Questions tagged [class-ab]

This tag can be used to denote questions related to analogue amplifiers working in AB-mode.

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Gain expansion in class AB power amplifier

Why does gain expansion occur in class AB power amplifier? I can not understand the reason by analysing circuit? Is there any physical reason? Why we can not observe this phenomenon in class A ...
0 votes
1 answer
41 views

How to choose a BJT used as a diode-connected BJT

I am choosing components for the following circuit, which will be used as a class AB amplifier: The resistors will be chosen to bias the transistors. I chose Q1 such that the quiescent current Iq = 1....
4 votes
2 answers
97 views

Biasing a DIY current feedback opamp

For a personal project, I'd like to make a discrete current feedback opamp. Here's a simplified schematic: The question is about how to bias Q3/Q4. For a nice class-AB output, the sum of both Vbe's ...
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1 vote
3 answers
183 views

A/B power amplifier: difficulty getting a full output voltage swing

I have been designing an A/B voltage amplifier using the TIP31C/32C power transistors (schematic shown below.) I have a significant loss in voltage gain which I haven't able to negate. Is this ...
1 vote
2 answers
151 views

Voltage follower configuration

for the LM4952 chip (class AB amplifier), I wanted to add an NE5532 OA in voltage follower configuration at its input. That to take care of whatever input source will be plugged into it. Is it a good ...
1 vote
0 answers
72 views

Wouldn’t diode forward drop increases the cutoff voltage?

This video seems to be a great explanation of class ab but the schematic shows diodes that should have a forward voltage of .7 plus the forward voltage of the base-emitter drop. He describes it as if ...
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0 votes
1 answer
152 views

How does class AB amplifier biasing work exactly? [duplicate]

Can somebody please explain in both cases the biasing method? I don't understand the following points: It's OK that we need ~0.7V for PNP and NPN base-emitter voltage, that's why a diode is used for ...
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6 votes
3 answers
625 views

Class AB power amplifier from "Electronic Devices" by Thomas L. Floyd

I am an electronics engineer. I work as an industrial automation engineer in industry. As an electronics engineer, I love amplifiers and other stuff. I was reading Electronic Devices by Thomas L. ...
2 votes
2 answers
234 views

How to increase CE amplifier gain to 12?

The gain needs to be increased to 12, currently it is at 10 but I cannot seem to increase this any more. The circuit topology cannot change, but the component values can - except R4, the 56 kΩ ...
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1 vote
3 answers
288 views

Class AB power amplifier output clipping when input exceeds 1.7V

I have a 3 transistor Class AB power amplifier that I referenced from a working design which has different design parameters and biasing than what I need. How I intend on using it, it will be used to ...
1 vote
1 answer
107 views

Forcing the bias current of a voltage feedback amp into a larger Class AB by a resistor

Can I force any voltage feedback amp to flow current in one side of its output stage (therefore moderate over-biasing it to work in an extended class-AB area), by simply connecting a power resistor ...
5 votes
2 answers
675 views

How to bias a MOSFET class AB amp?

I'm working on a class AB amplifier that is used to either source or sink current. The reason for using MOSFETs is space constaints and that high power BJTs are only available in large leaded packages....
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-1 votes
1 answer
308 views

Class AB Amplifier With Single Supply [closed]

I'm designing an amplifier which is to be run off of a single 20 V supply (in the circuit, V+ = 20 V, V- = GND). Q2 and Q3 are used to bias Q4 and Q1. Since the circuit is running off a single 20 V ...
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0 votes
1 answer
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BJTs dangerously getting hotter as drawn current accumulating

I already ask a few questions on this project (so i won't explain everything again as it would be too long). I basically have a high power opamp (OPA462) to which i feed a signal (but i offset it ...
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3 votes
6 answers
939 views

Why only common collector method is used in class AB amplifiers?

I have recently started to study about class AB amplifiers online, as a newbie, i have found every schematic of the class AB amplifier is in common collector circuit just like this Schematic i find ...
0 votes
1 answer
100 views

How should I size the transistors in the class AB linear amplifier

If I want to design a class AB linear amplifier as the following one, how should I determine the width of the pmos and nmos? Class AB amplifier specifications: Vdd: 6V Input: 0.5V to 5.5V Output ...
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77 views

Class AB linear amplifier design

I am trying to design a class AB linear amplifier. The required peak current is 450mA. I am just using an ideal biasing at this stage. The schematic is as follows: Here are the resulting waveforms. ...
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0 votes
0 answers
62 views

Class AB amplifier using push-pull pair signal decay

I'm trying to build a class AB amplifier with push-pull pair of power transistors for audio amplifier. the circuit works fine with low voltage(~0.2V) but the input peak voltage varies between 0.2 - 2V....
0 votes
1 answer
64 views

Adjustable power supply from +5V to -5V

Depending on the orientation of a nulling coil I need an adjustable voltage supply from ~+5V to -5V upto ~200mA. I've tried a few circuits similar to Class AB amplifiers such as the one shown below, ...
0 votes
1 answer
209 views

Class AB Amplifier - Weird oscilloscope output

I have built this little kit for a class AB Amplifier. This is the schematic if you do not want to follow the link It works fine, I can hear decent sound. I then tried to check the output with an ...
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0 votes
1 answer
368 views

Calculating output impedance without measuring open-loop output voltage of a push-pull Class AB MOSFET Amplifier

So I am building and analyzing a Class AB / push-pull amplifier implemented with MOSFET as depicted in the following schematic: R2 is the load. The input is an AC signal with 3V amplitude and 1KHz ...
0 votes
1 answer
137 views

Complementary pair - Role of capacitor on emitter

I bought this little kit for a class AB amplifier. The second stage is quite clear (and typical), but I am struggling to understand the role of capacitor C2 on the emitter branch in the first stage. ...
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2 votes
4 answers
6k views

Design a class AB audio amplifier

I am required to design a class AB audio amplifier to deliver 10W to an 8Ω speaker as shown, but I don't know where to start. The bandwidth is to cover the range from 20Hz to 18kHz. Input voltage is ...
1 vote
2 answers
83 views

What is the role of the Op-Amp integrator in this circuit?

Helo dier community! I got a 400 Hz broken Power Inverter and reverse-engineered the circuit just for the simplicity of repairing it. Then I got deeper in and started to understand the engineering ...
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3 votes
3 answers
343 views

What do these components of an AB amplifier do?

I'm trying to learn about class AB amplifiers by reverse-engineering a few I see here on SE. I borrowed this schematic from this question as a starting place. Ignoring the fact that the circuit lacks ...
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3 votes
1 answer
269 views

How is the quiescent current and emmiter resistor determined on the driver and pre-drivers of a class-AB audio amplifier output stage

I am reading online about discrete audio amplifiers. I have learned about the input differential pair, the voltage amplifier stage, and now I'm learning about the output stage. I have learned that you ...
1 vote
1 answer
274 views

Cross coupled Class AB output stage

A simple question about ClassAB common source amplifier. There are two circuits which I have attached with this question, the one on the left is a standard cross coupled circuit which I have taken ...
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1 vote
1 answer
340 views

How do analyze input impedance of Class AB amplifier biased with resistors?

EDIT: I realize that the original circuit is deeply flawed and will burn up upon re-entry. Thanks to anyone who can help me understand why! I'm learning to analyze Class AB amplifiers, but haven't ...
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1 vote
1 answer
57 views

What equation do I use for simple class AB input impedence?

I'm a novice at this. I've done some figuring and would love to know if I've got this correct before I move to more complicated circuits. I have the simplest Class AB amplifier and I'd like to know ...
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1 vote
3 answers
172 views

Amplifier power problems, power supply limitations, or end stage base current draw

So I am experimenting with various signal generating, op-amp and power amplifier circuits. And I have limited access to technology. Where I am at, everything you buy is twice the price because of ...
0 votes
3 answers
142 views

How can I overcome the distortion using in this circuit by using same products as we see in picture ? Or we can use 2n700 series, 3906 and 3904 bjts

Or we can use 2n700 series, 3906 and 3904 bjts. My aim is 10W, gain 100-1000 (adjustable), 50hz-20khz amplifier by using this basic components.
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1 vote
2 answers
120 views

How can I calculate low and high frequency in my circuit?

How can I calculate low and high frequency in my circuit? I have used an 8-ohm speaker.
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1 vote
1 answer
815 views

LTSpice produces incorrect simulation for Class AB amplifier

I have been building a Class AB amplifier simulation using LTSpice. While it simulates well for transient analysis (voltage gain of 0.9 at peak), using ac analysis the the voltage gain drops to 0.268....
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0 votes
1 answer
651 views

Class AB Amplifier - Q point

In a class AB amplifier, why is the Q point much closer to the cutoff voltage as compared to a Class A amplifier which is at the center. Wouldn't this clip the AC signal if its too close to Vce. ...
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1 vote
2 answers
174 views

Two-stages class AB amplifier

I'm studying the following two-stages class AB amplifier: Basically it is a standard two-stages op-amp (i.e. the cascade of a differential pair with active current mirror followed by an inverter with ...
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