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参数资料
| 型号： | LM234H/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 模拟信号调理 |
| 英文描述： | SPECIALTY ANALOG CIRCUIT, MBCY3 |
| 封装： | METAL CAN, TO-46, 3 PIN |
| 文件页数： | 12/14页 |
| 文件大小： | 759K |
| 代理商： | LM234H/NOPB |
Application Hints (Continued)
The set current (I
SET) is the sum of I1 and I2, each contrib-
uting approximately 50% of the set current, and I
BIAS.IBIAS is
usually included in the I
1 term by increasing the VR value
used for calculations by 5.9%. (See CALCULATING R
SET.)
The first step is to minimize the tempco of the circuit, using
the following equations. An example is given using a value of
+227V/C as the tempco of the LM134 (which includes the
I
BIAS component), and 2.5 mV/C as the tempco of the
diode (for best results, this value should be directly mea-
sured or obtained from the manufacturer of the diode).
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 R
2 = 1.33k
) with less than
a 0.75% error.
00569728
FIGURE 3. Zero Tempco Current Source
LM134/LM234/LM334
www.national.com
7
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| LM234S8 | 制造商:Linear Technology 功能描述: |
| LM234Z | 功能描述:基准电压& 基准电流 3-Term Adjust Currnt RoHS:否 制造商:STMicroelectronics 产品:Voltage References 拓扑结构:Shunt References 参考类型:Programmable 输出电压:1.24 V to 18 V 初始准确度:0.25 % 平均温度系数（典型值）:100 PPM / C 串联 VREF - 输入电压（最大值）: 串联 VREF - 输入电压（最小值）: 分流电流（最大值）:60 mA 最大工作温度:+ 125 C 封装 / 箱体:SOT-23-3L 封装:Reel |
| LM234Z | 制造商:STMicroelectronics 功能描述:IC - Adjustable Current Source |
| LM234Z-3 | 功能描述:基准电压& 基准电流 RoHS:否 制造商:STMicroelectronics 产品:Voltage References 拓扑结构:Shunt References 参考类型:Programmable 输出电压:1.24 V to 18 V 初始准确度:0.25 % 平均温度系数（典型值）:100 PPM / C 串联 VREF - 输入电压（最大值）: 串联 VREF - 输入电压（最小值）: 分流电流（最大值）:60 mA 最大工作温度:+ 125 C 封装 / 箱体:SOT-23-3L 封装:Reel |
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