Dual Power Supply In A Pinch

July 2, 2022 by Chris Lott 14 Comments

Recently I needed a dual voltage power supply to test a newly-arrived PCB, but my usual beast of a lab power supply was temporarily at a client’s site. I had a FNIRSI programmable power supply which would have been perfect, but alas, I had only one. While digging around in my junk box I found several USB-C power-delivery “trigger” boards which I bought for an upcoming project. These seemed almost too small for the task at hand, but after a little research I realized they would work quite well.

The ones I had used the Injoinic IP2721 USB-C power delivery chip, commonly used in many of these boards. Mine had been sold pre-configured for certain output voltages, but they were easy to re-jumper to the voltages I needed, +5 VDC and +20 VDC. The most challenging aspect was physically using them — they are the size of a fingernail. This version had through-hole output pads on 0.1″ centers, so I decided to solder them to the base of a standard MTA pin header. A few crimps later and I was up and running, along with the requisite pair of USB-C cables and power adapters.

For just a few dollars each, these trigger boards are useful to have in your toolbox, both for individual projects and for use in a pinch. We reviewed these modules a couple of years ago, and check out the far more flexible PD Micro that we covered last year.

Junk I Bought: My PSU Just Won’t Do

May 31, 2022 by Jenny List 98 Comments

I have an Acer monitor that I’ve owned for around 15 years, and thanks to my having paid extra at the time for the model sporting a DVI socket for HDMI compatibility it still finds a place as one of my desktop monitors. It has a power brick that supplies it with 1 2V at 4.5 A, and over the years this has developed an annoying whine. Something’s loose in the magnetics, and I really should replace it. So off to AliExpress I went, and dropped in an order for a 12 V, 5 A power brick.

It’s No Heavyweight

A PSU brick, marked as 12V 5A — So far so good…

These units are pretty standard, a box about 130 mm by 60 mm with an IEC socket at one end and a trailing cable at the other for the low voltage. I’ve had enough of them pass through my hands over the years to know what to expect, so I was dismayed to find when I received my PSU that it was suspiciously light. 86 g compared to the around 250 g I’d expect, so I began to smell a rat. Time for a teardown, and a descent into the world of small switch-mode mains power supplies.

Normally it should be easier to break into Fort Knox than to crack open a mains power supply, because for safety they are ultrasonic welded together. The few times I’ve done it have required some Dremel time and a bit of swearing, so when this case turned out to open fairly easily by levering with a screwdriver it was evident this wasn’t a high-quality item. Sure enough my suspicions were confirmed, for there inside was a much smaller board. It’s clear this isn’t a 5 A power supply, so just what have I received? Continue reading “Junk I Bought: My PSU Just Won’t Do” →

Laptop USB-C Charging Hack Lets You Leave The Brick At Home

April 17, 2022 by Dan Maloney 47 Comments

At their best, laptops are a compromise design. Manufacturers go to great lengths to make the slimmest, lightest, whatever-est laptops possible, and the engineering that goes into doing so is truly amazing. But then they throw in the charger, which ends up being a huge brick with wire attached to it, and call it a day.

Does it have to be that way? Probably, but that doesn’t mean we can’t try to slim down the overall footprint of laptops at least a little. That’s what [Joe Gaz] did when he hacked his laptop to allow for USB-C charging. Tired of the charger anchoring down his HP X360, [Joe] realized that he could harvest the PCB from a USB-C charger adapter dongle and embed it inside his laptop. We’ve seen similar modifications made to Thinkpads in the past, and it’s good to see the process isn’t that far removed with other brands.

After popping open the laptop, which is always an adventure in reverse mechanical engineering, he found that removing the OEM charger jack left just enough room for the USB-C charger. Mounting the board required a 3D printed bracket, while enlarging the original hole in the side of the laptop case took some cringe-inducing work with a file. It looked like it was going to be pretty sloppy at first, but he ended up doing a pretty neat job in the end. The whole modification process is in the video below.

The end result is pretty slick — [Joe] can now carry a much more compact USB wall-wart-style charger, or eschew the charger altogether and rely on public USB charging stations. Either way, it sure beats lugging a brick around. If you’re interested in laptop hacking, or even if you just want to harvest the goodies from a defunct machine, check out this guide to laptop anatomy by our own [Arsenijs Picugins].

Continue reading “Laptop USB-C Charging Hack Lets You Leave The Brick At Home” →

A Simple Linear Power Supply, Done Well

April 5, 2022 by Jenny List 45 Comments

When reaching for a power supply design it’s normal here in 2022 to reach for a switching design. They’re lightweight, very efficient, and often available off-the-shelf at reasonable prices. Their benefits are such that it’s become surprisingly rare to see a traditional linear power supply with a mains-frequency transformer and rectifier circuit, so [ElectroBoy]’s dual voltage PSU board for audio amplifiers is worth a second look.

This type of linear power supply has an extremely simple circuit consisting of a transformer, bridge rectifier, and capacitors. The transformer isolates and steps down the AC voltage, the rectifier turns it into a rough DC, and the capacitors filter the DC to remove as much AC ripple as possible. In an audio power supply the capacitors have the dual role of filtering and providing an impulse reservoir for the supply in the event of a peak in demand imposed by the music being played. Careful selection is vital, with in this case a toroidal mains transformer and good quality capacitors being chosen.

The choice between a linear power supply such as this one and a switching design for high quality audio is by no means clear-cut, and may be something we’ll consider in our Know Audio series. The desirable properties are low noise and that impulse reservoir we mentioned, and it’s probably fair to say that while both types of power supply can satisfy them. With the extra expense of a toroidal transformer a linear supply is unlikely to be the cheaper of the two, but we suspect the balance tips in its favour due to a good linear supply being the easier to design.

Hacked DSP5005 unit showing amp-hours screen

Another DPS5005 Alternative Firmware

January 22, 2022 by Dave Rowntree 9 Comments

These cheap Chinese-built programmable power supplies are nothing new, we’ve been using them for years. They’re not particularly good power supplies, since current feedback is in software, but for some tasks they’re a great fit and you can’t argue with the price. Alternative firmware projects have also been a thing for a while too, but none we’ve seen have been quite as capable and polished as this latest DPS firmware project by [Profi-max.] We’ve not come across the source code yet, but at least the binary image is freely downloadable.

The firmware has some interesting features, such as programmable pre-sets intended for battery charging applications. In fact, there is a dedicated battery charge mode screen. We want to warn, however, that charging lithium ion batteries with this might not be at all wise, not in the least because of a lack of protection hardware in place. It would be very easy to destroy the unit or overheat a battery this way! However, if you must do this, there are a few features to help you out, such as a handy ‘counters’ screen showing approximate charge delivered.

Remote programmability is, as usual, via the easily hacked in serial port, with firmware support for Bluetooth serial modules if wired USB serial doesn’t suit. For those who like to mount things differently, the screen can be rotated by holding a key on power-up, or if you hook up a MPU6050 accelerometer/gyro module it will even do it automatically!

To update a stock DPS unit, the only requirements are access to an ST-Link compatible programmer dongle, to target the STM32 SWD programming interface, and the STM32CubeProgrammer utility. Open source alternatives to that are also available, stlink comes to mind as a good option. Once you have the module PCB popped out of its plastic casing, only three wires need tacking onto a handy set of pads to complete the connection to the programmer dongle. Pretty simple stuff.

If you’re looking for a similar project, with source immediately available, then checkout the OpenDPS project we covered a few years ago, and if you’re thinking of going crazy, building a DIY open source electronics lab, we got you covered.

Continue reading “Another DPS5005 Alternative Firmware” →

Custom Christmas Light Controller Blocks Blinks

December 27, 2021 by Tom Nardi 8 Comments

Finding that his recently purchased LED Christmas lights defaulted to an annoying blinking pattern that took a ridiculous seven button presses to disable each time they were powered up, [Matthew Millman] decided to build a new power supply that keeps things nice and simple. In his words, the goal was to enable “all lights on, no blinking or patterns of any sort”.

Connecting the existing power supply to his oscilloscope, [Matthew] found the stock “steady on” setting was a 72 VAC peak-to-peak square wave at about 500 Hz. To recreate this, he essentially needed to find a 36 VDC power supply and swap the polarity back and forth at the same frequency. In the end the closest thing he could find in the parts bin was a HP printer power supply that put out 30 volts, so the lights aren’t quite as bright as they were before, but at least they aren’t blinking.

To turn that into a pair of AC square waves, the power supply is connected to a common L298 H-Bridge module. You might expect a microcontroller to show up at this point, but [Matthew] went old school, and created his two alternating 500 Hz square waves with a 555 timer and a 74HC74D dual flip-flop.

Unfortunately, he didn’t have the time to get a custom PCB made before Santa’s big night. Though as he points out, since legitimate L298s are backordered well into next year anyway, having the board in hand wouldn’t have helped much. The end result is that the circuit has to live on a breadboard for the current holiday season, but hopefully around this time next year we’ll get a chance to see the final product.

Quick And (Not Very) Dirty Negative Voltage Supply

November 16, 2021 by Adam Zeloof 11 Comments

There comes a time in every hardware hacker’s career during which they first realize they need a negative voltage rail in their project. There also comes a time, usually ~10ms after realizing this, when they reach for the Art of Electronics to try and figure out how the heck to actually introduce subzero voltages into their design. As it turns out, there are a ton of ways to get the job done, from expensive power supplies to fancy regulators you can design, but if you’re lazy (like I am) you might just want a simple, nearly drop-in solution.

[Filip Piorski] has got you covered there. In a recent video, he demonstrates how to turn a “China Special” $1 buck converter from Ebay into a boost-buck converter, capable of acting as a negative voltage supply. He realized that by swapping around the inputs and outputs of the regulator you can essentially invert the potential produced. There are a few caveats, of course, including high start-up current and limited max. voltages, but he manages to circumvent some of them with a little clever rewiring and a bit of bodge work.

Of course, if you have strict power supply requirements you probably want to shell out the cash for a professionally-built one, or design one yourself that meets your exact needs. For the majority of us, a quick and easy solution like this will get the job done and allow us to focus on other aspects of the design without having to spend too much time worrying about the power supply. Of course, if power electronics design is your thing, we’ve got you covered there, too.

Continue reading “Quick And (Not Very) Dirty Negative Voltage Supply” →