Pepping up a Silicon Chip SC480 audio amplifier - Page 3

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Re: Pepping up a Silicon Chip SC480 audio amplifier

"Eeysore"

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** Shame how Ft is a strong function of Vce and Ic.

Ft drops like a stone below 0.5 amps and above 5 amps for those devices -
and nearly all other power BJTs are much worse.



.....    Phil





Re: Pepping up a Silicon Chip SC480 audio amplifier



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**As Phil has already stated, MOSFETs are MUCH better at HF than even the
Toshiba BJTs.


--
Trevor Wilson
www.rageaudio.com.au



Re: Pepping up a Silicon Chip SC480 audio amplifier
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yeah, but I'd want to be damned sure its not going to burst into
oscillation at 200MHz. especially when I jam 200MHz up the input :)

mostly, this little amplifier was good enough to solve the immediate
problem (needed 100kHz), and now I've vandalised it further, it'll
probably do everything I want. it had the added advantage that I could
buy it in one bag from Jaycar, and spent 1hr putting it together. it
took longer to drill the heatsink than build the kit.

Cheers
Terry

Re: Pepping up a Silicon Chip SC480 audio amplifier



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Don't forget the nice beefy driver stage to charge and discharge that gate
capacitance.

Graham


Re: Pepping up a Silicon Chip SC480 audio amplifier
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In the '90s I did a design for a low-power 2MHz diagonal half-bridge
SMPS. INitially I used FETs, but when I looked at the H-field emanating
from the gate traces (which were constrained to be on one layer, and
long), I changed the switching devices to bipolars - for the same speed
I required much less peak driver current. Sure, I had to cough up some
continuous driver current, but that was a lot less than the peak.

I have a SMPS Im finishing off now that sucks 1W@12V, just to drive the
gates of 6 hefty FETs - so much that I actually dropped Fsw to keep it
under control. Once this design is in production I will design a
resonant gate driver, and see how low I can reduce the gate losses.

oh yeah Graham, I cant see ABSE, so if you could email me those Toshiba
datasheets it would be appreciated.

Cheers
Terry

Re: Pepping up a Silicon Chip SC480 audio amplifier
finger to keyboard and composed:

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http://www.toshiba.com/taec/Catalog/pages/search.jsp
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7673.pdf
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7890.pdf

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Pepping up a Silicon Chip SC480 audio amplifier
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ta. If I wasnt so dim, I could have typed them into google. duh.

Cheers
Terry

Re: Pepping up a Silicon Chip SC480 audio amplifier

"Eeysore"
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** Not at all necessary for either wide small signal bandwidth ( as wanted
by the OP) or where the load Z is fairly high - as is also the case with the
OP's stated needs.

Mosfet gate drive is requirements are  VERY  modest when the output power
level is lowish.

In any case, even with high power operation and parallel groups of lateral
mosfets, the standard drive circuit is nothing more than a pair of  TO92
plastic pack transistors like the MPSA42 and MPSA92 and gives slew rates of
about +/- 50 volts per uS or 100kHz at full power.




.....   Phil






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