Snubber Circuit Help

Thread Starter

swsean

Joined Jul 8, 2019
22
Hi guys, I am doing my FYP and I am facing a few problems.
I have designed a TRIAC Phase firing circuit.
For the phase firing circuit, I added a snubber circuit for it to function properly.
I am having problems choosing a suitable capacitor. So far I have found this model.

Its rating is 1000VDC, I am not sure if i can convert it to VAC instead.

1594103415521.png
Below attached is the simulation circuit on LTSpice

All help will be appreciated. Thanks in advance
 

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MrAl

Joined Jun 17, 2014
7,667
Hi guys, I am doing my FYP and I am facing a few problems.
I have designed a TRIAC Phase firing circuit.
For the phase firing circuit, I added a snubber circuit for it to function properly.
I am having problems choosing a suitable capacitor. So far I have found this model.

Its rating is 1000VDC, I am not sure if i can convert it to VAC instead.

View attachment 211520
Below attached is the simulation circuit on LTSpice

All help will be appreciated. Thanks in advance
Hi,

I guess you have not learned yet the difference between AC and DC rated caps?
 

MrAl

Joined Jun 17, 2014
7,667
Do you guys know any capacitors that I can use? The ac mains in where I'm living is 240Vac
Hi,

Did you try Mouser or Digikey?
They have a lot of parts.
Look for something with a rating of 250vac not just 250v though.
It is possible a regular ceramic would work but it is better to get one with an AC rating.
 
Last edited:

Thread Starter

swsean

Joined Jul 8, 2019
22
I have an additional question.
On the datasheet provided for the MOC3021 optocoupler, this is the provided circuit application
1594170056412.png
On the photo, the capacitor is polarized. Thus, it is not a AC capacitor.
Does anyone know if a AC capacitor will work? Is it possible to use a DC capacitor instead?

Your help will be very much appreciated. Thanks in advance.
 
Last edited:

MrAl

Joined Jun 17, 2014
7,667
I have an additional question.
On the datasheet provided for the MOC3021 optocoupler, this is the provided circuit application
View attachment 211591
On the photo, the capacitor is polarized. Thus, it is not a AC capacitor.
Does anyone know if a AC capacitor will work? Is it possible to use a DC capacitor instead?

Your help will be very much appreciated. Thanks in advance.
Hi,

The capacitor is just drawn that way sometimes. The only time you can assume it is polarized is when there is a little "plus" sign associated with the capacitor symbol. In this case it would be at the top. But there is none. Also, if it was really DC why would they be using a triac opto coupler.
Triacs are used with AC. But if you examine the circuit you should note if you see any rectifiers. Do you see any rectifiers and the input power is AC?
 
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