Questions tagged [triac]

A TRIAC is a component often used to control high power currents, both as a switch and as a "dimmer"-like construction for controlling lamps or electric engines.

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Confusion with TRIAC firing and zero crossing point

The reason for firing a TRIAC very close to the zero crossing point is explained as to avoid RF or EMI interference. Below is an excerpt from a book: What I'm having trouble to understand is that, if ...
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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 ...
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55 votes
5 answers
48k views

Triac versus Relay

What are the scenarios where Triacs can not replace a relay or vice-versa?
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11 votes
2 answers
65k views

how does the circuit of a basic Variable speed electric drill work?

i am trying to 'automate' the control of an electric drill motor that im taking from a garden variety Variable Speed drill (from Harbor Freight) it has a universal AC motor which I basically ...
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7 votes
2 answers
3k views

Triac spurious triggering issue

I have a circuit where I am using triacs to switch home appliances like fan, tube light etc. This is the circuit I am using: (TRIAC1, TRIAC2, TRIAC3 come from arduino GPIO pins) First load is a fan ...
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1 vote
1 answer
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How is the gate trigger resistor value calculated for a triac

As per the application notes of bta08-600cw, to control a three phase induction motor, for triggering the triac gate, the value of resistor is shown as 510 ohm. How is this value arrived at? What ...
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2 votes
1 answer
343 views

Help for TRIAC strange behavior

I try to rebuild an electronic board for an old potter's wheel. I try to build a "Phase Angle Control" with BTA16-800BWRG and MOC3043SR2M to control motor speed (the old board seem to use this ...
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  • 466
19 votes
2 answers
31k views

Choosing TRIAC snubber resistor for multi-purpose switching

I'm designing a circuit to switch a 240V AC load and haven't done a lot with AC power control before. I'm planning to use a Fairchild MC3043-M optically coupled TRIAC driver along with a BT138-600 NXP ...
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8 votes
2 answers
39k views

How do I drive a TRIAC from a microcontroller (for low voltages)?

As a followup to this question, I would like to figure out how exactly one might go about driving a TRIAC from a microcontroller (for low-voltage applications, such as 24VAC). Imagine a scenario where ...
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11 votes
2 answers
5k 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 ...
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6 votes
6 answers
8k views

What would a professional use to switch sprinkler solenoids?

As evidenced by several previous questions of mine, I'm working a project to design a sprinkler controller. This involves driving one of 16 solenoids (well, probably only one at a time...) based on a ...
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4 votes
4 answers
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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 ...
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2 votes
2 answers
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 ...
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5 votes
1 answer
462 views

TL431 crowbar simulation problem

I'm trying to simulate crowbar circuits, which is mentioned on page 8 of ON SEMI TL431 datasheet (https://www.onsemi.com/pub/Collateral/TL431-D.PDF). I'm using TINA TI for this. There are two circuits,...
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1 vote
3 answers
4k views

TRIAC Firing angle vs power delivered to load, how calculate?

I'm building a phase control system for simple power control to a given load (heater for example.) I need an equation to find the relationship between angle of TRIAC firing vs power delivered to load (...
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4 votes
2 answers
4k 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?
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2 votes
3 answers
233 views

TRIAC keeps failing

IMPORTANT UPDATE (Update 6), scroll down to see. I have been trying to make an AC (air conditioner) soft starter for my home AC unit. I have built the following circuit and connected it to my AC unit ...
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2 answers
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Do I need zero-crossing detection for controlling a heater?

I need to control a heater element (about 500W) using arduino. For switching part I would go with zero-crossing SSR or zero-crossing optoisolator and triac (the second seems to be cheaper). The ...
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1 vote
3 answers
6k views

Dimmable AC LED controlled by Arduino

I am a beginner, and I have a school project that requires me to use Arduino or any other microcontroller to control an LED light. After some research, I found out that not all LEDs support dimming, ...
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1 vote
2 answers
3k 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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1 vote
1 answer
76 views

Triac driving motor with limit switch, needs protection?

I'm trying to drive a bunch of motorized ball valves from an ESP32. These valves have a 230V AC motor with one common wire, and two wires to set direction (open/close). When powered between common and ...
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16 votes
2 answers
8k views

What's the difference between 3 and 4 quadrant triacs?

I'm looking at triac datasheets, in particular this datasheet for BTA16 series triac. The "electrical characteristics" section is split into two parts: snubberless/logic level (3 quadrants) and ...
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13 votes
3 answers
17k 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 ...
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11 votes
4 answers
38k 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 ...
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10 votes
3 answers
3k views

Are TRIACs symmetrical?

When debugging a circuit using a micro-controller and triac to control AC current I ran into an issue (the triac wouldn't switch off) that was only resolved by flipping the polarity of the triac. The ...
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4 votes
1 answer
17k 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. ...
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4 votes
1 answer
16k 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 ...
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3 votes
3 answers
14k views

Trouble with triac driven dimmer circuit

I have a dimmer circuit that produces the following wave forms. Red: Triac Gate Signal Yellow: 120v 60Hz AC Wave (not triac output) I would assume that given this signal, the triac should flip on ...
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14 votes
1 answer
7k views

Using an RC snubber with a triac. Is this design safe? (simulation included)

I'm designing an ac switch for a washing machine motor. No speed control is intended, only a switch to turn the motor on for 10 seconds and off for 10 seconds. I'm using a MOC3063 zero-detecting triac ...
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  • 569
5 votes
2 answers
3k views

Control AC load with microcontroller. TRIAC behaviour problem

As per the title of this question i'm trying to control an ac resistive load. So far i had little success and i'm experiencing "strange", to me at least, behaviour from the triac(s) i tried. first of ...
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4 votes
1 answer
5k views

LTSpice, MAC97A8 TRIAC model, Vgs error

I'm having some difficulty getting LTSpice to like a TRIAC model. The specific error it throws is "Missing model definition for VGT-0.65". The trouble is that VGT is a subcircuit parameter, not a ...
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0 votes
6 answers
23k views

How to throttle power consumption of a heating coil?

Which is an appropriate but simple electrical circuit to reduce the energy (power) consumed by a heating coil which has an AC feeding without generating an asymmetric load (large DC component, e.g. ...
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9 votes
1 answer
7k views

Current limiting at mains voltage

I am driving a BTB16-600BW triac using a MOC3052 exactly as suggested in the MOC3052 datasheet: The current into the power triac gate is limited using the highlighted resistor. My triac requires at ...
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5 votes
2 answers
4k 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....
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5 votes
3 answers
2k views

Mains triac safety circuit design

I am investigating using a triac instead of a relay to control 250V 10A devices. However all the 600V 16A triacs come in TO-220 packages. According to AS/NZS 3100 and AS/NZS 60335.1 I need at least ...
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4 votes
3 answers
7k views

What is the holding current on a triac?

What does the Holding Current characteristic mean on a triac? What does this mean for switching loads less than the Holding Current? For example the Sharp S108T02 has a max 50 mA Holding Current.
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3 votes
2 answers
453 views

Getting problem in triac based fan speed control

I'm using this circuit to control the speed of ceiling fan. The fan speed is divided into 8 steps. (0:off & 8:full speed) with 100us gate pulse. This circuit works with incancescent light bulb ...
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3 votes
1 answer
3k views

Driving a 24VAC solenoid with arduino using a octocopuler and a triac

Following a previous question I have redesigned my schematic: I'm trying to energize a solenoid used to open and close a 24VAC sprinkler valve I have the following questions : 1) The GPIO leg can ...
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2 votes
1 answer
874 views

Analog Dimmer Circuit Analysis

I am trying to analyse the basic circuit of a dimmer. I don't have much experience in AC circuits, so I am not sure how do I need to proceed. My circuit is the next: I have something like this: I ...
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  • 525
2 votes
1 answer
1k views

will snubber pass voltage thourgh it?

We are doing home automation project. In that we are using triac for ac switching and snubber circuit (R=100ohm, c=10nf) for its protection. Here we have inductive and resistive load, for inductive ...
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1 vote
3 answers
2k views

Triac Operation: Gate connects to A1 not working?

I have tested the above circuits and found that I can switch on the triac with the circuit at the top, but not with the bottom circuit. In my understanding, the Triac can be triggered on no matter ...
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1 vote
2 answers
5k views

Triac Switch Circuit using MOC3021 and BT136

I am tinkering with BT136 & MOC3021 optocoupler to control AC loads, and below is the schematic i have put together. I have a few doubts here. Is the value of 100 ohm 1 watt correct on pin 6 of ...
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1 vote
1 answer
681 views

Triggering of TRIAC for Crowbar Protection

I am reading the datasheet of TRIAC (T1235T-8G). I am not sure how to trigger the TRIAC and what do they mean by ...
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0 votes
2 answers
201 views

TRIAC motor control. Why is my resistor burning?

I have designed a digital motor controller using the following circuit. One of my resistors keeps overheating. There is a zero-cross detector elsewhere in the circuit used to time the firing of the ...
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6 votes
7 answers
14k views

How do I get proportional 240V AC output from an Arduino-based PID controller to "dim" a rice cooker for a Sous-Vide project?

I'm making a PID controller for Sous-Vide, using an Arduino. I'm trying to decide how to control the output. Using an SSR as an on-off switch on 240V AC will probably give me the result I'm looking ...
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5 votes
1 answer
182 views

Why "substrate" is exposed through a "do not connect" pin at all?

I've were reading through MOC3041 opto-isolated triac when I noticed this part: "Substrate". It's also repeated later on one page down further, but there's no explanation. I guess that might be the ...
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4 votes
3 answers
3k views

Solid State Relay Vs Triac

The general and simplified view of my circuit is something like that: Using a microcontroller I want to select between two sound signal sources (S1 or S2). S1 is a signal that comes from a microphone ...
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  • 145
3 votes
2 answers
2k views

Can I place 220V Live traces on top and bottom of PCB?

Can I place 220V/10A max Live on top and bottom of PCB and let them cross over on 2 different layers. Is it safe? Is there a minimum distance of some rule that we need to follow. Attached image with ...
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3 votes
1 answer
3k views

Where should I place the capacitor in this TL431 + TRIAC crowbar circuit?

I'm building a replacement power supply for my C64 and want to add some protection against overvoltage. For that purpose, I tried to find a suitable crowbar circuit that would short-circuit the supply ...
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  • 587
3 votes
1 answer
484 views

Questions regarding eliminating hysteresis in ac dimmer

In the following circuit it says: “This hysteresis effect can be eliminated however, using the circuit from a detailed application note from Littelfuse shown in Fig. 6.4.4. Here the capacitor C1 is ...
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