Not content with what's available off the shelf, Dr. Scott M. Baker has developed a habit of building his own benchtop power supplies — and his latest design takes its input via Power over Ethernet (PoE).
"What can I say, I like building power supplies," says Baker of his latest project. "Seriously though, I’ve been looking for a reason to play with these DPS5005 and related modules ever since seeing them on popular forums and video blogs. The DPS5005 is relatively well regarded, and has the potential to replace the benchtop lab supply that I regularly use for casual use.
"The DPS5005 is a DC-DC converter. Since it is a DC-DC converter, you have to have a DC source to drive it. A lot of people use a 48V power brick, as they are commonly available. I figured, I’ve already got a 48V PoE switch, in fact I have several of them, I’ll just use one of those. These switches are typical for people using PoE cameras, and recently they have become quite handy for running a Raspberry Pi using the Raspberry Pi PoE hat accessory."
The resulting design, which is based on the Texas Instruments TPS2378 PoE controller's reference design, accepts a PoE input on an RJ45 jack, which goes into a pair of bridge rectifiers — as it's not guaranteed which cable pair will carry the power at a given time — to prevent polarity issues, while a PTC fuse acts as "insurance against something going horribly wrong," Baker explains. "Then we have a TVS diode to handle transient suppression, and a decoupling capacitor."
After debugging a relatively minor issue — "it’s important to draw about 0.44 W of power," Baker explains, "or the switch will decide there’s no load and turn the device off," which led to the addition of load resistors and an LED in the second layout - the finished, surprisingly compact, PCB is housed in a custom 3D-printed case with a front-mounted colour display, switch, controls, and the regulated power outputs.
More information on the build is available on Baker's blog.