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PICList Thread
'[OT] Ringing Chokes and batteries'
1999\11\08@172758 by Wagner Lipnharski

picon face
Hello dear Alice, looking for a small step up conversion circuit?
What are you trying to power up?
What is the input and output Voltage x Current?
:)

Wagner.


Example of a simple circuit:
                                Diode
                           .------>|------------o---o  High V
                           |                    |
                           3| <- point A        |
                           3|                  --- HV C
                           3|                  ---
                           3|                   |
+1.5V----o------------------3| <- point B        |
        |                  3|                  GND
        R                  3|
        |      Nc----------3| <- point C
        o------P           3|
        |      Ne--.       3|
        |          |       3| <- point D
        |         GND       |
        |                   |
        '---------||--------'
                  C

This circuit use a "one coil" transformer with two taps.

At power on, all points have the same +1.5V.

1) Resistor R makes the NPN transistor conducts

2) Current Flows from ground to point C, via coil to B to +1.5Vdc.

3) Point C is grounded

4) Point D will develop a voltage below ground

5) Point A will develop a voltage higher than +1.5V.

6) Voltages goes increasing

7) Voltage at point D is enough negative to cut off transistor
   via capacitor C.

8)  Transistor opens, Point C goes floating.

9)  High + Voltage at Point A is rectified and stored at HV C.

10) Capacitor C (blocking the transistor) starts to discharge via R
   and coil taps D-B.

11) Upon C discharged, R is enough to turn on transistor again.

Cycle repeats in a frequency determined by R, C, and the transformer
itself.

This kind of configuration was widely used, using a cheap small
transistor audio output transformer (transistor radio), connecting the
secondary in series with the primary.  Some different configuration was
used at those toys to catch your friends with 500Vac from a single
cell... remember?  Nasty salty taste of high V... :)

!!! Watch out kids, don't do it at home, you can kill the cat !!!

1999\11\08@180057 by Alice Campbell

flavicon
face
> Date:          Mon, 8 Nov 1999 17:26:08 -0500
> Reply-to:      pic microcontroller discussion list <spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
> From:          Wagner Lipnharski <.....wagnerlKILLspamspam@spam@EARTHLINK.NET>
> Organization:  UST Research Inc.
> Subject:       Re: [OT] Ringing Chokes and batteries
> To:            PICLISTspamKILLspamMITVMA.MIT.EDU

Well, i'm about to replace the 9v battery in my datalogger with two
AA 1.5v and a stepper to 5v, but i was curious how they worked, and
wanted to see for mysef.  I've been messing with switched capacitor
circuits, and saw the inductor circuit, but couldnt get it to work.
Then i wondered if i could run it at 3v, stepped up from 1.5v, and
let the pressure transducer work ratiometrically. The pressure sensor
only pulls a few mA, the pic and adc and memory chip only a few mA.
The problem with the switched cap design is the oscillator part, the
self-oscillation of the coil looked nicer.

alice

> Hello dear Alice, looking for a small step up conversion circuit?
> What are you trying to power up?
> What is the input and output Voltage x Current?
> :)
>
.

1999\11\08@192057 by Chris Eddy

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Alice;

Ah! you want to drive a pressure transducer.  Is it a bridge style?  And you hav
e
a 1.5V rail?  Why not connect the + on the transducer to the rail and generate a
negative on the - side?  If you use an op-amp in a servo setup, you could drive
the - terminal until one of the return terminals is regulated to 0VDC, and the
other terminal would then be a ground referenced signal.  Linear Technology (ref
Jim Williams, bridge transducer circuits) is fond of these methods.  If you step
up to 3V, you would have to deal with a 1.5V common mode with a 1.5V rail, which
is ugly.  With the ground reference, you can then avoid an instrumentation
amplifier.  If you need to measure bipolar signals, you could be in the thick of
it again, as your PIC HATES any negative voltages on an analog pin.  Whacks the
other analog readings REAL fast.  Would this circuit have poor performance in
light of the total V applied to the sensor varying?  Do you have to use a bridge
with four varying elements to avoid this?  Hmm...

Chris Eddy
Pioneer Microsystems, Inc.

Alice Campbell wrote:

{Quote hidden}

1999\11\08@195159 by Alice Campbell

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Thanks Chris,
Yes, it (they) are bridge style, some have + swing, others both + and
- swing.  I'm trying to follow your description with my feeble brain,
but im not sure what a servo setup is.   Because of the millivolt
levels  out of the bridge, i still need some amplification to get the
signal into the range the adc0831 can read.  yes,
i will put in a better adc once i understand what im doing.  I rather
suspect that the wobbly voltage will turn the readings to mush but
its easy enough to put together on the breadboard and see.

I like the idea of using the pic to generate the voltage for
the bridge, and maybe the amp, yet still let the rest of the circuit
use lower voltage.  i am already controlling power to the peripherals
with the pic and i still have 2 free pins on port b.  anything to
squeeze a bit more out of the batteries...


alice

>
> Ah! you want to drive a pressure transducer.  Is it a bridge style?  And you h
ave
> a 1.5V rail?  Why not connect the + on the transducer to the rail and generate
a
> negative on the - side?  If you use an op-amp in a servo setup, you could driv
e
> the - terminal until one of the return terminals is regulated to 0VDC, and the
> other terminal would then be a ground referenced signal.  Linear Technology (r
ef
> Jim Williams, bridge transducer circuits) is fond of these methods.  If you st
ep
> up to 3V, you would have to deal with a 1.5V common mode with a 1.5V rail, whi
ch
> is ugly.  With the ground reference, you can then avoid an instrumentation
> amplifier.  If you need to measure bipolar signals, you could be in the thick
of
> it again, as your PIC HATES any negative voltages on an analog pin.  Whacks th
e
> other analog readings REAL fast.  Would this circuit have poor performance in
> light of the total V applied to the sensor varying?  Do you have to use a brid
ge
{Quote hidden}

1999\11\08@195417 by Eric Richards

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1999\11\08@202946 by Eric Richards

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Related: :wonderland:Untitled%2064:0000F407:69B1CC62:00000000:00000000

1999\11\08@210954 by Chris Eddy

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Alice Campbell wrote:

> Thanks Chris,
> Yes, it (they) are bridge style, some have + swing, others both + and
> - swing.  I'm trying to follow your description with my feeble brain,
> but im not sure what a servo setup is.

By servo, I mean using an op-amp to achieve a DC value.  Seems like your everyda
y
application, but sometimes a control loop is not exactly stable, and you have to
use
some RC tuning to 'slow' the op-amp down to the point where it centers your sign
al at
the proper DC level.  Refer to composite amplifiers (can't claim to have built t
hem,
but see applications from time to time).  In this case, you drive the bridge min
us leg
until one of the sensor return lines rests at ground.  Refer to Linear Tech's
application note 43, page 43-4.  The seventh application circuit is the one I am
refering to.  But, this circuit has an opamp that requires negative volts.  So,
instead
of having a negative supply well under the op-amp's desired output, why not gene
rate a
negative votlage generator circuit controlled by PWM.  Instead of a Flyback styl
e, you
could use a 'buck boost' or a 'cuk' converter.  Ref Linear Tech's AN19, page 13-
15.
This way, you could take the same op-amp in AN43, and make it do the PWM.  Just
RC
filter the feedback value, and the op-amp becomes very unstable.  It then oscila
tes
with the PWM frequency slewing back and forth to satisfy your 'servo setpoint'.

It's great stuff, good for days or even weeks of bench experimenting.

>  Because of the millivolt
> levels  out of the bridge, i still need some amplification to get the
> signal into the range the adc0831 can read.

If you do the ground centered bridge, you can do a straight non-inverting amplif
ier.
Nice and easy, one point adjust for the gain.  BUT, and it is a big one, if you
will be
going negative (bipolar), you must then setup the amplifier to drive your signal
centered about mid-rail.  Wait a minute.  If you have other circuitry and a proc
essor,
you must have a 5V rail.  The above discussion then refers to a +5V rail and a b
uck
boost that creates around -5V on the transducer.  But back to the amplifier.  Yo
u can
center the reference point on a non-inverting amp about the mid-rail.  Then posi
tive
and negative transducer readings will read above and below the mid scale reading
.

{Quote hidden}

The sad part in all of this is that the efficiency of the DC/DC converters is no
t all
that great.  Especially for low currents, where most of your current is Quesient
current.  The Capacitor switcher circuit generating -5V may be a good candidate.
 I
think that they have pretty good efficiency.

>
> alice
>

Chris Eddy

1999\11\09@071332 by paulb

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face
> Eric Richards wrote:

> Oh dear silly me
> I think this may work better.

 Sorry, it won't!  Wagner has the phasing wrong.  Have a think about
it, Wagner.
--
 Cheers,
       Paul B.

1999\11\09@090703 by Tom Handley

picon face
  Alice, what pressure sensor are you using and what is the application? I
have a lot of experience with absolute pressure transducers in the 0-15 PSI
range for use in barometers and altimeters. I've been using Sensym and now
Lucas NovaSensor's NPP-301 and NPC-1220 series.

  I normally recommend an instrumentation amp for this application. Either
a dedicated IA amp or individual op-amps. Also, stable bridge excitation.
There are a lot of ways to do this using a single supply.

  The Linear app note (AN43) Chris mentioned, is also in the 1993 Linear
Applications Handbook, Volume II. Another good source is Analog Devices'
Transducer Interfacing Handbook, and Instrumentation Amplifier Application
Guide 2'nd Edition.

  As far as power supplies, there are a variety of solutions that will
provide 5V from 1.5V. Charge pump converters/regulators have come a long
ways since the old '7660. TI, Linear, and Maxim have several with very
little ripple and currents from 50ma to 300ma using 3 or 4 caps. The MAX619,
for example, converts 2-3.6V to 5V regulated at 50ma and consumes 75ua. The
MAX682 converts 2.7-5.5V to 5V at 250ma and uses 100ua.

  - Tom

At 12:08 AM 11/8/99 PST, Alice Campbell wrote:
{Quote hidden}

------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

1999\11\09@124851 by Wagner Lipnharski

picon face
All the pressure transducers I used (Lucas NovaSensor), requires from 1
to 2mA (constant current) for bridge excitation, and it has an impedance
around 3500 Ohms, so it will generate from 3.5 to 7 Volts across the
bridge.  The bridge output sits in the middle of that voltage, with a
full scale around 100mV, 200mV or other.  If using 5Vdc to generate the
constant current, any instrumentation amplifier (+5Vdc and Ground) will
be able to deal with the common voltages.

But for some arrange like that I would *not* use a step up power supply
based on a single transistor and a coil, instead I would go to a
Maxim641 and a coil.  But why the old 641?  Because it is one of the few
that has an internal FET *and catch diode*, and an output to drive large
FET switchers, without much fuzz.  It also regulate the output voltage
to a fixed value, without any further regulation.

I use also the Max857 with no complain at all, it has the internal FET
switcher, requires the external Schokkty catcher diode and it can not
drive an external N channel FET switcher. If you are interested to see
this one drawing, click here: http://www.ustr.net/offers/board1diags.htm
and click over the second drawing.

Wagner.

1999\11\10@104753 by Glen

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alice since you have pic 2 pins

what about

vin------oooooooo----     ---------------- --------------------vout
                 L              |___| tx
|                        R
                                     |
|                        R        R1
                                     R
------                   R
                     resister     R                 /\    Diode           |

                                     R
|                        |------------a/d to 2nd spare pic pin
                                     |
|                        |
                                     |
|                       |
   pwm from 1st spare pic pin              |                       R

|                       R        R2

|                       R

|                        |
                                                           | ___________|
                                                                   TO GND

i've just started looking in this area as i have a little project i will be
doing
this seems to be one of the most simplest circuits & it should fit in a
small space.
glen


**********
Wagner Lipnharski wrote:

{Quote hidden}

1999\11\12@152309 by Glen

flavicon
face
sorry about that !!

VIN------ooooooooooo-----       ----->|--------------------
           L            | fet_|         |            |
                           |            R            cap
                           |            R            |
                           R            R            V
                           R            |_____
                           R            |        |  to 2nd pic pin
                           |            R        |     (A2D)
                           |            R        _
                           |            R        |
           To 1st pic pin  |            |        |
            pwm                         |        | GND



> i've just started looking in this area as i have a little project i will be
> doing
> this seems to be one of the most simplest circuits & it should fit in a
> small space.
> glen
>

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