using triac directly with uC

[skmdmasud]

Hi..
if i connect a triac directly with my uC pin then is there any change that switching the load on & off will reset my uC or make it behave abnormally. I will be switching AC water solenoid with this. I dont want to use optical isolators i want to keep parts to minimum. I dont want to use mechanical relays as from my previous experience they reset my uC very often. I have attached a sample diagram.

Regards
Masud

 

[MrAl]

Hi,

That should work ok but you may have to add a gate resistor (from gate to +5v in your schematic).

It appears that you are driving the gate negative, which is the best way to do it too.

Also, you dont need a crystal controlled uC oscillator. An RC oscillator built into many types of uC's should be fine.

Relays and other coil type devices (fans, etc.) develop high voltage spikes sometimes which bothers uC's on occasion. That happens when the coil is open circuited after being energized.

 

[skmdmasud]

Hi,

That should work ok but you may have to add a gate resistor (from gate to +5v in your schematic).

It appears that you are driving the gate negative, which is the best way to do it too.

Also, you dont need a crystal controlled uC oscillator. An RC oscillator built into many types of uC's should be fine.

Relays and other coil type devices (fans, etc.) develop high voltage spikes sometimes which bothers uC's on occasion. That happens when the coil is open circuited after being energized.

Hi MrAl
the diagram is from the web just to show the triac as an example.

If I touch the gate of the triac will it give me a 220V shock....or is it isolated.

 

[MrAl]

Hello again,


The gate is not isolated from the two main terminals.

However, the two main terminals and the gate may be isolated from the metal back of the (typically) T0-220 package. It depends on what version you buy. Some are isolated from the heat sink tab, others are not isolated. That's so that if you buy an isolated type you can mount it on a heatsink without making the whole heatsink live.

But the gate is not isolated. To get an isolated gate drive you could use an opto coupler, such as a triac opto coupler or a transistor type.

 

[schmitt trigger]

Yes, it will give you a shock if you touch the circuit.