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From: "John Jardine"
Subject: Re: The X converter
Date: Sun, 24 Nov 2002 23:48:25 -0000
NNTP-Posting-Date: 24 Nov 2002 23:36:42 GMT
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analog wrote in message news:3DE068EE.B3A6F0C6@ieee.org...
> Hi all,
> Here is a fun little circuit for your amusement. Shown below is a
> non isolated switch mode power converter that I call the "X" converter
> for obvious reasons. It has two capacitors and two inductors, each of
> which are split into two equal windings. It is capable of producing
> a non inverted output voltage from zero to many times the input
> voltage (just the thing when your application needs a regulated 12
> volt output from an unregulated 12 volt battery).
> When you ponder the schematic below, keep the following in mind:
> The output is non isolated and the same polarity as the input.
> When the duty cycle for Q1 is zero the output is zero.
> At 50 percent duty cycle the output is the same as the input.
> L1A and L1B are two equal windings on the core of L1.
> L2A and L2B are two equal windings on the core of L2.
> The winding polarities for L1 and L2 are indicated by the
> asterisks and are all positive when Q1 is on.
> +Vi o-+ +-o +Vo
> | |
> @)* @)
> L1A @) L2A @)
> @) @)*
> | |
> | C1 || |
> +-----. ,--||--+
> | \ / || |
> |+-+ \ / _|_
> o-|| Q1 X D1 /A\
> |+-+ / \ |
> | / \ || |
> +-----' `--||--+
> | C2 || |
> | |
> @)* @)
> L1B @) L2B @)
> @) @)*
> _|_ _|_
> //// ////
> The "X" converter is an almost unknown power converter topology based
> on split inductors. Its name comes from the x-shaped cross connection
> of components in the schematic of the most basic form of the topology.
> The split inductors add another degree of freedom that has kept the
> "X" converter virtually undiscovered in spite of efforts to classify
> all power converters with four or less energy storage elements.
> There are several forms of this topology with positive or negative
> output, with ground referenced switches, and with natural isolation.
> This power converter has the same static conversion characteristics as
> a buck-boost or a `Cuk converter, and it has reduced ripple current on
> both input and output ports (sometimes referred to as "zero" ripple).
> Although these ripple currents are not actually zero, it can be shown
> that the "X" converter has the very interesting and useful behavior of
> confining the bulk of its inductors' ramping magnetizing currents to
> internal loops. Through this mechanism, sometimes called "current
> steering", the "X" converter achieves ripple current characteristics
> similar to an equivalent buck converter with an input filter.
> Since the topology has four energy storage elements, its undamped dynamic
> behavior is somewhat unwieldy. The control-to-output transfer function
> has two left half s-plane complex pole pairs and a right half s-plane
> complex zero pair due to the lattice topology and the switching action.
> This combination yields 540 degrees of phase shift! With proper damping,
> the zero pair can be pulled into the left half s-plane such that it
> nearly cancels one of the pole pairs and the overall response appears
> almost second order.
> Getting ground referenced drive to Q1 may appear problematic due to the
> flying nature of the switch, but this is easily done simply by adding a
> small bifilar gate drive winding to L1B. Since first discovering it in
> the mid 80's I have built several versions of the "X" converter circuit.
> It is fun and easy to simulate in Pspice (both the frequency and time
I'm not a power designer but I think it's a super arrangement!.
First novel switcher idea I've seen in the past ten years. The 'Cuk' circuit
never really had much to offer.
Can't imagine why the power specialists haven't commented yet ?.
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