4N28S

Overview

The Lite-On 4N28S is a general-purpose, single-channel transistor output optocoupler housed in a 6-pin surface-mount PDIP package. It integrates an infrared emitting diode with an NPN phototransistor that includes a base terminal for enhanced switching performance and improved linearity. The device provides electrical isolation between input and output circuits, rated at 7.5 kVrms according to manufacturer specifications. Key electrical parameters include a minimum Current Transfer Ratio (CTR) of 10% and a typical rise/fall time of 3 microseconds. It operates within a temperature range of -55°C to 100°C and supports a maximum forward current of 80 mA.

Feature Summary

• Integrates an NPN phototransistor with a dedicated base terminal to facilitate external biasing for improved linearity and faster switching speeds compared to standard configurations.
• Provides high-voltage electrical isolation between the infrared LED input and the phototransistor output, ensuring signal integrity across isolated circuits.
• Designed for surface-mount assembly in a compact 6-pin SMD package, suitable for automated PCB manufacturing processes.

Applications

• Signal coupling in digital communication interfaces requiring galvanic isolation
• Switching applications in power supply feedback loops
• General-purpose logic circuit isolation

Procurement Notes

Verify the specific suffix code against the official Lite-On datasheet to confirm pinout orientation and packaging type, as variations exist within the 4N28 series. Ensure the component meets the required isolation voltage rating for your specific safety application. Cross-reference the CTR specifications with your design requirements, noting that values may vary by batch. Confirm compliance with relevant regulatory standards such as UL certification if required for end-product approval.

Selection Notes

Select the 4N28S when a base terminal on the phototransistor is necessary to control saturation or improve turn-off times in high-speed switching applications. Compare its CTR and isolation ratings against other single-channel optocouplers if higher gain or different package constraints are needed. Consider the surface-mount form factor for space-constrained designs where through-hole alternatives like the 4N28P are unsuitable.

Part Context

The 4N28S belongs to the broader 4N28 family of general-purpose optocouplers manufactured by Lite-On Technology Corp. This family includes various package options such as DIP and SMD variants, distinguished by suffix letters indicating physical configuration. The 4N28 series is widely recognized for its reliability in industrial and consumer electronics, offering a balance of performance and cost-effectiveness for basic isolation tasks.

Replacement Considerations

Direct substitutes include other 4N28-series devices from Lite-On with compatible pinouts, such as the 4N28M or 4N28G, provided the package style matches. Verify that alternative manufacturers' equivalents maintain similar CTR ranges and isolation voltages to ensure functional compatibility without redesigning the surrounding circuitry.

FAQ

What is the function of the base terminal on the 4N28S phototransistor?

The base terminal allows for external connection to adjust the phototransistor's operating point, enabling improved linearity and faster switching speeds by controlling the charge storage within the transistor.

What is the isolation voltage rating for the 4N28S?

According to Lite-On specifications, the 4N28S offers an isolation voltage rating of 7.5 kVrms.