I would like to experiment a bit with magnetic parametric amplifiers.
For that purpose, I believe I need a 200kHz sine wave generator with
a watt worth of output power. My obvious choice was to construct
a current-fed resonant Royer oscillator. For a 1nF tank capacitor
it implies a 633uH inductor (2x5 turns on a 6400nH/turn^2 way to
big toroidal core), 2x ZTX851, a 100k base polarization resistor,
1 turn of feedback winding, 15 turns on the load winding. The
current-mode choke is 7 turns on a 5500nH/t^2 core. The
supply voltage is 8V.
And it works like a charm, the output waveform is *very* close
to a sine, 183kHz is also great for the first shot. But it works
only when not loaded. Even a 910 resistor shunting the load winding
is sufficient to kill the oscillations. Well, it still oscillates,
but the waveform does not resemble anything typical. A train of
weak wave packets with 2 maxima each, strange.
There is something terribly wrong with my circuit, people are
using it for muli-watt backlight applications without much problems.
What proven oscillator design would you suggest using instead?
Best regards, Piotr
Reply by John Larkin●May 2, 20172017-05-02
On Tue, 2 May 2017 19:56:46 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:
>I would like to experiment a bit with magnetic parametric amplifiers.
>For that purpose, I believe I need a 200kHz sine wave generator with
>a watt worth of output power.
Most benctop function generators can just about do that.
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by George Herold●May 2, 20172017-05-02
On Tuesday, May 2, 2017 at 1:56:55 PM UTC-4, Piotr Wyderski wrote:
> I would like to experiment a bit with magnetic parametric amplifiers.
> For that purpose, I believe I need a 200kHz sine wave generator with
> a watt worth of output power. My obvious choice was to construct
> a current-fed resonant Royer oscillator. For a 1nF tank capacitor
> it implies a 633uH inductor (2x5 turns on a 6400nH/turn^2 way to
> big toroidal core), 2x ZTX851, a 100k base polarization resistor,
> 1 turn of feedback winding, 15 turns on the load winding. The
> current-mode choke is 7 turns on a 5500nH/t^2 core. The
> supply voltage is 8V.
>
> And it works like a charm, the output waveform is *very* close
> to a sine, 183kHz is also great for the first shot. But it works
> only when not loaded. Even a 910 resistor shunting the load winding
> is sufficient to kill the oscillations. Well, it still oscillates,
> but the waveform does not resemble anything typical. A train of
> weak wave packets with 2 maxima each, strange.
>
> There is something terribly wrong with my circuit, people are
> using it for muli-watt backlight applications without much problems.
>
> What proven oscillator design would you suggest using instead?
>
> Best regards, Piotr
What kind of power? Voltage and current.
I was thinking a sig. gen. and power opamp.
George H.
Reply by Tim Wescott●May 2, 20172017-05-02
On Tue, 02 May 2017 19:56:46 +0200, Piotr Wyderski wrote:
> I would like to experiment a bit with magnetic parametric amplifiers.
> For that purpose, I believe I need a 200kHz sine wave generator with a
> watt worth of output power. My obvious choice was to construct a
> current-fed resonant Royer oscillator. For a 1nF tank capacitor it
> implies a 633uH inductor (2x5 turns on a 6400nH/turn^2 way to big
> toroidal core), 2x ZTX851, a 100k base polarization resistor,
> 1 turn of feedback winding, 15 turns on the load winding. The
> current-mode choke is 7 turns on a 5500nH/t^2 core. The supply voltage
> is 8V.
>
> And it works like a charm, the output waveform is *very* close to a
> sine, 183kHz is also great for the first shot. But it works only when
> not loaded. Even a 910 resistor shunting the load winding is sufficient
> to kill the oscillations. Well, it still oscillates, but the waveform
> does not resemble anything typical. A train of weak wave packets with 2
> maxima each, strange.
>
> There is something terribly wrong with my circuit, people are using it
> for muli-watt backlight applications without much problems.
>
> What proven oscillator design would you suggest using instead?
>
> Best regards, Piotr
Generate at low level, buffer, filter, amplify the s**t out of it.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I'm looking for work -- see my website!
Reply by Tim Williams●May 2, 20172017-05-02
Well... what V, I and Z were you expecting? Because it doesn't sound like
much, assuming you chose the LC values intentionally.
1W at 50 ohms is 7V and 141mA, RMS. A Royer doesn't really work at
extremely low Q, so let's say the minimum Q should be 3, or a parallel
resonant tank of 16.7 ohms. Or 47nF and 13.3uH.
To keep it going under heavier loading, you probably want much less than
that, so the Q stays above 3 or 5, say, at the highest loading.
An ungapped winding doesn't mean much, either. You need air to store
energy!
And you should probably use power MOSFETs, like a pair of IRF540. No need
to worry about base current, or teensy BJTs puffing off when you inevitably
short it out. :-)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
news:oeah93$309$1@node1.news.atman.pl...
>I would like to experiment a bit with magnetic parametric amplifiers.
> For that purpose, I believe I need a 200kHz sine wave generator with
> a watt worth of output power. My obvious choice was to construct
> a current-fed resonant Royer oscillator. For a 1nF tank capacitor
> it implies a 633uH inductor (2x5 turns on a 6400nH/turn^2 way to
> big toroidal core), 2x ZTX851, a 100k base polarization resistor,
> 1 turn of feedback winding, 15 turns on the load winding. The
> current-mode choke is 7 turns on a 5500nH/t^2 core. The
> supply voltage is 8V.
>
> And it works like a charm, the output waveform is *very* close
> to a sine, 183kHz is also great for the first shot. But it works
> only when not loaded. Even a 910 resistor shunting the load winding
> is sufficient to kill the oscillations. Well, it still oscillates,
> but the waveform does not resemble anything typical. A train of
> weak wave packets with 2 maxima each, strange.
>
> There is something terribly wrong with my circuit, people are
> using it for muli-watt backlight applications without much problems.
>
> What proven oscillator design would you suggest using instead?
>
> Best regards, Piotr
Reply by Spehro Pefhany●May 2, 20172017-05-02
On Tue, 02 May 2017 11:29:20 -0700, the renowned John Larkin
<jjlarkin@highland_snip_technology.com> wrote:
>On Tue, 2 May 2017 19:56:46 +0200, Piotr Wyderski
><peter.pan@neverland.mil> wrote:
>
>>I would like to experiment a bit with magnetic parametric amplifiers.
>>For that purpose, I believe I need a 200kHz sine wave generator with
>>a watt worth of output power.
>
>Most benctop function generators can just about do that.
Yup. 10V peak ~= 7V RMS into 50 ohms is about 1W. Which is why the
function generator output amplifiers need to be beefy.
I had a look at one of the Agilent ones' output before sending it back
for repair (wasn't the output section, I suspect it lost its
calibration constants) .. parallel high frequency high performance
op-amps IIRC.
--sp
--
Best regards,
Spehro Pefhany
Reply by ●May 3, 20172017-05-03
On Wednesday, May 3, 2017 at 3:56:55 AM UTC+10, Piotr Wyderski wrote:
> I would like to experiment a bit with magnetic parametric amplifiers.
> For that purpose, I believe I need a 200kHz sine wave generator with
> a watt worth of output power. My obvious choice was to construct
> a current-fed resonant Royer oscillator.
> For a 1nF tank capacitor
> it implies a 633uH inductor (2x5 turns on a 6400nH/turn^2 way to
> big toroidal core), 2x ZTX851, a 100k base polarization resistor,
> 1 turn of feedback winding, 15 turns on the load winding. The
> current-mode choke is 7 turns on a 5500nH/t^2 core. The
> supply voltage is 8V.
If you make the choke too inductive in a classical Baxandall oscillator it can "squeg". This only happens if you use bipolar transistors as switches, and doesn't happen if you use MOSFET switches (though start-up voltages can go rather high with a high feed inductor).
With a supply voltage of 8V you can't just connect the gate of one MOSFET to the drain of the other - you get more than 20V between gate and source, and it can be even more during start-up.
The simplest MOSFET driven circuits can be difficult to get to start up neatly - using a pair of bipolar transistors to drive the MOSFETs offers a tidy solution - see the oscillator part of the circuit at the bottom of the page.
http://www.sophia-electronica.com/Baxandall_parallel-resonant_Class-D_oscillator1.htm
> And it works like a charm, the output waveform is *very* close
> to a sine, 183kHz is also great for the first shot. But it works
> only when not loaded. Even a 910 resistor shunting the load winding
> is sufficient to kill the oscillations. Well, it still oscillates,
> but the waveform does not resemble anything typical. A train of
> weak wave packets with 2 maxima each, strange.
If you load a Baxandall enough, the harmonic content of the output goes up a lot, and you can kill the oscillation completely. The late Tony Williams had found that a Q higher then ten didn't give you a better sine wave, and a Q less than five gave you something less than good.
> There is something terribly wrong with my circuit, people are
> using it for muli-watt backlight applications without much problems.
100k of base polarisation doesn't sound like much.
Spice it and look at the actual currents.
> What proven oscillator design would you suggest using instead?
Baxandall should work fine, but you do have to think about what is going on.
--
Bill Sloman, Sydney
Reply by Jan Panteltje●May 3, 20172017-05-03
On a sunny day (Tue, 2 May 2017 19:56:46 +0200) it happened Piotr Wyderski
<peter.pan@neverland.mil> wrote in <oeah93$309$1@node1.news.atman.pl>:
>I would like to experiment a bit with magnetic parametric amplifiers.
>For that purpose, I believe I need a 200kHz sine wave generator with
>a watt worth of output power. My obvious choice was to construct
>a current-fed resonant Royer oscillator. For a 1nF tank capacitor
>it implies a 633uH inductor (2x5 turns on a 6400nH/turn^2 way to
>big toroidal core), 2x ZTX851, a 100k base polarization resistor,
>1 turn of feedback winding, 15 turns on the load winding. The
>current-mode choke is 7 turns on a 5500nH/t^2 core. The
>supply voltage is 8V.
>
>And it works like a charm, the output waveform is *very* close
>to a sine, 183kHz is also great for the first shot. But it works
>only when not loaded. Even a 910 resistor shunting the load winding
>is sufficient to kill the oscillations. Well, it still oscillates,
>but the waveform does not resemble anything typical. A train of
>weak wave packets with 2 maxima each, strange.
>
>There is something terribly wrong with my circuit, people are
>using it for muli-watt backlight applications without much problems.
>
>What proven oscillator design would you suggest using instead?
>
> Best regards, Piotr