Help With Royer Oscillator
Kooner
I have a working Royer Oscillator. This version is not current fed. It
is a push push tolpolgy and the LC oscillationis are set by the
transformer inductance and winding capacitance. The schematic looks
like a multivibrator except the reistors in the collectors are
replaced withthe half primaries of the pushpull transformer.
This circuit has BJTs and has a sine wave output but I when I replace
them with Mosfets the output is square wave. I've been simulating this
thing for a week now and can't get the output to be sinewaves liek the
BJT version.
In the BJT version there are caps connected from the base of one BJT
to the collector of the other BJT and they stay charged to twice Vcc.
The current that charges these caps flows though the BE didoe. With
mosfets that current path is not there so they don't stay charged to
twice Vcc. I think there might be other differences too.
Can anyone point me to link with some more info on using Mosfets in a
Royer Osciilator? Is there a way to post a schematic here?
Jason.
John Larkin
wrote:
Post the schematics, and we can better understand the situation.
John
dagmarg...@yahoo.com
> Hello,
<snip>
> Is there a way to post a schematic here?
You can post a schematic several ways.
-- You can draw simple schematics in ASCII characters in fixed-width
fonts, and post directly to the newsgroup.
-- You can cut, paste, and directly post the (ACSII) contents of an
LTSpice .asc file directly to the newsgroup.
-- you can post a .JPG, .PNG, or other binary image to
alt.binary.schematics.design
-- you can post a graphic to your own website, or a 3rd-party photo
site.
--
Cheers,
James Arthur
Tim Wescott
A quick search on Royer oscillator got me this page:
http://wiki.4hv.org/index.php/Royer_oscillator,
which has one made with MOSFETs. Neither of their circuits have any
caps from collector to base.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
Jim Thompson
wrote:
>On 01/24/2011 01:49 PM, Kooner wrote:
>> Hello,
>>
>> I have a working Royer Oscillator. This version is not current fed. It
>> is a push push tolpolgy and the LC oscillationis are set by the
>> transformer inductance and winding capacitance. The schematic looks
>> like a multivibrator except the reistors in the collectors are
>> replaced withthe half primaries of the pushpull transformer.
>>
>> This circuit has BJTs and has a sine wave output but I when I replace
>> them with Mosfets the output is square wave. I've been simulating this
>> thing for a week now and can't get the output to be sinewaves liek the
>> BJT version.
>>
>> In the BJT version there are caps connected from the base of one BJT
>> to the collector of the other BJT and they stay charged to twice Vcc.
>> The current that charges these caps flows though the BE didoe. With
>> mosfets that current path is not there so they don't stay charged to
>> twice Vcc. I think there might be other differences too.
>>
>> Can anyone point me to link with some more info on using Mosfets in a
>> Royer Osciilator? Is there a way to post a schematic here?
>
>A quick search on Royer oscillator got me this page:
>http://wiki.4hv.org/index.php/Royer_oscillator,
>which has one made with MOSFETs. Neither of their circuits have any
>caps from collector to base.
That BJT version is a guaranteed croaker (Needs diodes to limit
reverse Vbe). Did Larkin draw that up ?:-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | 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 |
Remember: Once you get over the hill, you pick up speed
Phil Allison
"Tim Wescott"
>
> A quick search on Royer oscillator got me this page:
> http://wiki.4hv.org/index.php/Royer_oscillator,
> which has one made with MOSFETs. Neither of their circuits have any caps
> from collector to base.
** That is one brutal looking circuit !!!!
At the start, both MOSFET gates are permanently biased hard on with a 12V
zener regulated supply !!
Then somehow it starts ( ??) and each MOSFET is able to rob bias from the
other when it's turn comes to be fully conducting.
It says also a 10 amp supply is needed and the 0.68uF, 250V cap "Must Be
Good" .
Brutal.
.... Phil
John Larkin
wrote:
>On 01/24/2011 01:49 PM, Kooner wrote:
>> Hello,
>>
>> I have a working Royer Oscillator. This version is not current fed. It
>> is a push push tolpolgy and the LC oscillationis are set by the
>> transformer inductance and winding capacitance. The schematic looks
>> like a multivibrator except the reistors in the collectors are
>> replaced withthe half primaries of the pushpull transformer.
>>
>> This circuit has BJTs and has a sine wave output but I when I replace
>> them with Mosfets the output is square wave. I've been simulating this
>> thing for a week now and can't get the output to be sinewaves liek the
>> BJT version.
>>
>> In the BJT version there are caps connected from the base of one BJT
>> to the collector of the other BJT and they stay charged to twice Vcc.
>> The current that charges these caps flows though the BE didoe. With
>> mosfets that current path is not there so they don't stay charged to
>> twice Vcc. I think there might be other differences too.
>>
>> Can anyone point me to link with some more info on using Mosfets in a
>> Royer Osciilator? Is there a way to post a schematic here?
>
>A quick search on Royer oscillator got me this page:
>http://wiki.4hv.org/index.php/Royer_oscillator,
>which has one made with MOSFETs. Neither of their circuits have any
>caps from collector to base.
The critical bit is L1. The op said that his circuit is "not current
fed"; if he has no L1, it's not a Royer, it's a square-wave
multivibrator. And if he's trying to resonate the primary, it will be
very inefficient. We need a schematic.
John
Kooner
Ok, thanks. How's this:
http://www.flickr.com/photos/58722598@N07/?saved=1
- This is part of a schematic from an old design I got my hands on,
these are not the original component values but the circuit still
works.
- The simulation run is from 0 to 8uS. Once it starts to oscillate it
doesn't stop.
- I probed the base and collector of both transistors and the cap
above Q1 (5 traces total). Maybe it's not a Royer but it does
oscillate and produce sinewaves.
- Notice Vcap (C1) charges to about 9.5VDC and holds. This doesn't
happen if I use mosfets.
- The other thing I notice is the connection from the 5V supply to the
500K resistors is not needed. The circuit will still oscillate,
getting base drive from the transformer.
With mosfets I don't get sinewaves, more like squarewaves. It has
something to do with caps C1 and C2, they don't charge to a DC level
with mosfets.
I really hope I can get this thing to produce sinewaves with fets.
Jason.
Kevin McMurtrie
Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com>
wrote:
The first schematic is used for many CCFL drivers, and they never have
diodes. I think the error is in the number of windings on the base
drive.
--
I will not see posts or email from Google because I must filter them as spam
Wimpie
Hello Jason,
You are right, this is not a royer circuit.
When using BJT, you have a path via the BC diode, so this is a form of
negative feedback resulting in lower average base voltage.
The DC base current is limited by R2, R3, hence the collector current
(via HFE).
When using a mosfet, you don’t have a BC diode and current is only
limited by the mosfet itself (and wire resistance).
When (for example) Q2 (but now a mosfet) is on, it will not go off.
This is because of the high input impedance, the gate voltage will not
drop (as happens with the BJT. It will only go off when for some
reason the current through the mosfet becomes soo high, that it will
go into current saturation (So drain voltage starts to rise). When
the drain voltage of Q2 starts to rise, you may have sufficient loop
gain so that it will oscillate. You may probe the drain current, it
may be high (depending on the mosfet you selected).
You can make a royer oscillator sith mosfets, but you need additional
components to mimic BJT behavior.
Best regards,
Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me.
Bill Sloman
If it had an L1 - between the battery and the centre tap - it wouldn;t
be a Royer oscillator but a variant of the Baxandall Class-D
oscillator.
The original Royer circuit switched because the transformer core
saturated, killing the base drive. Most practical Royer circuits rely
on limiting the base drive so the "on" switching transistor comes out
of saturation when its collector curent gets high enough.
In either case, resonance between the inductance of the transformer
and the odd capacitance doesn't have a first order effect on the
frequency of oscillation, though it can mess up switching times.
The Baxandall circuit seems to have been invented to cope with the
relatively high inter-winding capacitances of high-raion step-up
transformers.
Jim Williams re-invented it - many years after Baxandall had published
the circuit in the Proceeding of the (British) IEE - and described it
as Royer circuit in his series of application notes on driving cold-
cathode back-light for lap-top computers.
http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm
--
Bill Sloman, Nijmegen
legg
<bill....@ieee.org> wrote:
<snip>
>> The critical bit is L1. The op said that his circuit is "not current
>> fed"; if he has no L1, it's not a Royer, it's a square-wave
>> multivibrator. And if he's trying to resonate the primary, it will be
>> very inefficient. We need a schematic.
>
>If it had an L1 - between the battery and the centre tap - it wouldn;t
>be a Royer oscillator but a variant of the Baxandall Class-D
>oscillator.
>
>The original Royer circuit switched because the transformer core
>saturated, killing the base drive. Most practical Royer circuits rely
>on limiting the base drive so the "on" switching transistor comes out
>of saturation when its collector curent gets high enough.
>
>In either case, resonance between the inductance of the transformer
>and the odd capacitance doesn't have a first order effect on the
>frequency of oscillation, though it can mess up switching times.
>
>The Baxandall circuit seems to have been invented to cope with the
>relatively high inter-winding capacitances of high-raion step-up
>transformers.
>
>Jim Williams re-invented it - many years after Baxandall had published
>the circuit in the Proceeding of the (British) IEE - and described it
>as Royer circuit in his series of application notes on driving cold-
>cathode back-light for lap-top computers.
>
>http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm
The misnaming is understandable - Jim Williams described it as a Royer
circuit, as do LT app notes covering PWM control of the current feed.
RL
E
"Kooner" <jjko...@gmail.com> kirjoitti
viestissä:887fd778-34b2-4d8d...@v31g2000pri.googlegroups.com...
What is wrong with using BJT, if that already works?
Joel Koltner
notes some years ago, and being interested in the oscillator he was using
there did enough digging to realize that it wasn't really a classic Royer
circuit, but I never did follow through enough to analyze it as a Baxandall.
---Joel
Kooner
> "Kooner" <jjkoo...@gmail.com> kirjoitti
> viestissä:887fd778-34b2-4d8d-a65e-7f05b6def...@v31g2000pri.googlegroups.com...
>
> - Show quoted text -
Good question...I'm working on a redesign that must work at an input
voltage of 1.0VDC. The oriignal design also works at 1.0VDC but uses
germanium transistors. I can't use them for several reasons. Other
options are to boost the input and use silicons BJTs or to use Mosfets
that have a very low Vth. I chose the Mosfet path but maybe I should
try BJTs.
Jason.
Bill Sloman
The Baxandall circuit "squeggs" if you use too big an inductor and BJT
switches. This doesn't show up in LTSpice simulations, probably
because the Gummell-Poon model of the BJT isn't good enough. The are
suggestions that using MOSFET switches avoids the "squegging".
--
Bill Sloman, Nijmegen
Wimpie
Look for the original royer circuit (with the emitter coupled BJT,
center tapped resonant circuit between the collectors). This circuit
starts to oscillate from the BE forward voltage (so about 0.7V) and
provides a sinewave (while the transistors are switching). When
properly designed it has good efficiency over a wide range of load
variation (collector efficiency > 80%).
If you apply no load, it will take long time before the output is
stable. This is because of the stored energy in the series inductor.
If you make sure power supply doesn't come up quickly, this LF ripple
behavior will be minimal.
For those who want to design these oscillators for higher voltages,
the collector peak voltage is about 3*(supply voltage).
If you don't like the transformers, make a class-C collpits
oscillator. This also starts from about 0.7V. Disadvantage of this
circuit is that you need a higher loaded Q factor to avoid envelope
instability (so you need slightly bigger magnetics).
Kooner
>
> --
> Bill Sloman, Nijmegen
Hi Bill,
Thanks, for the link. I'm running simulations with Simetrix and I will
build something in the lab this week. Could you tell me how the Q of
this circuit is defined?
If it's a parallel resonant circuit we're talking about, is it Q = R/
sqrt(L/C) ?
where sqrt(L/C) = sqrt (500uH / 100nH) = 70.7
and R = 10K x turns ratio squared ~ 10K x 100 = 1 Meg?
I can see that won't give a Q between 5 and 10 so I'm doing something
wrong here....
Jason.
Joel Koltner
news:bcbc6f72-61d5-41d1...@d11g2000yql.googlegroups.com...
>If it's a parallel resonant circuit we're talking about, is it Q = R/
>sqrt(L/C) ?
>where sqrt(L/C) = sqrt (500uH / 100nH) = 70.7
I'll buy that.
>and R = 10K x turns ratio squared ~ 10K x 100 = 1 Meg?
Isn't his turns ratio sqrt(500uH/50uH), so the 10k would actually reflect as
100k?
Of course, Q would still be much higher than 5-10, but I don't think his first
circuit there is supposed to be a realistic example. Once he drops the
resistor to 22ohms, the Q would be 22*10/70.7 or 3.11, which is on the low
side of Tony's recommended values... which I think Bill did purposely to
demonstrate the distorted waveforms.
Anyone have a PDF of Baxandall's paper around, per chance?
---Joel
nicsky
>>
>>
>>
>> > On Jan 24, 4:49=A0pm, Kooner <jjkoo...@gmail.com> wrote:
>>
>> > > Hello,
>>
>> > <snip>
>>
>> > > Is there a way to post a schematic here?
>>
>> > You can post a schematic several ways.
fixed-wi=
>dth
>> > fonts, and post directly to the newsgroup.
=
>an
>> > LTSpice .asc file directly to the newsgroup.
>> > alt.binary.schematics.design
>> > =A0-- you can post a graphic to your own website, or a 3rd-party
photo
>> > site.
>>
>> > --
>> > Cheers,
>> > James Arthur
>>
>> Ok, thanks. How's this:
>>
>>
>> - This is part of a schematic from an old design I got my hands on,
>> these are not the original component values but the circuit still
>> works.
>>
>> - The simulation run is from 0 to 8uS. Once it starts to oscillate it
>> doesn't stop.
>>
>> - I probed the base and collector of both transistors and the cap
>> above Q1 (5 traces total). Maybe it's not a Royer but it does
>> oscillate and produce sinewaves.
>>
>> - Notice Vcap (C1) charges to about 9.5VDC and holds. This doesn't
>> happen if I use mosfets.
>>
>> - The other thing I notice is the connection from the 5V supply to the
>> 500K resistors is not needed. The circuit will still oscillate,
>> getting base drive from the transformer.
>>
>> With mosfets I don't get sinewaves, more like squarewaves. It has
>> something to do with caps C1 and C2, they don't charge to a DC level
>> with mosfets.
>>
>> I really hope I can get this thing to produce sinewaves with fets.
>>
>> Jason.
>
>Hello Jason,
>
>You are right, this is not a royer circuit.
>
>When using BJT, you have a path via the BC diode, so this is a form of
>negative feedback resulting in lower average base voltage.
>
>The DC base current is limited by R2, R3, hence the collector current
>(via HFE).
>
>limited by the mosfet itself (and wire resistance).
>
>When (for example) Q2 (but now a mosfet) is on, it will not go off.
>This is because of the high input impedance, the gate voltage will not
>drop (as happens with the BJT. It will only go off when for some
>reason the current through the mosfet becomes soo high, that it will
>go into current saturation (So drain voltage starts to rise). When
>the drain voltage of Q2 starts to rise, you may have sufficient loop
>gain so that it will oscillate. You may probe the drain current, it
>may be high (depending on the mosfet you selected).
>
>You can make a royer oscillator sith mosfets, but you need additional
>components to mimic BJT behavior.
>
>
>Best regards,
>
>
>Wim
>PA3DJS
>www.tetech.nl
>without abc, PM will reach me.
http://cds.linear.com/docs/Application%20Note/an118fa.pdf
And there is a good youtube video all about these things!
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