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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Simplifying this circuit using optotriacs?

I'm currently trying to create an interface between my Arduino-compatible (NodeMCU) and my OpenTherm boiler. OpenTherm is a protocol used by some boilers (mainly in Europe) which allows for the ...
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3answers
1k views

Audio soft mute using optically isolated MOSFET

I have an audio signal running through a device that switches it over using a mechanical relay, as a result of the DC offsets and the parasitic capacitance on the output (which also connects to a high ...
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141 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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57 views

Sizing the input current of a isolated standalone MOSFET gate driver for a stable output

After a suggestion from my previous question I'm planning to use this Photovoltaic isolated MOSFET gate driver to trigger a trigger input of this DAQ. It seems these devices do not require an ...
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182 views

Help identifying this circuit and understanding how it works

So I'm hoping to make a few modifications to my computer case and have found that a number of the LED elements have an associated circuit to them. I want to be able to understand what I'm doing and ...
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1answer
707 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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2answers
132 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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680 views

Using an optocoupler to put an AC signal on a DC bias

Expanding from this question Can an opto-isolated input be analog?: Can you use an optocoupler to take an AC signal and attach it to a DC bias? More specifically, can you take something like a 1V ...
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2answers
1k 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 ...
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4answers
539 views

Comparator output not fully switching on MOSFET

First Question for me. I have benefited from other answers here but have not fully resolved my problem. Here's my problem... The LM311 Comparator output does not drive the N channel MOSFET fully on....
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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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52 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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1answer
65 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
53 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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612 views

Optocoupler 24V input misbehaving

I have an optocoupler circuit that is used to accept 24V input (100 ms pulses) and interfaced to a microcontroller. The schematic is as follows: Opto: BL817C or TLP621. TLP621 datasheet As per my ...
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72 views

phoresistor vactrol tremolo noise

I made an optocoupler by shrink tubing a generic photo resistor and a cold white led. Then used it in the following setup to be able to control audio level to achieve tremolo effect: simulate this ...
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36 views

High Speed Piezoactuator Driver-Unexpected (Low) Voltage Output

I'm working on a project that requires charging and discharging a piezoactuator (150V, 1.5μF) extremely fast, IE total slew time allowed ~50μs (so somewhere around a 11A pulse). My background is in ...
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95 views

Switching circuit and reducing noise

Need your opinion in a design I'm working on. Please see circuit below. So I need to control the mcu GPIO based on the incoming 24V signal. The signal is attached below. My issue is this 2 times out ...
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133 views

Using NPN transistors as switches for low-current, 3VDC infrared transmitter device

I'm currently trying to hack up an IR remote for electric holiday candles so that I can use Amazon Alexa or Google Home to turn them on or off. To do so, I need to trigger the switches on the hand-...
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156 views

Swap main terminals of zero-crossing triac

The question I have is maybe silly, but I cannot find strictly related info. When designing a mains switch with an optotriac driven triac (or discrete SSR for you), during layout I swapped the ...
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466 views

30A Relay resets Atmega8A MCU as it engages. Are these PCB layouts to blame?

I am designing a PCB that uses an ATMega8A MCU to switch two high power relays (Songle SLA-12VDC-SL-A). I have used 2 separate approaches with the same disappointed result: the ATmega8A will reset as ...
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103 views

FET Default on, Turn off with Optocoupler

I am relatively new to electronics and having trouble designing a circuit for a redundant power supply, which I would like to switch to battery if the voltage regulator turns off. This will be ...
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240 views

Adding resistor in parallel to digipot

I'm trying to control a device using a digital potentiometer (AD5245S). In my application I can't tie the low-ref of the potentiometer and ground, so I'm using an I2C optical isolator (ISO1541) to ...
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257 views

Driving an optoisolator with a 2N2222?

I'm driving an opto-isolated MOSFET gate driver with a 2n2222 transistor from a 3.3V microcontroller (TI Tiva C, 2-8mA max per pin). The IX3108G that I selected needs 10-16mA to be driven ON. This ...
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1k views

Can You Drive Back-To-Back MOSFETs (aka a Solid State Relay) Without Using An Optocoupler?

I was wondering if there was any way of driving back-to-back MOSFETs (with their sources and gates tied together as shown in the following image) without using an optocoupler? The reason is that ...
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1answer
40 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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1answer
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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1answer
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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1answer
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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31 views

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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1answer
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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2answers
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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1answer
57 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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22 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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1answer
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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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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24 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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1answer
90 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
63 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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36 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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42 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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86 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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296 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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158 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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2answers
296 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
104 views

Reverse function optocoupler in series with physical NC switch?

I've read this answer (reverse function optocoupler) but my case is different: I've got a CNC mini lathe. I have a limit switch on one of the lathe's axis ends (X+) wired as NC to my Gecko G540 ...
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1answer
108 views

Using LEDs in series with optocoupler for biosensor

Long time lurker, first time asker. I've been working through a biosensor schematic from a BME class to build an EKG (I'm a physician, aware of risks of these devices etc) (typical voltages being ...
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86 views

Why use opto-isolation in this way?

I'm synchronizing two FLIR cameras and FLIR's use of opto-isolation in this document doesn't make sense to me. Could someone explain the benefits of using opto-couplers as FLIR describes? The two ...