3-pin negative output voltage regulator (500 mA type)# Technical Documentation: AN79M18 Negative Voltage Regulator
## 1. Application Scenarios
### 1.1 Typical Use Cases
The AN79M18 is a monolithic integrated circuit designed as a fixed -18V negative voltage regulator , primarily used to provide stable DC power supply in electronic systems requiring negative voltage rails.
Primary applications include:
- Op-amp power supplies : Providing negative rail voltage for operational amplifiers in audio equipment, instrumentation, and signal conditioning circuits
- Analog circuits : Powering analog subsystems in mixed-signal designs where dual (±) power supplies are required
- Communication equipment : Negative voltage generation in RF circuits, modems, and telecommunication devices
- Test and measurement : Laboratory power supplies and measurement equipment requiring regulated negative voltages
- Industrial controls : Motor drive circuits, sensor interfaces, and control systems
### 1.2 Industry Applications
Audio/Video Equipment:
- Professional audio mixers and amplifiers
- High-fidelity audio systems
- Video processing equipment
- Broadcast studio equipment
Industrial Electronics:
- PLC (Programmable Logic Controller) systems
- Process control instrumentation
- Data acquisition systems
- Industrial automation controllers
Telecommunications:
- Base station equipment
- Network infrastructure
- Signal processing units
- Line interface circuits
Medical Electronics:
- Patient monitoring equipment
- Diagnostic instruments
- Laboratory analyzers
- Medical imaging systems
### 1.3 Practical Advantages and Limitations
Advantages:
- High reliability : Built-in thermal overload protection and short-circuit current limiting
- Low dropout voltage : Typically 1.7V at 500mA output current
- Good line regulation : Typically 0.01%/V
- Good load regulation : Typically 0.04%/A
- Wide operating temperature range : -40°C to +125°C
- No external components required for basic operation (except input/output capacitors)
- TO-220 package provides good thermal characteristics for heat dissipation
Limitations:
- Fixed output voltage : Cannot be adjusted (fixed -18V output)
- Negative voltage only : Requires proper polarity consideration in system design
- Limited output current : Maximum 500mA continuous output
- Requires heat sinking for high current applications or high ambient temperatures
- Input voltage constraints : Must maintain proper headroom (typically Vin ≤ -20.7V for regulation)
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
Pitfall 1: Insufficient Input Voltage Headroom
- Problem : Input voltage too close to output voltage causes dropout
- Solution : Maintain minimum 2.7V difference between |Vin| and |Vout| under all operating conditions
Pitfall 2: Inadequate Heat Dissipation
- Problem : Thermal shutdown during high current operation
- Solution :
- Calculate power dissipation: Pd = (|Vin| - |Vout|) × Iout
- Use proper heat sink based on maximum expected ambient temperature
- Consider derating above 25°C ambient
Pitfall 3: Improper Capacitor Selection
- Problem : Oscillation or poor transient response
- Solution :
- Use 0.33µF tantalum or 1µF aluminum electrolytic at input
- Use 0.1µF ceramic or 1µF tantalum at output
- Place capacitors close to regulator pins
Pitfall 4: Reverse Polarity Connection
- Problem : Device damage from incorrect polarity
- Solution : Implement protection diodes and clear polarity markings on PCB
### 2.2 Compatibility Issues with Other Components
Input Source Compatibility:
- Compatible with AC-DC converters, DC
