Variable DC-DC amplifier : from 0-3.3V to 0-12V

A

avass

New Member

• Feb 18, 2011

• #1

Sorry for the newby question, I'd really appreciate your advices / hints :

I am outputing 0-3.3V from a DAC which I'd need to linearly amplify to a variable range, such as 0-5V or 0-12V etc. Not sure about the impedance of the output, but I'd like to be able to handle at around 1A with a very little error on the output.

May I ask what approach / design / parts should I consider / use?

Thank you!

 

MikeMl

Well-Known Member

Most Helpful Member

• Feb 18, 2011

• #2

National makes "Power OpAmps" that are capable of +-30V at +-3A. It requires big split supplies and big heatsinks. **broken link removed** There are lots of others.

 

Last edited: Feb 18, 2011

A

avass

New Member

• Feb 18, 2011

• #3

Thanks. That made me realize that I forgot to mention that I have a limitation : Vcc=12V ( also, output is 0-max.12V )

 

Last edited: Feb 18, 2011

MikeMl

Well-Known Member

Most Helpful Member

• Feb 18, 2011

• #4

Cant be done. Power OpAmps are not rail-to-rail. The Vdd supply will need to be about 3V higher than the highest output voltage, and Vss about 3V lower than the lowest output voltage. If you really want 0-12V, you will need +15V and -3V supplies.

 

A

avass

New Member

• Feb 18, 2011

• #5

Thanks. How about some other way? Would a LT3080 based circ. be possible?

 

MikeMl

Well-Known Member

Most Helpful Member

• Feb 18, 2011

• #6

Looks like it makes a reasonable voltage follower, but still runs out of steam at about 10.6V

 

Attachments

• 3080.png

  26.8 KB · Views: 306

A

avass

New Member

• Feb 20, 2011

• #7

If I change the R2 with AD5293 ( variable digital potmeter ) using an LT1413 ( op amp - 12V ), the simulation shows that I'd get what I'm looking for. I also noticed, that the min.Vout is ~70mV, which I think is OK. Can you have a look at these please it this would really work? Thank you!

 

Attachments

• 19K.png

  8 KB · Views: 276
• 100K.png

  7.7 KB · Views: 278

Last edited: Feb 20, 2011

MikeMl

Well-Known Member

Most Helpful Member

• Feb 20, 2011

• #8

Your simulations have no load on the output (other than the feedback resistor). Try it when the opamp is driving a 12 Ohm load (to ground? or to +12V ?)

 

A

avass

New Member

• Feb 20, 2011

• #9

Yes, I've tried it with and seem to have worked with about 180 Ohm... May I ask where the 12 Ohm comes from? Why not some other number? I know I need to learn more and I really appreciate your advice. Thank you.

 

Last edited: Feb 20, 2011

MikeMl

Well-Known Member

Most Helpful Member

• Feb 21, 2011

• #10

You started this thread saying that you wanted 1A at 12V. R = E/I = 12/1 = 12Ω

 

A

avass

New Member

• Feb 26, 2011

• #11

You are absolutely right, my apologies... How about the attached? Yes, it seems to "crap out" at around 10.5V, but until that it seems to hold quite well...

 

Attachments

• PL_Stab.png

  14.6 KB · Views: 267

Last edited: Feb 26, 2011