Scott said:It ought to be in the 10's of henry region with that resistance. IIRC an
auto ignition coil is 20 henry's and several K ohms.
Look into using a gyrator. Art of Electronics has one type, there are
others. I think you might get some gyrators to go unstable (whether you
want it or not, it seems).
I've seen several articles for negative resistance oscillator design for
microwave vco's, that might not be of much use.
Although you might apply the concept of using a grounded-base
oscillator. Make a series tuned circuit with your inductor and a
resonant cap, and ground the base of a transistor. Then apply your
positive-feedback from collector output-port to emitter input-port.
--
Scott
**********************************
DIY Piezo-Gyro, PCB Drill Bot & More Soon!
http://home.comcast.net/~scottxs/
**********************************
Tony said:[snip]What i have: an inductor of unknown value, but most likely in
the henry region, with resistance from 4K to 10K. It is a
grounded inductor, and has so many turns that it cannot stand
current thru the coil - as it would saturate. I would like to
make an oscillator that uses the inductor as one of the frequency
determining components,
I wonder if it could be done with a variation of the
Baxandall sine wave oscillator. ie, Parallel-resonate
the coil and drive it with a switched constant-current
square-wave, with the polarity of the const-I being
swapped at each zero-crossing of the voltage across the
tank. Rough sketch below.
-+---+-----+- +Vs
| | R5
| R1 |
| | |/e
| +---|pnp C2
| | |\ +------||------+
| R2 | | |
0v--|\| | | C1 | RL L |
|S>---+ +--||--+--/\/\--////--+--0v
+-----+|/| | | |
| | R3 | | +------+
| | | |/ | | |
| | +---|npn | +-|\ |
| | | |\e | |O>--+
| | R4 | +----|/ |
| | | R6 |
| -+---+-----+- -Vs |
| |
+--------------------<--------------+
It's a pair of constant-current sources, alternately
switched by comparator/gate (S), which is driven by
the buffered sinewave across the resonant tank. C1
is a large dc-blocker and C2 is the resonating capacitor.
The Baxandall circuit requires a Q of roughly 5-10 for
best operation. So the design frequency will initially
be determined by Q = wL/R. With the rough numbers already
given this suggest an Fosc in the 6KHZ to 10KHZ region.
That then determines the value of C2, which will be around
500pF. C2 includes the Cstray of the inductor.
The impedance of the tank at Fres is Z = L/CR, so will
be up in the 300k region. With 15v supplies, and a few volts
across the tank, the required switched currents would then
be of the order of +/- 20-40 uA or so.
All numbers above winged on the fly, and to be confirmed.
An interesting possibility could be to use a single OTA as
the switching constant-current source. An OTA has a voltage
adjustable current output and this could be used to
stabilise the amplitude of the voltage across the tank.
C2
+------||------+
__ +Vs | |
0v--+---| \| C1 | RL L |
R1 |OTA>----||--+--/\/\--////--+--0v
+--+|__/| |
| | -Vs | +------+
+----|->--+ | | |
| +-------<---R2---|--+-|\ |
| | |O>--+
| C3 +----|/ |
+--R3--+---||--+ |
| | D |
| /|--+--+---R4---|<|--+
+--<O| |
\|--+ +---R5---|>|--+
| D |
0v-+- |
-+- -Vs
The same +1 buffer looks at the voltage on the tank
and now switches the polarity of the OTA's output
current via R2 and R1. R1 and R2 should probably be
sized for a 2V or so peak voltage across R1.
Actually I'm not quite certain of the last sentence.
An OTA has a linear (log) region of about 100mV or
so. So there may be a need to check that there is
enough loop gain for oscillation with R2:R1 ratios.
The additional opamp is an erroramp/integrator that
compares the half-wave rectified AC via R4 against
a reference current from R5, and sets the required OTA
output current via R3. R3 should be sized for about
100uA through it when the integrator is at pk +Vout,
(R3= 250k-ish with 15-0-15 supplies). R4 and R5 should
be sized so that the ratio of R5/R4 is about 4.7/1
(giving ACVpk= -Vs*2/3 approx).
Ummm... haven't a clue whether the above will work or
not. Suggest you SPICE it first.
Robert Baer said:It seems the Q of the inductor is much less than one.
I tried "jarring" it with a square wave thru a capacitor (series
C-LR) and it made no observeable difference with a capacitor from
500pF to 2.2uF; looked like a low loss wide band "attenuator".
Tried square waves from 0.01Hz to 1MHz...only on the low end
did i see the typical RC droop..
C2
+------||------+
__ +Vs | |
0v--+---| \| C1 | RL L |
R1 |OTA>----||--+--/\/\--////--+--0v
+--+|__/| |
| | -Vs | +------+
+----|->--+ | | |
| +-------<---R2---|--+-|\ |
| | |O>--+
| C3 +----|/ |
+--R3--+---||--+ |
| | D |
| /|--+--+---R4---|<|--+
+--<O| |
\|--+ +---R5---|>|--+
| D |
0v-+- |
-+- -Vs
.................... R1 and R2 should probably be
sized for a 2V or so peak voltage across R1.
Actually I'm not quite certain of the last sentence.
An OTA has a linear (log) region of about 100mV or
so. So there may be a need to check that there is
enough loop gain for oscillation with R2:R1 ratios.
--|\
|O>--
--|/
/|--
--<O|
\|--
[/QUOTE]--|\
|O>--
--|/
/|--
--<O|
\|--
Tony, what are those symbols? Opamps?
What's the "o" for? opamp?
Yes.... just me being a little too sketchy.
--|\
| >O--
--|/
/|--
--O< |
\|--
--|\
| >--
--|/
/|--
--< |
\|--
__
--|- \
| >--
--|+_/
'course I go for this mess, attempting to add the
opamp's + - pin names,
Tony said:Robert Baer said:What i have: an inductor of unknown value, but most likely in
the henry region, with resistance from 4K to 10K. It is a
grounded inductor, and has so many turns that it cannot stand
current thru the coil - as it would saturate. I would like to
make an oscillator that uses the inductor as one of the frequency
determining components,
[snip]
I wonder if it could be done with a variation of the
Baxandall sine wave oscillator. ie, Parallel-resonate
the coil and drive it with a switched constant-current
square-wave, with the polarity of the const-I being
swapped at each zero-crossing of the voltage across the
tank. Rough sketch below.
-+---+-----+- +Vs
| | R5
| R1 |
| | |/e
| +---|pnp C2
| | |\ +------||------+
| R2 | | |
0v--|\| | | C1 | RL L |
|S>---+ +--||--+--/\/\--////--+--0v
+-----+|/| | | |
| | R3 | | +------+
| | | |/ | | |
| | +---|npn | +-|\ |
| | | |\e | |O>--+
| | R4 | +----|/ |
| | | R6 |
| -+---+-----+- -Vs |
| |
+--------------------<--------------+
It's a pair of constant-current sources, alternately
switched by comparator/gate (S), which is driven by
the buffered sinewave across the resonant tank. C1
is a large dc-blocker and C2 is the resonating capacitor.
The Baxandall circuit requires a Q of roughly 5-10 for
best operation. So the design frequency will initially
be determined by Q = wL/R. With the rough numbers already
given this suggest an Fosc in the 6KHZ to 10KHZ region.
That then determines the value of C2, which will be around
500pF. C2 includes the Cstray of the inductor.
The impedance of the tank at Fres is Z = L/CR, so will
be up in the 300k region. With 15v supplies, and a few volts
across the tank, the required switched currents would then
be of the order of +/- 20-40 uA or so.
All numbers above winged on the fly, and to be confirmed.
An interesting possibility could be to use a single OTA as
the switching constant-current source. An OTA has a voltage
adjustable current output and this could be used to
stabilise the amplitude of the voltage across the tank.
C2
+------||------+
__ +Vs | |
0v--+---| \| C1 | RL L |
R1 |OTA>----||--+--/\/\--////--+--0v
+--+|__/| |
| | -Vs | +------+
+----|->--+ | | |
| +-------<---R2---|--+-|\ |
| | |O>--+
| C3 +----|/ |
+--R3--+---||--+ |
| | D |
| /|--+--+---R4---|<|--+
+--<O| |
\|--+ +---R5---|>|--+
| D |
0v-+- |
-+- -Vs
The same +1 buffer looks at the voltage on the tank
and now switches the polarity of the OTA's output
current via R2 and R1. R1 and R2 should probably be
sized for a 2V or so peak voltage across R1.
Actually I'm not quite certain of the last sentence.
An OTA has a linear (log) region of about 100mV or
so. So there may be a need to check that there is
enough loop gain for oscillation with R2:R1 ratios.
The additional opamp is an erroramp/integrator that
compares the half-wave rectified AC via R4 against
a reference current from R5, and sets the required OTA
output current via R3. R3 should be sized for about
100uA through it when the integrator is at pk +Vout,
(R3= 250k-ish with 15-0-15 supplies). R4 and R5 should
be sized so that the ratio of R5/R4 is about 4.7/1
(giving ACVpk= -Vs*2/3 approx).
Ummm... haven't a clue whether the above will work or
not. Suggest you SPICE it first.
Robert said:It seems the Q of the inductor is much less than one.
I tried "jarring" it with a square wave thru a capacitor (series C-LR)
and it made no observeable difference with a capacitor from 500pF to
2.2uF; looked like a low loss wide band "attenuator".
Tried square waves from 0.01Hz to 1MHz...only on the low end did i see
the typical RC droop..
Winfield Hill
I would normally use this for an opamp...
__
--|- \
|O >--
--|+_/
....and this for a comparator....
__
--|- \
|C >--
--|+_/
__
--|- |\
| | >--
--|+_|/
... but The Boss is on my back about the height
of the weeds, so I was in hurry......
OK, I see where you're coming from. I've been using
this for comparators, a vertical line at the output,
Oops, I see where she's coming from. Watch out! :>)
Thanks,
- Win
whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
Win, I think the vertical line is "standard" notation.
Jim Thompson wrote...
That would be nice, I've been using it for over 30 years,
but I don't recall seeing it on other people's drawings
(this could be my forgetfullness). For example, do you
use it yourself? Can you give us a reference or guidance
for its being a standard notation? Also, can we safely
mention it in our book's next edition?
Thanks,
- Win
whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)
I've been using it for years... observe my S.E.D/Schematics Page...
but my "square" part is more rectangular (narrower) and the triangular
part has 45° angles relative to the rectangle.
I can't really provide a reference, but I see it a lot.
Actually, musing over it, you might surf thru Analog Devices parts...
I think that's where it originated.
Tony said:I nearly went for series-resonance initially, to
get the inherent dc-blocking. But then realised
that an inductor that large must have a significant
Cstray, which ruins any chance of a simple C-L+R
series-resonance.
So the apparent lack of Q that you observed may just
have been determined by the low output impedance of
the square wave voltage generator.
Fred said:It's a PoS- better to think "door stop" ....
Fred said:Tony said:Robert Baer said:What i have: an inductor of unknown value, but most likely in
the henry region, with resistance from 4K to 10K. It is a
grounded inductor, and has so many turns that it cannot stand
current thru the coil - as it would saturate. I would like to
make an oscillator that uses the inductor as one of the frequency
determining components,
[snip]
I wonder if it could be done with a variation of the
Baxandall sine wave oscillator. ie, Parallel-resonate
the coil and drive it with a switched constant-current
square-wave, with the polarity of the const-I being
swapped at each zero-crossing of the voltage across the
tank. Rough sketch below.
-+---+-----+- +Vs
| | R5
| R1 |
| | |/e
| +---|pnp C2
| | |\ +------||------+
| R2 | | |
0v--|\| | | C1 | RL L |
|S>---+ +--||--+--/\/\--////--+--0v
+-----+|/| | | |
| | R3 | | +------+
| | | |/ | | |
| | +---|npn | +-|\ |
| | | |\e | |O>--+
| | R4 | +----|/ |
| | | R6 |
| -+---+-----+- -Vs |
| |
+--------------------<--------------+
It's a pair of constant-current sources, alternately
switched by comparator/gate (S), which is driven by
the buffered sinewave across the resonant tank. C1
is a large dc-blocker and C2 is the resonating capacitor.
The Baxandall circuit requires a Q of roughly 5-10 for
best operation. So the design frequency will initially
be determined by Q = wL/R. With the rough numbers already
given this suggest an Fosc in the 6KHZ to 10KHZ region.
That then determines the value of C2, which will be around
500pF. C2 includes the Cstray of the inductor.
The impedance of the tank at Fres is Z = L/CR, so will
be up in the 300k region. With 15v supplies, and a few volts
across the tank, the required switched currents would then
be of the order of +/- 20-40 uA or so.
All numbers above winged on the fly, and to be confirmed.
An interesting possibility could be to use a single OTA as
the switching constant-current source. An OTA has a voltage
adjustable current output and this could be used to
stabilise the amplitude of the voltage across the tank.
C2
+------||------+
__ +Vs | |
0v--+---| \| C1 | RL L |
R1 |OTA>----||--+--/\/\--////--+--0v
+--+|__/| |
| | -Vs | +------+
+----|->--+ | | |
| +-------<---R2---|--+-|\ |
| | |O>--+
| C3 +----|/ |
+--R3--+---||--+ |
| | D |
| /|--+--+---R4---|<|--+
+--<O| |
\|--+ +---R5---|>|--+
| D |
0v-+- |
-+- -Vs
The same +1 buffer looks at the voltage on the tank
and now switches the polarity of the OTA's output
current via R2 and R1. R1 and R2 should probably be
sized for a 2V or so peak voltage across R1.
Actually I'm not quite certain of the last sentence.
An OTA has a linear (log) region of about 100mV or
so. So there may be a need to check that there is
enough loop gain for oscillation with R2:R1 ratios.
The additional opamp is an erroramp/integrator that
compares the half-wave rectified AC via R4 against
a reference current from R5, and sets the required OTA
output current via R3. R3 should be sized for about
100uA through it when the integrator is at pk +Vout,
(R3= 250k-ish with 15-0-15 supplies). R4 and R5 should
be sized so that the ratio of R5/R4 is about 4.7/1
(giving ACVpk= -Vs*2/3 approx).
Ummm... haven't a clue whether the above will work or
not. Suggest you SPICE it first.
I am fairly certain that it is impossible to make a stored energy
oscillator out of this piece of junk for the simple reason that the SRF
will occur long before Q reaches 1- you just end up with a 10-pound
relaxation oscillator. The most common approach to make any LC resonate
leads to ridiculous parameters:
Please view in a fixed-width font such as Courier.
+---------------------------+
| |
| |
| |
| |\ A x Vo |
+---|+\ v R |
| >----+---/\/\---+----+ <-Vo
+---|-/ | | |
| |/ \ | \
| R2 | Rc
| \ | \
| | | |
+-----------+ === )
| C | L )
R2 \ | )
A = 1+ -- R1 | |
v R1 \ | |
| | |
+----------+----+
|
---
sum currents at Vo node:
Vo x (1-A )
v 1
----------- + Vo x sC + Vo x --------- =0
R Rc + sL
Rc x R x C
==> oscillation at A = 1 + ----------
v L
2
2 1 - Rc x C /L
W = --------------
osc LC
Rc= coil ESR at oscillation frequency
[/QUOTE]+------||------+
__ +Vs | |
0v--+---| \| C1 | RL L |
R1 |OTA>----||--+--/\/\--////--+--0v
+--+|__/| |
| | -Vs | +------+
+----|->--+ | | |
| +-------<---R2---|--+-|\ |
| | |O>--+
| C3 +----|/ |
+--R3--+---||--+ |
| | D |
| /|--+--+---R4---|<|--+
+--<O| |
\|--+ +---R5---|>|--+
| D |
0v-+- |
-+- -Vs
I am fairly certain that it is impossible to make a stored energy
oscillator out of this piece of junk for the simple reason that
the SRF will occur long before Q reaches 1- you just end up with
a 10-pound relaxation oscillator. The most common approach to
make any LC resonate leads to ridiculous parameters:
Fred said:Tony Williams wrote...[ snip interesting circuit ]I am fairly certain that it is impossible to make a
stored energy oscillator out of this piece of junk ...
Oh-oh! Time for a breadboard maybe............
[ snip ]
Well, it oscillated quite nicely, and ...
