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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Triac versus Relay

What are the scenarios where Triacs can not replace a relay or vice-versa?
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25 votes
5 answers
6k views

Why are relays still used in electric ovens?

I bought a new electric fan oven recently. It has a digital thermostat and control system. Yet much to my surprise, I can hear a relay clicking on and off inside it to control the power to its heating ...
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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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18 votes
3 answers
14k views

What does a TRIAC do?

I'm hoping someone on here can give me a simple explanation of what a TRIAC does. To give this request some context, I'm an embedded systems software engineer, so I interface with hardware, but I ...
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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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14 votes
7 answers
5k views

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

I am building my own disco/party lights. 230 V/60 W bulbs, and ideally I would like to switch them on and off at 5 Hz. I was planning on a simple setup with an Arduino controlling the lights. My ...
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  • 181
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
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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12 votes
3 answers
3k views

Controlling High Voltage device with Arduino

I want to control lava lamps using Arduino. I think it shouldn't be hard project, but I have no experience with hardware projects so I'm not sure witch design will feet best for me. I consider using ...
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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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11 votes
4 answers
4k views

Validate Triac circuit

I'm designing a device to switch a heating device driven by mains power. I've done quite a lot of research and realize there's a lot of information out there but as i'm dealing with potentially deadly ...
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  • 483
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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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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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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  • 5,459
10 votes
4 answers
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TRIAC dimmer, circuit design help (resistive load)

Okay guys, I've been tasked with making a light-dimming control system for a 240V heat lamp dissipating around 250W. I need to adjust the heat output on the lamp by control from a microprocessor. I'm ...
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10 votes
3 answers
19k views

Difference between optoisolator(optocoupler) and solid state relay?

I have been looking into relays and optoisolators. I am aware that there are different optoisolators, with some having a transistor on the detector side which allows current to flow in one direction ...
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9 votes
5 answers
20k views

What does "dV/dt" mean for TRIACs?

This is probably obvious, but since I still don't have an engineering education, I ran into this problem: What does dV/dt mean? What does it affect on a TRIAC?
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4 answers
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When should I fire the TRIAC's gate when controlling an inductive load (AC motor)?

I'm using a combination of opto-triac + TRIAC to control a 230V AC motor with a microcontroller. For detecting the zero-crossing of the voltage I'm using another optocoupler. I know that the AC motor ...
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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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8 votes
3 answers
10k views

SSR vs optocoupler with TRIAC output

I've designed (and mostly implemented, now) a system for turning on and off 24VAC solenoids. In order to achieve this, I used optocouplers with TRIAC output (Sharp PR26MF1xNSZ series). The datasheet ...
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8 votes
3 answers
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Crowbar circuit causes unexpected behavior for op amp circuit

I am using an op amp to amplify an input signal from a microcontroller, which in general is working fine. For over voltage protection, I added the crowbar circuit taken directly from figure 32, page ...
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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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7 votes
3 answers
4k views

How to design a snubber for optotriac

I've seen in several places this snubber circuit composed of 2.4K and C1 in this particular case. My question is - what's the purpose of this network exactly and how are the values for the resistor ...
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  • 5,463
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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  • 7,562
7 votes
2 answers
6k views

Why do we use a diac for triggering a triac?

I mean, Wouldn't it be possible to give a gate pulse on triac directly? I have seen in many phase control application circuits like fan speed control,the usage of diacs to trigger a triac.
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7 votes
1 answer
3k views

Using a triac to switch on/off a single phase AC motor

I want to use a triac controlled by a suitable optoisolator such as a MOC3020 to switch a single phase AC motor on and off, like the ones you'd find in a typical desk fan or a blender or similar. I ...
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  • 5,758
7 votes
1 answer
831 views

Triac Turn-on Stress Calculation

When snubbing a triac, one of the concerns is minimizing turn-on stress as your snubber triac discharges across the newly-shorted terminals of the triac. This paper says that the main concern is ...
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7 votes
2 answers
3k views

Is there a good reason to use an SCR based speed controller instead of a TRIAC?

I tried to purchase a switch for a reciprocating saw with variable speed for my Dewalt DW304. I discovered the part is no longer available. Instead, I bought a similar switch used on the later model ...
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6 votes
3 answers
4k views

Snubber causing more problems than benefits

When designing and building a simple motor controller i used 2 snubber circuits, one to protect the main triac and another one the smooth the communication between the phototriac and the main triac. ...
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  • 109
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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  • 4,520
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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6 votes
2 answers
2k views

Turn a mains light on slowly

I've been looking at creating a simple circuit to slowly turn a halogen daylight bulb on over about 30 minutes as soon as power is supplied to simulate dawn. I've got a 240VAC 42W halogen bulb that ...
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5 votes
2 answers
629 views

Why do we bother with SCRs?

As far as I know, SCRs are basically the DC-only cousin of a TRIAC. However, in my travels I have not encountered a TRIAC being much different in price than a similarly spec'd SCR, so I guess I don't ...
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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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  • 177
5 votes
2 answers
2k views

Can electronics be damaged by plugging into a lighting dimmer circuit?

So my stupid room is wired so all of the lower receptacles are driven from the electronic wall dimmer. Stupid me plugged in my brand spanking new brother laser printer into the lower receptacle. It ...
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5 votes
2 answers
462 views

What is the intended use of high current SSRs and triacs?

I answered a question recently regarding power dissipation in solid state relays. This is the calculation: Consider this 40 A rated triac - BTA40. Vto = Threshold voltage = 0.85V = Voltage drop ...
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  • 7,562
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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5 votes
1 answer
4k views

Troubleshooting a Triac Motor Control Circuit

I have a Xytronic 988 soldering station. It has a regular soldering iron on the left and an iron with a vacuum pump on the right. It has served me well over the years and one day when I was swapping ...
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  • 191
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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  • 591
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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  • 96
5 votes
2 answers
2k views

TRIAC turning on asymetrically by itself when it gets warm

I've got a simple triac phase angle controller which is very similar to the MOC3021 data sheet app circuit. Most of the time everything is fine. The circuit looks like this: The triac is a BTA06-600B ...
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  • 151
4 votes
2 answers
1k views

Arduino Dimmer Shield Schematics Interpretation

I've read so much about Thyristors, Triacs and Rectifiers on the last days that I'm almost understanding my schematic, but I'm not there yet - I need some help. Overview: I'm making a home automation ...
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4 votes
4 answers
3k views

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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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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  • 213
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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  • 10.5k
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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  • 13.5k
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
4 votes
1 answer
615 views

240V PCB Layout - Critique on design requested

Hi all, I was wondering if I could get some critique on my first PCB layout. The schematic is a direct copy from here. It is for a 240V Dimmer 10A, and I am after comments on my PCB design. For ...
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4 votes
1 answer
675 views

Why 2 zero-crossing detection circuits in heater?

I reverse engineered the power board of an electric heater. I think, I understand most aspects of this circuit. One thing is not entirely clear to me though: The circuit seems to have two distinct ...
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