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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TRIAC driver circuit behavior when switching low current loads

I'm doing a project that involves switching different kinds of loads (edit: by that I mean loads that go from just a couple mA, up to 5A or so) using the usual TRIAC + opto-isolator combo (in my case, ...
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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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251 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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63 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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185 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
777 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
156 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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697 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
609 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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33 views

TRIAC not triggering

I am attempting to make a circuit that would allow me to control a standard CFL 13W lamp with a microcontroller. As the lamp would run on AC power, I am making use of the following circuit using a ...
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1answer
67 views

Control 5V relay board with Raspberry PI GPIO

I would like to control one of these 8-relay boards with my RPI GPIOs. Please check the below schematic - it shows the parts involved for one of the 8 relays. JD-VCC is connected to 5V of the RPI, ...
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40 views

HCPL-3700 voltage detector opto influencing DUT due to low input impedance. Pump float and controller

I am trying to monitor the state of a float in a septic tank using the HCPL-3700. The float is connected to two screw terminals on the controller panel. This float is normally-open with 120VAC ...
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94 views

Can I use an optocoupler to switch an analog signal?

I have this setup to select 1 of 4 signals, pass it through a sensor, then output it to its own output line. It must also maintain all the signals at the output at all times, using optocouplers as ...
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52 views

interfacing MOC3021 with high current back to back scr

I want to drive two back to back thyristor with moc3021 for soft starter.Here is the circuit: This circuit works for medium power SCR such as BT152,But I want to drive a couple of disk thyristor that ...
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263 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
75 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
55 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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2answers
202 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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1k 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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86 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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1answer
411 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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40 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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99 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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142 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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173 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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534 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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110 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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246 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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261 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
37 views

Sensing doorbell directly off the secondary of the bell transformer, with an ESP

New here, and not so skilled, so be kind to me... I've got a very simple electric, old fashioned "ding-dong" doorbell, that I'd like to migrate to the 21st century. It's basically a ...
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2answers
44 views

How to use an optocoupler with a transistor on both sides?

I am trying to switch a 17VDC 30mA load with a Raspberry Pi. To provide electrical isolation, I am using a two channel optocoupler, a TLP621-2 (datasheet). The second channel is currently unconnected. ...
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39 views

4N33, optocoupler, photodarlington, getting voltage without connecting any supply

We are using 4N33, optically coupled isolator (datasheet link). The circuit is shown below. In the schematic with R3--> 10K, it was not working so we change to 200K ohm, C2 & ZD1 are not ...
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33 views

Why does my input current inverter is high?

I have a problem with input current in my inverter is high. My inverter will use for solar panel and using boost converter to convert dc voltage 12-18 Volt to 24 volt. I'm using P channel mosfet ...
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46 views

Need help in zero cross circuit by using op-amp

I worked on zero crossing circuit by using opto-coupler.Circuit is It is working okay.Zero_crossing signal is There is a 2-3 ms of signal loss is happening with 50Hz of AC signal.I don't want more ...
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24 views

Optocupler-Mosfet output for various output

I'm designing a board equipped with a MCU (atmega4809) that need to control different type of industrial graded equipment at 24VDC. These will be mainly a relay or a solenoid coil for pneumatic valve. ...
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30 views

Is this Opto-coupler + MOSFET + Relay schematic correct for my application?

I have an ESP32, with a floating voltage supply with 3.3V. I want to use it's GPIO to turn on/off a solenoid valve that works at 12V and draws a current of about 2A. I figured that a proper way of ...
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1answer
29 views

Alternatives to MID400

I'm trying to detect when 24vac is flowing between the "R" and "Y" terminals on my central air conditioner's thermostat using an Arduino Mega2560. I know from the answers to earlier questions posted ...
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27 views

back to back SCR firing circuit

I am trying to design a 3-phase soft start circuit.Are these two circuits different? My PCB design and RC snubber between anode & cathode is based on the second one.I want to make sure my circuit ...
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19 views

Voltage spikes on output of zero crossing triac optocoupler

I have one connection of the output of the coupler connected to the gate of a triac. The other connection is to one side of the triac. This side of the triac is also connected to a 77 ohm load. At the ...
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46 views

How to fix triac control module?

This is scheme of triac control module. I'm using optotriac MOC3041 (T1 on scheme) and triac BTA140 (T2 on scheme). Is it possible that my control module doesn't work correctly due to too small ...
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40 views

Is this the right way to connect a Brushless Motor Driver Output Signal to a CNC BreakoutBoard?

I will purchase a Spindle Brushless Motor Driver to drive my Lathe Spindle, and I need to know if I´ll be able to connect an output signal from the Driver to my CNC BreakoutBoard (BOB), which is a ...
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68 views

Wiring a USB device to act as a Serial port

I'm trying to make a cable that will go from a laptop usb port through an opto-isolator to a 4-pin connector on a circuit board, and I'm trying to communicate via Asynchronous IN/OUT. I have some ...
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52 views

How to separate magnitude and phase response in Proteus?

I have an all-pass filter in Proteus, which in theory doesn't change phase. but changes amplitude. How can I see both of the graphs? Here are the needed scheme and its analogue in Proteus. Although I'...
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54 views

How to detect unknown circuit button press without interfering with circuit

I have a membrane keypad in my dental chair where part of the it’s logic system is burned. So one of the buttons I need, that turns on and off a head lamp, doesn't work anymore. So with an arduino I ...
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23 views

How to adapt to a different power supply for H11F3?

I'm interested in using a circuit from edn.com to get a more linear response from an opto-FET. But I want to use a 9V power supply instead of 15V. I guess I need to change some of the resistor ...
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41 views

Someone has a circuit for a isolated driver (both input and output) to my project?

I'm working on a self-oscillator Buck converter. My simulation on PSIM has a perfect output, as you can see. But I need a more realistic simulation on another software (with Spice models), so I need a ...
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1answer
38 views

Direct contact to infrared receiver from microcontroller

I have posted this question also on arduino forum but can't get more answers there. So basically I have an old DVD player that has an IR (infra red) receiver and I would like to automate it with a ...
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1answer
35 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 ...