Synthesising sine waves is a crime against nature. I urge you to reconsider.
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nice with a shop kitty,
Haha! Good reply. :) Actually, that Old Tony is one of the best metalworkers out there on YT and I really enjoy watching his films and those of Tubelcaine, Myfordboy and so forth as well. Interesting when he was cutting that left-hand thread he didn't pre-cut any relief on the RHS of it. I wouldn't have got away with that, but his machining skill level is orders of magnitude better than mine. And so is his video editing ability. The bastard.
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It's legal in most states if it's over 16 bits.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
It's not a matter of legality; more one of morality. But if you can live with yourself, then fine.
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Does LTC make any class D amp modules included with LTSpice? I'm curious now about how using a DC servo loop into a first stage opamp driving the D-amp as a power buffer, instead of a cap would work out in practice.
The problem with that XLR transformer driver circuit as drawn in a modification is that while there are two feedback loops, one local to the op-amps and one around the opposite side current sense resistor, it's assumed that the phase of the AC signals on both inputs of the op amps will be similar.
but the phase shift produced by the class D output filter complicates things, where to put the sense resistor. If after the output filter need to compensate the phase shift somehow and if before need to filter the switching frequency down to DC. It may not be nearly as easily workable in the class D bridged power-buffer topology as with linear amplifiers driving the transformer, bridged.
It's just a phase I'm going through.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Putting it after the LC also means have to take the (possibly not well- defined) R of the L into account as a component of the current sense impedance.
We plan to put the current sensor just before the customer output, which is after the filter inductors and the isolation transformer. Probably a resistive shunt, isolated by a small audio transformer.
It will be an interesting control loop, synthesizing the output impedance.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
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use a h-bridge instead and do everything in software/FPGA ?
Voltages are relative, so it might fight to maintain its output offset compared to what? The ground pins, I expect. If you used only one output per package, you could maybe servo the grounds to eliminate the offset.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
The TI switcher is a class-D h-bridge. I wouldn't want to try to go linear.
We do plan to do all the processing in an FPGA.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
mandag den 3. juni 2019 kl. 01.36.05 UTC+2 skrev John Larkin:
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I wasn't thinking linear but pwm directly from the FPGA to a powerstage, ju st like numerous variable frequency drives and brushless DC motor drives
If you're going to use transformer isolation for the shunt, you might as well use a current transformer instead. That way you can have less voltage per turn of the core for a given customer-visible output current, so a smaller core and/or better accuracy. Probably better frequency response too. You'd also face less modifications if you ever needed to switch to a hall effect sort of current sensor, if you wanted to extend the frequency range downwards.
We considered that, using GaN fets. The amp would be tiny. But the TI thing has current limiting, thermal limiting, all sorts of protections. We'd have to add that to a home-made H-bridge.
Are there any integrated h-bridges with all the suitable protections? My FPGA guys wouldn't mind outputting PWM (or delta-sigma?). I should look into that.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
A shunt+signal transformer is a lot smaller than a CT, and generally has better frequency response. I could use a tiny surface-mount shunt and a small step-up transformer, standard parts. 50 or 100 mV drop in the shunt would be fine.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Why not just monitor the current flowing through the transformer with a low value resistor, low pass filter the voltage and look at it with a low-offset op amp?
-- Bill Sloman, Sydney
The output offset is what a speaker (or my transformer) would see, at the full-bridge output. There's probably a feedback loop from the outputs to the input diffamp; the numbers look about right.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
As just a half-baked idea, could you use two transformers? Keep your toroid for the power, plus a second light-weight transformer in parallel that's exposed to the toroid's same volt-seconds, to sense any imbalance?
Then the sensing transformer could be anything you like (E-core, pot-core, gapped, toroid, saturable cored, etc.), and you could sense saturation, hysteresis, use a flux gate, Hall sensor, or whatever crazy scheme you wanted to monitor any imbalance.
Just a notion for the notion bin...
Cheers, James
mandag den 3. juni 2019 kl. 05.24.59 UTC+2 skrev John Larkin:
ote:
a TI
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ter need
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ifiers
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just like numerous variable frequency drives and brushless DC motor drives
this is a bit slow
maybe?
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