4 N 33 Photodarlington Optocoupler (ON Semiconductor) – 6-Pin DIP

Description

The 4N33 Photodarlington Optocoupler, manufactured by ON Semiconductor (onsemi), is a highly reliable optical isolator designed to protect sensitive low-voltage logic circuits from dangerous high-voltage transients. It consists of a Gallium Arsenide (GaAs) infrared emitting diode optically coupled to a silicon photodarlington transistor, all housed within a standard 6-pin Dual Inline Package (DIP).

Available at Tomson Electronics, the 4N33 stands out due to its photodarlington output stage, which provides a significantly higher Current Transfer Ratio (CTR) compared to standard phototransistor optocouplers like the PC817. This makes it exceptionally useful for driving relays, interfacing with heavy industrial loads, and amplifying weak input signals while maintaining total galvanic isolation between the input and output stages.

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Specifications

• Manufacturer: ON Semiconductor (onsemi)
• Model: 4N33
• Output Type: Photodarlington Transistor
• Package Type: 6-Pin DIP (Through-hole)
• Current Transfer Ratio (CTR): > 500% (Minimum)
• Isolation Voltage: 5300 Vrms (Minimum)
• Input Forward Voltage (Vf): 1.2V Typical
• Maximum Collector-Emitter Voltage (Vceo): 30V

Datasheet

Download 4N33 (ON Semiconductor) Datasheet PDF

Applications

• Microcontroller Protection: Creating a safe isolation barrier between low-power boards (like Arduino or ESP32) and high-voltage industrial machinery.
• Relay Driving: Utilizing the high CTR of the Darlington pair to directly drive heavier loads like mechanical relays or solid-state switches.
• Logic Ground Isolation: Eliminating ground loops and electrical noise interference between different subsystems in complex electrical panels.
• Motor Control: Isolating the noisy electrical spikes generated by DC motors and stepper drivers from the central logic controller.

Frequently Asked Questions (FAQ)

Q: What is the advantage of a "Photodarlington" output over a standard optocoupler?
A: A standard phototransistor (like the 4N35 or PC817) has a lower Current Transfer Ratio (CTR), typically around 50-100%. A photodarlington output uses two internal transistors to multiply the gain, offering a CTR of over 500%. This means a very tiny input current on the LED side can control a much larger current on the output side.

Q: Will this fit on a standard breadboard?
A: Yes, the 4N33 comes in a standard 6-pin DIP package with a 2.54mm (0.1 inch) pitch, making it perfectly compatible with solderless breadboards, perfboards, and standard IC sockets.

Q: Why are there 6 pins if I only need 4 for basic isolation?
A: While pins 1 and 2 are for the LED, and pins 4 and 5 are for the Darlington output, pin 6 provides access to the internal Base of the phototransistor. This allows advanced users to adjust the sensitivity, bandwidth, or switching speed using an external resistor, though it is usually left unconnected in basic applications.

Package Includes

• 1 × 4N33 Photodarlington Optocoupler (ON Semiconductor) – 6-Pin DIP