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Hey, that's wierd.

Started by Uncle Steve May 16, 2013
I'm seeing something really interesting with the coil I built.  I
wired up a buck converter circuit yesterday and tried it out, but just
with a switch and resistor tied to the gate of an IRF-1404PbF, which
lists a Total Gate Charge of 131nC, which I take to mean nano-
coulombs.  When the circuit is 'rested', power applied does what is
expected.

                                 10uH           0R1
 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout
        D|  _/S     |         |         |           |    | 
         | v |      |         |         |           |    |
         - - -      \         |         \           \    |
         -+---      / 2.2K    |         / 1M     1M /    |
          |         \         |         \           \    |
          \         /     1N ---        /           /    |
          / 4.7k    |    4004/-\        |           |   ---
          \         |         |         \           \   --- 3300uF
          /        \_/ LED    |         / 100K 100k /    |
 to SW    |        -+-        |         \           \    |
   -------+         |         |         /           /    |
                    |         |         |           |    |
                    |         |         |           |    |
 GND +--------------+---------+---------+-----------+----+----+ GND


Note that this test was without a load.  It worked a couple of times,
but I may have damaged the MOSFET.  When it worked, the MOSFET
wouldn't shut off.  I either the coil is generating a field that
induces current in the gate wire, or something similar.  No big deal,
I'll work out what's wrong because I had something similar set up on a
breadboard (without the inductor) and things switched on and off as
expected.

The weird thing is that a -.3.06V charge develops across Vout and GND
even if the circuit is completely disconnected from supply and GND.
So, sitting out in the open with a meter attached to the output,
voltage climbs over a period of minutes.  -2mV per second or so, but
it slows down as the voltage approaches the -.2V level.

My compass shows that there are varying magnetic fields throughout my
apartment, but even in locations where the needle does not appear to
be deflected from Magnetic North, the voltage climbs as described.
If I shorted the capacitor (at ~1V) to drain accumulated charge, would
I have induced some sort of charge on the negative plate that would
cause this to occur?  Or is this, as it appears, a phenomenon related
to the ambient magnetic fields occurring here where I am working?

I tried putting the circuit in a metal box, but obviously I had to
allow the DVM leads to exit the box so I could watch the DVM, and
continued to observe the negative voltage climb.  Weird, eh?


Regards,

Uncle Steve

-- 
There should be a special word in the English language to identify
people who create problems and then turn around and offer up their own
tailor-made bogus non-solutions designed to completely avoid the root
causes of the situation under consideration.  'Traitor' might be a
good choice, but lacks the requisite specificity.  One of the problems
with contemporary English is it lacks many such words that would
otherwise categorically identify certain kinds of person, place, or
thing -- making it difficult or impossible to think analytically about
such objects.  These shortcomings of the English lexicon are
representative of Orwellian linguistics at work in the real world.

On Thu, 16 May 2013 13:02:38 -0400, Uncle Steve <stevet810@gmail.com>
wrote:

>I'm seeing something really interesting with the coil I built. I >wired up a buck converter circuit yesterday and tried it out, but just >with a switch and resistor tied to the gate of an IRF-1404PbF, which >lists a Total Gate Charge of 131nC, which I take to mean nano- >coulombs. When the circuit is 'rested', power applied does what is >expected. > > 10uH 0R1 > 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > D| _/S | | | | | > | v | | | | | | > - - - \ | \ \ | > -+--- / 2.2K | / 1M 1M / | > | \ | \ \ | > \ / 1N --- / / | > / 4.7k | 4004/-\ | | --- > \ | | \ \ --- 3300uF > / \_/ LED | / 100K 100k / | > to SW | -+- | \ \ | > -------+ | | / / | > | | | | | > | | | | | > GND +--------------+---------+---------+-----------+----+----+ GND > > >Note that this test was without a load. It worked a couple of times, >but I may have damaged the MOSFET. When it worked, the MOSFET >wouldn't shut off. I either the coil is generating a field that >induces current in the gate wire, or something similar. No big deal, >I'll work out what's wrong because I had something similar set up on a >breadboard (without the inductor) and things switched on and off as >expected. > >The weird thing is that a -.3.06V charge develops across Vout and GND >even if the circuit is completely disconnected from supply and GND. >So, sitting out in the open with a meter attached to the output, >voltage climbs over a period of minutes. -2mV per second or so, but >it slows down as the voltage approaches the -.2V level. > >My compass shows that there are varying magnetic fields throughout my >apartment, but even in locations where the needle does not appear to >be deflected from Magnetic North, the voltage climbs as described. >If I shorted the capacitor (at ~1V) to drain accumulated charge, would >I have induced some sort of charge on the negative plate that would >cause this to occur? Or is this, as it appears, a phenomenon related >to the ambient magnetic fields occurring here where I am working? > >I tried putting the circuit in a metal box, but obviously I had to >allow the DVM leads to exit the box so I could watch the DVM, and >continued to observe the negative voltage climb. Weird, eh? > > >Regards, > >Uncle Steve
From the "body arrow" direction I assume the MOSFET is NMOS? Then the gate drive needs to be well above the +18V to turn it on. The "weirdness" you are seeing is probably due to not having everything tied to a common ground. Though you might need a tin-foil hat >:-} Or go to your local community college and take a few courses. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On May 16, 1:02=A0pm, Uncle Steve <stevet...@gmail.com> wrote:
> I'm seeing something really interesting with the coil I built. =A0I > wired up a buck converter circuit yesterday and tried it out, but just > with a switch and resistor tied to the gate of an IRF-1404PbF, which > lists a Total Gate Charge of 131nC, which I take to mean nano- > coulombs. =A0When the circuit is 'rested', power applied does what is > expected. > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A010uH =
=A0 =A0 =A0 =A0 =A0 0R1
> =A018V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > =A0 =A0 =A0 =A0 D| =A0_/S =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =
=A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> =A0 =A0 =A0 =A0 =A0| v | =A0 =A0 =A0| =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 |=
=A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> =A0 =A0 =A0 =A0 =A0- - - =A0 =A0 =A0\ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 \=
=A0 =A0 =A0 =A0 =A0 \ =A0 =A0|
> =A0 =A0 =A0 =A0 =A0-+--- =A0 =A0 =A0/ 2.2K =A0 =A0| =A0 =A0 =A0 =A0 / 1M =
=A0 =A0 1M / =A0 =A0|
> =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0=
\ =A0 =A0 =A0 =A0 =A0 \ =A0 =A0|
> =A0 =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 =A0 / =A0 =A0 1N --- =A0 =A0 =A0 =A0/ =
=A0 =A0 =A0 =A0 =A0 / =A0 =A0|
> =A0 =A0 =A0 =A0 =A0 / 4.7k =A0 =A0| =A0 =A04004/-\ =A0 =A0 =A0 =A0| =A0 =
=A0 =A0 =A0 =A0 | =A0 ---
> =A0 =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0=
\ =A0 =A0 =A0 =A0 =A0 \ =A0 --- 3300uF
> =A0 =A0 =A0 =A0 =A0 / =A0 =A0 =A0 =A0\_/ LED =A0 =A0| =A0 =A0 =A0 =A0 / 1=
00K 100k / =A0 =A0|
> =A0to SW =A0 =A0| =A0 =A0 =A0 =A0-+- =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 \ =
=A0 =A0 =A0 =A0 =A0 \ =A0 =A0|
> =A0 =A0-------+ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 / =A0=
=A0 =A0 =A0 =A0 / =A0 =A0|
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =
=A0 | =A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =
=A0 | =A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> =A0GND +--------------+---------+---------+-----------+----+----+ GND > > Note that this test was without a load. =A0It worked a couple of times, > but I may have damaged the MOSFET. =A0When it worked, the MOSFET > wouldn't shut off. =A0I either the coil is generating a field that > induces current in the gate wire, or something similar. =A0No big deal, > I'll work out what's wrong because I had something similar set up on a > breadboard (without the inductor) and things switched on and off as > expected. > > The weird thing is that a -.3.06V charge develops across Vout and GND > even if the circuit is completely disconnected from supply and GND. > So, sitting out in the open with a meter attached to the output, > voltage climbs over a period of minutes. =A0-2mV per second or so, but > it slows down as the voltage approaches the -.2V level.
Maybe it the big cap? What happens if you pull that. I guess it's possible for an AC magnetic field to be turning on the 1n4004 diode during part of the cycle... and chargeing up (or down) the output.
> > My compass shows that there are varying magnetic fields throughout my > apartment, but even in locations where the needle does not appear to > be deflected from Magnetic North, the voltage climbs as described. > If I shorted the capacitor (at ~1V) to drain accumulated charge, would > I have induced some sort of charge on the negative plate that would > cause this to occur? =A0Or is this, as it appears, a phenomenon related > to the ambient magnetic fields occurring here where I am working?
I'm guessing the AC magnetic fields. (Which you can't see with a compass) George H.
> > I tried putting the circuit in a metal box, but obviously I had to > allow the DVM leads to exit the box so I could watch the DVM, and > continued to observe the negative voltage climb. =A0Weird, eh? > > Regards, > > Uncle Steve > > -- > There should be a special word in the English language to identify > people who create problems and then turn around and offer up their own > tailor-made bogus non-solutions designed to completely avoid the root > causes of the situation under consideration. =A0'Traitor' might be a > good choice, but lacks the requisite specificity. =A0One of the problems > with contemporary English is it lacks many such words that would > otherwise categorically identify certain kinds of person, place, or > thing -- making it difficult or impossible to think analytically about > such objects. =A0These shortcomings of the English lexicon are > representative of Orwellian linguistics at work in the real world.
On Thu, May 16, 2013 at 10:28:00AM -0700, Jim Thompson wrote:
> On Thu, 16 May 2013 13:02:38 -0400, Uncle Steve <stevet810@gmail.com> > wrote: > > >I'm seeing something really interesting with the coil I built. I > >wired up a buck converter circuit yesterday and tried it out, but just > >with a switch and resistor tied to the gate of an IRF-1404PbF, which > >lists a Total Gate Charge of 131nC, which I take to mean nano- > >coulombs. When the circuit is 'rested', power applied does what is > >expected. > > > > 10uH 0R1 > > 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > > D| _/S | | | | | > > | v | | | | | | > > - - - \ | \ \ | > > -+--- / 2.2K | / 1M 1M / | > > | \ | \ \ | > > \ / 1N --- / / | > > / 4.7k | 4004/-\ | | --- > > \ | | \ \ --- 3300uF > > / \_/ LED | / 100K 100k / | > > to SW | -+- | \ \ | > > -------+ | | / / | > > | | | | | > > | | | | | > > GND +--------------+---------+---------+-----------+----+----+ GND > > > > > >Note that this test was without a load. It worked a couple of times, > >but I may have damaged the MOSFET. When it worked, the MOSFET > >wouldn't shut off. I either the coil is generating a field that > >induces current in the gate wire, or something similar. No big deal, > >I'll work out what's wrong because I had something similar set up on a > >breadboard (without the inductor) and things switched on and off as > >expected. > > > >The weird thing is that a -.3.06V charge develops across Vout and GND > >even if the circuit is completely disconnected from supply and GND. > >So, sitting out in the open with a meter attached to the output, > >voltage climbs over a period of minutes. -2mV per second or so, but > >it slows down as the voltage approaches the -.2V level. > > > >My compass shows that there are varying magnetic fields throughout my > >apartment, but even in locations where the needle does not appear to > >be deflected from Magnetic North, the voltage climbs as described. > >If I shorted the capacitor (at ~1V) to drain accumulated charge, would > >I have induced some sort of charge on the negative plate that would > >cause this to occur? Or is this, as it appears, a phenomenon related > >to the ambient magnetic fields occurring here where I am working? > > > >I tried putting the circuit in a metal box, but obviously I had to > >allow the DVM leads to exit the box so I could watch the DVM, and > >continued to observe the negative voltage climb. Weird, eh? > > > > > >Regards, > > > >Uncle Steve > > From the "body arrow" direction I assume the MOSFET is NMOS?
No, P-channel, but I may have hooked it up backwards since I mistakenly soldered in a known broken n-channel MOSFET yesterday by accident. Nope. Was wired correctly, and it seems the gate is broken.
> Then the gate drive needs to be well above the +18V to turn it on.
> The "weirdness" you are seeing is probably due to not having > everything tied to a common ground. Though you might need a tin-foil > hat >:-}
If I unhook everything from the board except the DVM, the voltage does descend to ~-.3 V spontaneously. Perhaps it's a miracle. Or the Orbital Mind-Control Laser Cannon.
> Or go to your local community college and take a few courses.
That would be ideal. Regards, Uncle Steve -- There should be a special word in the English language to identify people who create problems and then turn around and offer up their own tailor-made bogus non-solutions designed to completely avoid the root causes of the situation under consideration. 'Traitor' might be a good choice, but lacks the requisite specificity. One of the problems with contemporary English is it lacks many such words that would otherwise categorically identify certain kinds of person, place, or thing -- making it difficult or impossible to think analytically about such objects. These shortcomings of the English lexicon are representative of Orwellian linguistics at work in the real world.
On Thu, May 16, 2013 at 10:39:47AM -0700, George Herold wrote:
> On May 16, 1:02&#2013266080;pm, Uncle Steve <stevet...@gmail.com> wrote: > > I'm seeing something really interesting with the coil I built. &#2013266080;I > > wired up a buck converter circuit yesterday and tried it out, but just > > with a switch and resistor tied to the gate of an IRF-1404PbF, which > > lists a Total Gate Charge of 131nC, which I take to mean nano- > > coulombs. &#2013266080;When the circuit is 'rested', power applied does what is > > expected. > > > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;10uH &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; 0R1 > > &#2013266080;18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; D| &#2013266080;_/S &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;| v | &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;- - - &#2013266080; &#2013266080; &#2013266080;\ &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;-+--- &#2013266080; &#2013266080; &#2013266080;/ 2.2K &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; / 1M &#2013266080; &#2013266080; 1M / &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; / &#2013266080; &#2013266080; 1N --- &#2013266080; &#2013266080; &#2013266080; &#2013266080;/ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; / &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; / 4.7k &#2013266080; &#2013266080;| &#2013266080; &#2013266080;4004/-\ &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; --- > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; --- 3300uF > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; / &#2013266080; &#2013266080; &#2013266080; &#2013266080;\_/ LED &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; / 100K 100k / &#2013266080; &#2013266080;| > > &#2013266080;to SW &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080;-+- &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; \ &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080;-------+ &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; / &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; / &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080;| > > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080;| > > &#2013266080;GND +--------------+---------+---------+-----------+----+----+ GND > > > > Note that this test was without a load. &#2013266080;It worked a couple of times, > > but I may have damaged the MOSFET. &#2013266080;When it worked, the MOSFET > > wouldn't shut off. &#2013266080;I either the coil is generating a field that > > induces current in the gate wire, or something similar. &#2013266080;No big deal, > > I'll work out what's wrong because I had something similar set up on a > > breadboard (without the inductor) and things switched on and off as > > expected. > > > > The weird thing is that a -.3.06V charge develops across Vout and GND > > even if the circuit is completely disconnected from supply and GND. > > So, sitting out in the open with a meter attached to the output, > > voltage climbs over a period of minutes. &#2013266080;-2mV per second or so, but > > it slows down as the voltage approaches the -.2V level. > > Maybe it the big cap? What happens if you pull that.
Get this: 4mV on my coffee table; 30mV on the balcony; 70mV 4" from a 15W CFL; 450mV with the coil touching the CFL spiral tube. 50mv in the shade, moving 8" into direct sunlight max 1.5V, although it varies depending on the orientation of the coil. It can't be sensitive to visible light. It just can't. What I did was disconnect the +terminal of the cap from the circuit. Removing the cap entirely... Same thing.
> I guess it's possible for an AC magnetic field to be turning on the > 1n4004 diode during part of the cycle... and charging up (or down) > the output. > > > > My compass shows that there are varying magnetic fields throughout my > > apartment, but even in locations where the needle does not appear to > > be deflected from Magnetic North, the voltage climbs as described. > > If I shorted the capacitor (at ~1V) to drain accumulated charge, would > > I have induced some sort of charge on the negative plate that would > > cause this to occur? &#2013266080;Or is this, as it appears, a phenomenon related > > to the ambient magnetic fields occurring here where I am working? > > I'm guessing the AC magnetic fields. (Which you can't see with a > compass)
The metal box seems to work as a Faraday Cage now, which pretty much means this circuit is RF sensitive. Why the magnitude of the signal varies so much in sunlight vs. shade is odd. Using my scope, which maxes out at a 72MHz sampling rate doesn't show a recognizable waveform. Regards, Uncle Steve -- There should be a special word in the English language to identify people who create problems and then turn around and offer up their own tailor-made bogus non-solutions designed to completely avoid the root causes of the situation under consideration. 'Traitor' might be a good choice, but lacks the requisite specificity. One of the problems with contemporary English is it lacks many such words that would otherwise categorically identify certain kinds of person, place, or thing -- making it difficult or impossible to think analytically about such objects. These shortcomings of the English lexicon are representative of Orwellian linguistics at work in the real world.
On Thu, 16 May 2013 13:02:38 -0400, Uncle Steve <stevet810@gmail.com>
wrote:

>I'm seeing something really interesting with the coil I built. I >wired up a buck converter circuit yesterday and tried it out, but just >with a switch and resistor tied to the gate of an IRF-1404PbF, which >lists a Total Gate Charge of 131nC, which I take to mean nano- >coulombs. When the circuit is 'rested', power applied does what is >expected. > > 10uH 0R1 > 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > D| _/S | | | | | > | v | | | | | | > - - - \ | \ \ | > -+--- / 2.2K | / 1M 1M / | > | \ | \ \ | > \ / 1N --- / / | > / 4.7k | 4004/-\ | | --- > \ | | \ \ --- 3300uF > / \_/ LED | / 100K 100k / | > to SW | -+- | \ \ | > -------+ | | / / | > | | | | | > | | | | | > GND +--------------+---------+---------+-----------+----+----+ GND > > >Note that this test was without a load. It worked a couple of times, >but I may have damaged the MOSFET. When it worked, the MOSFET >wouldn't shut off. I either the coil is generating a field that >induces current in the gate wire, or something similar. No big deal, >I'll work out what's wrong because I had something similar set up on a >breadboard (without the inductor) and things switched on and off as >expected. > >The weird thing is that a -.3.06V charge develops across Vout and GND >even if the circuit is completely disconnected from supply and GND. >So, sitting out in the open with a meter attached to the output, >voltage climbs over a period of minutes. -2mV per second or so, but >it slows down as the voltage approaches the -.2V level. > >My compass shows that there are varying magnetic fields throughout my >apartment, but even in locations where the needle does not appear to >be deflected from Magnetic North, the voltage climbs as described. >If I shorted the capacitor (at ~1V) to drain accumulated charge, would >I have induced some sort of charge on the negative plate that would >cause this to occur? Or is this, as it appears, a phenomenon related >to the ambient magnetic fields occurring here where I am working? > >I tried putting the circuit in a metal box, but obviously I had to >allow the DVM leads to exit the box so I could watch the DVM, and >continued to observe the negative voltage climb. Weird, eh? > > >Regards, > >Uncle Steve
Electrolytic caps are dissimilar plates in an acid bath, which is a lot like a battery. Local magnetic fields won't charge a cap. Hey, I have a Digikey bag-o assorted electrolytic caps over there on the floor... time to clean up maybe? They all measure positive, 10 to maybe 80 millivolts. If you short one, it starts recharging right away. The COE issues are interesting here. That 1N4004 is slow to use as the catch diode in a switcher. Better to a schottky, 1N5819 maybe. You're using an n-channel fet as a follower, so the gate drive had better swing from ground to +25 maybe. What's your switching frequency? -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
On Thu, May 16, 2013 at 01:12:24PM -0700, John Larkin wrote:
> On Thu, 16 May 2013 13:02:38 -0400, Uncle Steve <stevet810@gmail.com> > wrote: > > >I'm seeing something really interesting with the coil I built. I > >wired up a buck converter circuit yesterday and tried it out, but just > >with a switch and resistor tied to the gate of an IRF-1404PbF, which > >lists a Total Gate Charge of 131nC, which I take to mean nano- > >coulombs. When the circuit is 'rested', power applied does what is > >expected. > > > > 10uH 0R1 > > 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > > D| _/S | | | | | > > | v | | | | | | > > - - - \ | \ \ | > > -+--- / 2.2K | / 1M 1M / | > > | \ | \ \ | > > \ / 1N --- / / | > > / 4.7k | 4004/-\ | | --- > > \ | | \ \ --- 3300uF > > / \_/ LED | / 100K 100k / | > > to SW | -+- | \ \ | > > -------+ | | / / | > > | | | | | > > | | | | | > > GND +--------------+---------+---------+-----------+----+----+ GND > > > > > >Note that this test was without a load. It worked a couple of times, > >but I may have damaged the MOSFET. When it worked, the MOSFET > >wouldn't shut off. I either the coil is generating a field that > >induces current in the gate wire, or something similar. No big deal, > >I'll work out what's wrong because I had something similar set up on a > >breadboard (without the inductor) and things switched on and off as > >expected. > > > >The weird thing is that a -.3.06V charge develops across Vout and GND > >even if the circuit is completely disconnected from supply and GND. > >So, sitting out in the open with a meter attached to the output, > >voltage climbs over a period of minutes. -2mV per second or so, but > >it slows down as the voltage approaches the -.2V level. > > > >My compass shows that there are varying magnetic fields throughout my > >apartment, but even in locations where the needle does not appear to > >be deflected from Magnetic North, the voltage climbs as described. > >If I shorted the capacitor (at ~1V) to drain accumulated charge, would > >I have induced some sort of charge on the negative plate that would > >cause this to occur? Or is this, as it appears, a phenomenon related > >to the ambient magnetic fields occurring here where I am working? > > > >I tried putting the circuit in a metal box, but obviously I had to > >allow the DVM leads to exit the box so I could watch the DVM, and > >continued to observe the negative voltage climb. Weird, eh? > > > > > >Regards, > > > >Uncle Steve > > Electrolytic caps are dissimilar plates in an acid bath, which is a > lot like a battery. Local magnetic fields won't charge a cap. > > Hey, I have a Digikey bag-o assorted electrolytic caps over there on > the floor... time to clean up maybe? They all measure positive, 10 to > maybe 80 millivolts. If you short one, it starts recharging right > away. The COE issues are interesting here. > > That 1N4004 is slow to use as the catch diode in a switcher. Better to > a schottky, 1N5819 maybe. > > You're using an n-channel fet as a follower, so the gate drive had > better swing from ground to +25 maybe. > > What's your switching frequency?
>1Hz
It appears the gate was borken on the P-Channel MOSFET. I have purchased a replacement and will install it tomorrow. While walking downtown to the local electronics shop, I wondered if the voltage level I'm seeing is related to the diode capacitance. I'm sure if I removed all the resistors and reinstalled the cap that the sun would charge the capacitor quite a lot. Vf of the diode is slightly less than a volt at moderate power levels. The question in my mind is in determining what frequency of the EM spectrum it is that is exciting this circuit. Regards, Uncle Steve -- There should be a special word in the English language to identify people who create problems and then turn around and offer up their own tailor-made bogus non-solutions designed to completely avoid the root causes of the situation under consideration. 'Traitor' might be a good choice, but lacks the requisite specificity. One of the problems with contemporary English is it lacks many such words that would otherwise categorically identify certain kinds of person, place, or thing -- making it difficult or impossible to think analytically about such objects. These shortcomings of the English lexicon are representative of Orwellian linguistics at work in the real world.
On Thu, 16 May 2013 18:46:08 -0400, Uncle Steve <stevet810@gmail.com> wrote:

>On Thu, May 16, 2013 at 01:12:24PM -0700, John Larkin wrote: >> On Thu, 16 May 2013 13:02:38 -0400, Uncle Steve <stevet810@gmail.com> >> wrote: >> >> >I'm seeing something really interesting with the coil I built. I >> >wired up a buck converter circuit yesterday and tried it out, but just >> >with a switch and resistor tied to the gate of an IRF-1404PbF, which >> >lists a Total Gate Charge of 131nC, which I take to mean nano- >> >coulombs. When the circuit is 'rested', power applied does what is >> >expected. >> > >> > 10uH 0R1 >> > 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout >> > D| _/S | | | | | >> > | v | | | | | | >> > - - - \ | \ \ | >> > -+--- / 2.2K | / 1M 1M / | >> > | \ | \ \ | >> > \ / 1N --- / / | >> > / 4.7k | 4004/-\ | | --- >> > \ | | \ \ --- 3300uF >> > / \_/ LED | / 100K 100k / | >> > to SW | -+- | \ \ | >> > -------+ | | / / | >> > | | | | | >> > | | | | | >> > GND +--------------+---------+---------+-----------+----+----+ GND >> > >> > >> >Note that this test was without a load. It worked a couple of times, >> >but I may have damaged the MOSFET. When it worked, the MOSFET >> >wouldn't shut off. I either the coil is generating a field that >> >induces current in the gate wire, or something similar. No big deal, >> >I'll work out what's wrong because I had something similar set up on a >> >breadboard (without the inductor) and things switched on and off as >> >expected. >> > >> >The weird thing is that a -.3.06V charge develops across Vout and GND >> >even if the circuit is completely disconnected from supply and GND. >> >So, sitting out in the open with a meter attached to the output, >> >voltage climbs over a period of minutes. -2mV per second or so, but >> >it slows down as the voltage approaches the -.2V level. >> > >> >My compass shows that there are varying magnetic fields throughout my >> >apartment, but even in locations where the needle does not appear to >> >be deflected from Magnetic North, the voltage climbs as described. >> >If I shorted the capacitor (at ~1V) to drain accumulated charge, would >> >I have induced some sort of charge on the negative plate that would >> >cause this to occur? Or is this, as it appears, a phenomenon related >> >to the ambient magnetic fields occurring here where I am working? >> > >> >I tried putting the circuit in a metal box, but obviously I had to >> >allow the DVM leads to exit the box so I could watch the DVM, and >> >continued to observe the negative voltage climb. Weird, eh? >> > >> > >> >Regards, >> > >> >Uncle Steve >> >> Electrolytic caps are dissimilar plates in an acid bath, which is a >> lot like a battery. Local magnetic fields won't charge a cap. >> >> Hey, I have a Digikey bag-o assorted electrolytic caps over there on >> the floor... time to clean up maybe? They all measure positive, 10 to >> maybe 80 millivolts. If you short one, it starts recharging right >> away. The COE issues are interesting here. >> >> That 1N4004 is slow to use as the catch diode in a switcher. Better to >> a schottky, 1N5819 maybe. >> >> You're using an n-channel fet as a follower, so the gate drive had >> better swing from ground to +25 maybe. >> >> What's your switching frequency? > >>1Hz > >It appears the gate was borken on the P-Channel MOSFET. I have >purchased a replacement and will install it tomorrow.
If it's a p-fet, the drain should be on the right. And 4.7K is a really big (ie, slow) gate resistor. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On May 16, 2:30=A0pm, Uncle Steve <stevet...@gmail.com> wrote:
> On Thu, May 16, 2013 at 10:39:47AM -0700, George Herold wrote: > > On May 16, 1:02=A0pm, Uncle Steve <stevet...@gmail.com> wrote: > > > I'm seeing something really interesting with the coil I built. =A0I > > > wired up a buck converter circuit yesterday and tried it out, but jus=
t
> > > with a switch and resistor tied to the gate of an IRF-1404PbF, which > > > lists a Total Gate Charge of 131nC, which I take to mean nano- > > > coulombs. =A0When the circuit is 'rested', power applied does what is > > > expected. > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A010=
uH =A0 =A0 =A0 =A0 =A0 0R1
> > > =A018V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vou=
t
> > > =A0 =A0 =A0 =A0 D| =A0_/S =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0=
| =A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0| v | =A0 =A0 =A0| =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =
=A0 | =A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0- - - =A0 =A0 =A0\ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =
=A0 \ =A0 =A0 =A0 =A0 =A0 \ =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0-+--- =A0 =A0 =A0/ 2.2K =A0 =A0| =A0 =A0 =A0 =A0 /=
1M =A0 =A0 1M / =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 =A0 | =A0 =A0 =A0=
=A0 \ =A0 =A0 =A0 =A0 =A0 \ =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 =A0 / =A0 =A0 1N --- =A0 =A0 =A0 =
=A0/ =A0 =A0 =A0 =A0 =A0 / =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0 / 4.7k =A0 =A0| =A0 =A04004/-\ =A0 =A0 =A0 =A0| =
=A0 =A0 =A0 =A0 =A0 | =A0 ---
> > > =A0 =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0=
=A0 \ =A0 =A0 =A0 =A0 =A0 \ =A0 --- 3300uF
> > > =A0 =A0 =A0 =A0 =A0 / =A0 =A0 =A0 =A0\_/ LED =A0 =A0| =A0 =A0 =A0 =A0=
/ 100K 100k / =A0 =A0|
> > > =A0to SW =A0 =A0| =A0 =A0 =A0 =A0-+- =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0=
\ =A0 =A0 =A0 =A0 =A0 \ =A0 =A0|
> > > =A0 =A0-------+ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 /=
=A0 =A0 =A0 =A0 =A0 / =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 =
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 | =A0 =A0|
> > > =A0GND +--------------+---------+---------+-----------+----+----+ GND > > > > Note that this test was without a load. =A0It worked a couple of time=
s,
> > > but I may have damaged the MOSFET. =A0When it worked, the MOSFET > > > wouldn't shut off. =A0I either the coil is generating a field that > > > induces current in the gate wire, or something similar. =A0No big dea=
l,
> > > I'll work out what's wrong because I had something similar set up on =
a
> > > breadboard (without the inductor) and things switched on and off as > > > expected. > > > > The weird thing is that a -.3.06V charge develops across Vout and GND > > > even if the circuit is completely disconnected from supply and GND. > > > So, sitting out in the open with a meter attached to the output, > > > voltage climbs over a period of minutes. =A0-2mV per second or so, bu=
t
> > > it slows down as the voltage approaches the -.2V level. > > > Maybe it the big cap? =A0What happens if you pull that. > > Get this: > > 4mV on my coffee table; 30mV on the balcony; 70mV 4" from a 15W CFL; > 450mV with the coil touching the CFL spiral tube. =A050mv in the shade, > moving 8" into direct sunlight max 1.5V, although it varies depending > on the orientation of the coil. =A0It can't be sensitive to visible > light. =A0It just can't. > > What I did was disconnect the +terminal of the cap from the circuit. > Removing the cap entirely... =A0 Same thing. > > > I guess it's possible for an AC magnetic field to be turning on the > > 1n4004 diode during part of the cycle... and charging up (or down) > > the output. > > > > My compass shows that there are varying magnetic fields throughout my > > > apartment, but even in locations where the needle does not appear to > > > be deflected from Magnetic North, the voltage climbs as described. > > > If I shorted the capacitor (at ~1V) to drain accumulated charge, woul=
d
> > > I have induced some sort of charge on the negative plate that would > > > cause this to occur? =A0Or is this, as it appears, a phenomenon relat=
ed
> > > to the ambient magnetic fields occurring here where I am working? > > > I'm guessing the AC magnetic fields. =A0(Which you can't see with a > > compass) > > The metal box seems to work as a Faraday Cage now, which pretty much > means this circuit is RF sensitive. =A0Why the magnitude of the signal > varies so much in sunlight vs. shade is odd. =A0Using my scope, which > maxes out at a 72MHz sampling rate doesn't show a recognizable > waveform.
OK as a WAG maybe you are picking up some radio station or other RF. Does you 'scope do an FFT? Maybe you can see something there. George H.
> > Regards, > > Uncle Steve > > -- > There should be a special word in the English language to identify > people who create problems and then turn around and offer up their own > tailor-made bogus non-solutions designed to completely avoid the root > causes of the situation under consideration. =A0'Traitor' might be a > good choice, but lacks the requisite specificity. =A0One of the problems > with contemporary English is it lacks many such words that would > otherwise categorically identify certain kinds of person, place, or > thing -- making it difficult or impossible to think analytically about > such objects. =A0These shortcomings of the English lexicon are > representative of Orwellian linguistics at work in the real world.- Hide =
quoted text -
> > - Show quoted text -
"George Herold" <gherold@teachspin.com> wrote in message 
news:a92a2867-c6da-43f7-86c7-77fc88d90af4@v14g2000yqm.googlegroups.com...
On May 16, 2:30 pm, Uncle Steve <stevet...@gmail.com> wrote:
> On Thu, May 16, 2013 at 10:39:47AM -0700, George Herold wrote: > > On May 16, 1:02 pm, Uncle Steve <stevet...@gmail.com> wrote: > > > I'm seeing something really interesting with the coil I built. I > > > wired up a buck converter circuit yesterday and tried it out, but just > > > with a switch and resistor tied to the gate of an IRF-1404PbF, which > > > lists a Total Gate Charge of 131nC, which I take to mean nano- > > > coulombs. When the circuit is 'rested', power applied does what is > > > expected. > > > > 10uH 0R1 > > > 18V +---- ---------+---------+--^^^^^--+--/\/\/----+----+----+ Vout > > > D| _/S | | | | | > > > | v | | | | | | > > > - - - \ | \ \ | > > > -+--- / 2.2K | / 1M 1M / | > > > | \ | \ \ | > > > \ / 1N --- / / | > > > / 4.7k | 4004/-\ | | --- > > > \ | | \ \ --- 3300uF > > > / \_/ LED | / 100K 100k / | > > > to SW | -+- | \ \ | > > > -------+ | | / / | > > > | | | | | > > > | | | | | > > > GND +--------------+---------+---------+-----------+----+----+ GND > > > > Note that this test was without a load. It worked a couple of times, > > > but I may have damaged the MOSFET. When it worked, the MOSFET > > > wouldn't shut off. I either the coil is generating a field that > > > induces current in the gate wire, or something similar. No big deal, > > > I'll work out what's wrong because I had something similar set up on a > > > breadboard (without the inductor) and things switched on and off as > > > expected. > > > > The weird thing is that a -.3.06V charge develops across Vout and GND > > > even if the circuit is completely disconnected from supply and GND. > > > So, sitting out in the open with a meter attached to the output, > > > voltage climbs over a period of minutes. -2mV per second or so, but > > > it slows down as the voltage approaches the -.2V level. > > > Maybe it the big cap? What happens if you pull that. > > Get this: > > 4mV on my coffee table; 30mV on the balcony; 70mV 4" from a 15W CFL; > 450mV with the coil touching the CFL spiral tube. 50mv in the shade, > moving 8" into direct sunlight max 1.5V, although it varies depending > on the orientation of the coil. It can't be sensitive to visible > light. It just can't. > > What I did was disconnect the +terminal of the cap from the circuit. > Removing the cap entirely... Same thing. > > > I guess it's possible for an AC magnetic field to be turning on the > > 1n4004 diode during part of the cycle... and charging up (or down) > > the output. > > > > My compass shows that there are varying magnetic fields throughout my > > > apartment, but even in locations where the needle does not appear to > > > be deflected from Magnetic North, the voltage climbs as described. > > > If I shorted the capacitor (at ~1V) to drain accumulated charge, would > > > I have induced some sort of charge on the negative plate that would > > > cause this to occur? Or is this, as it appears, a phenomenon related > > > to the ambient magnetic fields occurring here where I am working? > > > I'm guessing the AC magnetic fields. (Which you can't see with a > > compass) > > The metal box seems to work as a Faraday Cage now, which pretty much > means this circuit is RF sensitive. Why the magnitude of the signal > varies so much in sunlight vs. shade is odd. Using my scope, which > maxes out at a 72MHz sampling rate doesn't show a recognizable > waveform.
OK as a WAG maybe you are picking up some radio station or other RF. Does you 'scope do an FFT? Maybe you can see something there. George H.
> > Regards, > > Uncle Steve
When all rational thoughts fail to find a solution the only thing left to investigate would be aliens. You might want to consider looking for the Mother Ship.