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Topic: Is this an appropriate circuit to drive my 8 ohm speaker using PWM? (Read 6 times) previous topic - next topic

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?

CrossRoads

Which circuit do you have wired up? There have been several posted.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.


CrossRoads

#23
Mar 03, 2011, 09:21 pm Last Edit: Mar 03, 2011, 09:23 pm by CrossRoads Reason: 1
Yes, for full on (12V - Vce)/8 = ~1.44 amp.
P=I^2R = 16W goin thru the speaker
P= IV = ~0.5*1.44 = 720mW dissipating in the transistor.

2N4401 absolute max 600mA - 1.44A would smoke 'em!
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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