BL> I haven't got the data sheets, but those little low-voltage IC
BL> switch-modes struggle to get 50% efficiency, and at 50% to get
BL> 6.3 at 3A you'll put in 12.6 at 3A... so what's the difference
BL> with a series regulator? Even if you got 70% (a miracle, IMO)
BL> you'd put in 2.2A...

DD> How does NatSem claim 70-80% efficieny for this thing then?
DD> (Later: yeah, false advertising). 

 It's a question fo how you measure it. They wouldn't actually lie,
but they pick the absolute *best* condition to do the measurement
(even if it never happens in practice). It's like Toyota claiming
114KW out of their 2.4 litre Camry engine. I'm quite sure there is
*some* way they can measure that much, but it's probably in vacuum
with the motor stripped and blueprinted. What you measure at the back
wheels in top gear is more likely to be 50KW.

 My favourite is "music power" for stereos. I actually invented that!
Our little hi-fi was a genuine 2W stereo, but we claimed a music power
of 10W. I couldn't actually measure it... but I could calculate it and
I got it up to 8W using a very short pulse on just one channel using a
regulated power supply. 

 Actually, it was total bullshit. Nowadays, computers don't even
bother to invent a theoretical power. They just claim 40W for a 2-inch
speaker!

BL> The series regulator has other advantages (besides keeping your
BL> feet warm on a cold night). The VCR motors take a high starting
BL> current before they get the wheels turning, and that's *just*
BL> what a switch-mode doesn't like.

DD> What VCR? 

DD> This is to run a small DVD player, which came with a mains
DD> switch-mode PSU. 

 Oh! Why does it take so much power? 20W is a hell of a lot for a
DVD. It should be closer to 8W... 5V at 1.5A.

Regards,
Bob




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