EL817S1A Optocoupler

Updated: 2026-09-19

Overview

The EL817S1A is a widely used optocoupler (or photocoupler) that provides electrical isolation between input and output circuits using an infrared LED and a phototransistor. It is housed in a compact DIP-4 package, making it suitable for space-constrained applications. This component is essential in scenarios where noise immunity and signal integrity are critical, such as in industrial automation, power supply feedback loops, and microcontroller interfacing. Its reliability and cost-effectiveness have made it a staple in B2B electronics procurement.

Structure and Working Principle

The EL817S1A consists of a GaAs infrared LED optically coupled to a silicon phototransistor. When current flows through the LED, it emits infrared light, which activates the phototransistor, allowing current to pass through the output side. This design ensures galvanic isolation, with typical isolation voltages ranging from 5kV to 5.5kV. The device operates with a forward current of 5–60mA for the LED and a collector-emitter voltage of up to 80V on the phototransistor side, making it versatile for low-to-medium voltage applications.

Key Features

The EL817S1A offers a high current transfer ratio (CTR) of 50–600%, ensuring efficient signal transmission. Its low power consumption and fast response time (typically 3–4μs) make it ideal for high-speed switching applications. Additionally, the optocoupler's wide operating temperature range (-55°C to +110°C) and robust construction allow it to perform reliably in harsh industrial environments. Its DIP-4 package is compatible with standard PCB mounting processes, simplifying integration.

Application Areas

This optocoupler is commonly used in power supply feedback circuits to regulate voltage while maintaining isolation. It is also employed in programmable logic controllers (PLCs), motor drives, and communication interfaces to prevent ground loops and noise interference. Other applications include medical equipment, where electrical isolation is critical for patient safety, and automotive electronics, where reliability under extreme conditions is required. Its versatility makes it a preferred choice for designers across industries.

Maintenance and Precautions

To ensure longevity, avoid exceeding the maximum forward current (60mA) or reverse voltage (6V) on the LED side. Proper soldering techniques (e.g., 260°C for ≤10 seconds) must be followed to prevent thermal damage. Storage should be in a dry, anti-static environment to avoid moisture absorption or electrostatic discharge. For high-voltage applications, maintain adequate creepage and clearance distances on the PCB to prevent arcing.

B2B Procurement Guide

When sourcing the EL817S1A, verify the manufacturer's datasheet for CTR and isolation voltage specifications to match your application needs. Bulk purchases (e.g., reels of 1,000–3,000 units) often reduce per-unit costs significantly. Reliable suppliers include authorized distributors of Everlight (the original manufacturer) or certified resellers. Lead times may vary, so plan procurement ahead for large-scale production. Consider alternative part numbers (e.g., PC817, LTV-817) for cross-compatibility if supply chain issues arise.