Simple laboratory power supply. Power supply enclosure Front panel of laboratory power supply

The long-term construction has finally come to the end! And now you can see a full-fledged multichannel laboratory power supply.

Laboratory power supply enclosure

The first task was to manufacture the case. The idea of ​​purchasing a plastic case for CEA disappeared quickly due to the high cost for it with such dimensions. Well, the toad is strangling to give more than a thousand for a piece of plastic. Therefore, it was decided to use 6 mm foamed PVC.

We cut PVC to the required dimensions:

We estimate how it will look and mark it up:

On the front side we mark and make holes for display elements, voltage adjustment and terminals.

We glue the body and try on the transformer.

Transformer TSA-70-6, but rewound to fit your needs

On one part, it gives out 25 volts 0.6 A, on the other part bipolar power supply +15 volts 0-15 volts 0.6 A. I don’t remember the winding data, but it’s not difficult to calculate it.

The insides of the laboratory power supply

Maybe someone already understood what parts the power supply was assembled from, who did not understand or does not know - these are already assembled boards of one-polar and bipolar power supplies from previous articles:

The source board is based on KR142EN12 and KR142EN18.

Board of a unipolar source on KR142EN12

See separate articles for the assembly and configuration of these blocks with circuits and printed circuit boards.

We continue to build. Used as DSN-DVM-368. I have already written about them. Miniature and quite working indicators.

First turn on.

Then we plug in everything else. And we get chaos from wires.

The top view shows that another power supply is installed for the digital voltmeter indicators. It did not work out to power it from ready-made power sources, so the indicators have the same minus and minus measurements in general, which will not allow taking the correct readings.

Everything fell into place.

We put things in order a little and cut off the excess.

To make it more convenient to use, I decided to design the front panel. Made it in CDR and laminated it

This completes the assembly and you can use

As a result:

2 independent adjustable channels

Possibility of parallel or serial connection of channels

1 channel bipolar:

15 V per polarity

current strength 0.6 A

2 channel unipolar

Indication: 3-digit LCD displays simultaneously for current and voltage

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When a CNC machine and modern power tools are available, it is not so difficult to make a transparent case from wood and plexiglass for a power supply unit (and other products) with your own hands. But how to get out of the situation if there is no such equipment, but there is a desire to work with these materials.

The following describes the process of making a homemade transparent case for a power supply using only simple and affordable tools. There are also many useful recommendations regarding the processing of plexiglass. You will learn how to cut it, adjust parts to size, drill holes in them, including rectangular ones. One of the simplest ways to connect wood and plexiglass is clearly shown. Additionally, there is information on how else you can bond these materials together.

Tools and materials

To make a homemade transparent case, you will need the following consumables:

• transparent plexiglass with a thickness of about 5 mm;
• wooden board or plywood with a thickness of at least 10 mm;
• countersunk screws - 12 pcs;
• small bolts with nuts - 4 pcs;
• rectangular button for 250 V and at least 2 A;
• sandpaper with grit P100 and P240;
• mineral or synthetic engine oil;
• assembled PCB with mounting holes.

To make a finished product out of all of the above, you should prepare the following tools and devices (only available and cheap ones are specially taken):

• electric drill;
• wood drills with a diameter of 3 mm and 10 mm;
• countersink;
• hacksaw for wood;
• clamp;
• hacksaw for metal with a cloth;
• crosshead screwdriver;
• ruler;
• black marker.

If you have an electric jigsaw, router, screwdriver and sander at your disposal, then all this will significantly speed up the manufacturing process. However, it is quite easy to do without these rather expensive tools. After all, one of the key tasks of the material is to show how to make a transparent case using only budget tools.

Manufacturing of wooden cabinet walls

Let's start with the simplest operation, that is, with the manufacture of body parts from wood, that is, its end walls. For these purposes, you can take either wooden planks with a thickness of at least 10 mm, or plywood of the same size. Even the remnants of some kind of platband or trimming of the lining will do. It is not recommended to use chipboard or OSB, as these materials are not very suitable for the manufacture of small products.
The dimensions of the parts in the example shown are 70x50x10 mm. Naturally, if you make a case for any of your products, then the width and height of the end walls are selected individually. It is advisable to leave only the thickness of the wood unchanged, since in thinner workpieces it will be difficult to manually make the correct holes by hand.
Cutting out such simple parts is cheapest with a regular wood saw. For a more accurate result, it is recommended to use a miter box and a butt saw. In fact, such small blanks can be made even with a hacksaw for metal. Again, if you have an electric jigsaw, the task is only simplified.
Much more important than cutting wood blanks is their adjustment. They must be absolutely the same and, at the same time, have the shape of a rectangular parallelepiped. Without professional carpentry tools, you can solve this problem with just one clamp and sandpaper with a grit of P100. The abrasive is fixed on a flat surface, and the parts are connected to one another and grinded until the edges are completely mated.

Manufacturing of body parts from plexiglass

Working with plexiglass without any CNC machines is a little more difficult than with wood. Although this is a rather malleable material, at first glance, if improperly processed, it constantly melts, bubbles, cracks and scratches. However, it is quite possible to cope with these difficulties, armed with the information presented below.
First of all, we determine the size of the parts. They are selected according to the length and width of the end walls made of wood. First, any two opposite sides are made, then a couple of the remaining ones. If anyone is interested, in the example, the dimensions of the side walls are 140x70 mm, and the upper and lower ones are 140x50 mm.
Now about cutting plexiglass. The cheapest and most reliable way to cut this material is to use a conventional metal hacksaw. You can also cut with a special knife, homemade tools, engravers, electric jigsaws, milling cutters, and so on.
If, nevertheless, it is decided to use a hacksaw for metal, then before doing the work you need to learn just a couple of tricks in order to avoid known problems. Firstly, with such sawing, plexiglass can melt due to friction. Secondly, the markings made with a marker can be difficult to wash off, especially if it is permanent. Thirdly, plexiglass is very easily scratched, which greatly spoils the appearance of the finished product (as in the photographs in the example).
So, let's look at methods for solving the above problems. To prevent plexiglass from melting when cutting with a blade for metal, it must be pre-treated with ordinary engine oil. Moreover, you can lubricate both the blade itself and the cutting line. If you apply oil to plexiglass, then it will be possible to cut it without any problems even with an electric jigsaw, and the material, at the same time, will not melt.
The first thing that comes to mind about removing a permanent marker is regular rubbing alcohol. Yes. It does a great job with marker marks, but there is one nuisance here. The fact is that when alcohol hits the edge of organic glass, it gives noticeable cracks. To avoid such problems, it is better to use a regular felt-tip pen for marking. An even better option would be a nail that can easily scratch the cut line into the plexiglass.
And the last moment. To protect acrylic glass from accidental scratches, it should be sealed with ordinary masking tape before cutting and processing. In the example shown in the photo, this was not done, and the result can be clearly seen. Although all the work was done very carefully. Masking tape will not interfere with sawing, sanding, drilling or assembly. And the problem with marker marks disappears automatically.
After cutting the plexiglass parts, they must be adjusted to size. This can also be done on sandpaper fixed on a flat base. At the same time, the material will also melt, but in this case it is better not to use oil. It is much more efficient to use ordinary water - it will perfectly cool the plexiglass during grinding, preventing it from melting.

Rectangular hole in plexiglass

If everything is more or less clear with round holes, then it is not so easy to make a rectangular socket for the same switch without special tools. There are two ways to accomplish this task. Both are simple.
If there is the same electric jigsaw (or manual), then we simply drill small holes in the corners of the future nest, put a nail file into one of them, and work around the perimeter. Don't forget about lubrication. If there are no jigsaws, then we take a conventional drill, the diameter of which is as close as possible to the width of the seat on the body. We drill one or two holes, and then finalize it to a rectangular shape using a regular cheap file.

In the latter case, the processing will be much faster and easier if the plexiglass is fixed beforehand. It is also worthwhile to first work with a file at an angle of 45 degrees on both sides of the workpiece, and only then align the edge at a right angle.

Assembling the body made of wood and plexiglass

When all the blanks are made, it remains only to collect them into one product. To begin with, let's look at the options for how to attach plexiglass to a tree. In this case, glue is not quite suitable, since its traces will be visible through the transparent material. In the end, all this will not look very good.

The simplest approach is countersunk head screws. If they are distributed symmetrically, then they will not spoil the appearance of the product. To assemble in this way, you will need a drill, a drill with a diameter smaller than the hardware itself, as well as a countersink.

Two adjacent blanks are mated and fixed to each other with a clamp. It is better to use two small ones, since the compression force plays a large role here. The fact is that when the drill passes through the plexiglass into the wood, with weak fixation of the parts, they must be displaced, which is unacceptable. When the holes are ready, we make a seat for the head and screw in the screws. We do the same with all the walls of the case.

It is also worth noting that the use of self-tapping screws is not always the best approach to solving such problems. Such a connection will lose strength after several assemblies and disassembly. Therefore, it should be used only in cases where your device will not be often opened.

If you need a transparent case with the possibility of endless disassembly, then instead of self-tapping screws, use special threaded bushings and countersunk screws. In this case, first the bushings are screwed into the tree, and already screws are screwed into them. Such a connection is absolutely not inferior to self-tapping screws in strength, but in terms of functionality it wins at times.
After the trial assembly of the case, all that remains is to integrate the filling into it. Holes are made in the bottom to fix the printed circuit board, and bolts and nuts are used to fix it. If there are special radio mounting racks with appropriate threads, then it is preferable to use them. The button shown in the example locks itself. Additionally, we provide outlets for wires or holes for connectors, and collect everything according to the diagram. If you wish, then add rubber or plastic feet.
As a result, we get an excellent transparent case for our crafts. Despite its rather fragile appearance, it is quite durable. In addition, plexiglass does not conduct current, therefore the case is safe from this point of view. If you do not like the presence of wood in the product, then you can use thick plexiglass instead. However, unlike wood, you will have to cut threads for screws or bushings in it.

This article is intended for people who can quickly distinguish a transistor from a diode, know what a soldering iron is for and which side to hold it on, and finally came to the understanding that without a laboratory power supply, their life no longer makes sense ...

This scheme was sent to us by a person under the nickname: Loogin.

All images are reduced in size, to view in full size, left-click on the image

Here I will try to give as much detail as possible - to tell you step by step how to do it with minimal costs. Surely everyone has at least one power supply unit lying under their feet after upgrading their home hardware. Of course, you will have to buy something, but these sacrifices will be small and most likely justified by the end result - this is, as a rule, about 22V and 14A ceiling. Personally, I invested $ 10. Of course, if you collect everything from the "zero" position, then you need to be ready to shell out about $ 10-15 more to buy the power supply itself, wires, potentiometers, knobs and other loose products. But, usually - everyone has such rubbish in bulk. There is also a nuance - you have to work a little with your hands, so they should be "no displacement" J, and something like this may work for you:

First, you need by any means to get an unnecessary but serviceable ATX power supply unit with a power> 250W. One of the more popular schemes is Power Master FA-5-2:

I will describe a detailed sequence of actions for this particular scheme, but they are all valid for other options.
So, at the first stage, you need to prepare a BP donor:

1. We remove the diode D29 (you can just raise one leg)
2. Remove jumper J13, find it in the circuit and on the board (you can use wire cutters)
3. The PS ON jumper to ground must be in place.
4. We turn on the PB only for a short time, since the voltage at the inputs will be maximum (about 20-24V) Actually, this is what we want to see ...

Let's not forget about the 16V output electrolytes. They may heat up a little. Considering that they are most likely "swollen", they still have to be sent to the swamp, it's not a pity. Remove the wires, they interfere, and only GND will be used and + 12V will then solder them back.

5. Remove the 3.3 volt part: R32, Q5, R35, R34, IC2, C22, C21:

6. Remove 5V: Schottky assembly HS2, C17, C18, R28, you can also "type choke" L5
7. Remove -12V -5V: D13-D16, D17, C20, R30, C19, R29

8. We change the bad ones: replace C11, C12 (preferably with a large capacity C11 - 1000uF, C12 - 470uF)
9. We change the inappropriate components: C16 (preferably at 3300uF x 35V like mine, well, at least 2200uF x 35V is a must!) And I advise you to replace the resistor R27 with a more powerful one, for example 2W and take 360-560 Ohm resistance.

We look at my board and repeat:

10. We remove everything from our feet TL494 1,2,3 for this we remove the resistors: R49-51 (release 1st leg), R52-54 (... 2nd leg), C26, J11 (... 3rd leg)
11. I do not know why, but R38 was chopped off by someone J I recommend that you chop it off too. It participates in voltage feedback and is parallel to R37. Actually R37 can be cut too.

12. we separate the 15th and 16th legs of the microcircuit from "all the rest": for this we make 3 cuts of the existing tracks and to the 14th leg we restore the connection with a black jumper, as shown in my photo.

13. Now we solder the loop for the regulator board to the points according to the diagram, I used the holes from the soldered resistors, but by the 14th and 15th I had to peel off the varnish and drill the holes, in the photo above.
14. The vein of loop No. 7 (regulator power supply) can be taken from the + 17V TL-ki power supply, in the area of ​​the jumper, more precisely from it J10. Drill a hole in the track, clean the varnish and go there! It is better to drill from the print side.

It was all, as the saying goes: "minimal revision" to save time. If time is not critical, then you can simply bring the circuit to the following state:

I would also advise you to change the high-voltage conduits at the input (C1, C2) They are small in capacity and are probably already pretty dry. 680uF x 200V would normally be there. Plus, it's not bad to alter the L3 group stabilization choke a little, or use 5-volt windings, connecting them in series, or remove everything altogether and wind about 30 turns with a new enamel wire with a total cross section of 3-4mm 2.

To power the fan, you need to "prepare" 12V for it. I got out this way: Where there used to be a field-effect transistor for the formation of 3.3V, you can "settle" a 12-volt KREN-ku (KREN8B or 7812 imported analog). Of course, there is no way to do without cutting tracks and adding wires. In the end, it turned out, in general, even "nothing":

The photo shows how everything coexisted harmoniously in the new quality, even the fan connector fit well and the rewound choke turned out to be quite good.

Now the regulator. To simplify the task with different shunts there, we do this: we buy ready-made ammeter and voltmeter in China, or in the local market (you can probably find them there from dealers). You can buy a combined one. But, we must not forget that their current ceiling is 10A! Therefore, in the regulator circuit, you will have to limit the current limit at this mark. Here I will describe an option for individual devices without current regulation and limited to a maximum of 10A. Regulator circuit:

To adjust the current limit, instead of R7 and R8, put a 10kΩ variable resistor, just like R9. Then it will be possible to use the all-round. Also worth paying attention to is the R5. In this case, its resistance is 5.6kΩ, because our ammeter has a 50mΩ shunt. For other variants R5 = 280 / R shunt. Since we took a voltmeter one of the cheapest, so it needs to be slightly modified so that it can measure voltages from 0V, and not from 4.5V as the manufacturer did. The whole rework is to separate the supply and measurement circuits by removing the diode D1. We solder the wire there - this is the + V power supply. The measured part remained unchanged.

The layout of the regulator board is shown below. The image for the laser-ironing method of manufacturing comes in a separate Regulator.bmp file with a resolution of 300dpi. The archive also contains files for editing in EAGLE. The last off. the version can be downloaded here: www.cadsoftusa.com. There is a lot of information on the Internet about this editor.

Then we fasten the finished board to the ceiling of the case through insulating spacers, for example, cut from a spent chupa-chups stick with a height of 5-6 mm. Well, do not forget to pre-make all the necessary cutouts for measuring and other devices.

Pre-assemble and test under load:

We are just looking at the correspondence of the readings of various Chinese devices. And below with a "normal" load. This is a car main light bulb. As you can see - almost 75W is available. In this case, do not forget to shove an oscilloscope there, and see the ripple of about 50mV. If there are more, then we recall the "large" electrolytes on the high side with a capacity of 220uF and immediately forget after replacing them with normal ones with a capacity of 680uF, for example.

In principle, we can stop at this, but in order to give a more pleasant look to the device, well, so that it does not look 100% homemade, we do the following: we leave our den, go up to the floor above and remove a useless sign from the first door we come across.

As you can see, someone has already been here before us.

In general, we quietly do this dirty business and begin to work with files of different styles and at the same time master AutoCad.

Then we sharpen a piece of a three-quarter pipe on emery and cut out the legs from a fairly soft rubber of the required thickness and superglue the legs.

As a result, we get a fairly decent device:

Several points should be noted. The most important thing is to remember that the GND of the power supply and the output circuit must not be connected., therefore, it is necessary to exclude the connection between the case and the GND of the power supply unit. For convenience, it is advisable to take out the fuse, as in my photo. Well, try to restore as much as possible the missing elements of the input filter, most likely they are not at all in the source.

Here are a couple more options for such devices:

On the left is a 2-storey ATX case with an all-round, and on the right is a heavily altered old AT case from a computer.

With laboratory power supply circuits - now the case. In the process of assembling the power supply unit, an old motherboard with a dual USB connector caught my eye, and I wanted to equip the unit with an output for connecting five-volt gadgets. While the connector is connected directly to the power supply output and before connecting the phone, I first set the voltage to 5 volts. In the future, I plan to install a buck DC-DC converter. The entire inner world of the PSU fit into a box with an outer size of 180 * 140 * 90. The PSU board had to be fixed at an angle, since the inner height of the box was slightly less than the size of the PSU board.

First, I mounted the controls on the front panel, a power cord socket and a radiator with a cooler on the rear panel. The cooler was deployed so that air was blown into the case - now air flows come out of the perforated holes in the case, cooling all the components of the power supply unit.

Another distinguishing feature of this power supply is that a small electrolytic capacitor is installed at the output of the circuit, which will not allow burning the connected LEDs. However, at the output, I decided to add a non-electrolytic capacitor, but not for the purpose of suppressing RF interference, but in order to fix the contact lamellas in one position so that they could not turn and close.