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Re: micropower boost circuit
On Sun, 22 Sep 2013 20:32:09 -0400, Michael Robinson wrote:

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If this is all so that you can turn on the high-side of an N-channel  
MOSFET, why not rethink?  Why not use a PNP BJT to turn it on?

You may end up with fewer parts if you use a light-duty PNP to get things  
going until a chip-based solution can kick in, and then just run with  
that.

Or, you may end up with the fewest parts if you just use a heavy-duty  
enough PNP as your switch, and forget about using a MOSFET entirely.

--  

Tim Wescott
Wescott Design Services
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Re: micropower boost circuit

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These generators' fields don't switch on the high side.
There are not lots of solid-state regulators available on the market for  
people that want to upgrade old six-volt bikes to solid-state from the  
original technology, mechanical devices.
I only know of one company that makes six volt solid-state regulators for  
these old bikes, which have fields that switch on the low side (negative  
ground).  And I think those regulators require a battery on the bike to  
work.
However, some people use magnetos, and run without a battery.  Nobody makes  
regulators for them, because it's a pain to design.  These marvelous  
suggestions you've made aren't going to solve the problem, unfrotunately...
I've come up with a design that takes extremely low voltage and boosts it,  
and it uses only jelly-bean parts:  eight transistors and about thirty  
passives.  In the original post I asked for some feedback from the people on  
the forum about the transistor that switches the inductor.



Re: micropower boost circuit
On Mon, 23 Sep 2013 20:35:39 -0400, Michael Robinson wrote:

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And got such good advise that there was no point in me chiming in!

We so often get folks on this group that are stuck in a narrow spot of  
the entirely wrong path, that most of the regulars will, at some point,  
try to make sure that you are, indeed, stuck at a narrow spot on the  
_right_ path.

That behavior has certainly benefited me in the past, when I was losing  
sight of the forest for the trees.

Are you actually supplying field to the generator with this boost  
circuit, or are you using it to power some switch?

If you need to boost just to get field -- yes, you need to boost starting  
from nothing, and go up from there.

--  

Tim Wescott
Wescott Design Services
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Re: micropower boost circuit
Tim Wescott wrote:
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Why?


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Not sure if that is necessary here but if one ever needs to get a field
going where there is no source for a gate or base voltage anywhere there
is an often forgotten part: The depletion mode FET. Those don't only
come in small JFET varieties but also as big fat MOSFETs with rather low
Rdson values.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit
On 9/23/2013 8:35 PM, Michael Robinson wrote:
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Can you post a neater version of the circuit so we can actually see  
what's going on?

Re: micropower boost circuit

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Sundays are supposed to be wasted.


--  

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

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Re: micropower boost circuit
Tim Wescott wrote:
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I don't think they work at less than 2.2V and abs max is 16V. Close call
for the abs max because Michael needs to use it up to there.

There are some micro-power devices that will start at less than 1V but I
haven't looked if any of them would go to 18V or more, so there'd be
some margin.

[...]

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit
On Sun, 22 Sep 2013 16:32:58 -0700, Joerg wrote:

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I totally missed Michael's "less than 1V" constraint.

You could fix the 16V in problem with an LDO, since efficiency doesn't  
matter -- but not with an internal-switch device.

--  

Tim Wescott
Wescott Design Services
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Re: micropower boost circuit
Tim Wescott wrote:
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The LT1615 probably comes close. But only close. This is one of those
jobs that in all likelihood has to be done with discretes.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit

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BINGO!
Takes eight transistors.
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Re: micropower boost circuit
Michael Robinson wrote:
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And cheap ones to boot :-)

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit
On 9/22/2013 7:32 PM, Joerg wrote:
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In an automotive app this may well need a lot more than 18 volts.  I'm  
not certain where this is connected in the wiring, but load dumps in  
autos often produce voltages well over the battery voltage, by 10's of  
volts.

We were designing a PSU for a military vehicle and had a transient spec  
of 100 volts!  I think the spec in today's cars is some 40 or 50 volts.

--  

Rick

Re: micropower boost circuit
rickman wrote:
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The OP didn't say it's for automotive. If it is, then it either needs to
be 80V tolerant or have a surge disconnect.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit
On 9/23/2013 10:44 AM, Joerg wrote:
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I guess technically he didn't say "automotive".  I assumed when I read  
"six volt generator" it was for a car.

--  

Rick

Re: micropower boost circuit
rickman wrote:
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If so, then that must be a really, really old one. Like my 16-horse
Citroen when I was young :-)

Its 6V DC generator was not capable of a serious load dump. In fact, I
rode it sans battery most of the time because 6V batteries were
expensive. Yet I still used the high beams, the radio and so on. The
crank gave me a good workout, especially in winter.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit
On 9/23/2013 11:54 AM, Joerg wrote:
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Why else would he be building his own regulator?  I figured it was for  
an antique auto.  The OP said, "(the armature voltage of an antique six  
volt generator)".


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I thought it was the starter motors that produced the load dump?

But then as I think about it a bit more, this is not really a regulator  
circuit as much as it is a boot circuit.  In a car you have a battery to  
supply the field coil current on startup.  So maybe this is for a six  
volt battery, but not a car.  I just can't think of another reason to  
use "an antique six volt generator"... maybe to power an antique six  
volt radio?

--  

Rick

Re: micropower boost circuit
rickman wrote:
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That was after my post and my crystal ball is in the shop right now :-)


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Usually it's the alternator, the kind with rectifiers. Happens if the
battery suddenly comes off or, if operating without battery, a major
load such as the rear window defroster goes offline.


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I don't know if there even are 6V alternators, except maybe for smaller
two-wheelers. They were usually brushed DC generators plus an external
regulator. With the one in my Citroen 2CV I was quite impressed. It had
the old style non-electronic point contact "bzzzt" regulator. Load dumps
left it fairly unfazed, I checked that with a scope to avoid wrecking my
precious old Becker car radio with shortwave range. It contained Ge
transistors that had become nearly unobtanium by then.

Best of all, the whole car had no belts. The generator sat right on the
crankshaft in a coaxial fashion.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: micropower boost circuit

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You went to a lot of trouble, Tim.  The least I can do is explain why the  
circuit has to run on a volt, so most likely a chip won't  work.
Vcc (the armature voltage of an antique six volt generator) isn't going to  
start at some higher voltage and drop to a volt, which might allow  
bootstrapping.  When the generator first spins up, Vcc comes up to about a  
volt because of residual magnetism in the soft iron pole shoes (possibly  
even a little less than a volt).  Whereupon, nothing more will happen:  
unless the booster produces some output, generator output will remain flat  
at one volt.  The booster has to take that one volt and boost it enough to  
turn on a mosfet, and drive current in the field coils around the pole  
shoes.  Then Vcc (the generator output) will rise.
The circuit I posted only needs two thirds of a volt to run, according to  
the simulator.  Eight transistors and about thirty passives.  It'll take up  
some board space, as you pointed out, but those forty jelly beans are still  
cheaper than the chip.  And I think the LT8410 requires 2.5 volts.  



Re: micropower boost circuit
On Sun, 22 Sep 2013 20:25:08 -0400, "Michael Robinson"

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Sometimes the thing to do is stick a lithium battery into the circuit. A
aa-sized 3-volt lithium will run some low-power circuits for decades. Or some
more voltage could actually bootstrap the field.

How about a 9-volt alkaline. They have 10-year shelf lives nowadays.


--  

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

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Re: micropower boost circuit
On Sunday, September 22, 2013 5:52:07 PM UTC-4, Tim Wescott wrote:
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Too complicated, and the requirements make little sense. I would explore the possibility of using a simple switched capacitor inverter at the other end of the field winding, but that's just me.
http://datasheets.maximintegrated.com/en/ds/ICL7660-MAX1044.pdf

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