Risking it all on a Poundland Purchase.

I think it's basically 100 mA or more if the device asks nicely* (up to 500 mA I think - or is it 1A?). Your laptop is just being stroppy. (Some devices like external HDDs expect to be connected to two USB sockets to provide enough power.)

  • I don't know how this 'negotiation' works. What about things like USB mug warmers?
Reply to
Max Demian
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That is absolutely appalling!

Reply to
Steve Thackery

I've broken many open, to pinch the small switched mode PSU out of them to use for something else. I've never seen one with any protection against the FET shorting (which would generate 12V output), but I've never had that happen yet either.

You can get ones which supply 4.2A now, for 2 x 2.1A USB outputs.

Reply to
Andrew Gabriel

I've taken to carrying a few around in my laptop bag. If I'm away at a meeting, there are always one or two people walking around trying to borrow phone chargers (most commonly iphone users).

Also, they are a bit fragile. You don't need to yank very hard on the cable for the conductors to break. I'm probably on the third one for my own use in a couple of years.

The style that Poundland do does change periodically, but they usually have at least one variety in stock.

Reply to
Andrew Gabriel

Many moons ago I bought a PSU 'kit' to supply 6v to the motor of a portable tape recorder. It was advertised as supplying 6V, 9V or 12V at up to 1A. It consisted of a 12V output transformer, a rectifier, a 12V Zener, a multi-tapped dropper resister and some capacitors for smoothing.

It would really only supply 1A at 12V; the use of the dropper resistor meant that it couldn't supply any other voltage with reasonable regulation - even a tranny with a push-pull output wouldn't have worked.

Reply to
Max Demian

DCIM (Digital Camera Images) and DCF (Design Rule for Camera File System) one of those 'standards' that is not quite a standard.

formatting link

Reply to
djc

It's still the case, but most USB ports don't police the current drawn against that negotiated, although the USB hub chips commonly used do include the logic to do so.

Nokia used a private scheme before USB power supported the passive signalling with resistors on the USB data lines. If fed with < 5.5V, the phone limited itself to low current draw. If fed with something fractionally higher (which is illegal in the USB spec), the phone assumed it was running from a charger and drew more current.

In theory, drawing more than 100mA required exchanging USB packets to ask if it's possible to do so, which required at least some microcontroller capability on the power driving side, which wasn't practical for USB power supplies and chargers. The current spec allows them to signal up to 2.1A available by the use of resistors tied to the data lines.

In the current USB spec, much higher power is available by negotiation (cranks up the voltage to limit the current in the connectors, and the cable has to be suitable too). It's intended to provide enough power to run a laptop. However, I've not yet seen any devices making use of high supply voltage USB.

Reply to
Andrew Gabriel

Yes. We had to spend about two-three months going though what had been done and redesigning/rebuilding the kit. It was also plauged with RF loops, leaks, etc.

By the time this all came to light the originator had changed job and employer. Heaven knows what happened next!

Jim

Reply to
Jim Lesurf

These days, a large order of a popular SMPSU chip works out cheaper per part than a row of fat power dropper resistors.

They can make the case a lot cheaper too, if there's not a lot of heat generated.

Reply to
Ian Field

The better ones have a row of tappings on the secondary - but the regulation still isn't great!

Reply to
Ian Field

There have been high profile prosecutions because formatted memory cards aren't necessarily empty.

Reply to
Ian Field

That's been the prime reason for using switching regulators in small wallwart powered devices (ethernet switches, routers etc) for over a decade now.

For once, a cost cutting measure that offers the end customer an even greater benefit in that you can replace a faulty wallwart[1] with any

6 to 15 volt DC wallwart with a matching or greater VA rating with impunity as long as the plug matches the socket.

If the plug doesn't match you can just cut the plug off the end of the old wallwart and graft it onto the end of the replacement walwart's lead (or, better still if you know how to use a toffee hammer and a hot glue gun, swap the complete lead over to the new wallwart).

This is an exercise I've done many times, usually to replace an inefficient wallwart with a more efficient one to save a watt or two on a 4 to 6 watt load. It's not a lot by itself but the savings can mount up on a bunch of such kit that's typically running 24/7 year in year out.

[1] Even the cheaper ac output transformer types can usually be replaced by a DC output wallwart on account the input circuit of the switching regulator has a fullwave bridge rectifier with a 16 or 25v rated smoothing cap through which the DC from the wallwart will be passed at the expense of about a 1.5 volt drop in the rectifier bridge. 6 volts might not be quite enough in this case. A 7.5v minimum up to a maximum of 15v should still be ok (and if the input cap has a 25v rating, you can use even higher output voltages right up to 25v - no artificial voltage veto as per the same circuitry typically used by laptop makers).
Reply to
Johny B Good

That's far from being a problem unique to memory cards. If you don't have access to a PC of some sort with a secure erase/format utility, you can always record a video or three after the in camera format using the most memory expensive video format possible.

It might take a few hours to over-write the incriminating evidence and need more than one video shot if hitting the 59 minute or 4GB limit with larger media and quite possibly a change of battery to boot but at least it's doable 'in the field' when away from a suitable PC.

A suitable scene to shoot such a movie of would be a distant scene at maximum zoom to enhance the heat haze shimmer or the traffic flow on a busy road to maximise the memory consumption rate. In the privacy of your own home a movie of the TV tuned into an action movie broadcast would also suffice. No worry about copyright infringement since you'll be formatting the card as soon as you've done with obliterating the evidence.

Reply to
Johny B Good

He went to work for Amstrad? :o)

Reply to
Huge

I was trying to remember which hard-drive manufacturer Amstrad took to court because their crappy drives were giving Amstrad a bad reputation.

Reply to
Ian Field

For a start, the wire-bonds to the chip die have to be there whether they're to PCB tracks or pins that will need soldering.

Solder joints were a reliability weak spot before dodgy RoHS solder.

Black-blob chips seemed to have flourished since RoHS.

Reply to
Ian Field

Having missed out at Poundland, I went in Lidl and this weeks weekly offers include a £3.99 cig-socket adapter with generous assortment of pluggable phone charging connectors.

Curiosity overcame my tight fisted ness - I'll crack it open later to see what's in it.

Reply to
Ian Field

Yesterday I managed to catch Poundland with some stock of USB adaptors (FX Factory brand) I only wanted it to break open and see what's in it, and for only £1 why not.

It uses the very popular MC34063 SMPSU chip, there was a low value resistor on the PCB that could only be for the current sensing pins, so I didn't need to trace out the circuit to find out.

Build quality is pretty much OK for something that only cost £1.

Reply to
Ian Field

So far I've cracked open a £3.99 one from Lidl and another from Poundland, neither looked conspicuously dodgy, but 12V down to 5V involves a buck regulator that has a (switching) series pass transistor - if that fails short circuit, the 12V will pass through like a dose of salts!

If the application is life support critical, any risk can be eliminated by a thyristor "crowbar" failsafe circuit. Easy enough to splice a breakout box into the lead or with a bit of manual dexterity could be squeezed into the existing case.

Home Bargains have a cigarette adaptor for £1.49, but it only has a white thin-wide connector - probably for ipad or something.

If you want a failsafe 12V to 5V converter; start with a buck converter that produces 3.3V - then use a flyback converter to boost it back up to 5V.

If the flyback transistor fails; it shorts the output and produces no voltage out - just in case the preceeding buck fails, its dead easy to rig the flyback section to latch up on overvoltage, also producing no output.

Reply to
Ian Field

I notice there are ebay traders offering this chip in ten off quantities at 99 pence, post free (Chinese suppliers) so you can see why these things can be knocked out for just one pound a piece and still allow for some profit (I'd imagine the rest of the bits would probably soak up another 40 to 60 pence worth of component costs when manufactured in bulk).

Reply to
Johny B Good

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