Hello everybody from Italy, this is my first post.

I need a step-down dc/dc converter to be used as a front end for a 2kW HF-generator.

The input voltage is 320V.

The output voltage will be adjusted directly from the HF-generator CPU in the range from 100V to 300V: the goal is adjusting the HF-generator power just acting on its supply voltage.

I was thinking to design a simple non-synchronous buck converter with a 300uH inductor, that should be fine for about 50kHz switching frequency.
My concern is that currently I'm not sure that the microprocessor on CPU card will be fast enough to close the loop. And also I'm afraid that its PWM output will not have enough resolution at 50kHz to guarantee a decent regulation. Therefore I would use a simple analog controller ic to generate the PWM and close the voltage loop. Then the HF-generator CPU will simply give the set to such controller ic and close the power loop.
What do you think about this approach ?

Considering that any power change will be very slow I guess that a voltage mode operating controller will be ok: can you suggest an easy-to-use controller ic that will not require plenty of external components ?
Thank you

 

What is the load?
Does it need to be isolated, probably not.
You have two wires "320V & 0V". Does the output need to be "Vout and 0V" where 0V is common or can it be "320V and Vout" where the 320V wire is common. Strange question, but it answers the question of top side switch verses bottom side switch.

 

Hello everybody from Italy, this is my first post.

I need a step-down dc/dc converter to be used as a front end for a 2kW HF-generator.

The input voltage is 320V.

The output voltage will be adjusted directly from the HF-generator CPU in the range from 100V to 300V: the goal is adjusting the HF-generator power just acting on its supply voltage.

I was thinking to design a simple non-synchronous buck converter with a 300uH inductor, that should be fine for about 50kHz switching frequency.
My concern is that currently I'm not sure that the microprocessor on CPU card will be fast enough to close the loop. And also I'm afraid that its PWM output will not have enough resolution at 50kHz to guarantee a decent regulation. Therefore I would use a simple analog controller ic to generate the PWM and close the voltage loop. Then the HF-generator CPU will simply give the set to such controller ic and close the power loop.
What do you think about this approach ?

Considering that any power change will be very slow I guess that a voltage mode operating controller will be ok: can you suggest an easy-to-use controller ic that will not require plenty of external components ?
Thank you

First, an observation, a 300uH inductor at 50kHz will not give you continuous mode operation (the ripple current is greater than the load current). This will complicate everything: your output caps will need to be huge and the current stress and heating of the inductor will also be significantly higher than they need be.
I would recommend a few things here: use current mode control if you can as it makes the loop stability far easier to deal with, use a dedicated controller IC intended for this kind of application unless you are quite confident of your DSP skills, rethink your choke and make the value bigger (in continuous mode and with a say 25kHz switching frequency, an air gapped thin lamination iron core inductor is a very real option for you, and much easier to get the inductance and the DC rating you need).
If you are new to DCDC design, this is an ambitious project but if you are careful, wear the appropriate safety gear in case of exploding semiconductors and you are determined, you will get there and it should be a rewarding experience. We all had to start somewhere. Not many start with one that can so easily become an incendiary device!
Good luck. Hope it works for you.