Hello fellow members its me once again

I am trying to build a low cost power supply so in order to accomplish my goal i have been diggin' into my beginner electronics book and there it mentions about snubbing AC. Which it is something i haven't even considered on the first place.

So with that idea in mind i went to my local electronics store. But they dont have them.

Looking at the circuit attached, i tried to find an equivalent to a snubber but using discrete components.

Unfortunatelly i have no idea how to calculate the wattage needed for such resistors and capacitor?.

Please, i would like someone give me a hand with this?.

Is it possible to build an RC snubber circuit with discrete components, if so., what would be the values i should choose? .

I just dont want to get hurt or injured or damage accidentally the components involved.

Thanks

 

The snubber is used to protect semiconductor switches during inductive switching.
And also in SMPS
In ur case at the input of a transformer is typically not necessary, but would not hurt to have.
A better approach is to use a MOV, Varistor is used to suppress large spikes that sometimes occur during storms and high load switching times. Try to get a MOV with the proper rating on the mains supply that you use and together with a fuse you will have sufficient protection

 

Okay i will see if i can get one of those. I believe you're refering to a Metal Oxide Varistor.

However if i want to introduce or place the snubber at the input of the transformer?. How i do that?. What wattage is needed for the resistor? (Is 100Ohm at 10W okay for 220 volts? )

I just dont want the resistor blows up when i plug the powersupply.

 

The transformer input that you show probably does not need a RC snubber across it. If you are blowing that 1 amp fuse. use a slo-blo unit and size it for 200% maximum I rating. For a MOV, a 250 VAC unit with a 40 joule rating (14mm) will be sufficient for most over-voltage events.

Cheers, DPW [ Everything has limitations...and I hate limitations.]

 

One of the commonest standard snubbers is 0.1uF plus 100 Ohms.

You can work out the impedance of the cap at your AC supply frequency, then from that work out the current through the 100 Ohms and therefore the power rating required.

If it's to be connected to the AC supply, the capacitor should be an X-type, rated for continuous operation on the AC line.

 

The following links might be of assistance to you:

http://www.hagtech.com/pdf/snubber.pdf

http://focus.ti.com/lit/an/slup100/slup100.pdf

 

Hi,
I'm a degreed electrical engineer and a professional power supply designer for over 35 years now. I've designed all types: switching, linear, dc-dc, dc-ac inverters, magnetic amplifiers and more.

In the circuit shown, since there appears to be a Transient Voltage Suppressor (TVS) on the AC Line side of the transformer, there is no need for a snubber, nor is there a need for an MOV. In fact, the MOV would make the power supply less reliable. Your TVS will do a much better job on input spikes like those caused by lightning. Since your power supply is not a switcher, there is absolutely no need for a snubber. It would be a waste and would do nothing. If you need help in picking out the TVS, I would recommend a 1.5 KW, with a breakdown voltage of at least 375V that's bidirectional.

Good luck,
Kamran Kazem

 

Hi,
I'm a degreed electrical engineer and a professional power supply designer for over 35 years now. I've designed all types: switching, linear, dc-dc, dc-ac inverters, magnetic amplifiers and more.

In the circuit shown, since there appears to be a Transient Voltage Suppressor (TVS) on the AC Line side of the transformer, there is no need for a snubber, nor is there a need for an MOV. In fact, the MOV would make the power supply less reliable. Your TVS will do a much better job on input spikes like those caused by lightning. Since your power supply is not a switcher, there is absolutely no need for a snubber. It would be a waste and would do nothing. If you need help in picking out the TVS, I would recommend a 1.5 KW, with a breakdown voltage of at least 375V that's bidirectional.

Good luck,
Kamran Kazem
Senior Member of IEEE with 30+ years of power electronics, & general analog, digital, & microprosessor design. BSEE & MBA from UC, Irvine
kkazem

Interesting Response

 

In fact, the MOV would make the power supply less reliable. Your TVS will do a much better job on input spikes like those caused by lightning.

OK buddy. It's time to tell me the difference between a MOV and TVS
< my mistake>

 

Rifaa, this may come as a 'shock' to you: (pun intended)

There are three significant advantages to using TSV rather than MOV's:

* Varistors (MOV's) typically have an order of magnitude more leakage current than TVS devices (mA verses µA).
* TVS devices avalanche and switch into conduction up to 5 times faster than MOVs, affording significantly faster reaction to transients.
* Metal Oxide Varistors degrade over time. The degradation is accelerated with increased temperature and repeated surge events.

 

Wow, i can't believe many people answered my post. First of all i want to say thank you to everyone who gave me a hint on how to solve my issue with snubbers.

Hi,
I'm a degreed electrical engineer and a professional power supply designer for over 35 years now. I've designed all types: switching, linear, dc-dc, dc-ac inverters, magnetic amplifiers and more.

In the circuit shown, since there appears to be a Transient Voltage Suppressor (TVS) on the AC Line side of the transformer, there is no need for a snubber, nor is there a need for an MOV. In fact, the MOV would make the power supply less reliable. Your TVS will do a much better job on input spikes like those caused by lightning. Since your power supply is not a switcher, there is absolutely no need for a snubber. It would be a waste and would do nothing. If you need help in picking out the TVS, I would recommend a 1.5 KW, with a breakdown voltage of at least 375V that's bidirectional.

Good luck,
Kamran Kazem

It seems kkazem has the expertise? to talk about all kinds of power supply.

However his response about TVS let me some confused.
Is there any way that this topic would be a little bit easier for non-experts like me?.

I hope i am not asking too much for this.

As far as i understand, in his oppinion there is no need for a snubber as well the MOV. (Is it really that will make the power supply less reliable if it is placed at the input of the transformer?). Because i dont know if there is any way to tell that?

Are you refering to a transient voltage suppresion diode?, like the ones on this picture? http://upload.wikimedia.org/wikipedia/commons/b/b0/Transils-01.jpeg

Is their operation simmilar as varistors? i dont know about the theoretical background of them. (TVS)

It seems interesting, i haven't any idea about their existence. (Sorry maybe i am so beginner).

The following links might be of assistance to you:

http://www.hagtech.com/pdf/snubber.pdf

http://focus.ti.com/lit/an/slup100/slup100.pdf

Thanks for these documents, they are very useful to me. They dont mention much about the power for use on discrete components, but the theoretical information is very good.

One of the commonest standard snubbers is 0.1uF plus 100 Ohms.

You can work out the impedance of the cap at your AC supply frequency, then from that work out the current through the 100 Ohms and therefore the power rating required.

If it's to be connected to the AC supply, the capacitor should be an X-type, rated for continuous operation on the AC line.

Yes, at my local electronics store they told me the most common ones were to use an RC network 0.1uf+100 ohms like the ones on this picture http://upload.wikimedia.org/wikipedia/commons/e/ec/Snubber.jpg, unfortunatelly they ran out of them.

OK buddy. It's time to tell me the difference between a MOV and TVS
They practically do the same thing.
If MOV makes a supply less reliable so will a TVS.
Being based on semiconductors they are all the same.

I beg to differ on this matter buddy. MOV will not make a supply less reliable.
In fact it will protect the supply during a surge.
I have seen plenty of blown MOV's and they do their job pretty well

Now i am confused, which makes the power supply less reliable, a MOV or the TVS?.

Well i think as far it protects the supply it is fine to me.

 

I think you missed my post. (you were posting while I was)

In post #14 you can see that the TVS is the better way to go..

So you shouldn't need the snubber.

 

So MOV is outdated now....

 

Rifaa, this may come as a 'shock' to you: (pun intended)

Hey retched... what does pun intended mean
is it a gesture or expression

 

So MOV's look capacitors and TVS looks diodes, am I right?

 

Rifaa, sorry bro, yes a pun is an expression for a descriptive word used in a meaning that can be taken two ways

Like: When the circuit worked, I was shocked!

I was surprised, not electrocuted, but because we are talking about electronics, That would be a 'pun'.

And TVA is diodes and a MOV looks like a cap. Correct.

 

Then I stand by what I said.
I have seen mov's a lot and it seems I have them both plenty of em' for that matter.
MOV's are used in supply's to protect them from excessive voltage, where else TVS are used where fast action is needed such as for phone and network equipments.
Which means MOV does not make a circuit less reliable, it's just that it's not as fast acting as TVS.
A supply designer or what ever bro, if you don't deal with items at assembly and trouble shooting level as I have been for so long then I guess you don't know what others may use components for, and if you don't personally experiment with such supplies then you never really know do you.

So retched what was that you was so "puned" about.

 

I think you missed my post. (you were posting while I was)

In post #14 you can see that the TVS is the better way to go..

So you shouldn't need the snubber.

Okay thank you, i believe my power supply would be better protected with the TVS in case you are refering to a Transient voltage suppression diodes (transil?) like these ones http://www.mdesemiconductor.com/DIODES.jpg , (will this be good for 220 VAC? http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BZW04-213RL-ND )

So MOV is outdated now....

How come has the MOV became outdated?. Is there any particular reason for that?.
Well i'm just a beginner.

Then I stand by what I said.
I have seen mov's a lot and it seems I have them both plenty of em' for that matter.
MOV's are used in supply's to protect them from excessive voltage, where else TVS are used where fast action is needed such as for phone and network equipments.
Which means MOV does not make a circuit less reliable, it's just that it's not as fast acting as TVS.
A supply designer or what ever bro, if you don't deal with items at assembly and trouble shooting level as I have been for so long then I guess you don't know what others may use components for, and if you don't personally experiment with such supplies then you never really know do you.

So retched what was that you was so "puned" about.

Okay message noted. Although it was not intended to me .

 

Thanks for these documents, they are very useful to me. They dont mention much about the power for use on discrete components, but the theoretical information is very good.

I am glad we can be of assistance to you. However, it is not clear to me what you mean by "They dont mention much about the power for use on discrete components." Thank you

 

Please expand "TSV" into whole words so I can look up this device.