I’ve got the power
A while back I tried (unsuccessfully) to become a distributor for everyone’s favorite power supply company, Triad. Discouraged by the rejection, I scooped up my humble ego and decided to try the next best thing: find a power supply that rivals Triad’s performance for use with MiSTer.
What specs matter when it comes to power supplies?
- The most obvious is the voltage. Most modern electronics operate at 3.3V or lower (1.8V is also common). 5V input feeds voltage regulators that are often chained together to improve efficiency. The DE10-nano schematic states that over voltage protection kicks in at 5.45V so a supply needs to stay under 5.45V. Meanwhile USB voltage specification is 5V +/- 5%, which equates to 4.75V - 5.25V.
- Voltage drop is the inverse relationship between current draw and voltage. Increased current draw results in a decrease voltage.
- Another performance consideration is DC overshoot. An ideal power supply goes from 0 to the target voltage instantaneously and with no oscillation.
Let's evaluate some of the results.
- Using a DC load tester, I increased the current draw from 0.0V until the load tester detects the voltage falls below its threshold at which point the test is complete. Note that this is testing to failure and should not be seen as expanding the usable current rating of the power supply. Strictly speaking, everything between 4.75V and 5.25V would be usable voltage, but I don't endorse operating electronics outside of the factory rated specification. Note that the DE10-nano by itself draws roughly 1.3A of current so the USB voltage stays within spec. The stock DE10-nano PSU performs decently as does the Triad. Note that the Triad gives you a solid 4A of current at 4.75V
- To bring the voltage drop testing into a more realistic scenario, I used it to power a MiSTer setup, through my switch + splitter (technically rated at 2A but let's ignore that for now). The DE10-nano, SDRAM, and accessories draw about 1.5A of current. But what happens when you power a 2.5" hard drive off of the USB hub alone? Well, it pulls down the voltage to the other USB devices and can cause wifi adapters to behave poorly. Now add to this a modern controller that charges at a few hundred mA of current, and the situation worsens. All 3 adapters (stock DE10-nano, Triad Magnetics WSU050-4000, and the MiSTer Addons one) hold up well with this simple test with the MiSTer Addons power supply holding its voltage the best under load. The switch + splitter also contributes a small amount of voltage drop (~0.1V).
- Finally, let's compare the DC overshoot between the Triad and my power supply. The Triad has a really sharp rising edge with 430mV of overshoot.
- The MiSTer Addons overshoot is slightly less overshoot (210mV) but with a slower positive rising edge. This is typically indicative of some type of filtering, perhaps RC, or LC.
By all available metrics, the new power supplies fit the bill extremely well. I've listed a handful of power supplies to gather user feedback prior to listing the remaining stock.
Did I get something wrong? Sound off in the comments below.