4N32 Optically Coupled Isolator Technical Summary

Overview

The 4N32 and 4N33 are optically coupled isolators designed to provide electrical isolation between input and output circuits. These devices utilize an infrared LED optically coupled to a phototransistor to achieve high voltage isolation while maintaining signal integrity. The 4N32 series is particularly noted for its very high current transfer ratio and robust isolation characteristics, making it suitable for demanding industrial and commercial applications.

These optocouplers are housed in standard plastic DIP packages and carry important safety certifications including Underwriters Laboratories (UL) and VDE approvals. The 4N32 series provides reliable performance in environments where electrical noise, high voltages, or ground potential differences could compromise signal transmission.

Key Features

• Very High Current Transfer Ratio (CTR): Minimum 500% ensures efficient signal transfer across the isolation barrier
• Excellent Isolation Characteristics: Typical isolation resistance of 10¹¹ Ω provides superior electrical separation
• Robust Package: Standard 6-pin plastic DIP package for easy integration
• Safety Certifications: UL recognition (File #E52744) and VDE approval (#0884, available with Option 1)
• Wide Operating Temperature Range: Suitable for industrial environments
• High Input-Output Isolation Voltage: Protects sensitive circuitry from voltage transients

Applications

The 4N32 optocoupler finds use in numerous applications requiring electrical isolation:

Industrial Control Systems

• PLC input/output isolation
• Motor control circuits
• Noise suppression in industrial environments

Power Supply Regulation

• Feedback isolation in switch-mode power supplies
• Voltage sensing with isolation

Medical Equipment

• Patient monitoring system isolation
• Medical device signal isolation

Telecommunications

• Line interface isolation
• Modem signal isolation

General Purpose Isolation

• Microprocessor system interfaces
• Ground loop elimination
• Analog signal isolation

Electrical Characteristics

Input Characteristics (LED Side)

• Forward Voltage (V_F): 1.2V typical at I_F = 10mA
• Reverse Voltage (V_R): 3V maximum
• Forward Current (I_F): 60mA maximum
• Power Dissipation: 100mW maximum

Output Characteristics (Phototransistor Side)

• Collector-Emitter Voltage (V_CEO): 30V minimum
• Emitter-Collector Voltage (V_ECO): 7V minimum
• Collector Current (I_C): 150mA maximum
• Power Dissipation: 150mW maximum

Transfer Characteristics

• Current Transfer Ratio (CTR): 500% minimum at I_F = 10mA, V_CE = 10V
• Response Time (t_r): 2μs typical
• Fall Time (t_f): 2μs typical

Isolation Characteristics

• Isolation Voltage (V_ISO): 2500V_RMS minimum
• Isolation Resistance (R_ISO): 10¹¹ Ω typical
• Capacitance (Input to Output): 0.5pF typical

Package Information

Physical Dimensions

The 4N32 is available in a standard 6-pin plastic dual in-line package (DIP) with the following dimensions:

• Package Type: DIP-6
• Body Length: 9.65mm (0.380 inch)
• Body Width: 6.35mm (0.250 inch)
• Body Height: 4.44mm (0.175 inch)
• Lead Pitch: 2.54mm (0.100 inch)

Pin Configuration

• Pin 1: Anode
• Pin 2: Cathode
• Pin 3: No Connection
• Pin 4: Emitter
• Pin 5: Collector
• Pin 6: Base (optional connection)

Marking Information

The device is typically marked with the following information on the package:

• Manufacturer logo or identifier
• Part number (4N32 or 4N33)
• Date code or lot number

Thermal Characteristics

• Operating Temperature Range: -55°C to +100°C
• Storage Temperature Range: -55°C to +125°C
• Soldering Temperature: 260°C for 10 seconds maximum

Reliability and Safety

The 4N32 meets stringent reliability and safety standards:

• UL Recognition: Component recognized under UL File #E52744
• VDE Approval: Option 1 devices available with VDE 0884 certification
• Isolation Voltage Test: 100% production tested at 2500V_RMS
• Flammability Rating: UL94 V-0 for plastic material

Design Considerations

LED Drive Circuit

For optimal performance:

• Use current-limiting resistor to maintain I_F within specified limits
• Consider CTR degradation over time when designing for long-life applications
• Minimize reverse voltage exposure to LED

Output Circuit Design

• Select load resistor to achieve desired output voltage swing
• Consider adding base resistor (Pin 6) for faster switching applications
• Maintain V_CE below maximum rating

PCB Layout Recommendations

• Maintain adequate creepage and clearance distances for high voltage isolation
• Minimize stray capacitance between input and output circuits
• Provide sufficient copper area for heat dissipation in high current applications

Conclusion

The 4N32 optically coupled isolator provides reliable, high-performance isolation for a wide range of applications. Its combination of high current transfer ratio, excellent isolation characteristics, and industry-standard packaging make it a versatile solution for designers needing to maintain signal integrity across potential barriers. With robust safety certifications and proven reliability, the 4N32 continues to be a preferred choice for critical isolation applications in industrial, medical, and telecommunications systems.