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Topic: Is this an appropriate circuit to drive my 8 ohm speaker using PWM? (Read 16770 times)previous topic - next topic

Vanyamba

That's a rather Lo-Fi approch, but with square wave input who cares, it will make noise.

Transistor is good noise filter.

Vanyamba

Not really.  In fact it is more often the opposite.

In order to switch a bipolar transistor, some amount of current required, isn't it?

Vanyamba

Yes. And every active component (and many passive components) are all sources of noise and/or distortion.

Sounds a bit paranoidal.
"This is my HiFiduino, baby." (c)

s3n4te

Okay I built the circuit, and the wonderful smell of magic smoke started to come out both bjts after decreasing resistance in the pot to 0 (I had to replace both). By the way, I kept the 4k and 1k voltage divider in the circuit. How do I calculate the power dissaption of the bjts in this type of circuit?

Okay, here is a more appropriate circuit.

The MOSFET I used is IRF3707Z, any higher current logic level MOSFTETwill work, such as the sparkfun sells.
The speaker is from mpa.com
http://www.mpja.com/prodinfo.asp?number=14618+SP
90dB. I use it in a fencing club to make a warble when a touch is scored, can be heard very well.

The current thru your BJT is (Vsource - Vce)/(sum of resistance in the rest of the path)

So (5V-0.5v)/(8ohm+pot)
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

s3n4te

I think I figured it out, since with 0 ohms at the pot, the voltage output of the opamp would be 1V, which means 12 - 1 = 11V must be dropped across the bjt. 1V/8ohms = 0.125 A ----> power disipation of bjt = 11V*0.125A = 1.375W > 0.6 W max of the transistor. Is this correct?

Which circuit do you have wired up? There have been several posted.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

This one: