OPA548: Ripple generator

Hi Iannis, 

Welcome to the E2E forum, and thanks for reaching out. 

I think you are on the right path, OPA548 is likely an ideal candidate for this type of use-case. 

A few questions. So we are trying to couple this varied frequency, varied amplitude sine wave onto a fixed 14V DC line?  

What is the load that the amplifier will be driving? Do you want the amplifier to provide this 14V DC line as well as the AC? 

Do you have an expected supply voltage that you will have access to? 

What provides the AC to the OPA? 

A lot of questions, but this will all help me understand the application a bit better

Thanks,

Jacob

Hi Iannis, 

Gotcha, thanks for the details. 

OPA548 is likely the preferred device for the current ranges you mention. 

I see there being two primary options:

1. The method we discussed earlier, using a bias T to couple the AC wave from the power OPA onto the existing DC source. The advantage of this solution is that the DC power does not source from the power OPA, so this can be beneficial depending on steady state loading conditions. The method however requires the LC network to be optimized for the desired frequency and, in this case we would need to set a pretty low frequency HPF.

2. We could alternatively use a summing amplifier or inverting amplifier to create the DC + AC wave. The disadvantage here is that the DC power now comes from the OPA supply rail, so we could potentially see large power losses depending on the setup. The advantage however is that we can avoid LC networks, and create accurate DC and AC amplitude over frequency. 

The frequency and amplitude ranges you mention are all reasonable for OPA548. 

Personally, I prefer option 2 as this is the method we often use for creating PSRR testers. Again, this however depends heavily on the DC current consumption of your design. 

Thanks,

Jacob