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Old 4th April 2014, 08:21 AM   #1
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Smile calculating the resistor & capacitor values in class a amplifier

Hi all,

I want to design own simple class a amp but i don't know how to calculating the resistor & capacitor values of class a amplifier e.g. Rc,Re and Rb.
tell me how calculate these values.


Regard's
Parveen
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Old 4th April 2014, 09:37 AM   #2
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Hi Parveen
Before we can help you, we need to know what amplifier design you are referring to.
Rc,Re,Rb means nothing unless you have a circuit which shows where they are and
what they do. Post the schematic or link to it so that others can clearly see what
your problem is.
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Old 4th April 2014, 10:01 AM   #3
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@Ian
i have 2n5296 transistor and wants to build simple class a amp as an experiment.

Schematic- Click the image to open in full size.
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Old 4th April 2014, 10:33 AM   #4
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I hope you appreciate that the components around this circuit will only give you a small signal amplifier - i.e. line level. C4 isn't necessary.

You need to start with the data sheet for the transistor in question and pick the operating point that you are aiming for.
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Old 4th April 2014, 12:07 PM   #5
DUG is offline DUG  Canada
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As KatieandDad says, pick your operating point.

(This may depend on what resistance value you need for Rl.)

Then, based on thermal stability requirements:

Vre (we were taught) should be about 10% of +Vcc. ( or a volt or two in the case of +Vcc>20V)

Knowing Ic and Hfe you should be able to get Ib.

Ir2 should be 9*Ib and Ir1 is 10*Ib. (not critical but just a suggestion)

Vr2 = Vre + 0.6V (or so...from data sheet @ Ic)

Vr1 = (+Vcc - Vr2 ) / Ir1

Vrl should be about 45% of +Vcc.

Then check power dissipation for all components to see if they will be OK.

That should get you started.

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Old 4th April 2014, 08:47 PM   #6
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Quote:
Originally Posted by parveen247 View Post
Hi all,

I want to design own simple class a amp but i don't know how to calculating the resistor & capacitor values of class a amplifier e.g. Rc,Re and Rb.
tell me how calculate these values.


Regard's
Parveen
You need to get yourself a copy of Practical Analysis of Amplifier Circuits thtough Experimentation (Lorne MacDonald). That will answer all these questions and more.
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