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Fast Mains Transient protection circuits....please compare.

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Flyback

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Hi,

Which of the two Mains Transient protection circuits (attached) will give the best mains transient protection…top or bottom?
There is also a Littelfuse surge protection device in the AC line (not shown here), but it has 1100V of let-through.
(we don’t have much room on the PCB)
 

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gophert

Well-Known Member
Most Helpful Member
Hi,

Which of the two Mains Transient protection circuits (attached) will give the best mains transient protection…top or bottom?
There is also a Littelfuse surge protection device in the AC line (not shown here), but it has 1100V of let-through.
(we don’t have much room on the PCB)
So you are asking, "which is better, shunt or series?" My answer, it can be done either way successfully. I am not going to look up data sheets for parameters on all of your part numbers to analyze your circuit.

Do you have a more specific question?
 

Flyback

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Yes , i believe the Capacitor coupled one is quicker because less semiconductors have to switch on for it to operate....would you agree?
 

shortbus=

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Another one of those things! Complains about how the rest of the world does/controls things but yet asks the rest of the world how it's done.
 

Flyback

Well-Known Member
Thanks, seriously, as you know, a Mains transient is up in 1us, and the circutiry to protect against it needs to be up and operating within that time...this is no normal spec for a circuit.........its not so simple to depict just which of the attached circuits will act in the nanoseconds in which they are required to act.

I am depicting that the capacitor coupled one is better (quicker), but i have to admit that its not a commonly found circuit....why so?........why is such an effective circuit not popular?...is their a dreaded gremlin hiding in the bushes?
Both circuits are good, but which is best in your opinion?
The circuit that shunts the transient looks good because it shunts the load so it doesnt see an overvoltage..but does any of us seriously expect a ZR431 to be able to regulate the voltage across the load to 404V in the case of a transient which skyrockets the voltage up in 1us...i doubt it.....that ZR431 is going to act like a comparator.......and given that it has to drive a PNP which then drives a FET, then thats going to create a delay in the response to the transient , and when we only have one microsecond in which to act, then this is knife-edge stuff.....thats why i say the capacitor coupled one is better (quicker).....but the capacitor coupled one doesnt have the nice feature of shunting the transient round the load...so there is a knife edge decision on the cards here.

The trouble with getting scope shots of transients and the circuit's response, is that the transient itself involves fast di/dt and dv/dt waveforms, which induce noise into the scope leads, and so make the visualisation of the circuit's behavioural response to the transient less accurate....hence i conjecture to ask the experienced opinions of experts within.
 
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rjenkinsgb

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Mains transient is up in 1us
... Which is why most mains-powered gear has inductive filtering at input - it both reduces stray emissions and blocks (or drastically reduces) transients, so a simple capacitor after the inductor can absorb a lot of the residual energy and slow it even more.

You are likely to need that for EMC compliance, so I'd not worry too much about the transient side until you have input filtering in place.

Anything getting past a good LC filter no longer has a fast DV/DT waveform to worry about!
 

Flyback

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Anything getting past a good LC filter no longer has a fast DV/DT waveform to worry about!
Thanks, with our case, the trouble is often that we can only fit in the smallest inductor, with the lowest current rating, and they start saturating if the transient is more than a certain size.

You are likely to need that for EMC compliance, so I'd not worry too much about the transient side until you have input filtering in place.
Thanks, as you know, with power factor corrected buck or flyback LED drivers, there is little capacitance on the DC bus…..thus what happens during power-on-at-mains-peak is that the EMC filter L’s and C’s ring with each other, and cause the DC bus to go up to up to twice mains peak…..and if you don’t have a current clamp at the input, then that twice mains peak voltage can overvoltage your led driver IC if it has a 450v vcc pin (ours does).

Therefore, the current clamp is needed before even thinking about mains transients…..and then the current clamp can be used also for mains transient protection……so its worth spec’ing it for that because you have it there anyway
 
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gophert

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Thanks, with our case, the trouble is often that we can only fit in the smallest inductor, with the lowest current rating, and they start saturating if the transient is more than a certain size.



Thanks, as you know, with power factor corrected buck or flyback LED drivers, there is little capacitance on the DC bus…..thus what happens during power-on-at-mains-peak is that the EMC filter L’s and C’s ring with each other, and cause the DC bus to go up to up to twice mains peak…..and if you don’t have a current clamp at the input, then that twice mains peak voltage can overvoltage your led driver IC if it has a 450v vcc pin (ours does).

Therefore, the current clamp is needed before even thinking about mains transients…..and then the current clamp can be used also for mains transient protection……so its worth spec’ing it for that because you have it there anyway

You always present your problems like nobody else has the same problem. With the number of high power LED installations out there, someone (many companies) have solved this. We just did a tear down on 12 different 480V and 277 LED lamps for warehouse / high-bay industrial buildings / big-box stores and parking lot lighting. They all worked well - what are they able to do that your driver cannot?
 

Flyback

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Our drivers are working fine but we always want to improve them and make them more cost effective.

Won't a simple zenamic (VDR) take care of that? I'd expect that to be a relatively slow and low energy pulse.
The thing is, on this prototype, we have to protect an IC with a 450v vcc pin........we cannot find TVS's which are rated at a voltage that
1...wouldnt trip on high mains
2...Trips enough to protect our 450v vcc pin.

As you know, the clamp voltage of TVS's goes up as the current in them increases, and it goes up enough to breach the 450v vcc pin.
 

gophert

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Funny part, two were made in UK. Someone recently claimed there is no electronics industry in the UK - it made me laught when I read that "Made in the UK" sticker.
 
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