Zeta flying capacitor

That's a fine choice above 150V or so.

Tim

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Seven Transistor Labs, LLC 
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Tim Williams
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Yup, though only for forward converter transformers, not Zeta.

Tim

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Seven Transistor Labs, LLC 
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Tim Williams

At 100kHz and 7cm L1 leads, 4cm L2 leads: L_L1=5907nH, C_L1/L2=76.4pF, L_leakage=78nH, so K=0.987. DCR_L1=1.2mOhm. The core has mu_r=60 (nominal), so the measured values seem about right.

Best regards, Piotr

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Piotr Wyderski

Nice!

"Massive at that impedance" being, the characteristic impedance is 32 ohms, but you're using it at -- what, even, 20V 4A (5 ohms switching impedance) is it? Or is it 80A, but is it ever supposed to be switching up there? -- dunno, I don't think you clarified that. Whatever it is, in any case.

Of course for the coupling capacitor, that fixes that, so then you're looking at, say you go with 100uF of ceramics, that's Zo = 28mohms and Fo =

57kHz. So 200kHz should be safely above that not to worry too much, but take care that the control loop cutoff is equally well below so as not to excite it. And that should pretty much be all you need to do.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
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Tim Williams

In the secondary supply mode it is supposed to conduct 40A DC continuous, 60A peak and work till 80A, where the overcurrent protection circuitry should stop the show. But its inductance for dI/dt limiting purposes is still useful to about 150A (assuming 1uH). Only DCR matters here, the 6:1 L swing is not a problem.

When charging, power flows the opposite direction, but the current is much lower, L changes by about 8% in that region. Don't know if it is good enough for the forward-derived Zeta, but the flyback-like SEPIC would have no problem with it.

4A is about C/20 and I have plenty of time, so the accu should like it.

The value of 200kHz was a SWAG to start somewhere, but the simulation shows that at 100kHz the parameters are still decent. So maybe there will be no practical need to approach the infrared switching frequencies. ;-)

Thanks, Tim, I will let you know about the prototype results.

Best regards, Piotr

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Piotr Wyderski

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