Output PWM'ed audio to speaker

[boylesg]

What is the best way to send PWM'ed audio from this circuit to a speaker?



[found at geekcircuits .com /wp-content /uploads /2010 /04 /2-channel-555-PWM1 .png]

 

[betwixt]

It depends on the loudspeaker and how much power you want. Some NE555 manufacturers specify as much as 200mA sink/source current which is enough to drive a medium to high impedance loudspeaker directly. The mass of the loudspeaker cone will be enough to average the PWM back to an analog level.

For higher power all you need to do is ensure enough 'logic level' voltage (whatever you decide that to be) can be driven to the loudspeaker output. Bear in mind the loudspeaker is actually being fed pulses at a higher frequency than it can respond to so for serious power applications you need to add an LPF to prevent the inductive losses of the speaker coil causing it to overheat. It would also be usual to add some kind of spike protection at the output so that the back EMF from the speaker doesn't present excessive voltage to the output stage.

Brian.

 

[BradtheRad]

Typical LC second-order filter to convert SPWM to audio.

The inductor and capacitor values need to be tailored to the load.

 

[Audioguru]

The geekcircuits article mentioned the circuit is driving 32 ohm headphones, not speakers.