TRIACs

[AtomSoft]

I have a triac here and want to use it to DIM a 125v (100W) light bulb. I want to use a PIC to control the DIM/BRIGHT-ness of the light.

Can someone post some links or general knowledge on how to accomplish this.
Ill post a link to the TRIAC i have in a minute ... have to step out fast.

 

[MrAl]

Hi there,


One way to do this is to sync the PIC to the line frequency via an input pin, sensing near to the zero crossing of the AC line.
You can then generate a delay of length up to the time for one half cycle of the line frequency. The shorter the delay the brighter the bulb, and the longer (up to the half cycle time limit) the dimmer the bulb will be. By varying the delay time the bulb can be dimmed to just about any level. At the end of the delay the triac gate is triggered so it turns the triac on. The triac turns off by itself at the zero crossing. In this way you generate pulses who's amplitudes vary with the line sine wave but are only as wide as one half the cycle time minus the delay time.

It's somewhat important that you dont allow the delay time to ever exceed the half cycle time or you'll end up with subharmonics which may make the bulb look like it is blinking sometimes as well as end up with other undesirable effects. One way to ensure this criterion is met is to set the max delay time to something like 95 percent of the time for one half cycle.

 

[AtomSoft]

Wow that just confused me... ill re read it in a minute or two

 

[AtomSoft]

I just found this which will help me alot:

Elektronika.ba - IR light dimmer v1

 

[MrAl]

Hello again,


Yes that looks like what i was talking about.

 

[AtomSoft]

Take a look at R3.. the 1Mohm Resistor... What wattage should i use?

 

[AtomSoft]

I will be changing this a bit. Using a PIC16F or PIC18F and my own IR code. Just will copy the triac stuff.

 

[AtomSoft]

@ MrAl

Could you possibly explain what needs to be done... i know you gave me a answer above but if possible to explain better it would be appreciated.

I just noticed that there is no code but only HEX files in that project, the schematic will help alot tho. But as for code wise im lost. I will of course SHARE the source with all as usual...

 

[AtomSoft]

could i not just use a DAC to control the TRIAC? Or a Digital Resistor ?

 

[AtomSoft]

Im going to read this. I think its what you where trying to explain to me lol

**broken link removed**

 

[AtomSoft]

Correct me if im wrong ...

i need to use a PIC with Clamping Diodes that clamp to VDD and VSS correct?

a large resistor to drop current correct?

The pic will either be HIGH or LOW depending on if the Sign is Above Zero Crossing (1) and Below Zero Crossing (0)... correct?

so i have to detect a zero crossing then get the time it takes from a zero crossing to a zero crossing. then decide whether to close the gate ?
Am i anywhere close on what i am assuming?

 

[AtomSoft]

So in the schematic from before.

D1 drops it to 5.6v and creates and D2 drops 0.6v so its 5v or so... They both create a VCC/GND half way rectifier?

 

[AtomSoft]

ok i dont want to kill myself doing this heh. (or blow up a pic in my face. I dont own safety goggles) can someone verify that a pic can handle 125v with a 1M ohm resistor on a pin with Clamps..

Also @ 125v a 1M resistor should drop current to about ... 0.000125 A or 125uA... correct?

 

[Nigel Goodwin]

Yes, perfectly fine - check the MicroChip application notes that do exactly that.

 

[AtomSoft]

Thanks a bunch...

By the way i have only 1 : BT136-600E on hand:

https://www.electro-tech-online.com/custompdfs/2010/07/BT136_SERIES_E.pdf

So if i blow it (im a re-tarted person sometimes) ill have to order some new ones.

Ill have to anyway if it works also lol

 

[AtomSoft]

How can i determine how much voltage a ZENER can handle? Or will any zener for 5.6v will do?

 

[AtomSoft]

1 more thing heh....

Can i use a TRIAC instead of a RELAY ? To switch on / off a device. Would it be ok?

 

[cobra1]

if it helps you i use triacs for turning on/off when using ac, i generally have the pic isolated from the mains using opto isolators, i am also currently working one a pic based light dimmer using a triac as output. still trying to get my head round the sync part

 

[AtomSoft]

i found something that should help us both... let me get the link (BASED ON AVR THO)

 

[AtomSoft]

Here it is:
AVR182: Zero cross detector :: AVR Freaks

What confuses me is on page 1 the schem... it shows a symbol for MAINS and MAINS GND.... i thought mains doesnt have a GND ???