A Tiny Bench Power Supply

One of the more popular projects for beginners in electronics is a power supply. Yes, you can always go to Amazon and buy a nice power supply, but unfortunately, we haven’t set up our Amazon affiliate links yet. Instead, we’ll have to go with the next best thing and check out [Tron900]’s mini bench power supply build. It’s extremely capable and cute as a button.

The design goals for this project were to build a small and compact unit using mostly salvaged and recycled components, with all through-hole circuitry. The best guide you’ll ever find for a DIY power supply is one of [Dave Jones]’ earlier video series going over the construction of an adjustable power supply based on an LT3080. [Tron] didn’t have this regulator on hand and wanted to base his design around an op-amp instead. After rummaging through his parts, he found what he was looking for: a TIP3055 power transistor, a neat enclosure that could double as a heatsink and an AD680 voltage reference.

The design of this power supply was simulated in SIMETRIX, and after a few revisions [Tron] had a circuit that worked reasonably well. The circuit was populated on a piece of perfboard, a fantastic front panel was constructed, and one of those ubiquitous volt/ammeter panels added.

This is just a one-off project, but the results are fantastic. This is a very small, very capable power supply that does everything [Tron] needs. It’s accurate enough, at least when measured with a fancy benchtop HP meter, and looks adorable. What more could you want in a benchtop power supply?

The Shocking Truth About Transformerless Power Supplies

Transformerless power supplies are showing up a lot here on Hackaday, especially in inexpensive products where the cost of a transformer would add significantly to the BOM. But transformerless power supplies are a double-edged sword. That title? Not clickbait. Poking around in a transformerless-powered device can turn your oscilloscope into a smoking pile or get you electrocuted if you don’t understand them and take proper safety precautions.

But this isn’t a scare piece. Transformerless designs are great in their proper place, and you’re probably going to encounter one someday because they’re in everything from LED lightbulbs to IoT WiFi switches. We’re going to look at how they work, and how to design and work on them safely, because you never know when you might want to hack on one.

Here’s the punchline: transformerless power supplies are safely useable only in situations where the entire device can be enclosed and nobody can accidentally come in contact with any part of it. That means no physical electrical connections in or out — RF and IR are fair game. And when you work with one, you have to know that any part of the circuit can be at mains voltage. Now read on to see why!

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Boost Converter Functionality at Rock-Bottom Prices

Linear voltage regulators are pretty easy to throw into a project if something in it needs a specific voltage that’s lower than the supply. If it needs a higher voltage, it’s almost just as easy to grab a boost converter of some sort to satisfy the power requirements. But if you’re on a mission to save some money for a large production run, or you just like the challenge of building something as simply as possible, there are ways of getting voltages greater than the supply voltage without using anything as non-minimalistic as a boost converter. [Josh] shows us exactly how this can be done using a circuit known as a charge pump to drive a blue LED.

One of the cool things about AVR microcontrollers is that they can run easily on a coin cell battery and source enough current to drive LEDs directly from the output pins. Obviously enough, if the LED voltage is greater than the voltage of the power supply, this won’t work. That is, unless you have a spare diode and capacitor around to build a charge pump.

The negative charge pump works by charging up a capacitor that is connected to an AVR pin, with the other side between the LED and a garden-variety diode to ground. That results in a roughly (VCC – 0.7) volt difference across the capacitor’s plates. When the AVR pin goes low, the other side of the capacitor goes negative by this same amount, and this makes the voltage across the LED high enough to light up. Not only is this simpler than a boost converter, but it doesn’t need any bulky inductors to work properly.

Will this work for any load? Am I going to start any fires by overdriving the LED? Luckily, [josh] answers all of these questions and more on the project page, and goes into some detail on the circuit theory as well. Granted, the charge pump doesn’t have the fine control over the power supply that you can get out of a buck or boost converter (or any switch-mode power supply). But it does have good bang-for-the-buck.

Converting An Easy Bake Oven To USB

[Jason] converted an Easy Bake Oven to USB. If you have to ask why you’ll never know.

Easy Bake Ovens have changed a lot since you burnt down your house by installing a 100 Watt light bulb inside one. Now, Easy Bake Ovens are [bigclive] material. It’s a piece of nichrome wire connected through a switch across mains power. Part of the nichrome wire is a resistor divider used to power a light. This light assembly is just a LED, some resistors, and a diode wired anti-parallel to the LED.

This is a device designed for 120 V, but [Jason] wanted it to run on USB-C. While there are USB-C chargers that will supply enough power for an Easy Bake Oven, the voltage is limited to 20V. Rather than step up the USB-C voltage, [Jason] added some nichrome wires to divide it into six equal segments, then wired all the segments in parallel. This lowers the voltage by one sixth and increases the current by a factor of six. Good enough.

The power supply used for this hack is the official Apple 87W deal, with a USB-C breakout board (available on Tindie, buy some stuff on Tindie. Superliminial advertising) an Arduino Uno connected to the I2C pins. A few bits of code later, and [Jason] had a lot of power coming over a USB cable.

With the Easy Bake Oven fully converted, [Jason] whipped up a batch of cookie mix. After about 15 minutes the cookies crisped up and started to look almost appetizing.

While the result is weird — who on Earth would ever want a USB-powered Easy Bake Oven — this is honestly a fantastic test of [Jason]’s USB-C PHY breakout board. What better way to test a USB-C than a big resistive load, and what better resistive load is there than an Easy Bake Oven? It’s brilliant and hilarious at the same time.

Open Source Firmware For A Cheap Programmable Power Supply

A few months ago, someone clued us in on a neat little programmable power supply from the usual Chinese retailers. The DPS5005 is a programmable power supply that takes power from a big AC to DC wall wart and turns it into a tiny bench-top power supply. You can pick one of these things up for about thirty bucks, so if you already have a sufficiently large AC to DC converter you can build a nice 250 Watt power supply on the cheap.

[Johan] picked up one of these tiny programmable power supplies. His overall impression was positive, but like so many cheap products on AliExpress, there wasn’t a whole lot of polish to the interface. Additionally, the DPS5005 lacked the ability to be controlled over a serial port or WiFi.

This programmable power supply is built around an STM32, with the programming pads exposed and labeled on the PCB. The changes [Johan] wanted to make were all in software, leading him to develop OpenDPS, a firmware replacement for the DPS5005. Continue reading “Open Source Firmware For A Cheap Programmable Power Supply”

Ultrasuede Bench Power Supply Got Style

From the look of it sitting on his bench, you’d never guess that [3nz01]’s power supply was actually a couple of el-cheapo modules from eBay, but now we all know the dirty truth.

Re-using or re-purposing an enclosure can be a great way to get a project done faster and get on to the next one. In [3nz01]’s case (tee-hee!), it was an old clock with a broken and annoying buzzer that needed to go. The clock was a nice piece of wood, but that Plexiglas front panel just wasn’t cutting it. That’s why it’s good to have a tailor for a father — a suitable piece of ultrasuede wrapped around the plexi makes the build look swank.

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Extech Power Supply: If it Ain’t Broke, Fix it Anyway

[Wolf] came into possession of an Extech power supply that wasn’t quite in working order. It has been used in battery manufacturing and was fairly corroded. He was able to fix it but found there was an issue with the power supply that wasn’t a defect. By design when you turn off the outputs, the voltmeters read zero. That means you can’t adjust the voltage to a known value without turning on the outputs. Sure, you ought to disconnect things before you adjust, but you can only hope you’ll remember.

At first, he tried to use the existing output control switch, but that really cut power. Instead, he turned to a small microcontroller board usually used for servo control. He added a few nice looking pushbuttons to the front panel. There was plenty of room in the enclosure to mount the controller board and four relays. You can see the final result in the video below.

Continue reading “Extech Power Supply: If it Ain’t Broke, Fix it Anyway”