Hey guys,

I need help designing a class ab amplifier to power an 8 ohm 0.2W speaker to create an alarm sound. I'm outputting a sine wave at 150Hz and 5Vpp from an external DAC connected to my TI microprocessor.

I have a couple NPN and PNP transistors, 2N3904 and 2N3906, which i plan on using.

If I hook up my speaker strait to the waveform asis I get a very soft alarm sound with an AC current of 3.7-4.3mA's going through it. Since its a 0.2W speaker I figured i need to amplifier this current to around 150mA to get a nice sound.

Questions 1: Is that the right logic?
Question 2: Is a class AB amplifier what I should use to increase my current to 150mA?
Question 3: If so, does anyone have a recommended schematic I should use?
Question 4: How should I calculate the resistor and capacitor values I should use?

Calling all analog wizards!
Any help would be greatly appreciated!

 

Why on earth would you want a class AB amp for a 200mW speaker in preference to a class A one?

 

I just thought it was a more elegant design, i guess, lol. So, you would recommend a class A amplifier then?

 

I would recommend an LM386.

 

You will max out the 0.2 watts at .223 amps peak with a voltage of 3.577 P-P
It will require a bit over 5 volts of supply to get there with this chip.

 

Hey guys,

I need help designing a class ab amplifier to power an 8 ohm 0.2W speaker to create an alarm sound. I'm outputting a sine wave at 150Hz and 5Vpp from an external DAC connected to my TI microprocessor.

I have a couple NPN and PNP transistors, 2N3904 and 2N3906, which i plan on using.

If I hook up my speaker strait to the waveform asis I get a very soft alarm sound with an AC current of 3.7-4.3mA's going through it. Since its a 0.2W speaker I figured i need to amplifier this current to around 150mA to get a nice sound.

Questions 1: Is that the right logic?
Question 2: Is a class AB amplifier what I should use to increase my current to 150mA?
Question 3: If so, does anyone have a recommended schematic I should use?
Question 4: How should I calculate the resistor and capacitor values I should use?

Calling all analog wizards!
Any help would be greatly appreciated!

This?

 

Couple of problems there, Ramussons. 1) 16% crossover distortion (by voltage comparison) and 2) the output coupling capacitor is sized for 70% voltage delivery at 200 Hz. Target is 150 Hz. 3) The input capacitor has an impedance of 1061 ohms and that means the transistors will need a current gain of over 100. Again, not good for distortion.

Still, the choice of circuits is up to EE_Eric

 

It's only an alarm. I don't think fidelity is of much importance; simplicity is.
100 uF @ 150 Hz = 10 ohms - ok for output.
At the most, the 1K at the input may require some trimming.

 

I need to create this amplifier using discete components

 

Please read through this thread
http://forum.allaboutcircuits.com/threads/audio-amplifier-design-basic-questions.104719/

 

Hello,

This sounds as homework.
Is it a college project?

Bertus