micropower boost circuit

[Joerg]

Why?



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.

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.

 

[Piotr Wyderski]

You really need to specify _how_ much less than a volt -- 0.9V in vs.
0.5V is a huge difference, and if you want it down to 0.1V then you're
probably in a world of hurt.

A joule thief based on a decent JFET will do the trick.

Best regards, Piotr

 

[Piotr Wyderski]

Below is something to begin with. One can add an additional
winding and get a flyback-like topology with an autotransformer
or to use this circuit to power/start a real switcher etc.
If "below one volt" means ~0.8V, then a BJT will be fine,
otherwise a JFET would be necessary. The high input voltage sector
is an exercise left to the reader. ;-)

Best regards, Piotr

Version 4
SHEET 1 880 680
WIRE 128 48 -64 48
WIRE 192 48 128 48
WIRE 240 48 192 48
WIRE 192 80 192 48
WIRE 240 80 240 48
WIRE -64 112 -64 48
WIRE 192 176 192 160
WIRE 240 176 240 144
WIRE 240 176 192 176
WIRE 128 192 80 192
WIRE 80 208 80 192
WIRE 128 240 128 192
WIRE 144 240 128 240
WIRE 80 304 80 288
FLAG -64 192 0
FLAG 192 272 0
FLAG 128 112 0
FLAG 80 304 0
SYMBOL njf 144 176 R0
SYMATTR InstName J1
SYMATTR Value 2N4393
SYMBOL ind2 176 64 R0
SYMATTR InstName L1
SYMATTR Value 100µ
SYMATTR Type ind
SYMBOL Misc\\battery -64 96 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 0.6
SYMBOL cap 112 48 R0
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL ind2 64 192 R0
SYMATTR InstName L2
SYMATTR Value 900µ
SYMATTR Type ind
SYMBOL cap 224 80 R0
SYMATTR InstName C2
SYMATTR Value 1n
TEXT -98 328 Left 2 !.tran 0.1
TEXT 240 328 Left 2 !K L1 L2 1.0

 

[John K]

A joule thief based on a decent JFET will do the trick.

Best regards, Piotr

The LTC3108 claims to operate at 20mV. It appears to use a depletion mode
mosfet driving a step-up transformer. Very simple, but the following
regulator is a nightmare:

"http://datasheet.octopart.com/LTC3108EGN#PBF-Linear-Technology-
datasheet-8701600.pdf"

JK

 

[John K]

The link did't work. Try it this way:

<http://datasheet.octopart.com/LTC3108EGN#PBF-Linear-Technology-
datasheet-8701600.pdf>

 

[rickman]

The link did't work. Try it this way:

<http://datasheet.octopart.com/LTC3108EGN#PBF-Linear-Technology-
datasheet-8701600.pdf>

Both links are truncated in my newsreader, but copying the text of the
link and pasting it into the browser address bar works just fine.