voltage and current amplifier

voltage amplifier does voltage amplification
current amplifier does current amplification

Is there something like power amplifier or power amplifier is just same as current amplifier?

Power is Joules per second, Current is Coulombs per second and Voltage is Joules per Coulomb. Can you see the relationship between them?

Adam

Hi,

From my understanding a Power Amplifier amplifies power. In these situation you don't talk about current or voltage, simply power. The way it deals with current and voltage will be related to the way you bias your transistor, so it really depends on what you want to do.

Do you have any other details about his?

okay another question which is slight away form this topic,sorry if the question is very basic
output of microphone (transducer) is voltage signal(voltage varying with time)
if the power amplifier want to amplify the current of this signal ,how could it be, because output of transducer is voltage signal not current signal.
help me understand this.Thank you

Are you sure that if you have a voltage varying in time you won't have a current varying in time? When you have a power amplifier you amplify the power not current or voltage. This means that even if you have a voltage signal as you say, in terms of power it will still have a value , let's say 20 dBm. When you use a power amplifier it will amplify that value to another one, let's say 30dBm. This means your power gain is 10 dB but to evaluate current and voltage you need to measure it.

Are you sure that if you have a voltage varying in time you won't have a current varying in time?

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sorry i am wrong,if there is voltage then there is also current and vice versa
i got the,if i need assistance later i drop the question here

Hi,

you can have voltage without current. (a battery for example) Only if you connect a load, then current flows...

It´s harder to have current without voltage. This is more like supercondctive coils work.


Klaus

A preamp for a microphone has a fairly high input impedance so it does not load down the voltage signal from the lower impedance mic.
A mic NEVER has its current amplified because the current is almost nothing.

A photo diode can be reverse-biased so it conducts leakage current only when lighted. The photo-diode can also generate voltage itself when used as a tiny solar cell.

Think of it this (simplified) way:

A voltage amplifier makes the voltage greater without necessarily supplying more current.
A current amplifier makes the current greater without necessarily supplying more voltage.
A power amplifier makes the voltage greater while supplying more current. It gives the voltage more 'push' so it can be delivered at higher current (heavier load).

Brian.

A preamp for a microphone has a fairly high input impedance so it does not load down the voltage signal from the lower impedance mic.

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may i know ,about the output impedance of pre amp(whether high or low) and input impedance of mic(whether high or low)

Hi,

My point of view:

* i see audio amplifiers as voltage amplifiers. because there is a fixed relationship of v-out/v-in.
* you can build current amplifiers. (for example BJT with the relation I-C/I-B) but usually they are a part of a circuit. For example OPAMP input stage. It has a fixed relationship I-out / I-in... then followed by a voltage amplifier stage, then followed by the output stage (again a current amplifier stage) (at least most of the OPAMPs)

the expression "power amplifier" often is used for an amplifier with a lot of output power (for example to drive a speaker). But i don´t know a single amplifer that could have a fix p-out/p-in relationship. It allways depends on load (impedance). So here i don´t see the expression "power" with the meaning "U x I"

Klaus

Bhuvanesh123 said:

may i know ,about the output impedance of pre amp(whether high or low) and input impedance of mic(whether high or low)

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Why do you need to know the output impedance of a preamp? It feeds the high impedance (10k or more) input of a power amp so it can be 1k or less. If it is an opamp then its output impedance is less than 0.1 ohms at DC and low frequencies and is about 0.75 ohms at high audio frequencies.

A mic does not have an input signal, it produces an output signal. A dynamic mic (coil and magnet like a little speaker) output impedance is about 600 ohms and an electret mic is about 3.3k ohms.

You need to know the input impedance of a preamp so it is not too low and load down the output level. It should be about 10 times higher than the mic impedance.