buffer circuit before rlc

[bhuvaneshnick]

what is the purpose buffer circuit(op-amp).and do we use same buffer circuit for low pass RC circuit or this is only for RLC circuit.thank you in advance

 

[ronsimpson]

A buffer has a voltage gain of 1. So the input voltage and the output voltage (Vs) are the same.
A buffer is used where the input signal is not strong (low current). The output can be high current.

A buffer can be used to drive almost anything. RC or RLC or CR or ..........

Example of a buffer:
You have a VCR that is used to drive one TV. At Walmart there 25 TVs on the wall with the same picture. The VCR can not send a signal to all 25 TVs. A buffer amplifier has a voltage gain of 1 so the voltage is the same. (input to output) The amplifier in this case can output the current to drive all 25 TVs.

 

[bhuvaneshnick]

why dont we increase the voltage rather than current

 

[ronsimpson]

why dont we increase the voltage rather than current

That depends on what we want to do.
In the case stated above where we are driving 25 TV sets with the same signal, we want the voltage to not increase, just the ability to drive more current.

I you want a amplifier to go from a small portable CD player to a very large speaker, when we want voltage and current amplification.

 

[tvtech]

That depends on what we want to do.
In the case stated above where we are driving 25 TV sets with the same signal, we want the voltage to not increase, just the ability to drive more current.

I you want a amplifier to go from a small portable CD player to a very large speaker, when we want voltage and current amplification.

RON...Thank You

Tough day here.

All the best
tvtech

 

[KeepItSimpleStupid]

Well, we talk about ideal OP amps and although they are not ideal, the buffer provides a low output Z, and low offset voltage, so your measurements are not impacted.

 

[bhuvaneshnick]

i am just lacking in basic.i am somewhat clear about what we discussing, before that if we wanna make all 25tv the same picture why do you saying we do no change the voltage and only the current.i dont understand the relation.thank you in advacne

 

[KeepItSimpleStupid]

Trust me, the TV example was a really bad one to use.

I'll try another which you may or may not have heard of. 70 V line to voice coil. This is used to distribute sound at many speakers. Each speaker has a transformer with "taps" for the amount of power. L pads might further be used to reduce the volume.

Your "typical" amplifier is designed have an 8 ohm speaker connected. When you connect two in parallel, the resistance becomes 4 ohms. 8 in parallel, 2 ohms. So, this amplifier has to be designed differently. Higher currents mean higher losses.

In the real word, we might talk of a voltage amplifier or a power amplifier, but rarely a current amplifier. In electronics a unity gain amplifier generally has a voltage gain of 1, but has current gain.

Your AC power line, is constant voltage. When a power company adds more generating capacity, the amount of current that can be supplied will increase.

The TV example is a really bad one because there are cable length attenuations, the need for 75 ohm terminations, the need for no reflections, impedance matching, losses in the taps and splitters and even that current at high frequencies would actually prefer a hollow tube and not a wire. This is not elementary.

 

[crutschow]

i am just lacking in basic.i am somewhat clear about what we discussing, before that if we wanna make all 25tv the same picture why do you saying we do no change the voltage and only the current.i dont understand the relation.thank you in advacne

A very basic relationship is Ohm's law that states the current in a simple resistive circuit is equal to the voltage divided by the resistance (I = V/R).

Lets ignore frequency affects and assume a low frequency signal to the TV. A TV set likes the input voltage to be within a fixed range, so you don't want the signal voltage to change no matter how many TVs are connected to the same signal source. But each connected TV takes a fixed amount of current which is calculated using Ohm's law as determined by the signal voltage and its input resistance. So if more TVs are connected you will require more current but at the same voltage.

 

[crutschow]

Deleted message.