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

[Jake]

jim were you using computers back when they were powered by giant heavy 
transformers regulated by TO-2 transistors controlled by an LM723???

On Tue, 8 Jan 2013, jim wrote:

>
>
> 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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