Re: More than 60% efficiency 5W travel charger


Fred Bloggs wrote:
dagmargoodboat@xxxxxxxxx wrote:
Fred Bloggs wrote:

dagmargoodboat@xxxxxxxxx wrote:

<snip>

Why not dump the linear regulator altogether and do as Tim suggests,
controlling and using the switcher directly to charge the battery?
That saves cost and cuts dissipation too.

Cheers,
James Arthur


The circuit is an off-line battery charger that uses an MCU together
with linear components to execute some kind of multistage battery
charger algorithm such as CC->CV->CV,trickle w/cutout at Imin; it very
well could be for LiPo. The so-called efficiency probably degrades
somewhat during the low output current CV trickle phase due to the
regulator circuit overhead, and is not a constant.


But ordinary LiPo charging doesn't require *that* much
sophistication: don't charge if the temp is too low or too high, and
precondition low-voltage cells @ <= 0.05C up to at least 3v.
Otherwise, apply current-limited constant-V until V=4.15 and
i=0.10*i(limit).

The switcher directly driving the battery--and being in turn
overseen/controlled by uC--seems perfectly capable of
applying/enforcing these rules. Cycle-skipping could save quiescent
dissipation when the unit is trickling or idle.

Unless this unit is somehow special, I don't see the problem with the
switcher driving the battery directly, nor the reason for the alternate
approach of the OP's block diagram.

Regards,
James Arthur


I don't see a whole lot of off-line switchers that charge Lithium
directly like that, the noise must be too much for precision voltage
regulation.

I've traced a unit or two ... I'll see if I can dig up a schematic to
post when I get home after the weekend. They're kind of cute.

Best,
James Arthur

.

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