DC Barrel jack size

That is not a sufficient description. They also vary in length.

There is also a 5.5 x 2.5 barrel jack. Google returns 1.1 million hits on this one and only 0.8 million hits on the 5.5 x 2.1 jack. So it's a toss up and not a fun one.

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** 5.5mm is VERY common. 2.1 is quite rare outside of cell phones.

..... Phil

5.5mm is the outer diameter, 2.1mm is the diameter of the inner pin and very common

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** The idiotic way the OP posed his Q threw me.

The inner pin size varies, think there are 4 different ones.

..... Phil

didn't think about search result numbers. I used to do that a lot but seems to me I haven't seen it on Google anymore so quit doing it.

We use a lot of 5.5x2.1 warts and cables and PCB connectors.

There are locking versions too. Some customers want something more secure than the usual one.

A better question might be, "what do products similar to what you're using/designing *tend* to use?" This can be embelished to address the voltage/current ratings as well as polarity.

If you're designing a product, give ample consideration to after-market supplies of compatible "power supplies" -- unless you intentionally want a captive market.

I've seen right angle connectors used in places where a straight-in connector wouldn't fit. And, connectors with exceedingly long barrels (mating receptacle is too far recessed inside the device). Both pose problems to the end user as he'll often be looking for something as a replacement for the power supply that he's misplaced.

Finally, *label* the power inlet so the voltage, current and polarity are obvious (not much you can do to address the physical characteristics) as well as the power supply. The latter is often difficult if you're just buying from People's Wall Wart Factory #886.

(I label every wall wart, brick, etc. with the model number of the device to which it mates. Often, that's still a bit of a puzzle as I might not remember that a "960 ultra" is a phone... but, at least it acts as confirmation when you *do* find both mating parts!)

[FWIW, a pTouch labeler ALWAYS finds application labeling *something*!]

We use 5.5 x 2.5 mm. That way when somebody tries to use the wrong wall wart, the connectors won't mate. Similarly we use 24V warts because that's the highest common voltage, making our boxes harder to blow up.

Cheers

Phil Hobbs

That was not the point of my post. I was trying to point out (obviously not very well) that there is room for confusion between the two connectors. The difference between the 2.1 and 2.5 mm inner conductor (which was obvious to everyone but Phil) is not easy to discern to the eye. Combine that with the length issue and unless you are selling both parts of the combo there is much room for a mismatch. Ask me how I know...

It all depends on the details of the requirements, but I don't think I would use a barrel jack in the first place. They were going to use one of these on the vent project I'm on with the only other experienced engineer and myself arguing to not. In the end another connector was picked because our power requirements increased and the only inexpensive power pack used a DIN circular connector. Unfortunately this locks into a specific manufacturer. Oh well...

yeah that.

USB C is becoming increasingly popular in new equipment.

There are a couple of little 3-lead switcher blocks, 78xx style, that will accept anything up to 72 volts. It's hard to blow them up.

I'm exploring the possibility of doing DIY PolyZens using SMT polyswitches and TVSes, mounted together on a little routed PCB paddle, with a copper pour on the common terminal and grounded via a trace.

Seems like it should do the business--any serious overvoltage will heat up that polyswitch well before the TVS fails or desolders itself.

Cheers

Phil Hobbs

2.1 mm

I did exactly that once. I tested it thoroughly, but despite that we had a few returns where the TVS had shorted. It was a 12V-only automotive product and it usually worked fine on 24V supplies, but some customers managed to find a set of conditions that broke it. We shipped around 50k units and I think only 12 came back with this problem.

John

A little universal input protection thing, a mouse-bite baby board maybe, would be great.

We used the TI E-fuse things on one project. They tended to blow up and were very hard to replace. Surface-mount real fuses have been problems too.

Lately I use a polyfuse and a TVS and a 24 volt input. That's not perfect but seems to be pretty good.

This Valcon 16-pin one is quite nice if you don't need the super-speed connections or just want to adapt a USB2 design:

It is the one used for the Raspberry Pi 4 power input. The key benefits are:

1) Through the board body solder lugs make it robust 2) Only 16 surface mount pins in one row so it is easy to hand solder if necessary 3) Visual inspection of all the connections is easy. John

Tyco used to make them: PolyZens, recently discontinued. They were even better because they laminated the polyswitch and the TVS together for improved coupling.

I suspect they never had the volume to bring the price down to an attractive level--it's hard to span a 2D space (voltage, current) with a

1-D product line.

Yup.

That's what we've been doing, mostly the Littelfuse RXEF series and SMBJxxx TVSes. I expect that the paddle thing will make a nice snap action.

Cheers

Phil Hobbs

That looks good, with the big thru-hole tabs. I'll get some.

We generally use an FTDI usb-serial chip into a uP UART, so speed is not an issue.

Radial thru-hole. Good. The surfmount polyfuses have issues.