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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1answer
44 views

Optocoupler 4N25 cut and saturation for zero crossing detector circuit

This is my first time working with an optocoupler and I'm trying to find the right resistors for a zero crossing detector circuit that has a 4N25 optocoupler, but the values I've calculated are not ...
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41 views

lm311 and optoisolator producing error when simulation is run

i have the following setup. the goal is to turn off the LED when the LM311 output is high and turn on the LED when the LM311 output is low. The LED of the optoisolator that is. On my software Proteus,...
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41 views

How to pass a signal over isolator with only one side powered?

I have a system composed of a 230VAC zone isolated from a human contact zone with a 7.5mm 2k5 space. On the human side there is a dry contact switch: I am searching for a less than 1€ solution to ...
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1answer
34 views

Resistors for zero crossing detector with optocoupler

I'm trying to understand how to calculate the right value for resistors R1 and R2 in this circuit using the 4N25 optocoupler, and with 12Vac. With 12Vac, Vp is 16.27v. In this case, the optocoupler ...
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48 views

TRIAC Failure - Short between input and gate?

I am having a spot of trouble with a TRIAC (T2535-600G) whose gate is triggered by a PIC microcontroller (PIC12F1501)through an opto-isolator (MOC3063SM). Normally, the TRIAC, labeled U2 in the ...
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3answers
995 views

High side mosfet 12V switch from isolated 3V3 GPIO

I want to switch power of 12V laser sensor from 3V3 STM32H753VI GPIO. I will power on or off for long time (It's not PWM here) I am not comfortable with Mosfet and Optocoupler so I need help to be ...
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2answers
43 views

Are there optoisolators available that output a photovoltage of at least 2-3 V?

For another circuit idea, I need several cheap simple isolated voltage sources to generate at least 2..3 VDC and a couple of µA. I was thinking of a blue LED in photovoltaic mode. Are such pieces ...
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33 views

Reference ground for Vgs on the source pin of an N-channel MOSFET

Hey fellas, So I'm trying to take advantage of n-channel mosfet's inherent low RdsOn, but also want a high-side configuration. I've got the following circuit here and it seems to work in this ...
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35 views

4N35 opto isolator with ESP32

I had an old Arduino setup where I used this chip to interface with another circuit which had some LEDs. The goal of the project was to signal the Arduino if the external circuit turned an LED on. In ...
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1answer
80 views

what does the reverse voltage rating on an optoisolator mean?

i am using a 4n25 for a high voltage detection circuit. it has a maximum reverse voltage of 5V. does this mean that the LED inside it can only take in a maximum of 5V in the reverse direction before ...
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1answer
46 views

How to opto isloate a pin and still use it as either an output or input at will

I am looking for a clever way to merge the two circuits. I want the freedom to configure the pin as input or output but still have the isolation. Not sure if this can even be done but I am for ...
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46 views

flyback compensation design

This is the control stage circuit of flyback, I want to use SIMPLIS to measure the bode plot to prove a theory is matched to simulation, I use Mathcad to draw the bode plot, the SIMPLIS result should ...
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60 views

Difference between different resistor configurations with optocoupler

I have 2 resistor configurations for an optocoupler. The first one (on the left) is the one I've used in some previous circuits. The second one (on the right) is something that I saw on the internet ...
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3answers
98 views

Optocoupler 220V to microcontroller

I have found optocoupler 220V to microcontroller circuit design like on photo: optocoupler 220V to MCU I wanted to use it to check 220V presence/absence with MCU. I need help with understanding how ...
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116 views

Improve the response of this circuit

I designed this circuit (shown below) to level shift an input PWM (10 kHz 5% duty) signal (from microcontroller, 0/+3V3) to 0 and -12V. When the input PWM is HIGH (+3V3) the output is at 0V while when ...
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29 views

Isolate a linear signal with a regular optocoupler

In a circuit that considers two different ground domains which can change dependant on the numbers of batteries in a series array (think smart battery), I'm trying to isolate a current sense ...
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1answer
70 views

External transformer for PCB made for someone else a few volts higher than circuit was designed for, will this damage the optoisolators?

I sold my first PCB to someone for a bowling lane project. This PCB has 10 opto-isolators(LTV-817) which are connected(after going through a bridge rectifier) to external switches going to a ...
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56 views

TL431 –parasitic capacitor

I read this document from ON Semi, it said the optocoupler features a parasitic capacitor, does this Copto can find in the datasheet? I read the VO617A datasheet, but I don't find any capacitor value ...
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2answers
56 views

optocoupler in flyback design

Recently, I am doing the flyback, when I design the control stage I have some questions: This is the optocoupler(PC817) I used and this figure is Current Transfer Ratio vs. Forward Current. There are ...
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75 views

Light dimmer not working

I made a light dimmer from this circuit below but doesn't seem to work. It seems to work with vloggers online but they are using 220V mains, I'm using 120V. I'm guessing resistors values may be the ...
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2answers
423 views

Can you safely connect the LED side of an optocoupler to AC Mains(120v)?

I have looked at several questions on EE.SE as well as searching the internet and nothing I came across has answered my question in a way that makes me feel safe dealing with mains. Having read many ...
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2answers
121 views

How to mitigate an unavoidable ground loop in a vehicle?

We have a display and a sensor that are installed in vehicles. The sensor is in a metal TO Can, and the manufacturer shorts the ground pin to the TO Can body for shielding. We mount that can in a ...
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2answers
55 views

How to tune period for MOSFET IRF3205 with gate driver optocoupler PC817?

I want to test 100W power output using coils for wireless power transfer project. I used 2 IRF3205 MOSFETs with 2 gate driver optocouplers PC817. I used Arduino for optocouplers. The problem is I don'...
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1answer
48 views

nRF52840 with optocoupler and mosfet

I would like to make a switch which will be able to switch on/off 12-60V low current devices using nRF52840, optocoupler and mosfet. I found this schematic and my idea was just to adjust R1 because ...
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2answers
153 views

How to drive a high side MOSFET with an optocoupler correctly?

I am trying to create an absolutely minimal motor driver, to create a <5$ low power odrive. But since I am only a software developer, I do not have a 100% understanding of analog components, and ...
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1answer
103 views

Purpose of base-collector resistor in open-collector opto-isolated GPIO output

I've been working with an opto-isolated output for a high-speed camera I'm interfacing with and was a little puzzled by the circuit they were using for an opto-isolated open collector output. As far ...
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1answer
24 views

optocoupler PS2501L-1-F3-A

I hope everyone is doing well. I am newbie in the electronics world. The optocoupler is PS2501L-1-F3-A. the 'In' is supposed to be the input of a dry contact ( GND or floating state ), In the ...
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1answer
45 views

Phototriac for low voltage AC motor control without external triac

I have a circuit that does not work as expected. It uses a MOC3023 phototriac to directly control a 12V AC pump. Since the motor is very low power I assumed I wouldn't need an external triac. This may ...
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19 views

NodeMCU/ESP8266 to drive pulse sensor?

I have a Daikin BRP069A61, which is a heatpump accessory that allows the heatpump te smartgrid controlled. In simple terms: It will turn on when PV-power is available and will limit power to whatever ...
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2answers
217 views

Will this circuit manage to kill a 2-stroke engine?

I'm currently building a project that involves a 2-stroke engine. I have tapped into the wires where you would normally place a kill switch in order to get power for some electronics. The voltage is ...
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3answers
131 views

Is an opto-coupler fast enough for this application?

I am counting the pulse edges from a quadrature encoder with an FPGA and using opto-couplers as the encoder is powered with 12V and the FPGA inputs are 3.3V. The encoder is 1000ppr with 2 channels and ...
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106 views

Optocoupler design - why does this circuit work?

I am busy with some calculations regarding the components around the optocoupler and I am now finding myself in a bit of a mental struggle. I have done quite a lot of reading (at least here, here, ...
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1k views

Can I connect 24V direct to optocoupler?

I would like to check sensor signal on MCU. Sensor signal is 24V. Therefore, i want to use optocoupler as an interface between MCU and sensor. NC1 is going to MCU pin. My question is if i can connect ...
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89 views

Mechanical relay circuit schematic and PCB. What is wrong here?

I built a relay that closes when a GPIO gives a GND signal. I have tested the circuit with a breadboard and it works with the same components (except breadboard uses THD diode and PCB uses SMD), but ...
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2answers
57 views

24VAC to 5VDC or 12VDC Trigger - Maybe optocoupler?

What I'm trying to achieve is taking a 24 to 30 VAC signal from an HVAC thermostat and converting it to possibly a 5VDC or 12VDC Trigger Input to a what I believe is a optocoupler/isolator type relay. ...
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1answer
37 views

Reverse engineer a TSOP 1730 IR Receiver Module?

I'm trying to reverse engineer a small IR Receiver module to interface it to a new uC board, I'm designing for it. The original uC mother board got blown. It's for a mate who wanted to use the same ...
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1answer
46 views

Which datasheet CTR value to use in optocoupler circuit?

I am looking to use the FODM8801C in my circuit: https://www.onsemi.com/pdf/datasheet/fodm8801a-d.pdf simulate this circuit – Schematic created using CircuitLab "Vout" node goes into ...
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80 views

Unable to read data from 74HC165

I am trying to read data from a circuit I created recently. But I do not understand if there's something I have missed in the same, since everytime I read data on my microprocessor, it always tells me ...
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6answers
1k views

Optocoupler with the same power supply

Often in MCU boards I see optocouplers even when the power supply is the same on both sides. Example: simulate this circuit – Schematic created using CircuitLab Here +3V3 and +12V have the same ...
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1answer
152 views

Read 12V input with Arduino/Teensy via PC817 (Optocoupler)

I have a SPST rocker switch with 3 terminals (Datasheet), which contains a dependent LED which is illuminated via 12V if the switch is on. I want to read the switch with an Teensy/Arduino. After some ...
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1answer
155 views

Solid State Relay using photovoltaic MOSFET driver

I am in the process of creating a High power Mosfet based SSR. The idea is using a photovoltaic MOSFET driver such as VO1263 (SIlabs have similar IC but it uses CMOS coupling to create the isolated ...
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1answer
54 views

Verifying electric brake current with opto-isolated feedback

I would like to find a way to sense (or detect) current through an opto-coupler. This opto is used to power an electromagnetic brake, but depending on the type of brake the current through it can ...
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1answer
63 views

How to choose resistors(RD & RL) for optocoupler circuit

I am working on a project in which I am driving 6 ultrasonic sensor 4 of them are NPN (NC) and 2 of them are NPN (NO) ,for safety of the MCU I am using optocoupler EL817 for isolation between ...
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66 views

Mechanical 5V Relay with High Voltage Trigger

I am trying to understand how to make a mechanical relay close with a 5V signal, from an ESP. Normally I would just try to find a module out there but I am trying to make this relay fit on my PCB. I ...
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1answer
70 views

Opto-isolator/ optocoupler for electric isolation in IC design

I came across while reading the opto-isolator technique used for electric isolation in embedded systems/ Integrated Circuits design that " Opto-isolator is not recommended for electric isolation ...
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1answer
62 views

Will this optocoupler circuit work for sensor and DC motor?

I am working on a project in which I need to operate a DC motor and some ultrasonic sensors. I want to operate the motor using motor driver DRV 8871 by giving logic signals and read sensor value on ...
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1answer
51 views

Resistor value calculation for optocoupler input

I am working on an optocoupler (LTV-845) circuit. Below is my working circuit: Forward current flowing to opto input would be (Vcc-Vf(LED)) / Rf = (24V-2.1V)/470 = 0.046A. Is my understanding correct?...
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36 views

How I can interface my inductive proximity switch with an MCU?

I want to use an inductive proximity switch (Leuze 50129985) with my MCU (Texas Instruments CC1350). For isolation, I want to use an optocoupler (Sharp PC817). [Links to datasheets.] How can I ...
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1answer
51 views

Only some of my inductive sensors are working with my board

I am working on a board which has six inductive sensors. I am using optocouplers for isolation between sensor output and MCU. Four of them work fine and two show very unreliable behaviour. When I ...
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1answer
47 views

How is this optoisolator being sensed by an input?

I'm trying to replace a mains input opto-isolator (pictured below) which is connected to an input on an industrial control board. I would have though shorting the input would be enough but this is not ...

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