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EL357 Optocoupler – Transistor Output

EL357 is a DC Input based, Phototransistor Output Optocoupler that is the exact equivalent of popular PC817 optocoupler. It uses an infrared LED and a simple NPN phototransistor inside the same package for isolated data communication between these two. It is available in industry standard dual-in-line 4 pin SMD packages.

It is very useful to isolate two separate circuits but still making communication between the two using a safer way. By using this optocoupler, one can achieve isolation up to 3750 VRMS.


Pin Description of EL357 Optocoupler

Pin Number

Pin Name




Anode pin of the Infrared LED



Cathode pin of the Infrared LED



Emitter pin of the NPN phototransistor.



Collector pin of the NPN phototransistor.


The pinout is shown in the below image-

EL357 Optocoupler Pin Description


Features and Specification of EL357 Optocoupler

  • 3750 VRMS isolation Test voltage
  • High Collector-Emitter Voltage VCEO = 80V
  • CTR value: 50~600% at 5mA Forward current and 5V Collector-Emitter voltage
  • Forward Voltage: 1.2V (Typ) , 1.4V (Max)
  • Collector Current: 50mA
  • Power Dissipation: 200mW


Note: Complete technical details can be found in the EL357 Datasheet, linked at the bottom of this page.


Alternative Product of EL357 Optocoupler

Exact equivalent for EL357 Optocoupler-

  1. PC817
  2. LTV817

Other alternative Optocouplers-

  1. 4N35
  2. IL420


EL357 Optocoupler - Overview

The EL357 Optocoupler is the exact alternative product of PC817. EL357 is a 4 pin SMD based package. This EL357 optocoupler provides a High isolation voltage between the input and output with a RMS voltage of 3750.

The NPN phototransistor offers 50mA of collector current with 200mW maximum power dissipation. The current transfer ratio is specified as 50~600% at 5 mA of forward current and 5V of collector-emitter voltage.


How to Use the EL357 Optocoupler

The below EL357 application circuit shows the standard 5V working of the optocoupler. It requires basic components, just two resistors.

EL357 Application Circuit

Optocouplers are required where two circuits are needed to be electrically isolated from each other but at the same time, the communication between the two circuits is required. An optocoupler has two sections, one is the LED section that emits light and the other section is the phototransistor section that detects the emitted light and works accordingly. The Circuit that needs to send the data is required to control the LED portion and the circuit that needs to process the data and work accordingly will have the control using the phototransistor.

In the above image, the interfacing is shown using a resistor of R1, that is used to limit the diodes forward current and the resistor in the collector will limit the collector current. If the LED will light up, the transistor will change the collector state from High to Low.


Applications of EL357 Optocoupler

  • DC-DC Converters
  • AC Detection
  • SMPS
  • Signal transmission between different potentials and impedances
  • High voltage and low voltage circuit communication
  • MCU based I/O operations where isolation is required
  • Sensitive consumer-grade applications
  • Industrial automation
  • Logic coupling with HF noise reduction


2D Model of EL357

The dimensions of EL357 is given below to help you with selecting the PCB footprint for EL357.

EL357 Dimensions

Component Datasheet

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