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On 25/10/2010 02:46 PM, scott wrote:
>> 2. I'm not aware of any way to change the voltage of a DC circuit.
>
> I made an example using that Java circuit simulation applet:
>
> http://tinyurl.com/2cplrbn
Hmm, interesting.
1. It's possible to edit the circuits. I never knew that.
2. It's possible to encode the circuit description in the URL. (I'm
pretty sure you'll quickly hit a limit on the maximum size for a URL!)
3. No matter what values I change, the circuit always stabilises to
exactly 8V.
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scott wrote:
> http://en.wikipedia.org/wiki/Charge_pump
That's freaky.
> I assume they must pass certain legal test standards for EM
> compatibility, but there are products that require stricter controls,
Like, a radio transmitter that's designed to run for hours or days on a
small battery? :-)
--
Darren New, San Diego CA, USA (PST)
Serving Suggestion:
"Don't serve this any more. It's awful."
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On 10/25/2010 7:17 AM, Invisible wrote:
> 1. Why do you need several different voltages?
Different components require different voltages. Sometimes you get lucky
and everything will run all one a single voltage. You may have high
intensity LED's that have a voltage forward of more than 3.3 volts, so 5
volts is a logical choice to power the backlight circuitry allowing the
LED's to function, but pumping 5 volts into a chip requiring 3.3 volts,
would possibly overheat at best or fry at worse, etc...
>
> 2. I'm not aware of any way to change the voltage of a DC circuit. You
> can use a resistor to limit current, but AFAIK there's no way to
> actually change voltages.
>
You're kidding, right?
You can affect voltage by either using a regulator (true, it does this
by altering current) or if you need more voltage than is supplied by the
source you can use a charge pump, which will increase voltage by
alternately charging and discharging a bank of capacitors configured in
a very specific way (lots of caps for that one)
>
> Mmm, interesting. (And ridiculously complicated.) I wonder how much of
> this stuff is to do with electromagnetic radiation? (You don't want EM
> interference stopping your motherboard working, and you don't want the
> board to radiate EM either...)
Filtering probably helps that. But at those timings every little thing
in the design becomes critically important. You can literally have a
parasitic capacitance completely filter out the signal.
--
~Mike
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On 10/25/2010 8:46 AM, scott wrote:
>> 2. I'm not aware of any way to change the voltage of a DC circuit.
>
> I made an example using that Java circuit simulation applet:
>
> http://tinyurl.com/2cplrbn
>
another simple charge pump based on a 555 timer.
http://tinyurl.com/2a8wf2x
--
~Mike
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>> I made an example using that Java circuit simulation applet:
>>
>> http://tinyurl.com/2cplrbn
>>
>
> another simple charge pump based on a 555 timer.
>
> http://tinyurl.com/2a8wf2x
Cool! I know also that you can use a circuit with inductors rather than
capacitors to make it more efficient, but the downside is the inductors need
more physical space than the capacitors on the board (only a problem if
space is very limited).
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On 10/26/2010 3:01 AM, scott wrote:
>>> I made an example using that Java circuit simulation applet:
>>>
>>> http://tinyurl.com/2cplrbn
>>>
>>
>> another simple charge pump based on a 555 timer.
>>
>> http://tinyurl.com/2a8wf2x
>
> Cool! I know also that you can use a circuit with inductors rather than
> capacitors to make it more efficient, but the downside is the inductors
> need more physical space than the capacitors on the board (only a
> problem if space is very limited).
>
>
>
I have yet to attempt a boost converter using an inductor. I should
attempt such a thing one of these days. ;) From what I understand, you
can get some pretty nasty high voltages with such a circuit. Probably
one of the reasons I haven't messed with it.
There's a regulator circuit geared toward LED use that, iirc used a very
small capacity that used the same theory to supply enough voltage to
overcome the high output LED's VF from a very small battery, even when
the battery is nearly spent and has a voltage drop. Something called a
joule thief. Essentially a boost converter using a transformer.
--
~Mike
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