Monolithic Buck-Boost Converter IC

Whew, what a mouthfull that was..

Hi everyone,

Could these be the perfect regulator chips?
Buck AND Boost
Min Vin=1.8, Max Vin=5.5

Anybody using the TI REG710-XX (3.3v or 5.5v) Regulator?
(Only 30ma output)

And: LTC3440

Or: For Luxeon Lovers...LTC3441 (I think this is a 1A)

Might even be able to solder these.

Different IC's recieved from Maxim are so tiny, a cricket
would have trouble soldering them.

It would be even nicer if they actually covered the range of a 2x123. I have no idea why people design circuits that cannot handle the obvious Li cells nominal 6 - 7 volt.

[ QUOTE ]
Heabob said:
Could these be the perfect regulator chips?
Buck AND Boost
Min Vin=1.8, Max Vin=5.5



[/ QUOTE ]

Probably quite useful for their intended use....but not for driving LEDs. I think we decided some time back that *current*, not voltage regulators are what we want? After all even Arc came to this conclusion a few years back.

Doug Owen

[ QUOTE ]
HarryN said:
It would be even nicer if they actually covered the range of a 2x123. I have no idea why people design circuits that cannot handle the obvious Li cells nominal 6 - 7 volt.

[/ QUOTE ]

'cuz it ain't obvious to a guy designing *computer* parts?

Doug Owen

Hi Again,

Thanks for the quick replys, guys.

I forgot to mention what my intended use for this was.

Wife's Christmas Snowman (has 3 flasher type incan. bulbs)

Fair amount of space inside. Runs on 3AAA Alkalines.

Already bought a 5mm "rainbow" led, flashing/fading,
3.5v @ 20ma.

Probably should just jumper out one battery slot and run
3v with a boost circuit like the "world torch kit"
Although, I would rather run it on 4.5v (more runtime)
Not in direct drive though.

Read somewhere about using a "ballast" Tungsten filament
bulb in series with LED being slightly better than a
resistor.

I've read alot of posts on this forum and can't seem to
find what I need.

How about a Si diode in series with 4.5 Volts for 3.8? That's 85% efficient, a tough goal for a converter....

Doug Owen

Thanks again Doug,

Interesting idea, and simple too.
You mean a signal diode like an IN914?
Used to just drop the voltage right?
What about limiting current to 20ma, I know a diode has
some internal resistance, but is it enough?
Will need to boost when Vbatt is < 2.5v, or will it run
down lower and just get dimmer?
I'm kind of new at this stuff, (built a few circuits, with
home made etched pcbs, about 20 yrs ago.)
Then came computers...

1N914 would be a good choice, as would 1N4148 or 1N400X, as all we need is the voltage drop (and enough current *capacity*).

All the 'self flashers' I've seen are self current limiting (as long as the voltage is reasonable)...if I'm wrong I'm sure to be corrected at the speed of light. Tough crowd here at CPF ya know.

Doug Owen

I also have some 1N4004's around, (a little more
beefy compared to 1N914)
Forgot to mention the data sheet for this LED (Vf=3.5)
Not sure if this is max, will check first.
Assuming that the LED "load" itself will drop the Vin
to within range, should be ok...?
Thanks again, for your help Doug.

[ QUOTE ]
Heabob said:
Whew, what a mouthfull that was..

Hi everyone,

Could these be the perfect regulator chips?
Buck AND Boost
Min Vin=1.8, Max Vin=5.5

Anybody using the TI REG710-XX (3.3v or 5.5v) Regulator?
(Only 30ma output)

And: LTC3440

Or: For Luxeon Lovers...LTC3441 (I think this is a 1A)

Might even be able to solder these.

Different IC's recieved from Maxim are so tiny, a cricket
would have trouble soldering them.

[/ QUOTE ]


I'll refer you to this thread:
LTC3441 Discussed in June

Thanks NewBie,
I do remember reading this thread before, WAY over my head.
You must be using some of these IC's in flashlights?
Kinda small packages for me to use.

Seen Any Buck-Boost IC's in TO-92 or SOT-23? Yuk Yuk...
(I'm dreaming again)

For 3 cell Alkaline
Vin=1.0v to 4.5v
Vout=3.3
Lux3 @ 700ma

(Just buy a pill, right?)

Works good using 2 diodes in series, as 1 diode was
giving me 3.9v at LED. Just a tad high.
Using 2 diodes, I get 3.1v.
A little low, but SAFE.
Probably easier just to direct drive it from 2 cells.
Thanks again Doug...