GPU Voltage lowers after a few seconds of load?

Question

I have a 650Ti, and I'm looking to overclock it. I'm using MSI Afterburner, and while I'm stress-testing etc. I have the logging graphs open.

Under max load, with no overvolting, the default voltage is 1075mV. However, I've noticed that the graphics card only keeps this voltage for a few seconds under moderate to heavy load, before going to 1067mV.

I can stop counteract this by increasing voltage by 12mV, so it starts at 1087mV and decreases to 1075mV, but I was wondering what's causing this temporary overvolt, and is there a way to stop it, to keep a stable max voltage?

Answer 1

TL;DR This is normal operation for power supplies in a dynamic system. There isn't much you can do to "fix" the voltage overshoot.

Overshoot is quite common in electronics when a power supply ramps up to match a load and then briefly exceeds the requirements and then has to pull back.

It is a feature of every adaptive system that uses a feedback loop to control their output.

More information at the Wikipedia page on overshoot.

This EE.se question Exact definition of overshoot

---

The essential problem is that when load increases on the output it causes a voltage drop at the power supply. This voltage drop causes the power supply to adapt and increase current (which increases the voltage out).

The problem is that for fixed loads the actual current drawn is dependant on voltage. If the voltage drops then it draws more current, as the voltage is increased by the supply then the current draw falls.

This change in current and voltage causes the apparent load to change in a way that is hard to compensate for. By allowing more current through the voltage will rise to a "good" level, but this will mean that the device no longer needs to draw as much current and causes it to show a lower load and the voltage rises further than expected. The supply then clamps back so the voltage drops slightly and the current increases again, causing voltage to droop again.

This cycle repeats until both supply and load settle down.