A DIY 5V-3V Switching Converter In The Space Of A TO-220 Package | Hackaday

We are fools for small projects. Put anything into a small enough package, and you may get our attention. Make these things small and useful, for example

, This excites me. It is a switch-mode power supply that takes up the same space as a traditional linear regulator.

It is true that the heavy work of [Kevin Hubbard]'s small step-down converter is done by the PAM2305 DC-DC step-down converter chip, which requires only a few supporting components. But the engineering staff [Kevin] put in it and squeezed everything onto the 9mm PCB waste board on the side, which is impressive. The largest passive component on the board is the inductor in 0805. Everything else is in 0603, so if you decide to use SMD welding technology, you can test it. Check the video after the break to understand the speed of the manual welding process.

The total bill of materials includes

With only one or two bucks running, the end result is that the power supply has a stable 750mA output that can handle a 1-A surge in 5 seconds. We want to know if there is a small radiator tab that might not help? With some black epoxy potting agent, at least TO-220 can look more perfect.

[Kevin]’s Black Mesa Labs has a history of developing interesting projects,

to

. We look forward to everything that follows-assuming we can see it.

Do you need a small DC/DC 3W switch to reduce 5V to 3V in the 7805 TO-220 pin? Or maybe just want to learn surface mount solder 0603 components. Check out this $3 OSH project from Black Mesa Labs. $ 0.60 PCBs from

, BOM from $2

.

-Kevin Hubbard (@bml_khubbard)

Man, I still feel weird when people say 0603 parts are difficult to weld... Then, I remember I manually installed some smaller components to make a living! Great little project to love these things: D

Well, if you have hand-eye coordination, they are actually not difficult. I occasionally solder (despite EE), but when I solder, 0603 is not that difficult. 0402s is the real tongue.

Most of our recent board of directors are 0201.

But hope you don’t have to solder by hand. I think 0603 is quite easy, 0402 is feasible, but it is best to observe under a good microscope, and 0201 is almost invisible on the finished PCB. I can solder them under the microscope with good tools.

The real question is whether there is a solder mask. Of course, hands must be firm, eyesight must be good, and optical gain must be appropriate.

If there is no solder mask, 0603 will be close to the trace width of most homemade PCBs, and the solder will flow around and the joint will become ugly.

I don't like 0402, but mainly because many are not even marked.

Sharp tweezers help a lot.

With this information, the IC can be changed to an IC with different input and output restrictions. Looking at Digikey, the TSOT-23-5 package suitable for this product has a maximum input voltage of 5.5v and a maximum output voltage of 5v.

Without changing the small board, there is no 9v battery to 5v Arduino battery, but it is still very useful.

If there is enough interest, I will study the changes in a wide voltage range. I am watching this part

. My requirement is that there is no external diode and no small 0805 chip inductors (2.2uH-4.7uH). This Rohm BD9C301FJ meets these two requirements and has a wide input range from 5V to 18V and an output range from 1V to 12V. The surface looks good. The price of the SOIC8 package is $1.70.

+1

almost finished. I want to add another resistor and possibly a ground ring at the top. View pictures here:

This is a 3A link with a wide input and output voltage range. It has not been established, but those who are interested can use it as soon as possible.

Why is it so cheap to get a CUI V7803W up to 72V? Or can the cheaper Murata OKI withstand voltages up to 35V? This is a good project worth learning, but for the actual circuit structure, there are already excellent dcdc converters that can replace 220-size linear devices...

Price and size are two outstanding advantages. CUI is a very bulky thing-if you are lucky, it can be installed at 780x (plus it only works with 500mA, which will cost you $10 in the first quarter). Murata OKI-78SR-3.3/1.5-W36-C is more compact and cheaper than CUI at only $4.30, but both components suffer a significant voltage drop – CUI is 9-72V in, and Murata is 7-36 . The CUI part is very useful for using a 9V battery as an input (or it will definitely be useful after the battery is exhausted), if you want to step down the 5V power supply to 3V3, then flattening *neither applies* (for example, because you There is already a 5V rail, but it needs a little 3V3 love).

If you are designing a product for production, the switch mode circuit will definitely become part of the PCB design, rather than being implemented as a replacement for TO220. However, when prototyping the design, it is very convenient to experiment with the power supply as a plug-in module, so if these are the parts you want to use in PCB integrated switch mode, why not use it for the prototype power supply?

So, what is the white paper used for welding?

"It happened too fast, officer, I'm not sure what happened!"

The white paper is actually the tape that holds the SMD components.

Thank you!

In order to get more power, you need a larger inductor, a larger heat sink will not help.

correct. But please also note that the inductor must have a very low DCR to get good efficiency. Otherwise, for this voltage range and taking into account the noise problem, it is impossible to discern the advantage over a decent LDO linear regulator.

What is the point of this interesting little project? If you need to be small, I will choose one of the complete modules that can provide the same output power in a miniature package. For example, using the TPS82150 in a 3.0x 2.8×1.5mm package, 3V to 17V input range and 1A continuous output current.

As for other DCDC converters in the TO220 package, there are already a large number of manufacturers to choose from, and a large number of manufacturers have poured into the market. Therefore, if you do not have very special requirements, you can perform some tests on the ready-made products. (If you only need one item, or only a few items, please remember to request samples;)

I have been using these, ages from 7 to 36 volts input 3.3 out.

This is a $0.50 test board to evaluate the switcher solution for my Spartan7 FPGA design (

). The final design is a 4-layer $60 fab, so I want to make sure that the switcher design is reasonable and not a risky project for FPGA design. Afterwards, I just thought that this is an interesting OSH gadget kit project for people who want to solder their own power supply for $2 (compared to $5 for off-the-shelf equipment).

Okay, that makes sense. But why would you pay $5 for a ready-made product? Take CUI VXO7803-500 as an example. 2.4 $ If you order individually from Mouser, you only need some input and output caps on the target board (which should be placed here anyway), plus a few cents.

The price of VXO7803-500 is really great. For my FPGA design, I stepped down 5V to 1V, and I cannot use this through-hole design. My TO-220 design is just a test board for making interesting DIY kits. The only advantage over off-the-shelf products is that the output voltage can be hard selected. 3V is just a common example.

I use TI TPS62160 switch mode IC for my design. It is suitable for voltages up to 17Vin, and can be programmed for various output voltages, 1A power, high switching frequency (using feedback resistors), and run to Vin = Vout. It has other functions such as EN and power good, which are very useful in sequential power configuration. Changing the value of one of the resistors in the BOM, I have 3V3 or 5V switching mode (or any of the many other voltages I don't use frequently).

At the beginning of this year, I laid out and manufactured many such devices in a TO220 PCB with a size of 8.24 x 12.53mm. The cost of each set of 3 PCBs is only $0.75 (in the PCB-other components are more). It is just for the tickets for the breadboard, or inserting the tickets in the slots that require linreg in other designs.

TI parts are certainly not the cheapest option, but I have them and all other support components (including wirewound SMD inductors) on hand. You stick to what you know and trust.

I neglected to mention that TI has some fixed output changes on this IC (3V3 and 5V), which slightly reduces the number of external parts. However, considering the cost of the IC, I prefer to use a pair of resistors to adjust a bunch of things (and I chose the resistor value so that one of them is 3V3 and 3V swamp standard 100K). 5V implementation).

TPS62150 and TP62160 are very similar parts, not typos.

I understand that something is designed and built for entertainment or education, but these versions have been available for many years and cost a lot of money.

Yes – Digikey’s fixed 3.3V drive is particularly good, only $4

. However, I cannot use the through-hole solution in the FPGA board design, so I designed my own single-sided surface mount only layout. The BML DC/DC "tool kit" is suitable for the DIY crowd and used as an education platform. After choosing the interesting 0603 welding, choose the resistance values ​​of R1 and R2 and get any voltage between 1.0V and 5.0V.

The speed-up capacitor in the feedback network should bypass the high resistance in the voltage divider-not the bottom resistance. In the reference circuit, a capacitor is placed here to increase the gain above a certain frequency. In the current configuration, the feedback circuit attenuates high frequency components.

You are right. The 100pF capacitor cover is incorrectly placed on the PCB layout. When it should be connected to GND, connect it to Vout. Gerbers will update within 24 hours and upload new shared projects to OSH-Park. Thank you.

A 100pF capacitor is fixed. New shared items are available here

I am a little wary of the EMI compliance of this kind of thing, and did not even say that off-the-shelf parts can do the same thing for less money and have been EMI certified.

Then there is the demand of people, who keep inventing some axles, they named the wheels as hubs, which may be a good thing for many people, but in this case, the only "performance" is to compress the parts into a small On the parts. board.

For most of us, this low fruit and the taste that might be poisoned by EMI seems tasteless, but it looks juicy enough that [Dan] picked it here and refluxed it. ...That's great!

I have been using China's small pressure reduction board for some time. They can be adjusted by a small but easily adjustable adjustment tank. They have a very wide input and output range. They have an efficiency in the range of 90% at 5v to 3.3v and have a rated current of at least 1 ampere. Oh, they removed 10 of them for $10,

Before I got them, I thought about replacing these potentiometers with fixed resistors, but now after using them for some things, they are actually very good. If I were to talk about a car project or other items that were subject to strong vibrations, I might consider changing the pot, but I have not felt the need to do so.

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