LTC Switcher CAD3 ?

Who needs that? ;)

Jamie

Grown-ups.

-- Bill Sloman, Nijmegen

Use coupled inductors - K1 L1 L2 L3 0.99 tells the program that L1, L2 and L3 are windings on a single transforemr with a coupling coefficient of 0.99

The John Chan model represents real, hysteretic inductors pretty accurately, if my limited experience is anything to go by.

The John Chan model allows you to do that

The John Chan model allows you to do that.

Go to "Help" and section L.Inductor.

There's not a lot wrong with the program, but you do have to work out how to get the most out of it.

-- Bill Sloman, Nijmegen

Then come back in a few years, if you have any left.

Jamie

I doubt if you'll ever grow up, and I doubt if I'd like what you might grow up into any better than I like the character that you are exhibiting at the moment.

Serious engineers do exploit the transformer-modelling options in LTSpice. Robert Baer isn't all that serious, or he would have been able to find them on his own - and even he recognised that an analog circuit simulation program ought to be able to simulate the trickier features of real transformers and had enough sense to ask about them.

Of course they do seem to have been too tricky for you to known about them in the first place.

-- Bill Sloman, Nijmegen

There are a lot of common things that could be ready-to-go parts, that instead require you to enter .model statements or other directives, which is a minor nuisance. Ideal diodes, transformers, controlled switches, ltline, a few things like that.

Lemme see..i want to make a DC-DC converter, using (guess what kiddies) a ferrite pot core, maybe some kind of controller to (at minimum) generate drive waveforms to power devices, some feedback from output to give line and load regulation. BUT..like i said, the NO mentioned does not allow me to select or try different transformers..

So i can pick a 2N2222 or a 2N3904 or a LT1026 or LT1105 or a 2W 110 ohm resistor or a 1uF 10V TDK X5R capacitor as if off the shelf. BUT. Transformers? Ferroxcube pot cores? Then accidentally overdrive them? Nope. You say i need to $pend $2,000 to IEEE to look at some paper i never heard about and that few others heard about if i want to know more than what is disclosed in that help section. Nobody gives the K or M of their transformers; i have to guess - and the numbers will most likely be wrong no matter what i pick. And.. nobody mentions that those values are non-linear and what changes them.

em?

er

nd

The K for most ungapped ferrtie cored transformers is in the 0.99 to

We've just measured a coupling of 0.98 in a gapped RM14 core - EPCOS gapped it down from 6000uH/root turn for an ungapped pair to 630nH per root turn by grinding back the centre pillar by 0.4mm,

M is K.square root L1.L2 IIRR

The transformer equations are

V1=3D L1.dI1/dt + M.dI2/dt

V2=3D M.dI1/dt + L2.dI2/dt

The John Chan model explicitly deals with the non-linear elements - though it leaves coupling severely alone. Coupling does decline dramatically if you saturate the ferrite, but real circuits blow up if you saturate the ferrite. Ferrite permeability does rise with field at low field values, but not all that much, and you can usually get away with ignoring the effect on coupling - which usually isn't a critical parameter.

-- Bill Sloman, Nijmegen

Here's a pretty good modeling example for transformers. Transformers are sort of a black art, it's rare to design one perfectly the first time around.

Cheers

Engineers.

AFAIK, SwitcherCad disappeared from the LTSpice suite at version IV, and is unsupported.

Several years ago, now.

There's now LTPowerCad, a Microsoft Excel based thing.

LTSpice can do transformers, saturable inductors, and hysteretic model inductors. RTFM.

So make your own macro model and implement them, sheesh.

I've seen several manufacturers (VAC is one) state inductance and leakage of their products (which correspond to k and M), though unfortunately the most common often don't (Pulse, Murata, etc.).

For regular SPICE, I wrote my own based on the saturable core model (which might be Chan, I don't remember), which includes the calculations to go from engineering units (short-circuit leakage, winding inductances) to turns ratios and coupling. The circuit forms an inductive tee network, where the core is the middle element shunting to ground: when permeability is high, core inductance is very high, and little is dropped across the leakage elements. When the core saturates, its inductance drops by up to a factor of mu, causing k to fall. LL remains constant, which is realistic because absolute LL is determined by winding geometry, independent of core.

Tim

Or buy a bunch of parts and test+breadboard. Works for me.

Last project I needed a model, I overestimated leakage and DCR intentionally, and made it work. Boards came in: much better performance, and no problems with ringing (note that lower leakage means higher ringing frequency and lower impedances, making them harder to dampen).

That ISDN transformer looks a lot bulkier than Ethernet transformers. How much flux goes into one of those?

Tim

That's a 4-winding unit, 1:1:2:2, wired as a 5:1 step-up. I'm applying

It's often easier to drop parts into a breadboard than to characterize parts, create a model, and simulate. Measure temperatures with an IR gadget instead of simulating core losses.

Besides, a boy needs to solder once in a while.

If you don't need isolation, you could do a 1:4 and add it to the top of the

tm

It needs isolation, or rather the customer thinks it does.

Here's the circuit:

and here's the board.

The dual-winding Coiltronics DRQ inductor/transformer is cute and cheap, but turned out to be fairly inefficient and marginal for the loads we might see. The Coilcraft toroid is a beast.

That IR inverter driver chip is great.

I think that should be "per turn squared".