Increase output drive by adding push/pull

Well Steven, I have actually been sending some articles on this topic over to AudioXpress. The 1st was just using a unity gain buffer, the BUF634A which is one option. The next, just ready to publish uses the small audio dual TPA6120A2 which is really the THS6012 die, which is the model you will need to use - that dual has a solid +/-400mA output . That model really missed on the input current noise, which is the next article - but if inside the loop, that is a don't care. 

The articles talk about what you need to consider for loop stability including the packaging prop delay. What part you use for power boost needs to start with the core amplifier and desired overall BW, output Current, slew rate, etc. 

What is your core amp and overall swing needs and BW?

Hi Steven,

what is your application? Audio? What output currents are we talking about? Have you thought about paralleling of OPAmps?

Kai

I looked into the BUF602 and BUF634A. While they are overkill being that I am using them in an audio bandwidth application they are pretty much what I was looking for. Though my post asked for increasing drive current what I actually need is to clamp the output of the op-amp at lower rails than the opamp. I could use diodes but they do not behave the way I need due to the soft knee at cutoff. The discrete solution works but is cumbersome to use and I have not been successful at eliminating the crossover distortion.

Do you know of a similar part that is less overkill without the high drive or bandwidth?

Michael, Thanks for the response. As you will see in the other responses what I actually need is the clamp the output of the opamp at lower rails than the opamp is using. The opamp is not critical so a TL072 would work and the BW is in the audio range. Do you know how the BUF634 or BUF602 behave when the input exceeds the rails?

Steve Jaszkowiak

Steven,

The obvious choice is to change the op amp supply voltages. There is also TL7726 hex clamp. 

Some specifics for the clamp voltages would be helpful.

Kai, I actually don't need that much drive current, what I need is to clamp the output at rails lower than that of the opamp. It needs to behave very well when the signal gets near to and exceeds the rails with no inversion or HF spikes. The discrete transistor approach works but I am not able to get low enough crossover distortion.

Thanks for your response

Steve Jaszkowiak

Well Steven

There are parts specifically designs with very fast output limiting and recovery with externally set limiting voltages. THey also have much  better linearity near limit than most other solutions

Look at the OPA688 for low gain or OPA689 for high gain, both are +/-6V max supply and probably way too fast for you, but that comes along with the sub 2nsec recovery from limiting. 

Ronald, thanks for getting back. I can't change the supply voltages. I will definitely look into the hex clamp though. The opamp is using a single ended 12V supply and the clamping voltage needs to be +/- 200mv.

Steve Jaszkowiak

Michael,

Those look like they wood work great. Unfortunately they are obsolete. Do you know of anything close to those?

Thanks

Steve Jaszkowiak

Ooops I gave you the original BB versions we did, they have been upgraded to a more recent process as the OPA698 and OPA699

Michael,

Thanks, it looks like those may do the job. Thanks again.

Steve Jaszkowiak