Voltage Controlled Adjustable Buck Regulator

[dugherd]

I would like to design a 3.7 - 12 V, 3 A adjustable supply with 12V input. The output voltage is to be controlled by 0-5V signal.

My thought was to use a buck regulator like the LM2678-ADJ or similar. And control the feedback with the 0-5V signal. Are there any ideas on how to approach this? Or, is there a better or common solution for this?

My first shot at this used an OPA548 but when operating at outputs of 4V or so it is just too hot and I would like to avoid paralleling an additional op-amp. So, would like to find another solution.

Thanks for your help!

[jeroen79]

As far as I can tell from the datasheet is that the LM2678-ADJ will try to maintain 1.2V on the feedback pin.
You could use an opamp to compare the control voltage to the output and then bias it's output to 1,2V when there is 0 error.



How did you use the OPA in your trial?

[dugherd]

My original design used the OPA548 as a non-inverting amplifier with gain of 2.4. But, for the particular application the normal operating point is at about 4.4Vout and 1.3A. Operating here the OPA dissipates ~10W. So, I would like a more efficient solution which led me to looking at replacing the op-amp with the adjustable buck regulator.