Voltage Follower: help me with calculations

[MNomanA]

mosfet voltage follower

Hello everyone,

Can we use LM741(max power 500mW) or TL071(max power 680mW) as a voltage follower at the output stage of a voltage amplifier to drive
1. 32 ohm load(headphones)
2. 8 ohm load(speaker)
?

the maximum peak voltage appearing at the load will be 5 volts(10 V pk-pk)....

i did the simulation in multisim 2001 .... the rms value of the current through the 32 ohm load was 104 mA and through 8 ohm was 390 mA .......

if i m right the rms power at the 32 ohm load will be calculated like this 0.104*0.104*32 = 346 mW(rms) .....if the calculation is right then the op amps can be used to drive the 32 ohm load..... isn't it?

for the 8 ohm load with same calculations the rms power will be 1.22 watts ...... so the opamps can't be used for 8 ohm?

what i want to ask is that am i doing right calculations ...are they done this way?
and are the two op amps capable of driving the 32 ohm load at the specified current(104 mA rms or 150 mA pk) ? .... and 8 ohm load at(390mA rms)

please help me and solve my problem.....

Thanx for any help
MNomanA

 

[on1aag]

Re: Voltage follower

Hi MNomanA,

Your simulator sucks, a look at the datasheet of the µA741 tells me
that the short circuit current lies somewhere between 10 and 40 mA
depending on the temperature.
So the maximum output power in a 32Ω load will be (10*10E-3)sq * 32/2.
If you are satisfied with 1.6 mW it's fine with me. :twisted:

on1aag.

 

[MNomanA]

Re: Voltage follower

Thanx for the help.......
It seems Multisim has errors.....
I haven't looked at the current rating..... I didn't know if it exists..... I thought the calculation has to do something with max power dissipation.....
A class A mosfet voltage follower can be used here, i think, for the 32 ohm load......but for 8ohm load it will get too hot.....

Thanx
MNomanA