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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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31 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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34 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 work fine for me if I leave the snubber out. However, ...
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54 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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24 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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37 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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2answers
82 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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86 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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1answer
30 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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45 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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18 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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34 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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47 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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2answers
58 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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1answer
35 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
43 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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2answers
55 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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1answer
159 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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2answers
59 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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5answers
603 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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31 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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1answer
30 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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1answer
57 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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2answers
67 views

Replace optoisolator with a resistor

I found this circuit that I wanted to quickly implement. He is using an optoisolator and feeding back the output using it. I understand that the optoisolator is isolating the sensitive circuit from ...
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2answers
65 views

Reverse Polarity Optoisolator

I am looking to detect, if battery is connected to board or not, by adding optoisolator to a battery and connect it to micro controller, before reverse polarity protection circuit. (Which is MOSFET ...
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3answers
105 views

Why optocouplers for MIDI Out/Thru?

I found this article: midi-in-through-out Credits by Zynthian I like that it has notification LEDS for MIDI in/out/thru. However, I also notice there are optocouplers for MIDI Out and Thru, while ...
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106 views

Optocoupler Failures

I am designing a small PCB that has several digital and relay outputs. The signals to and from the board will be 24VDC, while the logic on the board will be 3.3VDC. There will also be 12VDC for the ...
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2answers
60 views

Voltage drop after optocoupler

I don't know what's wrong... I have an ATTiny13 which gives a dummy impulse turning a fan on and off every 2 seconds; so the plan. I attach two power sources (for dummy purpose) before and after the ...
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1answer
673 views

How safety capacitor replaces optocoupler

I see some phone chargers using safety capacitor (after some research I found its safety capacitor)But not optocoupler to isolate in and out . How safety capacitors replace the optocoupler
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1answer
58 views

Modification to Arduino 12V Detection Circuit

I'm upgrading the interior lights on an older model vehicle. The plan is to tap into the very simple lighting circuit (always hot with a switch for on-off-door) to detect each scenario. Light switch ...
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1answer
51 views

What is the expression for collector current (Ic) in function of CTR for optocoupler?

I'm just asking about expression for collector current (Ic) of optocoupler in function of CTR because my simulation results doesn't fit with the CTR=Ic/If equation. Simulating the part CNY17-3 with ...
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2answers
93 views

Reading an optocoupler datasheet and calculating the resistors for its input/output

This is a continuation from this question (sort of) I want to replace the relays from an existing circuit with optocouplers and had trouble how to read the optocoupler datasheets as well as ...
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1answer
119 views

Understanding the difference of optocouplers vs relays and choosing the right replacement

I'm a bit overwhelmed by the sheer amount of variations in optocouplers and since I've never used one before in any project I don't really know what criteria to look out for. A colleague of mine ...
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1answer
60 views

Opening and closing a pair of terminals

I have a device running at 12vdc that has a pair of terminals that can be opened and closed for the device to operate. I understand how to use an optocoupler to open and close the terminals, however ...
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3answers
113 views

Optocouplers vs Voltage Dividers

I have a device that has a terminal that goes to 5v at certain times. I wish to sense that voltage with an ESP32. I have built this circuit using an optocoupler: simulate this circuit – ...
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23 views

Combined 25V/OPEN and 25V/0V Input circuit

I am designing a board for digital inputs in which I will be receiving 2 types of inputs, 25VDC/OPEN and 25VDC/0V, 10 inputs each. The input signals have different specs but is it OK to design same ...
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3answers
537 views

Normally Closed Optoisolators

I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for ...
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1answer
93 views

LEDs and high currents

In smartening up my doorbell I've been playing with my illuminated pushbutton and have fallen into a bit of a rabbit hole. The doorbell normally: simulate this circuit – Schematic created using ...
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1answer
78 views

Optocoupler - Make active low output at active high

I'm currently working on a project and it consists of amplifying a 5V signal from an Arduino to 24V. I made my circuit and hooked it up to a oscilloscope and it shows that the output of the ...
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1answer
109 views

Digital inputs problem [duplicate]

I'm designing a digital I/O module which isolated with optocouplers. I'm done with the outputs, but having a confusion about input side. I will have some switches and sensors to read as inputs, but ...
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2answers
106 views

I/O Module with optocouplers

I'm designing an I/O module by using optocouplers for the inputs and outputs which I want to control by a microcontroller. Here are my questions: In the datasheet of optocoupler's output current (...
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2answers
98 views

What is the purpose of the optocoupler in this circuit to drive the mosfet/relay?

I'm currently trying to understand a circuit for an ESP8266 relay board. As you can see in the schematics below, an optocoupler is used to drive the relay mosfet. I do not understand, why they are ...
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5answers
112 views

Relay control by using microcontroller

I'm working on a I/O module to control AC, DC motor and lamps by using relays. But I don't know how to control the relays. Some says I should use optocoupler, some says transistor array. I found an ...
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3answers
67 views

Single GPIO for optocoupled input and output

I want to use a single GPIO pin as optocoupled input and output (at random discretion). Will the following scheme work for any possible combination of input and output? Especially when optocoupler 1 ...
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0answers
95 views

How to use 4N27 optocoupler? [duplicate]

I was wondering why the 4N27 optocoupler has a pin for base of the phototransistor - and of course how to connect it. I've usually dealt with PC817 optocouplers and connected them according to the ...
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1answer
150 views

Why does this Mosfet get Hot?

I have an IRF740 mosfet that doesn't get hot in one circuit but then gets completely hot in another identical circuit and for the life of me can not figure out why. Well the circuits aren't exactly ...
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1answer
55 views

What could be the reason SPICE is outputting very different CTR curve for this optocoupler?

For a 4N25/26 I tried to plot the CTR vs LED Current graph by simulating the following circuit. To obtain results similar to the one in the datasheet I keep Vce constant at 10V and sweep the forward ...
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1answer
88 views

Does Hall flow sensor require an optocoupler when using STM32 MCU?

I'm using an STM32F103 to measure water flow through a pipe using Hall flow sensors. My power supply is 12V DC to 5V/3.3V DC. STM works with 3.3V and Hall sensors with 5V levels. I've configured the ...
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1answer
43 views

Optocouplers common resistor

I have seen optocoupler series with common cathode and resistor on every anode. My question is whether or not one resistor on the cathode side will be sufficient, with the right wattage, of course, ...
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2answers
61 views

Can we extract CTR parameter of an optocoupler from its SPICE model this way?

Regarding 4N26 optocoupler, I tried to obtain the following results from the datasheet by LTspice: So as in the test condition I set the forward current 10mA and I set the Rload such that Vce = 10V. ...
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1answer
46 views

How to estimate the overall CTR of this optocoupler from its test conditions

As a part of a system I need to replace a proper opto-coupler with an old one which had insufficient CTR for the given circuit section without changing any other component: The pulse input is 0..5V ...