Help amplifying microcontroller PWM audio

[yardleydobon]

I'm outputting PWM audio from a microcontroller. I want to drive an 8ohm 0.5W speaker with 5V. I tried pulling the speaker with a 2N7000, but it's still too quite. I'm wondering if I use a bigger transistor, is possible to get good amplification just by pulling the speaker? I'd also like to try out something like a class D amplifier output stage chip to drive the speaker. I'm looking for something like a half bridge or a full bridge that will run at 5V. Can someone recommend something like that?

[elevator]

Originally Posted by yardleydobon

I'm outputting PWM audio from a microcontroller. I want to drive an 8ohm 0.5W speaker with 5V. I tried pulling the speaker with a 2N7000, but it's still too quite. I'm wondering if I use a bigger transistor, is possible to get good amplification just by pulling the speaker? I'd also like to try out something like a class D amplifier output stage chip to drive the speaker. I'm looking for something like a half bridge or a full bridge that will run at 5V. Can someone recommend something like that?

National has a good range of 5V amp chips, both in class AB and D.
Example, LM48510 - Boosted Class D Audio Power Amplifier which brings 1.2W at <0.1% THD. Inputs are always analog though, so you will have to low-pass your microcontroller output first.
Another way is to directly feed a full bridge via two complementary mosfet pairs then low-pass the output through an LC network.
You can find full bridge driver chips, too. Much depends on your PWM frequency.
E

[nigelwright7557]

Look up IR2110 and IR2113.

[yardleydobon]

I would like to try using a MOSFET driver IC to drive the speaker directly, and by directly I mean connect the speaker wires directly to the IC instead of using external MOSFETs. I'm thinking I should put a capacitor in series with the speaker though so the low side will have something to pull when it's on. Has anyone tried this? Can someone recommend a good chip to use this way?

[tawen_mei]

Yes that would work, with a capacitor in series. Since you're driving a 0.5W speaker, I assume you just want sound and don't care about quality. The output impedance being approximately 1 ohm in a typical low-side MOSFET driver means poor damping factor and not very flat frequency response when driving a real speaker, but nonetheless would work reliably.