555 does Class D Audio?

So?

You ask a question in the subject header, but then don't elaborate on what you might be asking.

In the early seventies, there was a class-D amplifier in Elementary Electronics that used a 555. It was the class-d equivalent of a cheap and dirty amplifier, not intended for hifi but there are lots of times one needs nothing more than a loud amplifier. It was a useful learning tool, since the circuit was simple, and simple circuits help to convey basics.

Michael

I guess I was just expressing shock that such a beast could exist.

Is even the 555 necessary? Can a simple class D amplifier be built with discretes? Like you said I'm just looking for the basics, to learn. Even 1 W would be plenty.

Thanks,

Michael

None sense . Class D audio uses junk box parts ..

and very few .

Class D , if its not close to 20khz , can be done with any

simple ckt that has a low output Z .

Simple op amps with cheap NPN ( emmiter follower) in VCC+

lead ,, another PNP in VCC- , as the LH0002 is .

As the op amp draws from supply , it also pulls current thru

the discrete NPN or PNP , cause its in series with Supply leads .

Its merely the voltage gain from an op amp , then current gain from

low cost bipolars in the Vcc inputs .

to filter out the square wave , make total inductance of the load and its resistance , a time constant of about

50 to 100 microseconds .

A buck regulator is a switch then an inductor then output power supply cap . Pick inductor to filter out above 10khz , pick transistor to have high drive .

now oscilate it with a LM431 .

Now add music .

two of these , one for plus side , one for minus side .

BW is so high , and the filter allows no ripple , noise is low .

When BW is 100 times higher than the output freq , you can do it many ways ,, cheap .

--------------------------------

BTW Dont buy welders from

I paid $650 , transistors broke off cause heavy heat sink is hooked to transistor legs , breaks them off .

Heat sink is NOT secured to PCB !!!

Then the 2 outs are switched in series for Plasma , in parallel for welding ... 90 amps thru relays , contacts will not last . Hi quality welders have a front panel switch , with hvy contacts .

JUNK ..

A conceptual class D amp can use a triangle generator and comparator to drive on/off output switches. The triangle sets the threshold of the comparator. When the audio exceeds this threshold, the output is high, otherwise low. The triangle frequency is higher than the audio range, so you don't hear the switching.

If you draw the triangle and a much-lower-frequency sine wave out on paper and look at where they cross, you can see that the comparator will end up with a duty cycle proportional to the instantaneous signal amplitude. That's class D!

Best regards,

Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card!

Bob Masta Inscribed thus:

Nice concise description of class D !

--
Best Regards:
                Baron.

In practise, there's no fundamental duffernce betwen a class D audio and a pwm motor controller.

See 4QDTEC.com ... I was with Clive Sinclair when he marketed a couple of class D audio amps.

--
------------------------------------------------------------------
Richard Torrens. News email address is valid - for a limited time only.
http://www.Torrens.org.uk for genealogy, natural history, wild food, walks, cats
and more!