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'[EE]:: Ringing choke converter'
Having a semantics based discussion with a friend:
In a "ringing choke converter" energy is transferred from an input
energy source to an output one by successively adding energy to an
inductor from the input source and then connecting the inductor to the
output source and allowing it to assume a voltage which allows it to
deliver current to the output. The current in the inductor does not
change instantaneously at the time the energy input is removed (this
being a fundamental property of inductors). To accomplish a
non-stepped continuation of the current flow the inductor voltage will
usually change polarity when the input energy source is disconnected.
1. What does the term "ringing" refer to in this type of converter.
2. Would one necessarily expect to see an oscillatory waveform at
the inductor switch for this to be a ringing choke converter.
It is my understanding that the "ringing choke" converter is really a
resonant flyback converter. There is the addition of a small winding in
phase with the primary that provides negative feedback to turn the
switch off. It sounds like what you are describing is a boost-mode
converter, which is of course functionally the same as the flyback. The
secondary winding and the diode perform the functions of "connecting
the inductor to the output source .."
If this were the case, the "ringing" is the resonating function of the
resonant converter. There would not be a oscillatory wave - do you mean
sine-wave? - Then no. It would be a square wave.
Russell McMahon wrote:
I have always thought a "ringing choke" converter simply refered to a design that was self-excited, i.e. the switching element was driven by a winding on the main transformer rather than a separate control, e.g. PWM.
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Alan B. Pearce
>It is my understanding that the "ringing choke" converter is really
>a resonant flyback converter. There is the addition of a small
>winding in phase with the primary that provides negative feedback
>to turn the switch off.
Well, my understanding is a ringing choke converter is self oscillating,
where a flyback converter has an external drive signal (e.g. TV horizontal
output stage). The feedback winding provides forward drive (I use the term
advisedly to be able to refer to both bipolar and FET devices) to the 'high
current' switch to turn the switch on. The current in the primary winding
then increases according to the inductor time constant, until saturation is
reached. The forward drive from the feedback winding then collapses, turning
off the switch, which in turn causes the voltage across the windings to
reverse direction due to the stored magnetic energy. This in turn helps
remove the forward drive from the feedback winding, making it reverse drive,
helping turn off the switch. It is this reversal of the voltage across the
windings that is referred to as 'ringing', giving the converter its name.
>It sounds like what you are describing is a boost-mode converter,
>which is of course functionally the same as the flyback.
>The secondary winding and the diode perform the functions of
>"connecting the inductor to the output source .."
Agreed, the output is supplied by the stored magnetic energy, making the
design somewhat inherently short circuit proof.
>If this were the case, the "ringing" is the resonating function of
>the resonant converter. There would not be a oscillatory wave - do
>you mean sine-wave? - Then no. It would be a square wave.
I think they tend to be sinusoidal during the switch turn off, due to the
manner in which the secondary is delivering current, but square wave during
the switch 'on' state.
One of the best references for these is the RCA Power Circuits Handbook,
various editions during the early 70s discussed these in detail. I think
Motorola had a similar handbook that may also have relevant info, but I saw
very few of their handbooks, working for the RCA agents at the time.
I once repaired a Amiga 500 power supply.
It was basically like a conventional flyback, but with a capacitor parallel to primary winding.
The primary side was self-oscillating in such way that the MOSFET started to conduct close bofore th evoltage across it was down to zero.
In that way it never switched on while it had high voltage, and also when it swithced off the voltage did not immediately jump high.
I guess the advantages is lower EMI and lower stress on the FET.
Waveforms are a kind of mix between flyback and sine.
On 10/5/07, Russell McMahon <paradise.net.nz> wrote: apptech
> 1. What does the term "ringing" refer to in this type of converter.
> 2. Would one necessarily expect to see an oscillatory waveform at
> the inductor switch for this to be a ringing choke converter.
I am not so familiar with RCC but Google may help here.
What I understand by a ringing choke converter is a converter where the coil
(secondary or primary) will perform a damped oscillation at its s.r.f when
turned off and energy is picked off in the secondary using some part of this
damped oscillation waveform. This implies that the driver has a holdoff period
when the ringing takes place. Typical example: TV CRT H.O.T. But this may be due
to teminology misunderstandings. A Tesla coil is also a ringing coil transformer
of sorts. I think that one can say that it's a ringing choke if the Q of the
coil plays some deliberate part in the energy transfer.
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