surge protection built into ordinary household electronics

All household goods have filters in now any way to pass EMC regs. They obviously use just enough to get through the regs as cost is important.

All household goods have filters in now any way to pass EMC regs. They obviously use just enough to get through the regs as cost is important.

I include surge suppression because it's a product selling feature.. It's zap proof! (To a degree..see fine print..)

I've been using these lately...

Wall wart?

Otherwise: Think fuse and MOV.

Yep, one fuse, 3 MOVs should do the trick.

I'm planning to put a little transformer, a FWBR, a cap, and a 5V regulator on the PCB. There will be a relay to switch 20A 120VAC, so I need to run 120VAC to the board anyway. What would a wall wart have in it?

The design calls for a transformer, a full-wave bridge rectifier, and a capacitor, then a regulator. Should I just put that ZNR surge absorber across the capacitor? How do I select the size?

Look at the datasheet and select the device based on your line voltage.. Similar devices can be found inside suppressor computer power bars It goes across the line..but more can be added..like across the ground to neutral and another from hot to ground.

Alone, a little linear supply (xformer/bridge/cap/reg) can probably handle huge line spikes before something blows.. For example...AFAIK ...MOV's or TVS's are not popular inside little wallwarts..

The inductance of the transformer, maybe core saturation,the step down ratio.. Also I think the reverse breakdown of the bridge . ...the capacitive reactance of the filter cap.. All these things attenuate spikes anyways.. And then... Some regulators are tough to kill.. So Mr. Spike has to beat up lots of parts to smoke your project.

While on the topic..Has anyone had a linear wallwart die under normal use? D from BC

Looks like Matt's just buiding some sort of 120V logic-controlled switch. (They actually have relays that do this sort of thing already, or PLC's, or even the stuff from

But to help Matt out, any surge would have to get through his regulator (xfmr, bridge, caps, and 7805?) to do any real damage. A single MOV across the AC input is a nice touch, but it's not essential. Matt, MOV's have issues too, mostly relating to design lifetime.

If you're going to sell these things, you need to keep prices low or competition will eat you alive. At the same time, you'll have to make sure meet all the regulatory requirements (for example, conducted and radiated emissions if your project uses any high frequency stuff - even the clock crystal on a microcontroller.) And depending on where you want to sell them, you may need an independent safety certification like UL, TUV, CE, etc... Which costs money. And don't forget RoHS restrictions.

Is there some special environment that these devices will be placed in that you're especially worried about surge protection?

Yes. A wall wart charger for an NiCd powered vacuum cleaner attachment. The charge rate was "set" by transformer sag. The circuit was: secondary---diode---NiCd Really "extensive" engineering. :-( Cheap piece of crap. Two shorted cells in the pack took out the wallwart. My guess is that there are lot of similar "circuits" for wallwarts.

Ed

Ed

Actually, I've tried to cheapen some designs and ...it can get difficult and complicated! It's tough to figure out a sneaky amount of components..

D from BC

No special environment---I'm just trying to avoid building a piece of junk. Just trying to conform to something like accepted practice ...

even toasters, lamps, alarm clocks, and jugs?

Bye. Jasen

and here I was with the impression that your two chips were connected directly to the line current.

put a ceramic capacitor of 1.0uF or larger in parallel with the main reservoir capacitor (this will swallow any short spikes) and make sure your regulator is sufficientyly heatsunk to handle a little over-voltage and normally operating below 80% of it's maximum input voltage (to deal with longer surges, and persistant overvoltage)

Bye. Jasen

How big are your jugs?

about 2200W

:)