I have a Pololu S18V20ALV SEPIC voltage regulator board that is wired to a high-amperage 5V USB power source on the input and a DC brushless fan on the output. The output is set to about 5.5V. Contrary to the typical behavior of a power supply where higher temperatures reduce maximum output, I've noticed that it delivers more power when hot:
- If I heat up the regulator by shorting the output pins for about ten seconds, then remove the short, the fan runs faster than it otherwise would.
- If I hook up a 10A ammeter to the output, the meter readout progressively increases from less than 1A to as high as 3A as the voltage regulator heats up. The limit is due to the thermal shutdown function on the TPS55340 regulator chip.
Why is my voltage regulator doing this? Is this behavior typical for a SEPIC converter? What implications does this have? (Does this mean that an overloaded SEPIC converter without thermal protection can experience thermal runaway and consequently catastrophic failure?)