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Class D, inductorless

I've not done an inductorless class D before. This will be under 1w of output, run off expensive battery power sometimes, and will be budget critical. The question is what frequency to pick.

What's the lowest frequency one could be run at? What percentage of random small transistors could operate adequately at that frequency?

I'm looking primarily for minimum cost & maximum transistor compatibility, and secondarily for low current consumption. A degree of sound quality compromise is ok, these will be running fairly small speakers.

NT

Reply to
tabbypurr
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Former regular Jan did this several years ago:

The ftp site seems to be locked down so you can't get at the source but you could probably email him for it, looks like he GPL-ed it

Reply to
bitrex

Wouldn't it be easier to buy an integrated class-D chip?

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Thanks. That type of approach isn't doable in this app though.

NT

Reply to
tabbypurr

I expect it would, but that doesn't fly in this case either. There's a lot I've not mentioned about this one, in short the basic topology is pretty well decided already and unlikely to be changeable at this point.

NT

Reply to
tabbypurr

It doesn't get much more dirt cheap than a 555 timer:

It doesn't even sound half-bad at the end of the video.

You could use a CMOS version with a driver transistor on the output to reduce quiescent power consumption. Pulling "RESET" low should shut down the output.

Reply to
bitrex

Like to invite EMC trouble?

--

-TV
Reply to
Tauno Voipio

It'll be in a tin can

NT

Reply to
tabbypurr

7400 series can be cheaper.

NT

Reply to
tabbypurr

Sorry, I don't follow. To make a class D amp (unless it's self-oscillating, which doesn't really seem appropriate in this case) you need at the very least a triangle/saw generator and voltage comparator - how do you intend to do that with a single 7400-series IC?

The 555 is an analog IC.

Reply to
bitrex

wn

Stage 1 produces a square wave, stage 2 turns it into a triangle wave. Stag e 3 preamplifies the analogue input, and its output plus the triangle wave are fed into stage 4. Add output transistors & choke. A range of 74 series gates can be used, as long as they can operate as a quad or hex invertor wi thout schmitt triggering.

NT

Reply to
tabbypurr

Maybe I'll have to build it & see.

NT

Reply to
tabbypurr

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