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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20
votes
4answers
19k views

How do I select the accompanying components for an optocoupler?

I'm using an optocoupler (MOC3021) to sense the On/Off state of an electrial appliance using a microcontroller ATmega16L. How do i go about doing this? My mains supply specs are 230V, 50Hz. How do I ...
0
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2answers
2k views

Using AC current to trigger Triac

I am trying to simulate the operation of an optocoupler with a triac to trigger the triac using the AC current. I have come across a few circuits that are all similar: My question is regarding the ...
22
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3answers
69k views

How to drive a MOSFET with an optocoupler?

What's the proper schematic for driving this MOSFET from a microcontroller pin through this or this optocoupler? The MOSFET will drive a motor @ 24V, 6A.
0
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1answer
917 views

How to control switch mode power supply feedback voltage through optocoupler?

The larger design is for a 170 V input, 500 V 2 mA output using a flyback converter. I will refer to the schematic on page 29 of the LT3751 switching controller, also found below. The feedback pin of ...
36
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8answers
18k views

Why are relays so frequently driven by optocouplers?

Since the advent of the many microcontroller development boards, like Arduino, there have been a number of relay modules sold to drive mains AC loads. A lot of these seem to use an optocoupler, ...
5
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1answer
8k views

AC detection for microcontroller

I need to monitor the state of multiple relays carrying 110VAC and 60VAC using a microcontroller (I will probably use an Arduino) to ensure the relays are working properly. To do this I have figured ...
9
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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 ...
5
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4answers
10k views

120VAC 60Hz Zero Cross Detector

I'm designing a digital phase-controlled light dimmer, and I need a zero-crossing detector circuit. From what I've read, it's a bad idea to wire the AC main directly to the microcontroller through a ...
9
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1answer
3k views

What are the differences between optoisolator output styles?

Digikey lists optoisolators with several output types: Darlington Darlington with base Photo FET Photovoltaic Photovoltaic, linearized Transistor Transistor, with base What are the differences among ...
7
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1answer
1k views

Using the VO2223A to switch a 230Vac LED lamp

I'm looking for something that can switch on and off a 230 Vac, 26mA LED lamp, under microcontroller control. Would a VO2223A, driven by (say) a PIC or Arduino, work as a low-current SSR? The load ...
7
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2answers
6k views

Arduino Uno with 12V pump: transistor or optocoupler+12V relay?

I'm not a real expert in electronics but I'm going to start a new project that has completely captured me. I need to drive a 12V pump with my Arduino Uno. The pump is "Dp0102" (12V, 0.7A). To power ...
3
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3answers
3k views

reverse function optocoupler

Ok, I know the basic function of an optocoupler is "turn on irLED, triggering a phototransistor and allowing current to flow"; an optical off then on switch. Is there a reverse optocoupler, i.e. "...
2
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2answers
3k views

Use a PC123 optocoupler for MIDI input

Im trying to connect a MIDI input cable to an arduino. To do that, I need an optocoupler, that secures the internal circuits from damage. This is the schematic as shown by the MIDI specification: ...
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1answer
525 views

Will this schematic work?

Newbie here, trying to learn electronics (Iam from SW background). Looking for someone to review the initial schematic and advise. Haven't ordered the parts yet, so appreciate any tips in finalising ...
6
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2answers
5k views

Under what conditions does an optocoupler work fastest?

I want to use the optocoupler FODM452R2 in my design. I want this optocoupler to run as fast as it can (i.e.; work with minimum propagation delay and least rise/fall times). What is the optimum R1, R2 ...
11
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2answers
4k views

Why Snub an Optoisolator?

I am using an optocoupler and a power triac to switch 120VAC supply to an ~108 watt fan. The datasheet for my optocoupler requires me to snub the optocoupler output when I'm switching an inductive ...
5
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3answers
4k views

Measuring voltage/current digitally on two separate power supply rails

I'm designing a dual-rail DC power supply, with the two rails completely separate (except for sharing a dual-secondary transformer). The main design should work as-is, only by adding a fuse + mains ...
5
votes
3answers
2k views

Why does this optocoupler circuit work without getting destroyed?

This circuit is being used for mains detection. Input is being fed directly from 220V 50Hz mains and output goes to Arduino which is running on 3.3V. Theoretically the optocoupler LED should burn out ...
4
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4answers
3k views

Sanity-check on snubber design

I keep frying resistors in the following optocoupler and triac snubber circuit, and I'm not sure whether to attribute this to bad design, or to faulty components. There are no observable sparks at ...
2
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2answers
2k views

Simple light bulb operated by button and optoisolator triac

I'm new to the world of electronics and I have a quite simple question. Can I control my light bulb with something like this schema? Power source is regular AC 230V (~320Vrms) source. Here is The ...
7
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2answers
14k views

driving a relay with transistor and Opto-isolator

I am very new in electronics. I am controlling a relay with stm32 micro controller. For the isolation I have used a 4N33 opto-isolator. As my relay coil needs around 250 mA, I used a mps222 ...
4
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2answers
557 views

Confusion about what should be a simple resistor-divider circuit

I'm reverse engineering a circuit in some industrial equipment, and I came across some curious behavior of the input circuit... The circuit is pretty simple, it is a resistor divider with a capacitor ...
1
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4answers
4k views

Can an opto-isolated input be analog?

Title says it all: can an opto-isolated input be analog or are they intrinsically digital? Why: I am looking to purchase a relay control board and am deciding between a few options. Here is my ...
5
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2answers
484 views

Current limiting with optocoupler

Update: I've removed all irrelevant information and simplified the question. The OPA548 operational amplifier provides adjustable current limit that can be controlled digitally with a current-out DAC....
4
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2answers
3k views

What does 'random phase' means in a triac driver?

I'm using this triac driver to control a triac. In its datasheet it says 'provide random phase control of high current triacs [...]'. What does that mean? It doesn't have zero-crossing detection?
4
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2answers
7k views

Need an optocoupler for getting directly proportional output galvanically isolated from the DC input

I want to use an optocoupler to linearly step down a DC voltage which willy vary from 0V to 400V. That is, I want the output to be directly proportional to the input and I want it to be galvanically ...
3
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3answers
2k views

Optoisolator with Logic Output - How To Use IC Circuit Example?

I'm looking at an Optoisolator with a Logic Output..It's an optoisolator with a Schmitt Trigger on the output. I think the datasheet is a little bare for my comfort level, so I'm looking for some ...
1
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2answers
902 views

Driving a 24V isolated load from a 3.3V MCU

I am looking to drive a 12-24V purely resistive load from a 3.3V MCU. I would like to use an opto-isolator to separate the circuits electrically. I've drawn up the following circuit, but I'm not ...
1
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1answer
5k views

AC Optocoupler for 230V line detection

I am trying to detect line voltage (230V AC, if the supply is ON/OFF) by a microcontroller with the help of an AC optocoupler. The optocouplers I have evaluated are PC814, H11AA1 and SFH620A-3, out of ...
1
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1answer
1k views

Isolating PWM From H-Bridge

I have a H-bridge based on FAN7392 drivers. This bridge works at 350VDC to output a approximately 240V 50Hz waveform. This circuit is isolated from rest of the board and I would like to maintain the ...
0
votes
1answer
57 views

Resistor value for Opto-coupler input

This question is in regards to the EL817 Opto-coupler(http://www.everlight.com/file/ProductFile/EL817.pdf). I'm trying to choose a suitable resistor to lower the current/resistor of the Opto's LED. ...
12
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2answers
14k views

Optocoupler input protection

I have to provide some isolated inputs that accept 12-24V. There should be some protection against reverse polarization, transient over-voltage and permanent over voltage (up to 40V) to some degree. ...
8
votes
1answer
11k views

How do I choose my optocoupler to drive a solenoid with a MOSFET?

I need to drive a solenoid with a MOSFET. The solenoid is an 8W solenoid and it will be connected to a +12V voltage. And this drive command have to be isolated with an optocoupler but I don't know ...
9
votes
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 ...
24
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4answers
11k views

Optocoupler with phototransistor base lead

I'm thinking about using 4N25 optocoupler - it has a separate lead for base of phototransistor. How do I use it? I suppose I can't leave it floating?
11
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4answers
36k views

Digital Dimmer With Microcontroller

I want to build a digital dimmer for resistive Loads. I have found this circuit for that: The input voltage is 220VAC 50Hz. The red box in the picture is for ...
10
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3answers
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 ...
8
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1answer
4k views

How is this 5-24V input circuit working?

Since I require some kind of wide range input (going to a microcontroller) for a new project, I looked through some designs that are already in use (or were considered at some point) for other ...
2
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1answer
9k views

TLP280-4 Optocoupler on 12/24V inputs

There is a STM32 device which has to detect several signals from other devices. The voltage of these signals can be 12V or 24V. Also these signals can be positive (i.e. 12/24V) or negative (connected ...
4
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1answer
13k views

Choosing components for a triac's snubber

I'm interfacing the BT139-600 TRIAC with this MOC3051-M Opto-triac. I want to build a snubber circuit for the TRIAC as shown in the MOC3051M opto-triac's datasheet @ page 8, figure 12. The load will ...
3
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1answer
2k views

Optocoupler (Analog or Digital)

I have got few analog and digital signal that needs to be galvanically isolated. I am thinking to use H11F1M for analog signals. I am not sure how to rig-up the circuit using this device. Specifically ...
3
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1answer
11k views

Why do we prefer zero-crossing optotriacs for driving triacs?

I usually see a special type of optotriac which has internal zero-crossing detection circuit in it. This type of optotriac is generally used for driving triacs. But, I don't understand its necessity. ...
2
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2answers
6k views

MOSFET switch using an optocoupler

With the parts in the mail, haven't had the time to test, but the simple question: will this work, or what improvements are needed? What it's supposed to do: a MOSFET switch for 12V, 0.5-3A loads, ...
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3answers
2k views

Digital Optical Volume Control with LED and photoresistor (light to seperate circuits, optical pot)

Story At first, I know the existence of a digital pot. 'Problem' is you need an IC to achieve this and also want to keep the circuits completly separated (and simple). Also want to use it with an ...
6
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2answers
2k views

Opto-isolator output from collector vs. emitter

I have an Isocom ISQ2X quad opto-isolator (datasheet) that I will use to drive a logic input. The opto-isolator's simplified model given by the datasheet is pictured below. The transistor base pin is ...
5
votes
1answer
4k views

Power MOSFETs and Gate drivers

I'm trying to finally apply what I learned at university in the course of power electronics. However I find that both that course and most of the books / online references are lacking on some points. ...
5
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2answers
3k views

Is a protection diode needed on a TRIAC optocoupler and what for?

Please refer to page nine of the Sharp S108T01 / S108T02 datasheet: Is this diode needed - why/why not? How do I choose the correct diode, if yes? UPDATE: Thank you all for your educational inputs....
4
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2answers
5k views

MIDI to Arduino with a 4N38 Optocoupler

I ordered a set of optocouplers the other day and was excited when they finally came in. Unfortunately, I've having a bit of trouble getting them to work. Simple on/off tasks work fine but when I ...
4
votes
1answer
2k views

how to calculate resistor value for optocoupler - 230V [duplicate]

I am trying to implement the following circuit. I am trying to understand how the resistance values are calculated. I followed this - "how do I calculate resistor value" According to my optocoupler (...
4
votes
1answer
713 views

Determining the input current of an optoisolator based on output current and CTR

I have an optoisloator (CTR min:20% max:400%) in my circuit whose output current (Ic) is around 10 mA. To facilitate this much output current, how to decide the input current(If)? whether i have to ...