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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I want to protect the output of a 24V 20A SMPS from spikes, surges, fast transients etc coming back down the line from the experiment.
Would a 27V 1500W TVS diode across the ouput generally be considered sufficient, or should I be thinking more of a defence-in-depth strategy, with a parallel combination of TVS diodes, MOVs and gas discharge tubes to maximise protection with a generous amount of redundancy?
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
If the voltage into your experiment doesn't need to be perfectly constant, I would use a high value inductor on each line with a capacitor between them, on the output, forming a low pass filter. This doesn't rely on active components and is pretty bullet-proof.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I thought of something along those lines, Hen, but figured that a 20A common mode choke of more than a few mH would quickly become large and expensive.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I think the TVS will do the most, and several in parallel.
There is also a possibility ive seen before. a powdered metal toroid glued to a ferrite toroid then wound with a single wire will prevent fast energy changes, and block RF. add a capacitor and its pretty well armored.
Keep the powdered metal one smaller than the ferrite one. As the powdered metal stores some engery. thus increasing the TVS strain when they need to short.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
That's something I haven't seen before, Patrick. I'll see if I have any cores that might be useful lying about.
In the by and by I've been thinking of designing a foolproof attenuator so I can view the line state on my scope. In the years I've been a member here, I've seen one person after another get their gear zapped by spikes, so I thought that having a real look at back-EMF and other spikes under varying conditions would be a good place to start.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
So you'd use my inductor suggestion in the PI filter type circuit. I presume the TVS would do best on the end most cap, and that cap should be the smaller of the two caps.
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Protecting SMPS from spikes.
