BJT or OPAMp for amplifying

Thread Starter

captoro

Joined Jun 21, 2009
23
hello ,

I would like to know if it is better to use OPamp or single ( or cascading BJT) to amplify a 1v pk-pk to 12v pk-pk using a 12v source.
The frequency should be from 0 to 1mhz.

I am using the circuit found here:
https://forum.allaboutcircuits.com/attachments/common-emitter-speaker-amplifier-02-png.160975/

After tweeking, I get about 9v pk-pk at about 20khz , but when I go up to 100khz it falls to 7v pk-pk
Otherwise the signal is not clipped or distorted. with that circuit.

Would I be able to get what I want using more complex circuit , or using OPamp ??
Thanks
Ken
 

dl324

Joined Mar 30, 2015
10,541
It's going to be difficult to have 12V peak to peak signal using a 12V source.

What kind of load will the circuit drive? It can't be a speaker because you won't be able to hear much above 20kHz.
 

MrAl

Joined Jun 17, 2014
7,515
If you can stand to abandon the original (input) ground you might be able to use two op amps in a differential output configuration. You'd have to use rail to rail op amps too.

The idea is to use one as non inverting and the other as inverting, and take the output from the two outputs of the two op amps. That, theoretically, gives you a potential 12 volts peak to peak if the supply voltage is 12 volts DC and the load does not draw too much current.
Remember though the output ground can not be connected to the input ground.

You can use a transistor bridge and get close to 12v peak to peak if you are dealing with a rectangular wave output.
 

crutschow

Joined Mar 14, 2008
24,754
That transistor circuit shows it driving a speaker (which it can't do with a 10k collector resistor).
If you want to drive a speaker than you need an audio power amplifier, not an op amp.
But why do you want response to 1MHz (megahertz?).
Do you have an ultrasonic driver?
 

Thread Starter

captoro

Joined Jun 21, 2009
23
If you can stand to abandon the original (input) ground you might be able to use two op amps in a differential output configuration. You'd have to use rail to rail op amps too.

The idea is to use one as non inverting and the other as inverting, and take the output from the two outputs of the two op amps. That, theoretically, gives you a potential 12 volts peak to peak if the supply voltage is 12 volts DC and the load does not draw too much current.
Remember though the output ground can not be connected to the input ground.

You can use a transistor bridge and get close to 12v peak to peak if you are dealing with a rectangular wave output.
Not sure I understand what you are saying here. Does the circuit or similar circuit existe ?. I did not use those resistor values, i put POTS instead to get the proper sine wave. I wont be driving a speaker straight out of that . This is just a part of the project. for Now my source is 12v and I cant modify that.

ken
 

MrAl

Joined Jun 17, 2014
7,515
Not sure I understand what you are saying here. Does the circuit or similar circuit existe ?. I did not use those resistor values, i put POTS instead to get the proper sine wave. I wont be driving a speaker straight out of that . This is just a part of the project. for Now my source is 12v and I cant modify that.

ken
What do you mean does the circuit exist? It exists once you build it.

The build is very simple.
You make two op amp amplifiers. One is inverting, the other non inverting, both with the same gain.
You get your required output from the output of BOTH op amps. One op amp output is one output terminal, the other op amp output is the other output terminal.
If you have a 12v power supply and only one 12v power supply you get plus and minus 12 volts out of the two op amp outputs. That means you get 12v peak to peak with a sine wave input to both op amps and with only a 12v DC power supply.

Analysis:
When one op amp outputs +12v, the other op amp outputs 0v. To the load it looks like +12v peak.
When the previous op amp outputs 0v the other op amp outputs +12v. To the load it looks like -12 v peak.
This is the same basic idea as how an H bridge produces plus and minus from a single supply.
The only caveat is that you can not have a common ground between the input and output. SO just remember the load is "floating".


Do i have to draw a circuit?
 

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Thread Starter

captoro

Joined Jun 21, 2009
23
+ my question
What is the load you drive with 1MHz ±6V . . . ? 2Ω , 3Ω , 4Ω , 6Ω , 8Ω speaker ? piezo ? other
I have a pulse square wave which acts as a carrier. These pulses are 12v peak, from ground.
Basically I am heterodyning a DC woth an AC wave.
SO my AC sin wave should be from 0 to 12v.
I will post a schematic by tomorrow.

Ken
 

Thread Starter

captoro

Joined Jun 21, 2009
23
I have a pulse square wave which acts as a carrier. These pulses are 12v peak, from ground.
Basically I am heterodyning a DC woth an AC wave.
SO my AC sin wave should be from 0 to 12v.


Ken

Mods Note:
Please cut the useless part and compress the resolution of image file to as 800x600 or 1024x768 before you upload the file, the original file size about 1.6 Mb and I already compressed it to as 48 Kb, thanks for your cooperation.
 

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