ZHCSYA6D May   1998  – May 2025 LM138 , LM338

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 Recommended Operating Conditions
    3. 5.3 Thermal Information
    4. 5.4 Electrical Characteristics: LM138
    5. 5.5 Electrical Characteristics: LM338
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 NPN Darlington Output Drive
      2. 6.3.2 Overload Block
      3. 6.3.3 Programmable Feedback
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Operation With Low Input Voltage
      3. 6.4.3 Operation at Light Loads
      4. 6.4.4 Operation in Self Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      1. 7.2.1 Constant 5-V Regulator
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1 External Capacitors
          2. 7.2.1.2.2 Load Regulation
          3. 7.2.1.2.3 Protection Diodes
        3. 7.2.1.3 Application Curves
    3. 7.3 System Examples
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 接收文档更新通知
    2. 8.2 支持资源
    3. 8.3 Trademarks
    4. 8.4 静电放电警告
    5. 8.5 术语表
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

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7.1 Application Information

In operation, the LM138 develops a nominal 1.25-V reference voltage (VREF) between the output and adjustment terminal. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I1 then flows through the output set resistor R2, giving an output voltage calculated with Equation 1.

Equation 1. LM138 LM338
LM138 LM338 Typical Application CircuitFigure 7-1 Typical Application Circuit

Because the 50-µA current from the adjustment terminal represents an error term, the LM138 was designed to minimize IADJ 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 rises.