Drop-In Switch Mode Regulators

Perhaps the simplest way to regulate a DC voltage is using a voltage divider and/or an active device like a Zener diode. Besides simplicity, they have the additional advantage of not being particularly noisy, but with a major caveat: they are terribly inefficient. To solve this problem a switching regulator can be used instead, but that generally increases complexity and noise. With careful design, though, a switching regulator can be constructed to almost completely replicate a linear regulator like this drop-in TO3 replacement. (Google Translate from German)

While the replacement regulator was built by [Mr. Floppy], the units are being put to the test in the linked video below by [root42]. The major problem these solve compared to other switching regulators is the suppression of ripple, which is a high-frequency artifact that appears on the DC voltage. Reducing ripple in this situation involved designing low-inductance circuit traces on the PCB as well as implementing a number of EMI filters on both input and output. The final result is an efficient voltage supply for retrocomputers which has a ripple lower than their oscilloscopes can measure without special tools.

[root42] is not only testing these, but the linked video also has him using the modules to repair a Commodore 1541 which originally had the linear TO3 voltage regulators. It’s definitely a non-trivial task to build a switching power supply that meets the requirements of sensitive electronics like these. Switch mode power supplies aren’t new ideas, either, and surprisingly pre-date the first commercially-available transistor although modern ones like these are much less expensive to build.

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Fail Of The Week: A Potentially Lethal Tattoo Removal Laser Power Supply

Caveat emptor is good advice in general, but in the wilds of eBay, being careful with what you buy could be life-saving. To wit, we present [Les Wright]’s teardown and very ginger power-up of an eBay tattoo-removal laser power supply.

Given that [Les] spent all of around $100 on this widowmaker, we’re pretty sure he knew what he was getting himself into. But he likely wasn’t quite prepared for the scale of the sketchiness this thing would exhibit. The deficiencies are almost too many to number, starting with the enclosure, which is not only made completely of plastic but assembled from individual sheets of flat plastic stock that show signs of being glued together by hand. Even the cooling water tank inside the case is pieced together this way, which probably led to the leaks that corroded the PCBs. Another assembly gem is the pair of screws the big energy storage capacitor is jammed under, presumably to hold it in place — because nothing says quality like a BOM that can’t spring for a couple of cable ties. Click through the break to read more and see the video.

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Just How Dodgy Are Cheap USB Chargers Anyway?

Aside from apparently having both the ability to reproduce on their own and simultaneously never being around when you need one, USB chargers seem innocuous enough. The specs are simple: convert mains voltage to 5 volts, and don’t kill anyone while doing it. Both specs are typically met by most designs, but judging by [DiodeGoneWild]’s latest USB charger teardown, the latter only just barely, and with a whole lot of luck.

The sad state of plug-in USB power supplies is one of [DiodeGoneWild]’s pet gripes, and deservedly so. Most USB chargers cram a lot of electronics into a mighty small volume, and are built to a price point, meaning that something has to give in the design. In the case of the two units he tears apart in the video below, it’s pretty clear where the compromises are. Neither unit met the specs on the label in terms of current supplied and voltage regulation, even the apparently more capable quick charger, which is the first to go under the knife. The PCB within holds some alarming surprises, like the minimal physical isolation between the mains part of the circuit and the low-voltage section, but the real treat is the Schottky diode that gets up to 170°C under full load. Safety tip: when you smell plastic burning, throw the thing out.

The second charger didn’t fare any better; although it didn’t overheat, that’s mainly because it shut itself off before it could deliver a fraction of its rated 1 amp output. The PCB construction was shoddy in the extreme, with a squiggly trace standing in for a proper fuse and a fraction of a millimeter separation between primary and secondary traces. The flyback transformer was a treat, too; who doesn’t want to rely on a whisper-thin layer of cheap lacquer to keep mains voltage out of your phone?

All in all, these designs are horrible, and we have to thank [DiodeGoneWild] for the nightmares we’ll have whenever we plug into one of these things from now on. On the other hand, this was a great introduction to switch-mode power supply designs, and what not to do with our own builds. Continue reading “Just How Dodgy Are Cheap USB Chargers Anyway?”

Minimizing Stress On A Coin Cell Battery

When it comes to powering tiny devices for a long time, coin cell batteries are the battery of choice for things like keyfobs, watches, and even some IoT devices. They’re inexpensive and compact and a great choice for very small electricity needs. Their major downside is that they have a relatively high internal resistance, meaning they can’t supply a lot of current for very long without decreasing the lifespan of the battery. This new integrated circuit uses a special DC-DC converter to get over that hurdle and extend the life of a coin cell significantly.

A typical DC-DC converter uses a rapidly switching transistor to regulate the energy flow through an inductor and capacitor, effectively stepping up or stepping down the voltage. Rather than relying on a single converter, this circuit uses a two-stage system. The first is a boost converter to step the voltage from the coin cell up to as much as 11 volts to charge a storage capacitor. The second is a buck converter which steps that voltage down when there is a high current demand. This causes less overall voltage drop on the battery meaning less stress for it and a longer operating life in the device.

There are a few other features of this circuit as well, including an optimizer which watches the behavior of the circuit and learns about the power demands being placed on it. That way, the storage capacitor is only charged up to its maximum capacity if the optimizer determines that much charge is needed. With all of these features a coin cell could last around seven times as long as one using more traditional circuitry. If you really need to get every last bit of energy from a battery, though, you can always use a joule thief.

AC-DC Converter Is Reliable, Safe, And Efficient

When first starting an electronics project, it’s not uncommon to dive right in to getting the core parts of the project working. Breadboarding the project usually involves working with a benchtop power supply of some sort, but when it comes to finalizing the project the actual power supply is often glossed over. It’s not a glamorous part of a project or the part most of us want to be working with, but it’s critical to making sure projects don’t turn up with mysterious issues in the future. We can look to some others’ work to simplify this part of our projects, though, like this power supply from [hesam.moshiri].

The power supply is designed around a switch-mode topology known as a flyback converter. Flyback converters work by storing electrical energy in the magnetic field of a transformer when it is switched on, and then delivering that energy to the circuit when it is switched off. By manipulating the switching frequency and turns ratios of the transformer, the circuit can have an arbitrary output voltage. In this case, it is designed to take 220V AC and convert it to 8V DC. It uses a simplified controller chip to decrease complexity and parts count, maintains galvanic isolation for safety, and is built to be as stable as possible within its 24W power limitation to eliminate any potential issues downstream.

For anyone trying to track down electrical gremlins in a project, it’s not a bad idea to take a long look at the power supply first. Any noise or unwanted behavior here is likely to cause effects especially in projects involving sensors, ADC or DAC, or other low-voltage or sensitive components. The schematic and bill of materials are available for this one as well, so anyone’s next project could use this and even make slight adjustments to change the output voltage if needed. And, if this is your first introduction to switched-mode power supplies, check out this in-depth look at the similar buck converter circuit to better understand what’s going on behind the scenes on these devices.

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Spy Radio Setup Gets A Tiny Power Supply For Field Operations

[Helge Fyske (LA6NCA)] may not be an actual spy — then again, he may be; if he’s good at it, we wouldn’t know — but he has built a couple of neat vacuum tube spy radios in the past. And there’s no better test for such equipment than to haul it out into the field and try to make some contacts. But how do you power such things away from the bench?

To answer that question, skip ahead to the 3:18 mark of the video below, where [Helge] shows off his whole retro rig, including the compact 250-volt power supply he built for his two-tube 80-m Altoids tin spy transceiver. In the shack, [Helge] powers it with a bench power supply of his own design to provide the high anode voltage needed for the tubes, as well as 12 volts for their heaters. Portable operations require a more compact solution, preferably one that can be run off a battery small enough to pack in.

By building his power supply in a tin, [Helge] keeps to his compact build philosophy. But the circuit is all solid state, which is an interesting departure for him. The switch-mode supply uses a 4047 astable multivibrator chip as a 50-kHz oscillator, which switches back and forth between a pair of MOSFETs to drive a transformer. This steps up the 12-volt input to 280 volts AC, which is then rectified, filtered, and regulated to 250 volts DC.

To round out his spy rig, [Helge] also designed a tiny Morse key, which appears to be 3D printed and fits in its own tin, and a compact dipole antenna. Despite picking what appears to be a challenging location — the bottom of a steep-sided fjord — [Helge] was easily able to make contacts over a distance of 400 km. His noise floor was remarkably low, a testament to the solid design of his power supply. Including the sealed lead acid battery, the whole kit is compact and efficient, and it’s a nice example of what vacuum tubes and solid state can accomplish together.

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USB Power Isolator Keeps Smoke In

Anyone who’s done an electronics project knows the most important part of any good design is making sure to keep the magic smoke inside of all of the components. There are a lot of ways to make sure the smoke stays in there, but one of the most important is making sure that the power supply is isolated. If you’re using a USB port on a computer as your power source, though, it can be a little more complicated to isolate it from the computer.

The power supply is based around a small transformer with a set of diodes to act as a rectifier. Of course, while a transformer is great at isolating power supplies, it isn’t much good at DC. That’s what the ATtiny microcontroller is for. It handles the high-speed switching of the MOSFETs, which drive the transformer and handle some power regulation. There are two different power supplies created as part of this project as well — the first generates +5V much like a normal USB plug would have, and the other creates both +5V and -5V. It will be important not to mix these two up, or that tricky blue smoke may escape.

The project page goes into extensive details on the operation of the device, so if electrical theory is of interest, this will definitely be worth a read. Isolating a valuable computer from a prototype circuit is certainly important, but if you’re looking for a way to isolate a complete USB connection, look at this build which includes isolation for a USB to FTDI adapter.