my new 4.5kW class-d amp (crown BCA topology)

[mzzj]

OK ok, thats only for 20 second before 16A slow-blow fuse gives up.
setup
kludge power stage
highly refined modulator stage

Crown-BCA topology with full-bridge operated from +300V rail. 4.5++ kW to 5 ohms for short perioids, 2.2kW continuous. BIG 230/230v isolation transformer required for powering this up.

Still somewhat high losses on output stage, 2.2kW out with 85% effiency. Or something, havent calibrated my current shunts to measure efficiency any better than 5%

[ezis666]

Where is schematic???

[mzzj]

Originally posted by ezis666
Where is schematic???

Dont have such a thing yet.
well, here's output stage anyways. bit lazily drawn.
http://www.ee.oulu.fi/~masaj/class-d/output%20stage.JPG

[oldroborg]

Looks awesome, exactly what i'm looking for, what drivers do u use for the gate drive transformers? What is the switching frequency? How many mosfets have u turned to smoke Too many things to ask!

cheers,
Rob

[IVX]

very impressive, however driver pluged by too long wires..

[mzzj]

Originally posted by oldroborg
Looks awesome, exactly what i'm looking for, what drivers do u use for the gate drive transformers? What is the switching frequency? How many mosfets have u turned to smoke Too many things to ask!

cheers,
Rob

9Amp mosfet drivers from TI. these have proven to be very robust even without clumsy shottky diodes at driver chip output that are usually necessary to keep driver chips alive.

100khz swithing frequency as this is subwoo-amp. Gate drive DC-restoration circuitry limits full power -3db to around 1khz.

zero smoked mosfets, these are robust welding-machine models

Originally posted by IVX
very impressive, however driver pluged by too long wires..

too long wires between mosfets and driver or driver and modulator board? Yes, wires between mosfets and drivers are longish and their inductance is bit too much, but IMHO transformer leakage inductance is dominating and difficult to reduce.
I measured 260nH leakage(total) inductance in gate drive circuitry wich is already limiting factor in reducing switching times.


Modulator stage is something ugly, pre-prototype but seems to work considerably well.

[Pano]

Originally posted by oldroborg
Looks awesome, exactly what i'm looking for,

There you go, Rob. It is what you were looking for!
Could work well for your understage horns.

[mzzj]

Originally posted by mzzj

Still somewhat high losses on output stage, 2.2kW out with 85% effiency. Or something, havent calibrated my current shunts to measure efficiency any better than 5%

recalculation from heat sinks thermal mass gives effiency of 93-95% at 2.2kW and i am much more satisfied with that than 85%

1% current shunts and 1% voltage measurements give worst-case error of 4% wich is 8% max error in effiency. Now i calculated losses from aluminium blocks heat rise, errors are much smaller this way.
(voltage measurements maybe were even worser than 1% as RF from power stage was making interference to meters.)

[oldroborg]

Originally posted by mzzj

9Amp mosfet drivers from TI. these have proven to be very robust even without clumsy shottky diodes at driver chip output that are usually necessary to keep driver chips alive.

100khz swithing frequency as this is subwoo-amp. Gate drive DC-restoration circuitry limits full power -3db to around 1khz.

zero smoked mosfets, these are robust welding-machine models



too long wires between mosfets and driver or driver and modulator board? Yes, wires between mosfets and drivers are longish and their inductance is bit too much, but IMHO transformer leakage inductance is dominating and difficult to reduce.
I measured 260nH leakage(total) inductance in gate drive circuitry wich is already limiting factor in reducing switching times.


Modulator stage is something ugly, pre-prototype but seems to work considerably well.

Awesome, -3db at 1Khz is half an order of magnitude better than i'm aiming for I'm looking to build sub-amp(s) for <80hz work. For some reason i'd subconsciously discounted using transformer drive (winding transformers frightens me ) but now after seeing yours in the flesh i'm back on track, checked out the mosfets too, look interesting! Gonna see if i can use some torriods out of PC smps's to save winding them myself.....

cheers
Rob

PS any chance of a schematic of your modulator too

[mzzj]

Originally posted by oldroborg




PS any chance of a schematic of your modulator too

Cumming soon, maybe even this evening. Its christmas-time for high-power fanatics

Gate transformers solve lots of problems, ones I am using provide more than 4kV insulation for example... use kynar or teflon wire-wrap if you want good insulation.

For mosfets I may recommend SPW47N60C3 or similar rated coolmos, no need to parallei them anymore. Reason that I am using STWxxxx mosfets is that I happen to have bunch of them in my drawers. I have also 55Amp IRF´s warp speed IGBT´s but I havent tried them(yet).

Edit: there is no use for toroids in pc-power supplies, iron powder is not suitable for GTDs and they are too small for output filter chokes. I was planning to use 4pcs Amidon T-200A toroid of -26 material in final version, with around 30-50 turns of wire i believe. Or gapped EE55 cores as output toroids are pure pain in 4ss to wind.