Project FAQ

I’ve never built anything electronic before. Can I build the YJPS?

This is not a good first electronics project. Build something else to get some basic skills before proceding to this project. Power supplies are not as forgiving of mistakes as other circuits, and the YJPS is uncommonly complex for a linear power supply. You will need well-developed soldering (and perhaps troubleshooting) skills to build it.

I’ve built other things before. Can I build the YJPS?

The hardest part of assembling the YJPS is that there is one SO-8 surface-mount part. If you’ve never done surface-mount soldering before, it’s really not that hard at this scale. You don’t even need special equipment to do it. Watch Tangent Tutorial 3: Surface Mount Soldering Techniques to see how easy it is.

Because this supply has such a wide bandwidth, it can be tricky to troubleshoot. If it doesn’t work the first time you turn it on, you will need a good understanding of the circuit, and possibly access to an oscilloscope to troubleshoot it. The most likely part to cause difficulty is the SO-8 op-amp, so you may also need surface-mount desoldering skills.

Is the YJPS dangerous?

Absolutely. You will be exposed to AC line power wires while building it, and the filter capacitors store a lot of energy. You must exercise due caution while building it to avoid electrocution. Wall power can kill!

This is a do-it-yourself project. That means that all benefits are yours, and all of the responsibility is yours.

How much current can a YJPS put out?

Worst case with the stock design puts the YJPS into current-limiting mode with a load of about 330 mA. Since this depends on the gain of the pass transistor and real transistors almost always exceed this spec comfortably, the real limit is likely to be significantly higher, but it’s impossible to say where your supply will hit its limit without measuring your Q2’s hFE. See the R6 discussion for more details, including ideas on increasing this current limit.

You can push the design past these limits with component tweaking, but I really have no idea how far you can expect to push it. Wild guess? I’d be surprised to see a YJPS exceed 1.0 A.

If you were hoping to get amperes out of this power supply, best look elsewhere. The YJPS is specifically designed to achieve excellent low-noise performance in low-power circuits. It would be possible to design something around the same principles for high-current use, but it would necessarily be a different beast.

What voltage range can I get out of a YJPS?

With only resistor changes, the YJPS can range from about 7 V to 30 V. With IC changes, you might push the low end of the range as far down as 3 V or so, and the high end to 48 V or so.

Beware that IC changes mean likely degradation of the YJPS’s excellent specs, and should only be done by someone with a proper test bench setup, so as to verify that the new design still works as well as it ought. If the extent of your test equipment is a cheap DMM, do yourself a favor and stick with the stock design.

If you have to get outside the “resistor changes only” range, the best place to start investigating is the U2 and D4 part selection guides.

If your need is for a low output voltage, bear in mind that the YJPS is a “high drop-out” design, very much opposing the popular trend toward ever lower drop-out voltages. If you manage to achieve 2.5 V regulated, you’ll have done so by pushing efficiency below one-third. (That is, at least two-thirds of the power going into the supply will be turned into heat!) The YJPS’s efficiency gets better at higher voltages, though even at its best it will never win any “green” awards. Beware also that low-voltage applications tend to be high-current applications, which also fights against the YJPS design principles; see the previous FAQ item.

The upper 30 V limit comes from the design limit for the recommended error amplifier IC. The schematic values intentionally stop a volt shy of this to account for component tolerances. Rather than push this chip past its design limits, if you have to get past 30 V, you’ll want to look at changing this IC out for something with a higher voltage tolerance. Based solely on datasheet surfing, I think the OPA604 might be a good choice, but I must stress that I haven’t tried it and don’t know of anyone who has. If it does work, it should let you raise the upper limit to 48 V; I can’t see pushing the YJPS much farther without major design changes. Don’t forget to look at capacitor voltage tolerances and such if you go down this path.

There’s an awful lot of stuff to read here. Do I have to read it all?

The more you read, the more likely you’ll build the power supply correctly. Anything dealing with line voltage is dangerous, so it is a very bad idea to try and skip steps with this project.

How much do all the parts cost?

Very roughly, $100 US. This includes the circuit board, the Hammond enclosure, and all of the optional parts. It doesn’t count shipping.

What’s the best way to save money on parts?

The line filter can be left out without a huge penalty in performance. Also, you may find that putting the YJPS and the circuit it’s powering into a single large case is less expensive than putting each into their own smaller case.

If that doesn’t save enough money, I don’t recommend any further attempts to reduce the cost of this design. Anything further is likely to remove its value over inherently less expensive designs, like the TREAD.

Can I use parts not mentioned in your parts list?

The parts table doesn’t list everything that will work. It’s more a list of examples than anything. Before buying a part not mentioned on these pages, do a search in the DIY archives on Headwize and Head-Fi; someone else may have used the part and reported on it, or there may be advice there saying why a given part is a bad choice for the YJPS. If you can’t find any information there on the part and you aren’t savvy enough to be able to pick parts on your own, please ask on the forums about it. Often a part that looks like it will work, won’t.

I don’t want to chase down all these parts. Can I buy a kit?

Sorry, I have no plan to offer a kit for this project.

I have a question. Who do I ask?

First, look through this documentation. It improves regularly with reader feedback, so the answer is often here if you look carefully enough.

If you can’t find it here, do a search in the Headwize and Head-Fi DIY forum archives. Asking a question that’s been answered before (sometimes many times before) is a waste of the other forum members’ time and yours. If the answer is in the archives, it’s quicker to search the archives than to post the question and wait for people to answer.

If the answer is not in the archives, go ahead and post the question to the forum. It’s better to post publicly than ask people via email or private messaging because you get more answers and the answers are archived for future builders to find.

This space intentionally left blank. :)