[Noisebridge-discuss] DC-DC Power conversion - Cheapish finds!

[jim]

There's always homebrewing: 
* a voltage divider to the base of a transistor 
with appropriate volt and amp specs in emitter 
follower configuration (emitter is about 0.7 V 
below the voltage at the base. 
* an LM 338 in TO3 case: these provide up to 
five amps. Heatsink advised for over 1 amp. 




On Tue, 2013-01-08 at 08:35 -0800, akleider at sonic.net wrote:
> I see that Jameco also sells this kit (and at less cost than does Adafruit.)
> 
> http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2155516_-1
> 
> > it might be useful to examine (it was to me) the mintyboost circuit (uses
> > a
> > buck converter). there's a great write up by ladyada here:
> > http://www.ladyada.net/make/mintyboost/process.html
> >
> >
> >
> > nick
> >
> >
> > On Tue, Jan 8, 2013 at 5:27 AM, Jake <jake at spaz.org> wrote:
> >
> >> For me, when i want a DC stepdown regulator up to an amp or so (maybe
> >> two
> >> amps) i just grab a cellular phone car charger.  They are all the same,
> >> a
> >> tiny circuitboard inside with a DIP version of the 34063 buck converter.
> >>
> >> up to 14 or 15 volts input, 5 volts output, just drop it in.  If you
> >> need
> >> a different output voltage, just add a resistor across one of the two
> >> resistors in the resistor-divider network.  If you need more than 15
> >> volts
> >> input (up to 40v) just replace the capacitor with a higher voltage
> >> (unless
> >> it is already rated at least 10% higher than your working voltage).
> >>
> >> If you need more current, and/or want to be able to make buck converters
> >> from scratch, the LM2576 is great.  There is a fixed 5v-output version
> >> (so
> >> the only parts you need are inductor, diode, and two capacitors) or a
> >> variable output version (add two resistors to select voltage).  It's
> >> simple
> >> enough that you can put it together without a circuitboard if you're in
> >> a
> >> hurry.  Just ask Zach!
> >>
> >> The LM2576 goes up to 40V input, and the LM2576-HV goes up to 60V!
> >> Both can put out THREE AMPS of current.
> >>
> >> http://www.ti.com/lit/ds/**symlink/lm2576.pdf<http://www.ti.com/lit/ds/symlink/lm2576.pdf>
> >>
> >> Garrett, when you mentioned the 7805 you missed that we were talking
> >> about
> >> PWM-style buck converters, which are up to 90% efficient.  A 7805 linear
> >> regulator is basically just an automatic resistor which burns up the
> >> extra
> >> voltage, times the current you're using.  So, powering something with 5V
> >> from a 15V power source, you're literally burning off twice as much
> >> power
> >> as you're making use of (33% efficiency).
> >>
> >> -jake
> >>
> >>
> >> Garrett wrote:
> >>
> >>> This is better/cheaper for 5V 500mA from 6.5-36V:
> >>> http://www.digikey.com/**product-detail/en/V7805-500/**
> >>> 102-1709-ND/1828602<http://www.digikey.com/product-detail/en/V7805-500/102-1709-ND/1828602>
> >>>
> >>> And the big brother for 1000mA:
> >>> http://www.digikey.com/**product-detail/en/V7805-1000R/**
> >>> 102-2178-ND/2352137<http://www.digikey.com/product-detail/en/V7805-1000R/102-2178-ND/2352137>
> >>>
> >>
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> >>
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