Firing Triac without using MOC

Hi friends,
I usually fire Triacs with the help of MOC3021. Now I am going to make a small circuit where there is not enough space to put micro+MOC+Triac. That's why I want to drive the triac directly from micro as I've seen this done somewere. How should I proceed with this? I don't want to take any risk as I'm dealing with mains electricity.
Hope someone can help.
Thanks.

Hi,
The method is not very hard. What you have to do is know when you are about to fire. In the 1st and 3rd quadrants apply a "0" to the triac gate to turn it on and in the 2nd and 4th quadrants apply a "1" to turn it on. Be careful though as you may misfire the triac which may result in disaster. It is however advisable to use such as driver as MOC for safety as you won't be misfiring.

Hope this helps.
Tahmid.

Hi,
Thanks for the reply.
Can I drive the triac straight from the micro pin or do I need to use any driver. How much current will I need to turn the gate on?

Hi,
For current requirement, you need to check the datasheet. It may vary from triac to triac. Depending on that you need to decide on either to use a driver or not. This driver may be a simple transistor to supply current, nothing too complicated.
BTW, which microcontroller are you using?

Hope this helps.
Tahmid.

Thanks for the reply.
The datasheet states Ig 5-10mA. So, I think I don't need transistor, right?
I'm using PIC12F629. I want to build an IR remote, something similar I saw in the market, for turning 2 bulbs on or off and a fan with speed regulation. For the bulbs, I can turn on off the outputs. But how do I control the speed of the fan?
I've used phase control before for fan control using MOC. Should I use this? Or should I do it in some other way?

The transistor is not required, but maybe used for safety. You can go ahead with phase control, but I think coding will be easier using pulse-skipping modulation. I've done something similar and so I think PSM is easier. There are many details for this available online.

Hope this helps.
Tahmid.

Thank you so much Tahmid. I'll use transistor for safety. I'll try both phase angle and pulse-skipping processes and find the suitable one. Hope can get help from you if i am stuck.
thank you again.

In the 1st and 3rd quadrants apply a "0" to the triac gate to turn it on and in the 2nd and 4th quadrants apply a "1" to turn it on.

Click to expand...

It's not clear, which circuit you imagine, but I fear the suggestion is wrong. Most triacs can be triggered in all four quadrants, in other words, you can apply either a positive or a negative voltage referenced to MT1 (main terminal 1, sometimes also named anode 1) to fire it, independant of the voltage polarity at MT2.

But if you consult triac datasheets, you'll notice, that the quadrant IV gate current is considerably higher or even unspecified. Some newer devices are explicitely designed as 3-quadrant triacs, that are not guaranteed to fire in the 4th quadrant. So if you intend to trigger a triac with a DC voltage, it's reasonable to use a negative gate voltage, utilizing quadrants II and III. For a single supply circuit, e.g. with a microcontroller, this means connecting MT1 (and usually the neutral wire of your AC power supply) to V+, and fire the triac by pulling G to V-. A sensitive triac can be controlled by a uP port pin directly. I don't see a particularly saftey risk by doing so, many home appliances are designed this way. The basic safety risk is introduced operating the processor without isolation to the power circuit, so all control elements must be isolated instead. Of course, a current limiting gate resistor is required in any case. For higher trigger currents use a driver transistor.

P.S.: To clarify the quadrant specification

Hi FVM
Thanks for your detailed information regarding Triac and Quadrants. I just want to use Triac instead of Relay in my circuit, that's all. Thanks for the explanation.

When line hot is MT1 and load is between MT2 and neutral, then, what should be the gate firing mechanism in 1st and 3rd quadrants?

When line hot is MT1 and load is between MT2 and neutral, then, what should be the gate firing mechanism in 1st and 3rd quadrants?

Click to expand...

The connection of the power circuit doesn't change the trigger signal requirements. If you are using a direct connected trigger circuit (no MOC30xx), then the circuit must be connected to MT1 and G.