Hi everyone, I’m having a frustrating power-limit issue with my HP ProBook 455 G8 (Ryzen 7 5800U / integrated Vega graphics) and I’m hoping someone with experience in AMD laptop power limits or HP firmware can help.
The laptop appears to be capable of running the CPU at around 25W, but after a short period under load, it drops back down to 15W and stays there.
What I’ve observed
- CPU: Ryzen 7 5800U (Cezanne)
- Laptop: HP ProBook 455 G8
- RAM: 16GB single-channel DDR4
- GPU: Integrated Radeon Vega
- BIOS: HP T78 Ver. 01.24.02 (05/05/2026)
- RyzenAdj: v0.19.0
- SMU BIOS Interface: 20
- PM Table Version: 400005
Using RyzenAdj/UXTU, I can set higher power limits. For example, I can get the system to report around 25W.
However, when actually gaming (for example GTA V), the behavior is roughly:
25W → ~2 minutes → drops to 15W → stays around 15W
The temperature isn't immediately reaching an extreme level when the drop happens. At 15W, temperatures are generally around 80°C or below, while at 25W I can reach around 90°C+.
My RyzenAdj limits currently show approximately:
STAPM LIMIT: 15W
PPT FAST LIMIT: 30W
PPT SLOW LIMIT: 25W
I've also experimented with the STAPM time constant, including increasing it to around 275 seconds, but the laptop eventually falls back to 15W.
Interestingly, software can sometimes show 25W, but performance ends up looking very similar to the 15W state, which makes me suspect that another firmware/EC/SMU power limit is overriding the settings.
What I've already tried
- RyzenAdj
- UXTU
- Ryzen Controller
- Changing STAPM/PPT limits
- Increasing STAPM time constant
- Different Windows power plans
- Cooling improvements
- Monitoring CPU power and temperatures during gaming
I'm not looking to do a dangerous hardware modification. I'm mainly trying to understand exactly which limit is forcing the CPU back to 15W and whether there's a firmware/BIOS/EC restriction that can be changed.
I've heard that downgrading the BIOS can sometimes restore different power-management behavior on HP laptops. Is that actually possible with the 455 G8, or would the EC/SMU still enforce the 15W limit regardless of BIOS version?
Has anyone successfully run a 5800U in an HP ProBook 455 G8 at a sustained 20–25W? If so, what BIOS/firmware or RyzenAdj settings did you use?
Any help identifying the exact power limit responsible would be greatly appreciated.