V METAL FILM BOX PDF資料下載
參數(shù)資料
| 型號： | LM117 |
| 廠商： | 意法半導體 |
| 英文描述： | CAP .047UF 100V METAL FILM BOX |
| 中文描述： | 為1.2V到37V電壓調(diào)節(jié)器 |
| 文件頁數(shù)： | 5/15頁 |
| 文件大小： | 469K |
| 代理商： | LM117 |
Application Hints
In operation, the LM117HV develops a nominal 1.25V refer-
ence voltage, V
REF
, between the output and adjustment ter-
minal. The reference voltage is impressed across program
resistor R1 and, since the voltage is constant, a constant
current I
1
then flows through the output set resistor R2, giv-
ing an output voltage of
Since the 100 μAcurrent from the adjustment terminal repre-
sents an error term, the LM117HV was designed to minimize
I
and make it very constant with line and load changes.
To do this, all quiescent operating current is returned to the
output establishing a minimum load current requirement. If
there is insufficient load on the output, the output will rise.
External Capacitors
An input bypass capacitor is recommended. A 0.1 μF disc or
1 μF solid tantalum on the input is suitable input bypassing
for almost all applications. The device is more sensitive to
the absence of input bypassing when adjustment or output
capacitors are used but the above values will eliminate the
possiblity of problems.
The adjustment terminal can be bypassed to ground on the
LM117HV to improve ripple rejection. This bypass capacitor
prevents ripple from being amplified as the output voltage is
increased. With a 10 μF bypass capacitor 80 dB ripple rejec-
tion is obtainable at any output level. Increases over 10 μF
do not appreciably improve the ripple rejection at frequen-
cies above 120 Hz. If the bypass capacitor is used, it is
sometimes necessary to include protection diodes to prevent
the capacitor from discharging through internal low current
paths and damaging the device.
In general, the best type of capacitors to use are solid tanta-
lum. Solid tantalum capacitors have low impedance even at
high frequencies. Depending upon capacitor construction, it
takes about 25 μF in aluminum electrolytic to equal 1 μF
solid tantalum at high frequencies. Ceramic capacitors are
also good at high frequencies; but some types have a large
decrease in capacitance at frequencies around 0.5 MHz. For
this reason, 0.01 μF disc may seem to work better than a 0.1
μF disc as a bypass.
Although the LM117HV is stable with no output capacitors,
like any feedback circuit, certain values of external capaci-
tance can cause excessive ringing. This occurs with values
between 500 pF and 5000 pF.A1 μF solid tantalum (or 25 μF
aluminum electrolytic) on the output swamps this effect and
insures stability. Any increase of load capacitance larger
than 10 μF will merely improve the loop stability and output
impedance.
Load Regulation
The LM117HV is capable of providing extremely good load
regulation but a few precautions are needed to obtain maxi-
mum performance. The current set resistor connected be-
tween the adjustment terminal and the output terminal (usu-
ally 240
) should be tied directly to the output of the
regulator rather than near the load. This eliminates line
drops from appearing effectively in series with the reference
and degrading regulation. For example, a 15V regulator with
0.05
resistance between the regulator and load will have a
load regulation due to line resistance of 0.05
x I
. If the set
resistor is connected near the load the effective line resis-
tance will be 0.05
(1 + R2/R1) or in this case, 11.5 times
worse.
Figure 2 shows the effect of resistance between the regula-
tor and 240
set resistor.
With the TO-3 package, it is easy to minimize the resistance
from the case to the set resistor, by using two separate leads
to the case. However, with the TO-5 package, care should be
taken to minimize the wire length of the output lead. The
ground of R2 can be returned near the ground of the load to
provide remote ground sensing and improve load regulation.
Protection Diodes
When external capacitors are used with any IC regulator it is
sometimes necessary to add protection diodes to prevent
the capacitors from discharging through low current points
into the regulator. Most 10 μF capacitors have low enough
internal series resistance to deliver 20A spikes when
shorted. Although the surge is short, there is enough energy
to damage parts of the IC.
When an output capacitor is connected to a regulator and
the input is shorted, the output capacitor will discharge into
the output of the regulator. The discharge current depends
on the value of the capacitor, the output voltage of the regu-
lator, and the rate of decrease of V
. In the LM117HV, this
discharge path is through a large junction that is able to sus-
tain 15A surge with no problem. This is not true of other
types of positive regulators. For output capacitors of 25 μF or
less, there is no need to use diodes.
The bypass capacitor on the adjustment terminal can dis-
charge through a low current junction. Discharge occurs
when either the input or output is shorted. Internal to the
LM117HV is a 50
resistor which limits the peak discharge
current. No protection is needed for output voltages of 25V
DS009062-5
FIGURE 1.
DS009062-6
FIGURE 2. Regulator with Line
Resistance in Output Lead
L
www.national.com
5
相關PDF資料 |
PDF描述 |
|---|---|
| LM317AS | 3-Terminal Adjustable Regulator |
| LM117H | 3-Terminal Adjustable Regulator |
| LM117HV | REFLECTIVE PHOTOSENSOR SMD |
| LM317AE | 3-Terminal Adjustable Regulator |
| LM317E | 3-Terminal adjustable regulator |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM117.TO66 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage Regulator |
| LM117.TO66-8QR-B | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage Regulator |
| LM117/883 | 制造商:n/a 功能描述:117/883 SEE NOTES |
| LM117_07 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:3-Terminal Adjustable Regulator |
| LM117_08 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:1.2 V to 37 V adjustable voltage regulators |
發(fā)布緊急采購，3分鐘左右您將得到回復。