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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2answers
92 views

HCPL3700 - 220V sensing circuit

I want to use HCPL3700 optocoupler for sensing 220V (line). I design a circuit but I want to ask some questions. HCPL3700 is an open-collector output so I pull-up Vout. In AC voltage sensing some ...
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1answer
658 views

Triac moc3041 resistors

I'm trying to understand few things about triacs etc. and I found datasheet for MOC3041 And there're two resistors which purpose I don't really understand. I'm talking about the 330Ohm and 360Ohm ...
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516 views

Speeding up turn-on and off with VOM1271 Photovoltaic MOSFET Driver (/optocoupler)

It's my first post here so please do not hesitate to tell me if I'm not doing it right :-) A bit of context : we need to switch an array of power resistors (1,3kW, 1ohms) in order to test under load ...
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6answers
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How to detect 220 VAC voltage using an opto-isolator

I created the following circuit. I plugged it in and it works!! Now I thought of adding an opto-isolator to the circuit in place of the LED. The value of C was the same. $$ X_c = {(({220volts-1....
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76 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
129 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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28 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 ...
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1answer
44 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
43 views

Suggestions on wiring PCA9685 i2c + TB67H303 motor ic

I'm trying to design a circuit in order to use the TB67H303 motor driver with the ATMEGA328p and the i2c protocol by using the PCA9685 controller. I never used the TB67H303 and the PCA9685 chips ...
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1answer
40 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
38 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
155 views

Overvoltage protection for AC relay dilemma

I am currently designing a safety-related device that has to open a relay when a certain event occurs. During most of its life, this relay will be closed, and only open if the safety event occurs, ...
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1answer
59 views

Resistance issue in a triac-optocoupler switch

I have made the following circuit to control my water pump with Arduino(UNO R3). I have tried many resistors (calculated myself) to limit current in the optocoupler and triac, but failed to carry the ...
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2answers
109 views

2EDN mosfet driver burns out when connected to PWM signal

Good day everyone, I am building a motor controller for a 250W DC motor. Today I was testing a part of my design, but somehow the MOSFET driver did not work. The Arduino send a 50% square wave (4kHz) ...
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1answer
37 views

Opto-coupler (CTR) and PWM/Relays

I'm VERY confused about saturation and calculating it. As i increase the resistance of photo diode of opto-coupler (4N35) the resistance between collector and emitter increases too. How the ...
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1answer
45 views

Opto-coupler circuit - selection of resitor [duplicate]

I have a circuit like below. I wanted to know how these resistance values were calculated. I wanted to use 12V/24V in place of 9V. Let me know selection of opto-coupler and resistance value.
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4k views

Arduino 4N35 input

I trying to interface the arduino digital pins through an optoconnector attached to an LED of a consumer electronic device. I have bought the recommended component for this. Before I would even get ...
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1answer
17k views

Optotriac+triac: how do I calculate the gate resistor

I am building a small circuit to turn on/off a 200W heater. I am using a MOC3023 and a BT136. At the datasheet of the the optotriac, this circuit is recommended: My question is how is the 180Ohm ...
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25 views

optocoupler components design

I'm new on this forum, I'h planning to deploy a lights home automation and need some help about how to calculate the resistors and capacitors associated to a PcF817 optocoupler in order to get 5V at ...
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1answer
44 views

Open Collector to drive PNP without Pull-Up

I need to generate a current signal between 12V and GND, which has to have galvanic isolation. For this, I want to use an optocoupler. Maximum permittable rise / fall time: < 1µs Output side Vcc: ...
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1answer
50 views

Reading a low voltage signal from a battery connected to a transformer

So currently I am trying to read the current draw from a battery that is being run through a transformer to generate an arc to light a gas burner. I have a roughly 1 ohm piece of wire that I am ...
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1answer
173 views

Induced power supply noise on switch contact

I have a circuit that has a 24V section and a 5V section, separated by opto-isolators and an isolated DCDC converter. Both sides of the DC-DC have decoupling caps, and the MCU has one per Vcc pin. ...
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33 views

Triac Driver Datasheet - LED Trigger Current

Looking at the datasheet for MOC30xx (here: http://www.farnell.com/datasheets/1806097.pdf) I see the following note on p4 under the table outlining the respective LED Trigger Currents of the various ...
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2answers
67 views

Purpose for Shunt Resistor on Opto Isolator Input?

I was looking at a BeagleBone Black Cape and became curious on an input circuit to the BeagleBone GPIO (used for a NPN proximity sensor). Upon further reverse designing, I notice a // 220Ω shunt ...
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2answers
34 views

optocoupling a triac: correct pins

I was reading PLEASE BE AWARE THAT... the moc output MUST BE between the triac pins A2 and G it is never written in any datasheets but it MUST be so or your triac won't commute ... https://www....
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122 views

Resistor getting hot - up to 50°C. Is it an issue of the resistor wattage or nature of the resistor?

I am using an FOD817DSD optoisolator. According to the datasheet: CTR: 300% - 600% @ 5 mA VF = 1.2 V (typical) @ If = 20 mA. We have 10 optoisolators on the PCB which is connected to some other ...
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1answer
66 views

Interfacing a microcontroller digital IO

I'm working with some microcontrollers, and I'm quite confused about how to interface the digital I/O. I've already see some projects with opto-couplers on outputs, other ones with buffers, so I'm ...
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1answer
54 views

Optocoupler circuit accept input between 3-50 volt

How can an optocoupler be used in order to accept a voltage range for example between 3-50 volt to a digital input pin of 3 volt like on the Raspberry? What would a typical circuit look like in order ...
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69 views

How make a pulse acquisition from an electrical meter directly into a raspberry pi?

I would like to acquire pulse informations from a french electrical meter. There is a picture of the outputs of this electrical meter. These pulses vary in frequency and after acquisition, we can ...
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1answer
183 views

Automotive Arduino

I was designing a circuit to manipulate in's and out's in a car. I use a step down converter to power up the Arduino. The inputs, in the left of the Arduino are: GIN : General grounded Input. ...
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4answers
48 views

Normalised Current Transfer Ratio of Opto-Coupler

My understanding is that the Current Transfer Ratio of an opto-coupler defines the relationship between the current flowing through the LED, and the maximum supply current of the output. e.g. "5ma ...
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2answers
45 views

24V signal switching optccoupler

We have a robot, and it has 32 digital output, fed into a homemade PCB. On the PCB we have optocouplers, which have a forward voltage around 1.2-1.3V. So I need to drop the voltage a lot. That's why ...
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14k views

Difference between Zero-Crossing Optoisolator and Regular Optoisolator

I am trying to find any documentation on what the purpose is of a Zero-Crossing Circuit TRIAC Optoisolator. The datasheets don't explain the concept well enough. If you do answer, please include ...
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1answer
329 views

Opto-coupled EIA-422 receiver (understanding suggested circuits)

I am looking at a standard for communication of marine electronics (NMEA). The standard is electrically essentially EIA-422 but it prescribes opto-coupled differential receiver pins without connection ...
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1answer
793 views

optocoupler H22A2 driving a plc input

https://www.vishay.com/docs/83741/83741.pdf example 2 I have existing H22A2 optocouplers that I am trying to run 12vdc through to get a plc input to turn on and off. I am using a 1k resistor on the ...
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1answer
434 views

Latching/Non-Latching Relay Driver Circuit with darlington optocoupler

I'm designing a circuit where an ESP8266 controls two types of relays, a single coil latching relay and a normal non-latching relay. The relays are power relays use to control low power electrical ...
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1answer
5k views

MIDI IN : many circuits

I'm building a MIDI IN to serial port RX cicruit (for Raspberry Pi, or Arduino, or anything else...) using a 6N138 optoisolator. But I find many different circuits, I don't know why there are so ...
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1answer
624 views

High side RC ESC switch

I've been designing a test bench for RC propulsion systems and for that I thought it would be nice to be able to switch the power to the ESC on/off. For this I designed a simple circuit which I ...
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0answers
90 views

Driving of a MOSFET using optocoupler in 180-to-24V buck converter

i have a problem with driving a MOSFET in a converter, let me explain. I need to build a Buck Converter with the following requirements: Input 180 V (From a 120 VRMS rectifier circuit) Output 24 V No ...
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2answers
82 views

Triac Switching circuit with Optocoupler

I am trying to control home devices using a microcontroller and a TRIAC. For switching, I intend to use an optocoupler and triac-based circuit. The circuit is given below (also plenty are available on ...
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2answers
348 views

How can I use half-wave rectified 120VAC to activate a PLC input?

I am working with a CLICK PLC with the C0-08NA 120VAC input module. According to the documentation, the C0-08NA's equivalent input circuit looks like this: A device I need to interface with is ...
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2answers
169 views

Building a midi project with Arduino + scrap components (optocoupler and diode)

Original title: 300V output Optocoupler in a 5V circuit I'm (new to this) trying to build a midi controller (in and out) with arduino and scrap. I guess I had several questions in one so I changed ...
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0answers
75 views

Wide Range Input (Sinking/Sourcing) to Arduino

Figure 1: I am trying to create a circuit that will take a 24 to 3 v digital signal that I can connect to an arduino input. I'd like to have an indicator in the circuit to show that the signal is ...
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1answer
50 views

TL431A issue in voltage [closed]

I am using TL431A for my design. Input side 4.7V below emitter and collector should be short and above 4.7V no output. But in my design it's the opposite. Can anyone suggest how to attain ex cat ...
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1answer
968 views

Do I really need diodes to receive MIDI?

All the schematics above use a diode before the receiving pin on the optocouplers. The problem was, I never able to find the exact same diode as the schematics. Before, I'm using H11L1, but it never ...
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2answers
65 views

Optocoupler isolation necessary?

The circuit diagram below shows two possible options for a circuit: simulate this circuit – Schematic created using CircuitLab The difference between both circuits is the use of the ...
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2answers
148 views

Trouble with optocoupler 4n35

I'm trying to ride a full bridge inverter using SPWM to control the MOSFETs, the signal SPWM that I use to control the MOSFETs comes from an NI elvis, but it only provides 5V and I know the fact that ...
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2answers
2k views

AC Line detection using MID400

I want to detect an AC Line Voltage (230V RMS, 50 Hz) and interface it with a microcontroller. I am aware about two solutions: Using an optocoupler like PC817 (datasheet) using MID400 (home page, ...
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3answers
82 views

Replace some LEDs with diodes in relay circuit

I need to know if I can replace the input LEDs (IN1, IN2, IN3, IN4) by a diode or resistor and if this can help me to reduce the voltage consumption generated by these LEDs. The circuit is a 4 relay ...
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2answers
91 views

Zero crossing detector inconsistency

I designed the following zero crossing detector using an FOD819S optocoupler (U5): The source of the optocoupler is connected to a MB6F full-bridge rectifier (D2) which is supplied by a 9V ...