Hi superino
🙂Do you want to fix a static voltage for some reason? This is not a very good thing...dynamic vcore is a good technology and has very little impact on peformance...none in everyday computing.
However if you want fixed vcore you can
Set manual vcore...this will give same vcore even if CPU downclocks.
Disable speedstep and C1E in BIOS
Set performance power plan with "minimum processor speed" set at 100%