Push-Pull Amplifier Design: Help Needed!

  • Thread starter brad sue
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In summary, the speaker input current for the audio cross over project is 0.02 [A] and it needs to be increased to 0.61 [A] after the push-pull amplifier. The user is having trouble finding the right resistors and is using small-signal transistors which may not be sufficient for the desired output current. Suggestions were given to look for BJTs in TO-220 packages that can handle higher power levels.
  • #1
brad sue
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Hi,
I need some help with a push pull design.
As a project , I am doing a audio cross over. The problem I have is that I cannot find a way to drive enough current into the speakers.

For one speaker, the input current is 0.02 [A] and after the push=pull amplifier, I need to be able the supply a 8 ohms / 3 W speaker or a current of 0.61 [A]. I don't know how to find the values for the resistors.

I am using a NPN transistor 2N3904 and a PNP tansistor 2N3906.

please can someone help me ?

Thank you

B.
 
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  • #2
You're going to need a lot bigger devices than the 2N3904/6 small-signal transistors, in order to get the 600mA output current. You will also have bias current flowing through the transistors in Class AB configuration, so the power dissipated by the output transistors will be a bit higher still:

http://en.wikipedia.org/wiki/Electronic_amplifier

You can start by looking for BJTs in TO-220 packages that you can heat sink -- that should get you close to the power levels you are shooting for.
 
  • #3
Thank you berkeman,

Your suggestion were helpful. I got it right!
B
 

1. What is a push-pull amplifier?

A push-pull amplifier is a type of electronic amplifier that uses a pair of transistors to provide amplification. One transistor amplifies the positive phase of the input signal, while the other amplifies the negative phase, resulting in a more powerful output signal.

2. How does a push-pull amplifier work?

The two transistors in a push-pull amplifier work together to amplify the input signal. When the positive phase of the input signal is applied to one transistor, it amplifies it and sends it to the output. At the same time, the other transistor receives the negative phase of the input signal and amplifies it, also sending it to the output. This creates a more powerful output signal compared to using just one transistor.

3. What are the advantages of using a push-pull amplifier?

There are several advantages of using a push-pull amplifier, including higher efficiency, better linearity, and reduced distortion. The use of two transistors in a push-pull configuration allows for a more balanced amplification of the input signal, resulting in a cleaner and more powerful output signal. Additionally, push-pull amplifiers are more efficient in converting input power to output power compared to single-ended amplifiers.

4. What are the common design considerations for a push-pull amplifier?

When designing a push-pull amplifier, some important factors to consider include choosing the right transistors with proper characteristics, ensuring proper biasing and matching of the transistors, and minimizing parasitic effects such as capacitance and inductance. It is also important to carefully design the input and output matching networks to optimize the amplifier's performance.

5. What are some common applications of push-pull amplifiers?

Push-pull amplifiers are commonly used in audio amplifiers, power amplifiers, and radio frequency (RF) amplifiers. They are also used in various electronic devices such as televisions, radios, and smartphones. In addition, push-pull amplifiers are often used in high-power applications where efficiency and linearity are critical, such as in wireless communication systems and satellite transmitters.

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