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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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1answer
44 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
61 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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47 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
52 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
81 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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1answer
50 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
131 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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34 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
80 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
52 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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38 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
84 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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39 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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129 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
70 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
76 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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77 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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4answers
64 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
70 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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198 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
205 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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1answer
56 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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0answers
123 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
1k 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
84 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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210 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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3answers
117 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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1answer
79 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. ...
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1answer
76 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
41 views

Optoisolated MOSFET to control a load - should I take in consideration MOSFET typical use?

I've already asked a specific question, but I'd like to evolve it in a more general question. In a typical optoisolated IC like this: Should I or not interconnect control (-) and DC (-) or will I ...
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2answers
114 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 ...
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2answers
52 views

How to connect power phototriac's gate pin?

I have inherited a design that uses a power phototriac (basically an optotriac with a built-in TRIAC) -- the VO2223B -- that includes a pin to access the power TRIAC's gate (pin 5 below). The ...
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1answer
45 views

Pulldown on optocoupler's input side

I saw some schematic that uses optocoupler to make isolation to the MCU digital input pin. Schematic below. I was wondering why do they need R700 as a pulldown since the LED inside the optocoupler is ...
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1answer
77 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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4answers
3k views

Interfacing a button to a microcontroller (and PC) with a 50 m long cable

I am designing a board that will be plugged into a computer and will read the status of a button ~50 m away in an office environment (it's actually a lot closer, but the cable is long). I think ...
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2answers
85 views

Zero Crossing Signal Timing

I have a zero crossing circuit for dimming lamps exactly like the below According to my calculations: \$ I_{R7} = \frac {V}{R} = \frac {3.3}{10k} = 0.33~mA\$. Considering TCMT1109 transfer ratio ...
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1answer
116 views

Random values of voltage near ADC in current loop

I have implemented a circuit which allows to isolate a current-loop-based sensors. The schematic is as follows: Everything seemed to work good in the breadboard. Without a MAX14626 IC, the circuit ...
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1answer
180 views

BT136 TRIAC not closing on LOW signal to the MOC3021

I am trying to make an AC dimmer. I am following this schematics for my circuit, Circuit Link as you can see in the below picture that I am able to turn the signal on after a short while of zero ...
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2answers
237 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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6answers
185 views

Optocoupler Characteristics

In my application I need to isolate a PWM signal @ 1 kHz, which is generated from a Beaglebone Black microcontroller. In my signal, I want to have one hundred different steps in duty cycle (from 1% to ...
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1answer
122 views

Calculating resistors for an optocoupler controlling a pmos

I want to use a pmos (SI7157DP-T1-GE3, datasheet) as switch - controlled by an optocoupler (TLP291(V4GBTP,SE, datasheet) which is controlled by a teensy 3.6 (3V3 output voltage). Now I'm calculating ...
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0answers
78 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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3answers
128 views

Are activated open-collector and open-drain circuits wasting energy?

Consider the following reference circuit for a 6N137 optocoupler. My understanding is that this circuit uses a pull-up resistor on the output node so when the optocoupler led is activated, the ...
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4answers
434 views

Can an optocoupler be used as a switch [closed]

I am trying to replace a analog switch (the switch is a momentary button in a low current DC situation) with optocoupler. Is it possible to use an optocoupler as a switch (i.e. just on/off)? ...
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1answer
86 views

zero-crossing detection: to optocouple or not to optocouple?

That is the question. Most of the diagrams I have seen on the interwebs are of the opto-coupling school of thought: But the AVR182: Zero Cross Detector application note just throws in the resistors ...
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1answer
85 views

What's the difference between these varieties of octocoupler? [duplicate]

It looks like ON Semi makes a bunch of different kinds of optocouplers for various applications. The array of choices is kind of bewildering. What, exactly, is the difference between an optocoupler ...
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1answer
95 views

What is the difference between optoisolator and motor driver?

Suppose we need to control power of a device (12v, 500mA). I tried to use TLP281 board, which works, except that it inverts the output: device is powered when there is no control signal. For this ...
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1answer
66 views

Best way to shift automotive logic to Arduino TTL

My vehicle ignition switch voltage is 9V when the vehicle is not running. It is 6V when button is pressed. I need a way to convert this to TTL Arduino digital logic levels. I thought I could use a ...
0
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1answer
121 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
118 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....