Why are there so many DC barrel connectors?

[James Perrett]

The centre negative thing was around in the 60's and certainly used on Philips radios - probably other makes too.

I've just bought myself one of these which seems to handle most eventualities

https://cpc.farnell.com/powerpax/sw4177 ... dp/PW04007

[ef37a]

To get a bit serious...this plethora of DC connectors and standards is just one of so many examples of where a free market does not work for the good of the consumer or the planet.

A power supply delivering up to a few tens of watts from the AC mains supply is not a very challenging device to design and I am sure engineers over the years have asked their bosses why they need to design an in house variant when 'Acme' down the road have a perfectly usable product.

Very late in the day the EU is trying to rationalize the situation, let us hope they succeed?

I would suggest we need very few different supplies. My wish list,

5V at 2A, 4A
12V at 2A, 4A,
24V at 1A, 3A, 5A

Can anyone think of anything that needs more than 60W?

Dave.

[Martin Walker]

I've just bought myself one of these which seems to handle most eventualities

https://cpc.farnell.com/powerpax/sw4177 ... dp/PW04007

Looks like I'll be buying one of those too James, as it caters for almost any eventuality, including both positive and negative polarities - thanks for the link!

[Arpangel]

A switchable AC/DC supply would be very welcome.

[Nazard]

A switchable AC/DC supply would be very welcome.

For the first few times until you forgot whether you had it on AC, or, DC and plugged it in.........

[ef37a]

A switchable AC/DC supply would be very welcome.

For the first few times until you forgot whether you had it on AC, or, DC and plugged it in.........

Indeed and low power, under 10va say, transformers are VERY inefficient and consume almost the same power whether or not the device they are powering is turned on or not. SMPUs consume virtually no power when unloaded.
Thus 50Hz jobbys are banned by EU law unless they have a mains switch on them, in any case, the technology to make an SMPSU DC output supply is vastly different from a transformer supply.

On a related 'safety' note. I am also not in favour of external 230/115 switches having had several 'US' pre prod amps zapped by less than vigilant guitarists!

Dave.

[James Perrett]

A power supply delivering up to a few tens of watts from the AC mains supply is not a very challenging device to design

Indeed I seem to remember linear supplies being one of the very first topics we covered on my electronic engineering course. A good introduction to diodes and capacitors if I remember right although regulated supplies came a little later and I'm not sure whether we ever covered switch mode power supplies.

Can anyone think of anything that needs more than 60W?

The PSU for the laptop that I'm using seems to be able to supply around 200W. Laptops seem to have standardised on 19V, probably due to that being the charging voltage needed for 4 lithium ion cells in series.

[ef37a]

Well James, I had thought we would consider laptop chargers a special case?
They are much more complex than basic 'brute force' SMPSUs that are used to just supply a clean, stable voltage as (I think) they include 'smart' charging circuits to get rapid charging but keeping the batteries safe.
This old Lenovo does indeed have a 20V 90W supply.

However, I think the same rules should apply in that any '19 volt 100W' should be safe to use on any laptop that specifies such a power level? I once had to buy a whole new charger just because the LT cable had failed on mine and there is no way you can buy the OEM power plug.

I don't know if I am just incredibly lucky but having bought about six laptops over the last ten years I have never had a power supply fail internally.

Dave.