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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175 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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3answers
966 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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0answers
61 views

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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0answers
52 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 ...
2
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0answers
176 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 ...
2
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1answer
625 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 ...
2
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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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4answers
428 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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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
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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0answers
178 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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0answers
50 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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0answers
31 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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0answers
334 views

Is the ground necessary with an opto-isolated RS422 signal

I have 8 opto-isolated RS422 ports to install. All of them are coming from a single PC card. It provides the opto-isolation for every RS422 port. Every signal is opto-isolated from the PC ground and ...
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0answers
91 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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0answers
123 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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0answers
139 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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0answers
361 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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0answers
92 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 ...
1
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0answers
225 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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0answers
253 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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0answers
640 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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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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2answers
904 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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43 views

How to use 4N27 optocoupler?

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
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
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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0answers
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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34 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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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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0answers
92 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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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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2answers
93 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
47 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
46 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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0answers
76 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 ...
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1answer
98 views

how does single supply op-amp work while its non-inverting input is connected to ground?

In HCNR200 Datasheet, the page 11, figure 13-A, there is a sample that confused me. In this sample, the Vin is applied to the inverting input and if the electric current passes through PD1, PD1 ...
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0answers
73 views

P-channel FET and CNY17-3 opto isolator

Long story short, I want to have a relay turn OFF when the output of a 4017 goes high. So I installed an opto-isolator, connecting the LED to the output of the 4017, ie "on" until the ouput goes high....
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0answers
60 views

Acquire a “TIC” signal from a power meter

I'm trying to acquire the tic signal of a french power meter. From the datasheet available here of the TIC signal we can find out that the signal is (page 7/38): 6 Vrms +/- 10% at 50 kHz It comes ...
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3answers
65 views

Can you and/or why should you not replace optocouplers with transistors when dealing with slightly different voltage

I stumbled upon this: https://gyazo.com/9f495ed8e9005ab440db8061839f412a so the mdb bus is communicating at a 34v level and the other side is at 5 or 3.3v why are they coupled with a optocouplers ...
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1answer
77 views

Voltage sampling from 220vac to 5vdc

I made a 1 phase to 3 phase inverter using arduino and IR2104 to control the speed of an induction motor and it is working perfectly. To complete the protection scheme, I need to monitor voltage of ...
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0answers
44 views

Opto-coupler and switching digital pins

I'm a total noob when it comes to the use of opto-couplers, but I'm trying to connect up a couple of digital pins between an ESP32 and a small voice module. There are two pins that I need to switch ...
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0answers
64 views

LED and optocoupler MOSFET switch connected with an inductive load

I want to ask, if this circuit will work. I think the flyback from the inductive load the mosfet is connected to will break the optocoupler. The LED is connected through a resistor which should ...
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1answer
64 views

Achieve -12~12V PWM Signal isolate

I have used IL300 to isolate 0~5V PWM signal before and it works great. The circuit is shown below. But now I need to isolate -12 ~ +12V PWM signal. Is there any possibility or suggested circuit to ...
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2answers
81 views

A question about using optocoupler instead of FET for longer signal wires

After my previous question I had concluded to use the following circuitry to operate this solid state relay: But now I found out that, from the micro-controller(Arduino UNO) digital output pin to the ...
0
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1answer
156 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
63 views

Driving multiple loads with a single TRIAC and multiple optoisolators

I simulated this circuit in multisim. It is working fine. However, I am just curious to know if it is possible to drive multiple loads with multiple opto-isolators with single TRIAC? Something like ...
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0answers
238 views

How much current does an LED in optocoupler draw?

I am planning to actuate the relay (opto-isolated) using the GPIO pins of Nodemcu. NodeMcu's datasheet says that maximum current that can be drawn out of a GPIO pin is 12 mA. Any load more that may ...
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0answers
35 views

Low Voltage Marx Generator Switch

I have a low voltage Marx generator which is connected to a coil inductor, eventually forming an LC oscillator. I want to find a way to switch the circuit on, but because the voltage is low I cannot ...
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1answer
435 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 ...