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參數(shù)資料
| 型號(hào)： | LM231N |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 模擬專用變換器 |
| 英文描述： | Precision Voltage-to-Frequency Converters |
| 中文描述： | VOLTAGE-FREQUENCY CONVERTER, 0.1 MHz, PDIP8 |
| 封裝： | MDIP-8 |
| 文件頁數(shù)： | 7/15頁 |
| 文件大?。?/td> | 368K |
| 代理商： | LM231N |
Typical Applications
(Continued)
condition will usually apply under start-up conditions or in the
case of an overload voltage at signal input. It should be
noted that during this sort of overload, the output frequency
will be 0; as soon as the signal is restored to the working
range, the output frequency will be resumed.
The output driver transistor acts to saturate pin 3 with an ON
resistance of about 50
. In case of overvoltage, the output
current is actively limited to less than 50 mA.
The voltage at pin 2 is regulated at 1.90 V
for all values of
i between 10 μA to 500 μA. It can be used as a voltage ref-
erence for other components, but care must be taken to en-
sure that current is not taken from it which could reduce the
accuracy of the converter.
PRINCIPLES OF OPERATION OF BASIC VOLTAGE-
TO-FREQUENCY CONVERTER (
Figure 1
)
The simple stand-alone V-to-F converter shown in Figure 1
includes all the basic circuitry of Figure 3 plus a few compo-
nents for improved performance.
A resistor, R
=100 k
±
10%, has been added in the path to
pin 7, so that the bias current at pin 7 (80 nA typical) will
cancel the effect of the bias current at pin 6 and help provide
minimum frequency offset.
The resistance R
at pin 2 is made up of a 12 k
fixed resis-
tor plus a 5 k
(cermet, preferably) gain adjust rheostat. The
function of this adjustment is to trim out the gain tolerance of
the LM231/331, and the tolerance of R
t
, R
L
and C
t
.
For best results, all the components should be stable
low-temperature-coefficient components, such as metal-film
resistors. The capacitor should have low dielectric absorp-
tion; depending on the temperature characteristics desired,
NPO ceramic, polystyrene, Teflon or polypropylene are best
suited.
Acapacitor C
is added from pin 7 to ground to act as a filter
for V
. A value of 0.01 μF to 0.1 μF will be adequate in most
cases; however, in cases where better filtering is required, a
1 μF capacitor can be used. When the RC time constants are
matched at pin 6 and pin 7, a voltage step at V
IN
will cause
a step change in f
OUT
. If C
is much less than C
L
, a step at
V
IN
may cause f
OUT
to stop momentarily.
A 47
resistor, in series with the 1 μF C
, is added to give
hysteresis effect which helps the input comparator provide
the excellent linearity (0.03% typical).
DETAIL OF OPERATION OF PRECISION V-TO-F
CONVERTER (
Figure 4
)
In this circuit, integration is performed by using a conven-
tional operational amplifier and feedback capacitor, C
F
.
When the integrator’s output crosses the nominal threshold
level at pin 6 of the LM231/331, the timing cycle is initiated.
The average current fed into the op amp’s summing point
(pin 2) is i x (1.1 R
C
) x f which is perfectly balanced with
V
/R
. In this circuit, the voltage offset of the LM231/331
input comparator does not affect the offset or accuracy of the
V-to-F converter as it does in the stand-alone V-to-F con-
verter; nor does the LM231/331 bias current or offset cur-
rent. Instead, the offset voltage and offset current of the op-
erational amplifier are the only limits on how small the signal
can be accurately converted. Since op amps with voltage off-
set well below 1 mV and offset currents well below 2 nA are
available at low cost, this circuit is recommended for best ac-
curacy for small signals. This circuit also responds immedi-
ately to any change of input signal (which a stand-alone cir-
cuit does not) so that the output frequency will be an
accurate representation of V
IN
, as quickly as 2 output pulses’
spacing can be measured.
In the precision mode, excellent linearity is obtained be-
cause the current source (pin 1) is always at ground potential
and that voltage does not vary with V
or f
. (In the
stand-alone V-to-F converter, a major cause of non-linearity
is the output impedance at pin 1 which causes i to change as
a function of V
IN
).
The circuit of Figure 5operates in the same way as Figure 4
but with the necessary changes for high speed operation.
www.national.com
7
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM231N/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-to-Frequency Converter |
| LM231N/NOPB | 功能描述:電壓頻率轉(zhuǎn)換及頻率電壓轉(zhuǎn)換 PREC VLTG-TO-FREQ CONVERTER RoHS:否 制造商:Texas Instruments 全標(biāo)度頻率:4000 KHz 線性誤差:+/- 1 % FSR 電源電壓-最大: 電源電壓-最小: 最大工作溫度:+ 85 C 最小工作溫度:- 25 C 安裝風(fēng)格:Through Hole 封裝 / 箱體:PDIP-14 封裝:Tube |
| LM231N/NOPB | 制造商:Texas Instruments 功能描述:Voltage / Frequency (V/F & F/V) Converte |
| LM231WM | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Precision Voltage-to-Frequency Converters |
| LM2320-7 | 功能描述:線性和開關(guān)式電源 Euro-Cassette 50W (2x 12V) RoHS:否 制造商:TDK-Lambda 產(chǎn)品:Switching Supplies 開放式框架/封閉式:Enclosed 輸出功率額定值:800 W 輸入電壓:85 VAC to 265 VAC 輸出端數(shù)量:1 輸出電壓（通道 1）:20 V 輸出電流（通道 1）:40 A 商用/醫(yī)用: 輸出電壓（通道 2）: 輸出電流（通道 2）: 安裝風(fēng)格:Rack 長度: 寬度: 高度: |
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