A triac switching for isolation - Page 1
Forum section: electronics / projects

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 26, 2016, 06:20:13 am
content: Hello,I am trying to develop one of my power board that need to have power isolation between 220VAC and 3.3v dc.My photo-coupler is switching through a ARM base STM mictrocontroller.For the unavailability of mcu trigger in circuit simulation software , I have placed a 555 timer with comparative input signals.Take a look my simulation and tell me what should I develop more.

author: Zero999
author_rank: Super Contributor
timestamp: December 26, 2016, 10:26:06 am
content: What are your requirements?Why not simply use an optically isolated TRIAC such as the MOC3022 or MOC3041, depending on whether zero-crossing switch on is required or not?www.ti.com/lit/ds/symlink/moc3022.pdfhttps://www.sos.sk/productdata/29/85/1/29851/moc304x.pdf

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 27, 2016, 12:46:06 am
content: QuoteYou know 2 phase AC signal could have alternating phases. My power board has 2 sets of mentioned circuit. I need to configure a system where, one phase is conducting through TRIAC and other will inactive and vice-versa. The sign of current and voltage on MTI,MT2 of TRIAC depends on 4 axis consideration and pulse voltages applied to Gate.QuoteYes, my system contains MOC3020, but need a TRIAC also, (BTA40, BTA41, BTB41). In simulation software I didn't find a good couple of them.I think zero-crossing is required. Do you have any suggestion? Let me know what other parameter/factors I need to consider during simulation.

author: Zero999
author_rank: Super Contributor
timestamp: December 27, 2016, 05:35:12 pm
content: Quote from: Md Mubdiul Hasan on December 27, 2016, 12:46:06 amSorry, I don't understand what you're trying to do. A two phase AC signal is two sine waves with a 90ophase shift. A TRIAC won't give you a two phase signal.QuoteYes, a TRIAC is required with the MOC3022 or MOC3041. They are more suited to driving a TRIAC, than a photo transistor opto-coupler.The MOC3022 has no zero crossing and will turn on, whenever the photo diode is activated.The MOC3041 has a zero crossing unit, which means it will only turn on when the voltage across it is near zero.Zero crossing cuts down on noise because the TRIAC is only fired when the voltage is low, therefore there's no abrupt increase in current which emits electrical noise. It's useful whenever a load needs to be switched either on or off. The down side is zero crossing cannot be used with phase control. It's no good if you want to dim a lamp.There are schematics showing how to use the MOC3022 and MOC3041 on the datasheets which I provided links to in my previous post.QuoteWhat doesn't your simulation software include models of the MOC3022 & MOC3041? If so then it doesn't matter. You don't need to simulate the entire circuit. Just use the example schematics on the data sheets. Don't rely too much on simulation, which is not perfect. There are circuits which will work in simulation but not in real life and circuits which work in real life but not on most simulators.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 28, 2016, 12:43:41 am
content: QuoteLast post I have explained I have 2 similar circuit with 2 TRIAC .QuoteOkay, lets try with this one.QuoteWell said, noise lowering and full load switched on/off is necessary here. For the phase control we may use other facilities on circuit.QuoteMy simulation circuit is not much different with them,just need to have a RC filter for protecting TRIAC from voltage spikes.QuoteI agree with you, simulation can gives us an idea, before making the PCB in real or test them by scopes. Before starting work, I have read the operating points of TRIAC and photo-coupler..