# How to amplify an AC signal

#### simeonz11

Joined Apr 29, 2008
98
I wish to amplify a small AC signal to a big power signal .

I'm using this op amp made for hv operations , it says its made for hv . itr has a maximum current of 50mA .

http://focus.ti.com/docs/prod/folders/print/opa445.html

This is my circuit , the goal here is to power a transformer with this AC signal , using only batteries . I know emitter-follower , thats easy on its own , but This is an AC follower emitter so I just cant figure it out by myself now .

#### bertus

Joined Apr 5, 2008
19,952
Hello,

What frequency do you want to amplify?
How many gain do you need?
The OPA551 and OPA 552 will work upto ± 30 Volts.

Greetings,
Bertus

#### simeonz11

Joined Apr 29, 2008
98
anywhere from 50 to 15000 hz

I dont know how much current , enough to make my emitter follower where I= V/Rload

just that really , I want to mimic my wave and provide current based on whatever load I have ...

Nothing more than 4-5 amps .

#### bertus

Joined Apr 5, 2008
19,952
Hello,

In what resistance range will the load be?

It sounds like an audio amplifier to me.

Greetings,
Bertus

#### simeonz11

Joined Apr 29, 2008
98
Hi bertus

Nothing below 20 ohms , not too much power .

Its for a "special" science project .

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#### bertus

Joined Apr 5, 2008
19,952
Hello,

When you say 5 A and 20 Ohms the power will be ( P = I X I X R ) = 5 X 5 X 20 = 500 Watts.
For 5 A in 20 Ohms you will also need ( U = I X R ) = 5 X 20 = 100 Volts to get it.
This is quite a power.
If the resistance is even higher the power will rise too.

Greetings,
Bertus

#### simeonz11

Joined Apr 29, 2008
98
Hi Bertus.

That would be in the worst case scenario .

The resistance will be higher than 20 ohms .

I will never reach anything close to 500 watts load . Maybe not even 100 .

That would be defeating the purpose of my special project .

I am not worried about maximums here .

#### bertus

Joined Apr 5, 2008
19,952
Hello,

What will be the maximum load resistance?
You say it is higher than 20 Ohms, but not how high.
I think the current will not be higher than about 2 A.

Take a look at the attached PDF about voltage to current converters.

Greetings,
Bertus

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#### simeonz11

Joined Apr 29, 2008
98
Hi bertus,

Like I said , it all depends on the resistance of whats on my secondary side , it all depends .

I dont have any solid numbers but the goal here is to go for low amps .

Thx for that pdf , that howlad bidirectionnal current source looks good for my application , do you think so ??

#### simeonz11

Joined Apr 29, 2008
98
Ok I have identified 2 possible working circuit .

My goal is to run a transformer remember and immitate the wall plug only higher frequency.

I wanna know whats the difference between these 2 , what dooes the "current sense" do anyways ?

There is not much info on this bidirectionnal current sense .

is this needed at all , wich one of these would be best for my application , I have no idea about that Rsense thing

Also , wouldnt the transistors need diodes before them to protect them from reverse voltage ??

Theres gonna need a base resistor also ...

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