Questions tagged [opto-isolator]

An optoelectronic device which combines an optical transmitter and receiver in a single package; commonly used in galvanic-isolated control applications such as power supplies.

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39 views

Read proportional voltage with optoisolator with no ground loops

I have a variable output 0-5V which comes from a sensor and I would like to read it by using the analog input provided by my motor controller. The problem is that I need to avoid ground loops and so I ...
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43 views

Optocoupler voltage drop when connected to load

simulate this circuit – Schematic created using CircuitLab The inverter supplies max 25mA. The optocoupler draws 18mA. The optocoupler is supplying 1.7V to the sensor at node 1 instead of ...
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31 views

SIPMOS as current source

I read this question and I have the same issue: acquire and protect an input with 5-24V range. I wonder if nowadays I can use a BSS126 as current source transistor. It's a depletion mode N-channel, I ...
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59 views

Optocoupler with Arduino

I'm trying to input 12v into Ardunio Digital inputs. But since Arduino digital input max voltage is 5v, I would like to use an optocoupler as a switch for 12v input into 5v from Arduino itself. So I ...
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102 views

What is this Diode for?

This part of a schematic from the I/O board in the link below shows a 1N4148 diode in parallel with an optocoupler's input circuitry. What is this diode for? https://startingelectronics.org/projects/...
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40 views

Calculating power consumption of optocoupler

I am having trouble calculating the power consumption of this optocoupler (4n25). In the datasheet the input power dissipation stated as \$ P_{diss} = 100mW \$ and forward current of \$I_F = 60mA\$. ...
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78 views

How should trigger the 5V Relay with ESP8266? Using PC817 or Transistor? What is pros and cons?

Working on product but want some suggestion from great community members: Best approach to trigger the 5V Relay from ESP8266EX WiFi Module. I attached both schematics. In Schematic 1, Relay is ...
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74 views

How to build an opto-isolated analog input without an input-side supply?

I know the normal way of optically isolating an analog signal is to use an analog optocoupler with two detectors, and using an op-amp to servo the emitter voltage until the detector output matches the ...
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59 views

Current limit resistors for Optocoupler controlled Mosfet

Reading different design rules regarding optocouplers used as switch I have a question about the current limiting resistors R4 and R6 One aspect is the protection of the devices (e.g. ~200Ohm for a ...
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40 views

Switching a 5V power relay with optocoupler

I have looked at the schematics of a few 5V power relays and noticed different designs. Some use just a transistor to draw the higher current to switch the coil and some use optocoupler (surge ...
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15 views

Connecting phototriac substrate to adjacent pins

For a regulatory exercise I am analyzing the result of a short fault between a phototriac's substrate (MOC3023) and its anodes (one at a time). The datasheet warns ...
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60 views

Transformer open circuit output voltage and current limiting resistor at gate of Triac

Im kinda new to electronics and have some questions before i solder my projekt together. I want to make an Arduino controlled soldering iron and designed the circuit below. The optocoupler i used is a ...
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51 views

isolated 5v PWM to 0-10V

I'm trying to convert a 5V PWM signal to 0-10V through an optocoupler to drive a VFD. The output "0-10V" should be 0V when PWM duty cycle is 0%, and 10V when 100% (linearly !). Here is what I've come ...
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62 views

Controlling a 0-20mA transmitter from an isolated PWM signal

I'm trying to generate a 0-20mA signal for controlling an industrial actuator (the position of a 3-way valve) from a Teensy 3.2 system. Preferably, the mA-output should be galvanically isolated from ...
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76 views

Problems triggering opto-isolator with logic gate

I should start by saying I'm fairly new to electronics so bare with me as I struggle with some basic issues. What I'm trying to do is trigger a 5V opto-isolator from the output of a series of logic ...
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68 views

Proper usage of PC817 Optocoupler

I'm creating a logic based circuit and below is my schematic. The circuit first steps down a 24 VDC input to about 3.7 VDC using a 150K ohm resistance and a 5.1V Zener diode. This 3.7 VDC is fed to ...
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44 views

Why there is RC filter between optocoupler and schmitt trigger?

I want to use schmitt trigger after optocoupler to have clean signal and connect it to MCU.why there is RC filter between optocoupler and schmitt trigger in many designs? How should i connect ...
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117 views

Resistor parallel to optocoupler LED in Zener-stabilized circuit

I was watching a video about phone chargers where the following schematics was presented: simulate this circuit – Schematic created using CircuitLab In the video it was stated that this ...
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67 views

FT232R for RS-485 (DMX512) with Isolation - TX Optocoupler

I am trying to make a DMX controller board using the FTDI FT232R (FT232RL) chip for USB to UART and a MAX485 to output data over RS-485. I have a working prototype done, but for the finished product I ...
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78 views

24V Isolated digital input protection TVS

I am working on creating 24V industrial Grade(Like Siemens PLC I/O) Digital Input circuit,The micro will use the 3.3V supply. circuit works with TWO input signal one of them is 24V industrial "24V_sig"...
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63 views

Optocoupler/isolater circuit for 24VDC sense that transfers switch status to 3.3VDC microcontroller

hope everyone is having a good couple weeks before Christmas, I was given this question for an assignment How would you use an opto-isolator to sense a switch status in a 24VDC machine control ...
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106 views

How can an optocoupler detect the zero cross point in an AC wave?

I am having some trouble using Triacs in order to dim a light bulb operating at 220V AC, I am a student at school and I don't have any background about using Triacs or Diacs or so, so I seeked the ...
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54 views

AC line detection, with or without optocoupler?

If you want just to detect AC line (220VAC) existence using micro-controller, does using optocoupler has any advantages rather to simple RC circuit? Even if you want to meet EMC/EMI/Industrial ...
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113 views

Need help to design efficient zero crossing CURRENT detector : clamp diode solution

I try to design a replacement potter's wheel motor controller for an old potter wheel. I have solve my zero crossing voltage detector and TRIAC command. Now I begin to understand the importance of the ...
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22 views

HCPL3700M optocoupler: why is pulse generator connected to both AC and DC pins?

I'm reading the datasheet for the HCPL3700M AC/DC to Logic Interface Optocoupler. In a test circuit diagram, it shows a pulse generator connected to both the AC and DC pins (see attached). Why would ...
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Opto-coupler high vs low CTR

I want to understand how the CTR of an opto-coupler is linked with its other parameters, for example its switching speed or time delay between input and output or any other parameter. I am using ...
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98 views

What benefit are opto-couplers for relay switching providing, if both sides share the same ground?

I wanted to connect some relays to my Raspberry Pi (for 12V, not 230V) and I found the waveshare RPi Relay Board, which has the following schematic: I like that they spend some thoughts on filtering ...
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72 views

Optocouplers driving MOSFETs in an inverter

For many hours I was trying to simulate in LTspice XVII an optocoupler driver for MOSFETs in an inverter. My project is to build a SMPS with linear voltage stabilizer (I didnt put it on the schematic ...
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84 views

Is this optocoupler driving relay circuit reliable and works great?

This is the circuit that I have, the optocoupler is an EL817 and the transistor is a BC817, the 24V relay is an Omron g2r_1_e, a 24V coil relay. But when the optocoupler input is floating (not ...
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57 views

BT137 triac turns-on uncommanded

I am working with the following circuit, which is from the MOC3043M datasheet with a BT137 at the location of the unnamed triac: This circuit works fine for me if I leave the snubber out. However, ...
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62 views

Is it necessary to opto-isolate a darlington array output?

I've got the following circuit going: A Vishay opto-isolator (CNY74-4) that takes input from buttons that work on 24V, and outputs to microcontroller pins (an Olimex ESP32-PoE-ISO in my case). A ...
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27 views

Using Single isolated DC-DC converter for multiple opto-couplers in same circuit

I need to drive 4 MOSFETs with PWM of certain set frequency, whose outputs are connected to batteries. These 4 batteries are in series. I need to isolate input and output. Can I use a single Isolated ...
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43 views

Is 1.4mm Pad Distance at Optocoupler Pins for 230V/50Hz Mains Detector Enough?

For a project, I use an optocoupler to detect 230V/50Hz AC on a line - if a light switch connected to mains is pressed. For my calculation, I use 240V as a maximum AC voltage. It will limit the ...
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85 views

Are mechanical relay signal pins isolated from the output?

I am going to use a magnetic mechanical relay to switch 240v AC. I am using MPC250D6Z05APT, in its specification it did not say that the 5V signal is isolated from its output upon failure of the ...
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163 views

Driving relay directly from optocoupler, what is best?

I'm designing a smart socket using an ESP-32 and a mechanical relay that can drive 5A at 240VAC. Following typical relay driving circuits, I would like to use an optocoupler between the MCU and relay. ...
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34 views

Optocoupler output current selection

There is a solid state relay (AQH1213) that switches the load to 220 V using 5 V (Arduino). The insulation voltage between the low and high voltage circuits in this relay is 5 kV. The challenge is ...
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56 views

Precision opto-isolator voltmeter circuit

I'm trying to use a LOC110P to make an isolated voltmeter. Here's the schematic of the important bits: The left-hand side of the circuit is actually AC powered and the intent of the circuit ...
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21 views

Triac gate and T1 short circuit forever with inductive load

I am using MOC3042 with BT139 and snubber 390ohm/2W and 10nF/400V to on/off motor from microcontroller, I can't find data about the motor as it's an old one but it drives quite large shutter
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40 views

TLP281-4 optoisolator circuit question

I am working with TLP281-4 optoisolator, there is a board which used this IC in it. It connected like this: Why can't I connect 5V to the collector and take the output directly from between emitter ...
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48 views

Using a Optocoupler - Determining Parameters

I'm looking at possibly using an optocoupler to drive a higher powered circuit from a lower powered one. This is the device I am looking at: http://www.vishay.com/docs/83641/il755.pdf The circuit I ...
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66 views

How can I improve this digital-output / digital input (automotive)

I'm creating some circuits required in a student-built electric-vehicle application. There are no heavy loads on the low-voltage +12V system. What I have below is a circuit that does some threshold ...
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47 views

Resistor power dissipation when driving optocoupler from ac mains

I followed this: https://learn.edwinrobotics.com/230v110v-ac-mains-detection-using-arduino-raspberry-pi-and-esp8266-thing/#Step2 With the exception that I used an LTV-814 that doesn't require a ...
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1answer
57 views

Raspberry Pi input protection with optocoupler?

I need to isolate a noisy input to a Raspberry Pi 4. Would this be the most correct way to implement it? I feel like the protection on the input side of the Pi is overkill. Note: Schematic uses a ...
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70 views

24V signal to drive led

I have a PLC which gives 24V DC output. I would like to drive an external LED using 24V. Is this the correct way to drive an led? Which is the right method let me know any changes needed. simulate ...
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259 views

MeanWell 3-in-1 dimming

I've got a constant current MeanWell LED driver that has 3-in-1 dimming (100k potentiometer, 0-10V signal or 10V PWM), and would like to control the dimming with a microcontroller. I found a few ...
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74 views

Tri State/Floating Signal Detection

I'm working on a project for automotive environment in which I need to read signals from the power mirrors switch in a microcontroller. The power mirrors switch controls the mirror's moving directions ...
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622 views

Diminished data rate with logic output optoisolator

I am using a logic output type optoisolator (H11L1S) that has a nominal data rate of 1 MHz, yet in practice I can't even achieve 100 kHz. Where am I going wrong? Is this maximum data rate ...
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39 views

Triac design for switching load to resistive heater

I'm designing a triac-based relay circuit to switch ac mains on-off to a resistive heater. The app note (AN-3004) for the opto isolator I am using, the MOC3061, suggests using a gate resistor value ...
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56 views

Driving a TC4428 using PC817

I want to drive a mosfet using a mosfet-driver (TC4428). The frequency of turning on-off of mosfet is 5-10 Hz (yes Hz) and duty cycle is 10-20%. I use PC817 as ...
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75 views

230VAC line voltage sensing using MCU pin

I Am designing a circuit to detect the presence of AC line voltage.It is basically to detect the switch On/OFF for a load. Here is the circuit. Here Input resistor ladder to step down the voltage. ...

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