Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Push Pull Amplifier

Status
Not open for further replies.

pYrana13

New Member
Hi!

Im still newbie to this analog circuit design, so i have something to ask about the circuit in the attachment below. The circuit is Push Pull Class B Amplifier with AB Characteristic.

My questions are:

1)The purpose of mirror currents is to provide a current into to the collector of T5,right? For what purpose is it actually and how could i calculate the value of the current at the collector of T5? T7 and T8 are actually diode-connected Transistors, which have a role to eliminate the crossover distortion,right?

2)If the crossover distortion can be eliminated with the T7 & T8, what is the purpose of the negative feedback connection from Vout to the OP, if the switch in opposite direction from the one in the circuit. ( I assume that the feedback can eliminate the crossover distortion too)

3) How could i calculate the gain of the OP exactly?

4) Both Re1 and Re2 could reduce the power dissipation at the T1 and T2 right?

Thanks!!

Sorry for many questions, i have read a a lot and need some confirmation and guidance about this circuit.
 

Attachments

  • Picture 15.png
    Picture 15.png
    63.5 KB · Views: 3,177

audioguru

Well-Known Member
Most Helpful Member
How many websites did you post this on?

The transistors connected as diodes cause the bias current in the output transistors to be almost perfect for class-AB. The driver just needs its current adjusted a little higher. Since the opamp has an extremely low output impedance then the high output impedance current sources are not needed.

Negative feedback cannot eleminate crossover distortion because the distortion is high frequencies and the opamp has low open loop gain at high frequencies.
 

Electronworks

New Member
T7 and T8 may illiminate the cross over distortion. They will certainly reduce it. The overall feedback will take out the other non linearities in the circuit (not just at cross over). Looking at this circuit, these distortions will be minimal, but most audio amplifier designs close the feedback loop as good design practice to ensure systems stability and low distortion.

Current sources are an effective way of producing a bias for the diode connected transistors, but still allowing a lot of swing on the bases of the output transistors.

Gain of the circuit is (1+ 6k/1k5)

Re1 and Re2 prevent thermal run away. As the output transistors heat up, the Vbe goes down causing them to turn on further for a given drive voltage. When the current increases, the increased voltage drop across these resistors produces an opposing voltage to the Vbe to prevent the current escalating
 

audioguru

Well-Known Member
Most Helpful Member
The diode-connected transistors are supposed to be connected to the heatsinks of the output transistors. Then as the output transistors heat the diode-connected transistors the current does not increase in the output transistors due to heat.
 
Status
Not open for further replies.

EE World Online Articles

Loading
Top