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参数资料
| 型号： | LM134MWC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 模拟信号调理 |
| 英文描述： | SPECIALTY ANALOG CIRCUIT, UUC |
| 封装： | WAFER |
| 文件页数： | 18/20页 |
| 文件大小： | 362K |
| 代理商： | LM134MWC |
Application Hints (Continued)
With the R
1 to R2 ratio determined, values for R1 and R2
should be determined to give the desired set current. The
formula for calculating the set current at T = 25C is shown
below, followed by an example that assumes the forward
voltage drop across the diode (V
D) is 0.6V, the voltage
across R
1 is 67.7mV (64 mV + 5.9% to account for IBIAS),
and R
2/R1 = 10 (from the previous calculations).
This circuit will eliminate most of the LM134’s temperature
coefficient, and it does a good job even if the estimates of the
diode’s characteristics are not accurate (as the following
example will show). For lowest tempco with a specific diode
at the desired I
SET, however, the circuit should be built and
tested over temperature. If the measured tempco of I
SET is
positive, R
2 should be reduced. If the resulting tempco is
negative, R
2 should be increased. The recommended diode
for use in this circuit is the 1N457 because its tempco is
centered at 11 times the tempco of the LM134, allowing R
2 =
10 R
1. You can also use this circuit to create a current source
with non-zero tempcos by setting the tempco component of
the tempco equation to the desired value instead of 0.
EXAMPLE: A 1mA, Zero-Tempco Current Source
First, solve for R
1 and R2:
The values of R
1 and R2 can be changed to standard 1%
resistor values (R
1 = 133 and R2 = 1.33k) with less than
a 0.75% error.
If the forward voltage drop of the diode was 0.65V instead of
the estimate of 0.6V (an error of 8%), the actual set current
will be
an error of less than 5%.
If the estimate for the tempco of the diode’s forward voltage
drop was off, the tempco cancellation is still reasonably
effective. Assume the tempco of the diode is 2.6mV/C in-
stead of 2.5mV/C (an error of 4%). The tempco of the circuit
is now:
A 1mA LM134 current source with no temperature compen-
sation would have a set resistor of 68
and a resulting
tempco of
So even if the diode’s tempco varies as much as ±4% from
its estimated value, the circuit still eliminates 98% of the
LM134’s inherent tempco.
Typical Applications
Ground Referred Fahrenheit Thermometer
DS005697-15
*Select R3 = VREF/583A. VREF may be any stable positive voltage ≥ 2V
Trim R3 to calibrate
LM134/LM234/LM334
www.national.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM134Z | 制造商: 功能描述: 制造商:undefined 功能描述: |
| LM134ZT | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:Three terminal adjustable current sources |
| LM135 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:Precision temperature sensors |
| LM135_08 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:Precision temperature sensors |
| LM135A | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Precision Temperature Sensors |
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