triac connection

[Hihi]

hi there,i am usin a PIC now to control a triac,problem is, do i juz connect a triac like i do with a connection of transistor,e.g. base to input etc...,if so,how do i actually go abt controllin the dimness of the light,like usin a variable resistor to control the amount of current goin into the triac?pls tell me more abt triac...sorry,n how do i choose the approiate triac?

 

[Someone Electro]

No triacs are not made to be used that way.And triac is made to be only fully on or fully off.Becose of that you have to use PWM to dim an light.PWM is a short for pulse width modulation.This is aculy thruning it on,off,on,off... realy fast and varing the on period.50% is 1ms on an then 1ms off.

 

[Nigel Goodwin]

This is perhaps a little misleading?, PWM is 'mostly' used for DC control, triacs are an AC control device.

To dim a light using a triac you need to trigger it at a specific (and repeatable) point after zero crossing - the later you trigger it, the dimmer the light.

If you check the MicroChip application notes there is at least one about dimmers.

 

[Phasor]

50% is 1ms on an then 1ms off.

A 2ms period is fine for frequencies above 200Hz. I assume we're dealing with normal power frequency, though (50/60 Hz), so your minimum period is 10ms (50Hz) or 8.33ms (60 Hz)

 

[Someone Electro]

Oh yea.sorry