triac short circuit protection

[l90mehdi]

Posted on September 28, 2016 at 23:34

hi 

i am working on lighting dimmer.i want to protect triac when load is short.

so how can i do ?????

thank you

#triac

[Benoit RENARD]

Posted on December 06, 2016 at 09:54

Hello Medhi,

Triac is a device that is automatically turned off at the zero current when not drived by a gate current. No way to turn the device off when the current is flowing.

Even if the Triac technology allows high current robustness compare to MOSFET technology, if a short-circuit of the load appears when the Triac is ON, the way to protect the Triac is to add a fuse in series with the Triac and the load.

To design the fuse and to be sure that the Triac can withstand safely the high current before the cut-off event, take a fuse with a I²t parameter below the Triac specified I²t (see datasheet of your Triac).

Hope it helps,

Best RegardsBenoit  

[l90mehdi]

Posted on January 26, 2017 at 11:01

HI

renard.benoit

this is ture that when the triac is on and short circuit is occur so triac will be destroy.

now i am working on mosfet. it is working very good

thank you for replay.

[Benoit RENARD]

Posted on January 26, 2017 at 13:26

Hello Medhi

You're welcome.

Additionnal thinks regarding your choice:

To protect MOSFET against load short-circuit you need a specific complex circuit, monitoring the current with a shunt (with losses) to turn off the MOSFET in its SOA.

That's why the Triac is often preferred for dimmer purpose.

Others MOSFET drawbacks compare to Triac are: high power losses, price for a same current rating device, or very poor withstanding to lightning surge (Huge MOV is required)...

My advice is to reconsider your choice.

Moreover, according to your application requirement, a fuse is often mandatory for safety purpose, then no additionnal device/circuit to protect the Triac.

Hope it helps

Benoit

[l90mehdi]

Posted on January 26, 2017 at 15:08

HI

renard.benoit

yes. triac is better for dimmer. but i can not use fuse in my board. so when short circuit will be

occur the triac will be destroy.

now i use this schamatic. but with different part number.

line voltage in 220 volt rms with 311 volt peak.

load current is 3 amper.

so which parameter (rms or peak) should be to consider when read the datasheet and study soa curve ?

thank you