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SillyAmp

W

Winfield Hill

Jan 1, 1970
0
Jim said:
Concern for opto NPN punch thru during power-up... I could go
for a zener or some-such in there.

Silly man. No HV power supply I'm aware of has a fast enough
risetime at power-up to come close to creating such an issue.
Maybe if one was to use a HV switch in the power supply line,
but then the blame would lie in using the switch (been there,
done that, oops), not with the circuit. There is a danger if
(when) the output is instantaneously shorted, ameliorated with
a small output R.

____
V+ hv --o o-----,
+200 |
150k, 2W
| +/-170V
+---- 2.2k -------out
|
| Supertex DN2540
d depletion-mode
g ----,
s |
in--/\/\---, | 10V |
| +--|<|--+
| opto | |
a _|_ c |
_\V/_ ---> b |
k | e |
| | | ____ V-
gnd ---+-------+---o o---- -180

A higher-voltage version (+/-300V output) can be made with
a Supertex dn2470. That's a 700V depletion-mode MOSFET, the
record holder for such parts. Mouser stocks 'em.

This circuit would benefit from feedback. A Darlington NPN
would minimize the feedback-node bias current, and an offset
resistor could provide for bipolar inputs and correct for
the LED and BJT drops at the summing junction. A resistor,
say Vgs/I = 470 ohms, in the MOSFET's path would limit the
pulldown current to a few mA, to avoid overheating the FET.

V+ hv --/\/\---/\/\---, John's HV amp idea
+360 150k, 2W (2) |
| Rf/Rin = 60 +/-300V
,- Rf--+ to 1mA
Roffset | +---- 3.3k ----------- OUT
+5 ----/\/\-----+ |
Rin | | Supertex DN2470
IN ----/\/\------+ d depletion-mode
-5 to +5 | g ----,
| s |
| | 10V |
+5 --/\/-- c | +--|<|--+
b --' | |
e 470 |
| opto | |
a _|_ c |
_\V/_ ---> b |
k | e |
| | | fuse V-
gnd ---+-------+---o X o---- -320
 
T

Terry Given

Jan 1, 1970
0
Tim said:
Bring it on! I'd love to see anything about parametric amplifers-- the only
thing I can find on them is "they work by varying some part of the
circuit"...drrrrr...okay...

Ceramic caps would be a very accessible way to demonstrate one.

Tim

see if you can find anything on a "paraformer". Wanlass & Wanlass
dreamed it up when I was an itch in my daddy's pants IIRC.

the trick was to get a tap-wound C core, and cut it in half, then rotate
one half 90 degrees ?! The flux from one wouldnt couple to the other,
but it would modulate the permeability....

Cheers
Terry
 
F

Fred Bartoli

Jan 1, 1970
0
Terry Given a écrit :
see if you can find anything on a "paraformer". Wanlass & Wanlass
dreamed it up when I was an itch in my daddy's pants IIRC.

the trick was to get a tap-wound C core, and cut it in half, then rotate
one half 90 degrees ?! The flux from one wouldnt couple to the other,
but it would modulate the permeability....

I couldn't make sense of that so I had a look.

http://www.pat2pdf.org/patents/pat3061820.pdf

is probably what you were speaking about.

That one works because there's an additional *shared* piece of core
(flat plate between both C halves) that sees the two orthogonal fluxes,
hence it has its permeability modulated by one winding without
influencing the other.
 
T

Terry Given

Jan 1, 1970
0
Fred said:
Terry Given a écrit :


I couldn't make sense of that so I had a look.

http://www.pat2pdf.org/patents/pat3061820.pdf

is probably what you were speaking about.

That one works because there's an additional *shared* piece of core
(flat plate between both C halves) that sees the two orthogonal fluxes,
hence it has its permeability modulated by one winding without
influencing the other.

fun stuff eh Fred?

It was a long time ago I looked at the paraformer, but Im pretty sure it
was as I described it. I was interested in magamps at the time....

Cheers
Terry
 
T

Tony Williams

Jan 1, 1970
0
Terry Given said:
see if you can find anything on a "paraformer". Wanlass & Wanlass
dreamed it up when I was an itch in my daddy's pants IIRC.
the trick was to get a tap-wound C core, and cut it in half, then
rotate one half 90 degrees ?! The flux from one wouldnt couple
to the other, but it would modulate the permeability....

I've seen that applied to a toroid. Normal toroidal
windings, with another winding across the outside of
everything. The outside winding was supposed to
reduce the permeability. I still don't know whether
it was an April Fool's or not.
 
F

Fred Bartoli

Jan 1, 1970
0
Terry Given a écrit :
fun stuff eh Fred?

It was a long time ago I looked at the paraformer, but Im pretty sure it
was as I described it. I was interested in magamps at the time....

My first thought was that they're related, but mag amps windings are
coupled.

I still can't see how you can arrange 2 C cores halves to achieve
permeability modulation.

I've posted on abse another arrangement that can be used with 2
identical 'C' cores. But the C is almost closed.
 
F

Fred Bartoli

Jan 1, 1970
0
Tony Williams a écrit :
I've seen that applied to a toroid. Normal toroidal
windings, with another winding across the outside of
everything. The outside winding was supposed to
reduce the permeability. I still don't know whether
it was an April Fool's or not.

I've seen that too.
A more effective way is to make the toroid hollow (for ex. 2 C halves
used as the toroid section) so that both flux path are closed.

I've also seen, when searching about flux gates, some ways of making 3
orthogonal fluxes within one core. Can't remember what they were used for.
 
M

MooseFET

Jan 1, 1970
0
[....]

This circuit would benefit from feedback. A Darlington NPN
would minimize the feedback-node bias current, and an offset
resistor could provide for bipolar inputs and correct for
the LED and BJT drops at the summing junction. A resistor,
say Vgs/I = 470 ohms, in the MOSFET's path would limit the
pulldown current to a few mA, to avoid overheating the FET.

I'm going to suggest a modification or two:

Modified version
V+ hv --/\/\---/\/\---, John's HV amp idea
+360 150k, 2W (2) |
| Rf/Rin = 60 +/-300V
,- Rf--+ to 1mA
Roffset | +---- 3.3k ----------- OUT
+5 ----/\/\---- | - |
Rin | ! | Supertex DN2470
IN ----/\/\------+ ! d depletion-mode
-5 to +5 | ! g ----,
NEW --- ! s |
^ ! | 10V |
+5 --/\/-- c | ! +--|<|--+
b --+-- | |
e 470 |
| opto | |
a _|_ c |
_\V/_ ---> b |
k | e |
| | | fuse V-
gnd ---+-------+---o X o---- -320


Adding the diode (or diodes) marked "NEW" partially compensates for
the EB drop of the bipolar transistor.

If instead of a diode, we make that the E-B drop of a PNP emitter
follower, we can use a non darlington for the NPN feeding the LED.

If we place a resistor in parallel with the LED we can run the NPN
feeding it at a more well known current. This would make matching it
with the PNP better.

The capacitance of the 10V zener slows things down.

Many K
+V---/\/\-----
! 10V
------->!-----+----!<----
1N914
 
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