DC-DC converter, as it sometimes happens. Review of adjustable voltage converters (stabilizers, DC-DC converters) ⇡ General diagram of an ATX power supply
Linear and switching power supplies
Let's start with the basics. The power supply in a computer performs three functions. First, alternating current from the household power supply must be converted to direct current. The second task of the power supply is to reduce the voltage of 110-230 V, which is excessive for computer electronics, to the standard values required by power converters of individual PC components - 12 V, 5 V and 3.3 V (as well as negative voltages, which we will talk about a little later) . Finally, the power supply plays the role of a voltage stabilizer.
There are two main types of power supplies that perform the above functions - linear and switching. The simplest linear power supply is based on a transformer, on which the alternating current voltage is reduced to the required value, and then the current is rectified by a diode bridge.
However, the power supply is also required to stabilize the output voltage, which is caused by both voltage instability in the household network and a voltage drop in response to an increase in current in the load.
To compensate for the voltage drop, in a linear power supply the transformer parameters are calculated to provide excess power. Then, at high current, the required voltage will be observed in the load. However, the increased voltage that will occur without any means of compensation at low current in the payload is also unacceptable. Excess voltage is eliminated by including a non-useful load in the circuit. In the simplest case, this is a resistor or transistor connected through a Zener diode. In a more advanced version, the transistor is controlled by a microcircuit with a comparator. Be that as it may, excess power is simply dissipated as heat, which negatively affects the efficiency of the device.
In the switching power supply circuit, one more variable appears, on which the output voltage depends, in addition to the two already existing: input voltage and load resistance. There is a switch in series with the load (which in the case we are interested in is a transistor), controlled by a microcontroller in pulse width modulation (PWM) mode. The higher the duration of the open states of the transistor in relation to their period (this parameter is called duty cycle, in Russian terminology the inverse value is used - duty cycle), the higher the output voltage. Due to the presence of a switch, a switching power supply is also called Switched-Mode Power Supply (SMPS).
No current flows through a closed transistor, and the resistance of an open transistor is ideally negligible. In reality, an open transistor has resistance and dissipates some of the power as heat. In addition, the transition between transistor states is not perfectly discrete. And yet, the efficiency of a pulsed current source can exceed 90%, while the efficiency of a linear power supply with a stabilizer reaches 50% at best.
Another advantage of switching power supplies is the radical reduction in the size and weight of the transformer compared to linear power supplies of the same power. It is known that the higher the frequency of alternating current in the primary winding of a transformer, the smaller the required core size and the number of winding turns. Therefore, the key transistor in the circuit is placed not after, but before the transformer and, in addition to voltage stabilization, is used to produce high-frequency alternating current (for computer power supplies this is from 30 to 100 kHz and higher, and as a rule - about 60 kHz). A transformer operating at a power supply frequency of 50-60 Hz would be tens of times more massive for the power required by a standard computer.
Linear power supplies today are used mainly in the case of low-power applications, where the relatively complex electronics required for a switching power supply constitute a more sensitive cost item compared to a transformer. These are, for example, 9 V power supplies, which are used for guitar effects pedals, and once for game consoles, etc. But chargers for smartphones are already entirely pulsed - here the costs are justified. Due to the significantly lower amplitude of voltage ripple at the output, linear power supplies are also used in those areas where this quality is in demand.
⇡ General diagram of an ATX power supply
A desktop computer's power supply is a switching power supply, the input of which is supplied with household voltage with parameters of 110/230 V, 50-60 Hz, and the output has a number of DC lines, the main ones of which are rated 12, 5 and 3.3 V In addition, the power supply provides a voltage of -12 V, and sometime also a voltage of -5 V, necessary for the ISA bus. But the latter was at some point excluded from the ATX standard due to the end of support for the ISA itself.
In the simplified diagram of a standard switching power supply presented above, four main stages can be distinguished. In the same order, we consider the components of power supplies in the reviews, namely:
- EMI filter - electromagnetic interference (RFI filter);
- primary circuit - input rectifier (rectifier), key transistors (switcher), creating high-frequency alternating current on the primary winding of the transformer;
- main transformer;
- secondary circuit - current rectifiers from the secondary winding of the transformer (rectifiers), smoothing filters at the output (filtering).
⇡ EMF filter
The filter at the power supply input is used to suppress two types of electromagnetic interference: differential (differential-mode) - when the interference current flows in different directions in the power lines, and common-mode (common-mode) - when the current flows in one direction.
Differential noise is suppressed by capacitor CX (the large yellow film capacitor in the photo above) connected in parallel with the load. Sometimes a choke is additionally attached to each wire, which performs the same function (not on the diagram).
The common mode filter is formed by CY capacitors (blue drop-shaped ceramic capacitors in the photo), connecting the power lines to ground at a common point, etc. a common-mode choke (LF1 in the diagram), the current in the two windings of which flows in the same direction, which creates resistance for common-mode interference.
In cheap models, a minimum set of filter parts is installed; in more expensive ones, the described circuits form repeating (in whole or in part) links. In the past, it was not uncommon to see power supplies without any EMI filter at all. Now this is rather a curious exception, although if you buy a very cheap power supply, you can still run into such a surprise. As a result, not only and not so much the computer itself will suffer, but other equipment connected to the household network - switching power supplies are a powerful source of interference.
In the filter area of a good power supply, you can find several parts that protect the device itself or its owner from damage. There is almost always a simple fuse for short circuit protection (F1 in the diagram). Note that when the fuse trips, the protected object is no longer the power supply. If a short circuit occurs, it means that the key transistors have already broken through, and it is important to at least prevent the electrical wiring from catching fire. If a fuse in the power supply suddenly burns out, then replacing it with a new one is most likely pointless.
Separate protection is provided against short-term surges using a varistor (MOV - Metal Oxide Varistor). But there are no means of protection against prolonged voltage increases in computer power supplies. This function is performed by external stabilizers with their own transformer inside.
The capacitor in the PFC circuit after the rectifier can retain a significant charge after being disconnected from power. To prevent a careless person who sticks his finger into the power connector from receiving an electric shock, a high-value discharge resistor (bleeder resistor) is installed between the wires. In a more sophisticated version - together with a control circuit that prevents charge from leaking when the device is operating.
By the way, the presence of a filter in the PC power supply (and the power supply of a monitor and almost any computer equipment also has one) means that buying a separate “surge filter” instead of a regular extension cord is, in general, pointless. Everything is the same inside him. The only condition in any case is normal three-pin wiring with grounding. Otherwise, the CY capacitors connected to ground simply will not be able to perform their function.
⇡ Input rectifier
After the filter, the alternating current is converted into direct current using a diode bridge - usually in the form of an assembly in a common housing. A separate radiator for cooling the bridge is highly welcome. A bridge assembled from four discrete diodes is an attribute of cheap power supplies. You can also ask what current the bridge is designed for to determine whether it matches the power of the power supply itself. Although, as a rule, there is a good margin for this parameter.
⇡ Active PFC block
In an AC circuit with a linear load (such as an incandescent light bulb or an electric stove), the current flow follows the same sine wave as the voltage. But this is not the case with devices that have an input rectifier, such as switching power supplies. The power supply passes current in short pulses, approximately coinciding in time with the peaks of the voltage sine wave (that is, the maximum instantaneous voltage) when the smoothing capacitor of the rectifier is recharged.
The distorted current signal is decomposed into several harmonic oscillations in the sum of a sinusoid of a given amplitude (the ideal signal that would occur with a linear load).
The power used to perform useful work (which, in fact, is heating the PC components) is indicated in the characteristics of the power supply and is called active. The remaining power generated by harmonic oscillations of the current is called reactive. It does not produce useful work, but heats the wires and creates a load on transformers and other power equipment.
The vector sum of reactive and active power is called apparent power. And the ratio of active power to total power is called power factor - not to be confused with efficiency!
A switching power supply initially has a rather low power factor - about 0.7. For a private consumer, reactive power is not a problem (fortunately, it is not taken into account by electricity meters), unless he uses a UPS. The uninterruptible power supply is responsible for the full power of the load. At the scale of an office or city network, excess reactive power created by switching power supplies already significantly reduces the quality of power supply and causes costs, so it is being actively combated.
In particular, the vast majority of computer power supplies are equipped with active power factor correction (Active PFC) circuits. A unit with an active PFC is easily identified by a single large capacitor and inductor installed after the rectifier. In essence, Active PFC is another pulse converter that maintains a constant charge on the capacitor with a voltage of about 400 V. In this case, current from the supply network is consumed in short pulses, the width of which is selected so that the signal is approximated by a sine wave - which is required to simulate a linear load . To synchronize the current consumption signal with the voltage sinusoid, the PFC controller has special logic.
The active PFC circuit contains one or two key transistors and a powerful diode, which are placed on the same heatsink with the key transistors of the main power supply converter. As a rule, the PWM controller of the main converter key and the Active PFC key are one chip (PWM/PFC Combo).
The power factor of switching power supplies with active PFC reaches 0.95 and higher. In addition, they have one additional advantage - they do not require a 110/230 V mains switch and a corresponding voltage doubler inside the power supply. Most PFC circuits handle voltages from 85 to 265 V. In addition, the sensitivity of the power supply to short-term voltage dips is reduced.
By the way, in addition to active PFC correction, there is also a passive one, which involves installing a high-inductance inductor in series with the load. Its efficiency is low, and you are unlikely to find this in a modern power supply.
⇡ Main converter
The general principle of operation for all pulse power supplies of an isolated topology (with a transformer) is the same: a key transistor (or transistors) creates alternating current on the primary winding of the transformer, and the PWM controller controls the duty cycle of their switching. Specific circuits, however, differ both in the number of key transistors and other elements, and in qualitative characteristics: efficiency, signal shape, noise, etc. But here too much depends on the specific implementation for this to be worth focusing on. For those interested, we provide a set of diagrams and a table that will allow you to identify them in specific devices based on the composition of the parts.
| Transistors | Diodes | Capacitors | Transformer primary legs | |
| Single-Transistor Forward | 1 | 1 | 1 | 4 |
| 2 | 2 | 0 | 2 | |
| 2 | 0 | 2 | 2 | |
| 4 | 0 | 0 | 2 | |
| 2 | 0 | 0 | 3 |
In addition to the listed topologies, in expensive power supplies there are resonant versions of Half Bridge, which are easily identified by an additional large inductor (or two) and a capacitor forming an oscillatory circuit.
|
Single-Transistor Forward |
|
|
|
|
|
|
⇡ Secondary circuit
The secondary circuit is everything that comes after the secondary winding of the transformer. In most modern power supplies, the transformer has two windings: 12 V is removed from one of them, and 5 V from the other. The current is first rectified using an assembly of two Schottky diodes - one or more per bus (on the highest loaded bus - 12 V - in powerful power supplies there are four assemblies). More efficient in terms of efficiency are synchronous rectifiers, which use field-effect transistors instead of diodes. But this is the prerogative of truly advanced and expensive power supplies that claim the 80 PLUS Platinum certificate.
The 3.3V rail is typically driven from the same winding as the 5V rail, only the voltage is stepped down using a saturable inductor (Mag Amp). A special winding on a transformer for a voltage of 3.3 V is an exotic option. Of the negative voltages in the current ATX standard, only -12 V remains, which is removed from the secondary winding under the 12 V bus through separate low-current diodes.
PWM control of the converter key changes the voltage on the primary winding of the transformer, and therefore on all secondary windings at once. At the same time, the computer's current consumption is by no means evenly distributed between the power supply buses. In modern hardware, the most loaded bus is 12-V.
To separately stabilize voltages on different buses, additional measures are required. The classic method involves using a group stabilization choke. Three main buses are passed through its windings, and as a result, if the current increases on one bus, the voltage drops on the others. Let's say the current on the 12 V bus has increased, and in order to prevent a voltage drop, the PWM controller has reduced the duty cycle of the key transistors. As a result, the voltage on the 5 V bus could go beyond the permissible limits, but was suppressed by the group stabilization choke.
The voltage on the 3.3 V bus is additionally regulated by another saturable inductor.
A more advanced version provides separate stabilization of the 5 and 12 V buses due to saturable chokes, but now this design has given way to DC-DC converters in expensive high-quality power supplies. In the latter case, the transformer has a single secondary winding with a voltage of 12 V, and the voltages of 5 V and 3.3 V are obtained thanks to DC-DC converters. This method is most favorable for voltage stability.
Output filter
The final stage on each bus is a filter that smoothes out voltage ripple caused by the key transistors. In addition, the pulsations of the input rectifier, whose frequency is equal to twice the frequency of the supply network, penetrate to one degree or another into the secondary circuit of the power supply.
The ripple filter includes a choke and large capacitors. High-quality power supplies are characterized by a capacitance of at least 2,000 uF, but manufacturers of cheap models have reserves for savings when they install capacitors, for example, of half the nominal value, which inevitably affects the ripple amplitude.
⇡ Standby power +5VSB
A description of the components of the power supply would be incomplete without mentioning the 5 V standby voltage source, which makes the PC sleep mode possible and ensures the operation of all devices that must be turned on at all times. The “duty room” is powered by a separate pulse converter with a low-power transformer. In some power supplies, there is also a third transformer, which is used in the feedback circuit to isolate the PWM controller from the primary circuit of the main converter. In other cases, this function is performed by optocouplers (an LED and a phototransistor in one package).
⇡ Methodology for testing power supplies
One of the main parameters of the power supply is voltage stability, which is reflected in the so-called. cross-load characteristic. KNH is a diagram in which the current or power on the 12 V bus is plotted on one axis, and the total current or power on the 3.3 and 5 V buses is plotted on the other. At the intersection points for different values of both variables, the voltage deviation from the nominal value is determined one tire or another. Accordingly, we publish two different KNHs - for the 12 V bus and for the 5/3.3 V bus.
The color of the dot indicates the percentage of deviation:
- green: ≤ 1%;
- light green: ≤ 2%;
- yellow: ≤ 3%;
- orange: ≤ 4%;
- red: ≤ 5%.
- white: > 5% (not allowed by ATX standard).
To obtain KNH, a custom-made power supply test bench is used, which creates a load by dissipating heat on powerful field-effect transistors.
Another equally important test is determining the ripple amplitude at the power supply output. The ATX standard allows ripple within 120 mV for a 12 V bus and 50 mV for a 5 V bus. A distinction is made between high-frequency ripple (at double the frequency of the main converter switch) and low-frequency (at double the frequency of the supply network).
We measure this parameter using a Hantek DSO-6022BE USB oscilloscope at the maximum load on the power supply specified by the specifications. In the oscillogram below, the green graph corresponds to the 12 V bus, the yellow graph corresponds to 5 V. It can be seen that the ripples are within normal limits, and even with a margin.
For comparison, we present a picture of ripples at the output of the power supply of an old computer. This block wasn't great to begin with, but it certainly hasn't improved over time. Judging by the magnitude of the low-frequency ripple (note that the voltage sweep division is increased to 50 mV to fit the oscillations on the screen), the smoothing capacitor at the input has already become unusable. High-frequency ripple on the 5 V bus is on the verge of permissible 50 mV.
The following test determines the efficiency of the unit at a load from 10 to 100% of rated power (by comparing the output power with the input power measured using a household wattmeter). For comparison, the graph shows the criteria for the various 80 PLUS categories. However, this does not cause much interest these days. The graph shows the results of the top-end Corsair PSU in comparison with the very cheap Antec, and the difference is not that great.
A more pressing issue for the user is the noise from the built-in fan. It is impossible to directly measure it close to the roaring power supply testing stand, so we measure the rotation speed of the impeller with a laser tachometer - also at power from 10 to 100%. The graph below shows that when the load on this power supply is low, the 135mm fan remains at low speed and is hardly audible at all. At maximum load the noise can already be discerned, but the level is still quite acceptable.
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30 Sep 2015 TVN 5WI is a line of low noise DC/DC converters from the company and TRACO Power.Today I will write not only about the product that I tested, but also about how sometimes it happens when you plan one thing, but for some reason it turns out completely different.
In general, if anyone is interested, please see cat.
Recently, a colleague of ksiman posted “halves” of this converter, the same scarf, only without the display device, because in part these reviews complement each other.
In the comments I mentioned that I also plan to review this board. The review wrote that everything did not end very well (or rather, very badly). For me, everything was also not very smooth, although it ended better, but more on that later, but for now I’ll move on to the review of my version of this DC-DC converter.
In general, I saw such a small DC-DC converter and wanted to feel what it was like. I ordered it for review, received it after a while, but somehow I didn’t have time to deal with it and I generally put it aside for now.
After some time, I finally got around to it, took a number of photographs, felt it, and examined it.
It came in a small sealed package. 
It is small in itself, smaller than a matchbox.
The manufacturer claims the following characteristics:
Input voltage: 5V-30V
Output voltage: 0.8V-29V
Output current: 5A maximum (Heatsink required for currents greater than 3A)
Conversion efficiency: 95% (maximum)
Conversion frequency: 300KHz
Output ripple: 50mV (maximum)
Operating temperature: -40℃ to +85℃
Size: 51 x 26.3 x 114 
On the sides there are connectors for connecting to the power supply and to the load.
The assembly is neat, I can’t really say anything bad here. 
On top there are two trimming resistors, one regulates the current, the second, respectively, the voltage.
The current is adjustable in the range of 0.06-5.5 Amperes.
Voltage range 0.82-30 Volts
Also near the trimming resistors there is a red LED indicating the transition to current stabilization mode. 
The reverse side of the board can be said to be “bare”; there is only a shunt in the form of a 50 mOhm resistor.
By the way, I’ll immediately note that in devices of this type, where heat is transferred from the microcircuit to the board, for better heat transfer it is generally customary to make many transitions with metallization between the sides of the board. This, unfortunately, has not been done here. Therefore, installing a radiator from the reverse side is ineffective. 
As I wrote above, the converter consists of two boards. The DC-DC converter is no different from the converter I mentioned above. The difference between these two modifications is that mine had an indication board attached.
Moreover, it is connected through mounting racks.
The left two are the input of the converter board, the right ones, respectively, to the output.
This connection allows you to control the output voltage and measure the current flow.
The design turns out to be very convenient and simple. 
The converter is assembled using the XL4005E1 PWM controller. This is a PWM controller designed for 5 Amps output current and input voltage up to 32 Volts.
Judging by the datasheet, it’s a very good chip, but as practice has shown, it’s very “delicate.”
It is also worth noting the SK86 diode, judging by it has a maximum current of 8 Amps. To be honest, I don’t understand how it can dissipate the power that is released on it at such a current.
But in any case, the manufacturer installed a fairly powerful diode; they often install something worse. 
This photo shows the part responsible for adjusting the current limit and indicating the end of the charge (two small LEDs are visible on the right).
The power supply circuit can be seen in Ksiman’s colleague, for which many thanks to him :) 
There are two indicators at the top.
The top one, blue, displays the output voltage, up to 10 Volts is displayed in 1.23 format, above 10 Volts - 23.4. The last digit displays the symbol - V
The lower indicator, red, displays the output current in 1.23 format, the last digit displays the symbol - A.
On the left there is an RX-TX connector. This was one of the reasons why I ordered this board, I wanted to try connecting it to the computer, but alas, nothing worked out :(
The purpose of the right connector is completely unclear to me. 
The board was assembled, let's say, to a C level, it seems to be normal, but some sloppiness is clearly visible. 
The following are installed on the board:
Microcontroller
Shift register to control the indicator
Presumably the operational amplifier is sgm8592y
Voltage Stabilizer 7130H 
Now here's a small nuance. This is the second board, the first died a heroic death during testing and preparation of the review. I can’t say exactly what she died from, but it looked like this - The input voltage is about 28-29 Volts, a 10 Ohm resistor is attached to the output, I smoothly increase the voltage on the resistor using the trimmer resistor on the board, then there is a small click and the input voltage is at the output , breakdown of the power transistor.
There may be a defect, perhaps some kind of ripple or something else, but I would not recommend raising the input voltage too much, although the datasheet indicates 32 Volts and a maximum of 35 Volts.
It is better to limit it at 25-27 Volts.
After that, I ordered a second board, since quite a lot had already been done in preparation for the review.
When first turned on, the board is configured for an output voltage of about 5 Volts. The current is about 1 Ampere.
In the photo, the board is connected to a 24 Volt power supply from my recent one.
If you unscrew the voltage adjustment trimming resistor to the maximum, then the output voltage at idle is equal to the input. 
There doesn’t seem to be much to describe about the board, so I’ll move on to testing.
The following will take part in testing:
Reviewed board.
at 24 Volts.
Contactless
Electronic
Pen and paper :) 
The testing methodology was as follows:
The heating and ripple of the output voltage were measured at the following set voltages of 5-10-15-20 Volts, at each voltage load currents of 1-2-3 Amperes were set.
First, the characteristics were measured at 5 Volts, under a current of 1-2-3 Amperes, with an interval of 10 minutes, after which the board cooled down to room temperature and the cycle was repeated, but with the next voltage. A total of 12 measurements were obtained.
The dynamic display added problems; I had to take a bunch of pictures in order to then choose one that showed the maximum number of indicator digits. In general, the display has a rather low digit switching frequency, the flickering is a little but noticeable.
First check at idle speed, there is practically no pulsation.
The oscilloscope probe divider is set to 1:1. 
More detailed test results
3. 5 Volt 3 Ampere
4. 10 Volt 1 Ampere 
5. 10 Volt 2 Ampere
6. 10 Volt 3 Ampere 
7. 15 Volt 1 Ampere
8. 15 Volt 2 Ampere 
9. 15 Volt 3 Ampere
10. 20 Volt 1 Ampere 
11. 20 Volt 2 Ampere
12. 20 Volt 3 Ampere 
The entire verification cycle took about 3.5 hours.
Received temperature conditions:
The temperature of the PWM controller, diode, inductor and output capacitor was monitored.
When I tested it, I decided to check for 3 Amps, as it was written on the store page, I decided that I would sleep, I would sleep, there would be a couple of these lying around. But the experiment showed that the converter failed and the mikruha did not go into defense; the maximum temperature reached by the PWM controller was 110.2 degrees. 
A little about the use of the board
In the photo above you can see the factory 24 Volt power supply. But since there was an epic issue with reordering the board, then, as you understand, I started working on this device quite a long time ago, and I didn’t have a factory power supply yet, so I had to do it myself.
And the factory power supply, in my estimation, did not really fit into the case I chose, although it is much easier to use the factory one.
I have already described the power supply unit of my design in one of them, it is the same board, but some elements are installed larger/more powerful. If you're interested, I can post the diagram here with all the changes.
Thoughts out loud, maybe it’s worth getting into the production of construction sets.....:)
I prepared such a “constructor” for assembly :) 
Since initially I was still counting on about 25-28 Volts and 3 Amperes, I made the power supply with a reserve, 90-100 Watts. And since one of the key elements, the size of which directly depends on the power, is a transformer, I chose it with a reserve.
True, the board was not designed for this size, but with some tricks I finally got it in :) 
What came out was such a neat transformer. 
Another problem was that I needed to achieve a minimum thickness in the area of the low-voltage part so that the power supply elements did not interfere with the converter board.
Because of this, some of the elements had to be put down.
The board turned out to be a little ugly, but all the elements correspond to the calculated power, this was more important to me.
The output diode heatsink was an aluminum plate along the long side; for safety, I isolated it in the area where the feedback optocoupler was located.
He's not in this photo yet.
The heatsink of the PWM controller is cut from a special profile (I bought it from a meter, the board is routed for two types of heatsinks) 
The power supply turned out to be much larger in size than the converter board. 
But even here, not everything was simple.
I had some of the elements in stock, like any thrifty radio amateur, but some of the elements had to be purchased.
A PWM controller chip was also included in the shopping list.
The pulse power supply calculation program recommended that I use TOP249. But somehow it coincided that the store where I usually buy was closed and I went to another one, but they didn’t have 249, but there was 250, it’s a little more powerful. I thought it’s no big deal, I’ll buy it.
When I turned on the power supply for the first time, it showed no signs of life at all.
The only thing that was there was a voltage of 5 Volts on the control leg of the PWM controller, it should be there, but the PWM controller did not start.
Since I assembled quite a lot of different power supplies, I knew perfectly well that the rest of the circuit was in perfect order, and even if there were problems in the rest of it, it behaved differently, making attempts to start. But it was quiet here.
After rummaging through my supplies, I found a weaker PWM controller, TOP247, installed it and the power supply started up with half a kick.
It turns out that I bought a fake. If there is someone from Kharkov, then I can tell you where NOT to buy.
Moreover, the fake mikruha has laser markings, while the normal one has paint markings. 
In general, having overcome the next problem, I began further assembly.
I gathered everything I needed into a pile, terminals, variable resistors and handles for them, wires, power switch. 
The voltage adjustment resistor is connected with two wires, the current with three.
Since the above experiment showed that the board does not normally provide even 3 Amperes, I decided to make a limit of 2 Amperes, but I really wanted 3 :(
To do this, I placed a 5.1 KOhm constant resistor parallel to the outer contacts of the variable resistor. The maximum adjustment turned out to be approximately 2.3 Amperes.
I also limited the voltage adjustment range, and in the same way, but set the nominal value to 51KOhm, which turned out to be about 26 Volts.
At the same time, the above operations slightly stretched the adjustment scale and it became more convenient to use, 
Next, I marked and drilled/cut out all the necessary holes for the indicator, variable resistors, terminals, power cable and switch. 
At the last moment I almost forgot to connect the wires to the board. The thing is that I was thinking of gluing the board, so the wires would not be connected later. 
The board, resistors and terminal blocks are installed. Most of the insides are literally right next to each other, but everything fits in :) 
The wires to the power supply are soldered immediately before installation.
If it were a factory power supply, it would be more convenient, there are already terminals there. 
We tie the input wires together with zip ties so that they don’t get into the radiator, we arrange the rest and we can close them. 
That's it, the power supply is almost ready, the dark glass for the indicator is really missing.
In fact, the readings are better read than in the photo. With a flash, you can see the switched-off segments, but without a flash, the indicator starts to glare, so I couldn’t take a better photo, sorry.
I didn’t sign the control, in principle I did everything as logically as possible, the blue indicator is voltage, accordingly it is regulated by a variable with a blue handle, similarly to current.
I displayed an indication of the current limiting mode on the panel, but did not display the two LEDs indicating the charging mode, I don’t see the point in them. 
The current limitation turned out to be 2.23 Amperes, I think that in this mode the board will work without problems.
At first I wanted to attach a heatsink to the board, but then I realized the pointlessness of this idea, since the inductor, which needs to be increased, and the diode with the microcircuit heats up, and heat is poorly transferred to the back side of the board.
By the way, about the choke, theoretically this board with cooling should have produced 30 Volts 5 Amps, that’s 150 Watts. Formally, this is half of my laboratory 300 Watt power supply, but if you go into it and roughly compare the dimensions of the power elements, then the difference, as they say, is obvious. This board, even theoretically, will not be able to produce 5 Amps, unless with a different inductor and at a low output voltage. 
And so the summary:
pros.
Neat production, not great, but quite good.
The converter was tested at currents up to 3 Amps, although at high temperatures.
The accuracy of current and voltage measurements is quite good and did not cause any particular complaints.
Low ripple level, the maximum recorded is about 60mV at an operating frequency of 300KHz.
Compact design.
Minuses.
Large heating at currents of more than 2-2.5 Amps.
You should be careful when exceeding the input voltage or install a protective suppressor at the input.
The choke is wound with a thin wire
My opinion is that it can be operated quite normally at currents up to 2 Amperes. I was somewhat disappointed that I could not figure out the RF/TX signals. The converter can be modified with little effort, the inductor can be rewound with a thicker wire, reducing the number of turns by a factor of 1.5, or replaced with a more powerful one (this is better). Replacing the diode with a more powerful one, or even better, moving it, at least to the back side of the board, will improve the thermal operating conditions.
The declared efficiency of 95% is hardly achievable, but I think that the real one is somewhere nearby, but with a big reservation, under a certain operating mode. At a current of 3 Amps, about 4 Watts of heat were generated on the board (approximately), which gives us very low efficiency at a 5 Volt output. As the output voltage increases, the efficiency gradually increases, although StepDown should not have such a steep dependence.
In general, what can I say, I spent money on spare parts, a lot of time on assembling the power supply board, putting it all together, but as a result I received a power supply with the following characteristics:
Output voltage - 0.85-24 Volts.
Output current - 0.06-2.25 Ampere.
Not much, but it has the right to life, it’s just that the power supply could not have been made so powerful.
I hope that the information I provided was useful.
The product was provided for writing a review by the store. The review was published in accordance with clause 18 of the Site Rules.
One of the most popular devices in the workshop of a novice radio amateur is an adjustable power supply. I have already talked about how to independently assemble an adjustable power supply using the MC34063 chip. But it also has limitations and disadvantages. Firstly, it's power. Secondly, the lack of output voltage indication.
Here I will talk about how to assemble an adjustable power supply of 1.2 - 32 volts and a maximum output current of up to 4 amperes with a minimum of time and effort.
To do this we need two very important elements:
Transformer, with output voltage up to ~25...26 volts. I will tell you further about how to pick it up and where to find it;
Ready-made module of an adjustable DC-DC converter with a built-in voltmeter based on a microcircuit XL4015.
The most common and cheapest modules based on microcircuits XL4015 and LM2956. The cheapest option is a module without a digital voltmeter. For myself, I bought several versions of such DC-DC converters, but most of all I liked the module based on the XL4015 chip with a built-in voltmeter. This is what we will talk about.
This is what he looks like. I bought it on Aliexpress, here is the link. You can choose the one that suits you by price and modification through the search.
Reverse side of the board and side view.
Main characteristics of the module:
Let's not forget that manufacturers like to inflate the characteristics of their products. Judging by the reviews, the most optimal option for using this DC-DC module is to operate with an input voltage of up to 30 volts and a current consumption of up to 2 amperes.
DC-DC module control.
On the printed circuit board of the DC-DC module there are two control buttons and an output voltage regulator - a conventional multi-turn variable resistor.
Short press of the button 1 disables/enables the voltmeter indication. A kind of dimmer. Convenient when powered by battery.
Short press the button 2 you can switch the operating mode of the voltmeter, namely, displaying the input or output voltage on the indicator. When used in conjunction with a battery, you can control the battery voltage and prevent deep discharge.
Calibration of voltmeter readings.
First, use button 2 to select which voltage to display on the voltmeter display (input or output). Then use a multimeter to measure the DC voltage (input or output) at the terminals. If it differs from the voltage displayed by the voltmeter, then we begin calibration.
Press the 2nd button for 3-4 seconds. The display should go dark. Let's release the button. In this case, the readings on the display will appear and begin to blink.
Next, by briefly pressing buttons 1 and 2, we decrease or increase the value of the displayed voltage in steps of 0.1V. If you need to increase the readings, for example, from 12.0V to 12.5V, then press button 2 5 times. If you need to decrease from 12V to 11.5V, then, accordingly, press button 1 5 times.
After the calibration is completed, press button 2 for 5 seconds. In this case, the readings on the voltmeter display will stop blinking - the calibration is completed. You can also do nothing and after 10 seconds the voltmeter will exit the calibration mode.
In order to assemble a power supply, in addition to the DC/DC module itself, we need a transformer, as well as a small circuit - a diode bridge and a filter.
Here is the diagram that we have to assemble.
(The picture is clickable. Click it to open in a new window)
I’ll talk about transformer T1 a little later, but now let’s look at the diode bridge VD1-VD4 and filter C1. I will call this part of the circuit rectifier. Next in the photo are the necessary parts for its assembly.
I drew the layout of future printed tracks on the board with a marker for printed circuit boards. Before this, I made a sketch of the arrangement of elements on the board and routed the connecting conductors. Then, using the template, I marked the drilling locations on the workpiece. I drilled before etching in ferric chloride, since if you drill after etching, nicks may remain around the holes and easily damage the edging around the holes.
Then I dried the workpiece after etching and washed off the protective layer of varnish from the marker with White Spirit. After that, I washed and dried the workpiece again, cleaned the copper tracks with fine sandpaper and tinned all the tracks with solder. This is what happened.
A little about the miscalculations. Since I did everything quickly and on my knees, there were, of course, some “jambs.” Firstly, I made the board double-sided, but it wasn’t necessary. The fact is that the holes are not metallized, and then soldering the same connector into such a double-sided printed circuit board is not an easy task. On one side you can solder the contacts without any problems, but on the other side of the board you can’t. So I got tired of it.
Ready straightener.
Instead of the mains switch, SA1 temporarily soldered a jumper. Installed input and output connectors, as well as a connector for connecting a transformer. I installed the connectors with modularity and ease of use in mind, so that in the future it would be possible to quickly and without soldering connect the rectifier unit with different DC-DC modules.
FU1 used a ready-made fuse with a holder as a fuse. Very comfortably. And the live contacts are covered, and replacing the fuse without soldering is not a problem. In theory, a fuse in any design and type of housing is suitable.
As a diode bridge (VD1 - VD4), I used an RS407 assembly with a maximum forward current of 4 amperes. Analogues of the RS407 diode bridge are KBL10, KBL410. A diode bridge can also be assembled from separate rectifier diodes.
Here it is worth understanding that the adjustable DC-DC module itself is designed for a maximum current of 5 amperes, but it can withstand such a current only if a radiator is installed on the XL4015 chip, and for the SS54 diode on the board, the current is 5A - maximum!
Let’s also not forget that manufacturers tend to overestimate the capabilities of their products and their service life under such loads. Therefore, I decided for myself that such a module can be loaded with current up to 1 - 2 amperes. We are talking about a constant, long-term load, and not periodic (pulse).
In this situation, the diode bridge can be selected for a direct current of 3-4 amperes. This should be plenty to spare. Let me remind you that if you assemble a diode bridge from individual diodes, then each of the diodes included in the bridge must withstand the maximum current consumption. In our case it is 3-4 amperes. Diodes 1N5401 - 1N5408 (3A), KD257A (3A), etc. are quite suitable.
Also for assembly you will need an electrolytic capacitor C1 with a capacity of 470 - 2200 μF. It is better to choose a capacitor for an operating voltage of 63V, since the maximum input voltage of a DC-DC converter can be up to 36V, or even 38...40V. Therefore, it is wiser to install a capacitor at 63V. With reserve and reliability.
Here, again, it is worth understanding that everything depends on what voltage you will have at the input of the DC-DC module. If, for example, you plan to use the module to power a 12-volt LED strip, and the input DC-DC voltage of the module is only 16 volts, then the electrolytic capacitor can be supplied with an operating voltage of 25 volts or more.
I set it to the maximum, since I planned to use this module and the assembled rectifier with different transformers that have different output voltages. Therefore, in order not to solder the capacitor every time, I set it to 63V.
Any network transformer with two windings is suitable as transformer T1. The primary winding (Ⅰ) is network and must be designed for an alternating voltage of 220V, the secondary winding (Ⅱ) must produce a voltage of no more than 25 ~ 26 volts.
If you take a transformer whose output will be more than 26 volts of alternating voltage, then after the rectifier the voltage may already be more than 36 volts. And, as we know, the DC-DC converter module is designed for input voltage up to 36 volts. It is also worth considering the fact that in a 220V household power supply the voltage is sometimes slightly too high. Because of this, even if only briefly, a rather significant voltage “jump” may form at the output of the rectifier, which will exceed the permissible voltage of 38...40 volts for our module.
Approximate calculation of output voltage U out after the diode rectifier and filter on the capacitor:
U out = (U T1 - (V F *2))*1.41.
Alternating voltage on the secondary winding of transformer T1 (Ⅱ) - U T1;
Voltage drop ( Forward Voltage Drop ) on rectifier diodes - V F. Since in a diode bridge the current flows through two diodes in each half-cycle, then V F multiply by 2. For the diode assembly the situation is the same.
So, for RS407 in the datasheet I found the following line: Maximum forward Voltage drop per bridge element at 3.0A peak- 1 Volt. This means that if a direct current of 3 amperes flows through any of the bridge diodes, then 1 volt of voltage will be lost across it ( per bridge element - for each element of the bridge). That is, we take the value V F= 1V and, as in the case of individual diodes, multiply the value V F by two, since in each half-cycle the current flows through two elements of the diode assembly.
In general, in order not to rack your brains, it is useful to know that V F for rectifier diodes it is usually about 0.5 volts. But this is with a small forward current. As it increases, the voltage drop also increases V F at the p-n junction of the diode. As we see, the value V F with a forward current of 3A for diodes of the RS407 assembly it is already 1V.
Since the peak value of the rectified (pulsating) voltage is released on the electrolytic capacitor C1, the final voltage that we get after the diode bridge ( U T1 - (V F*2)) must be multiplied by the square root of 2, namely √2 ~ 1.41 .
So with this simple formula we can determine the output voltage of the filter. Now all that's left to do is find a suitable transformer.
As a transformer I used the TP114-163M power armor transformer.
Unfortunately, I did not find accurate data on it. The output voltage on the secondary winding without load is ~19.4V. The approximate power of this transformer is ~7 W. I counted by .
In addition, I decided to compare the data obtained with the parameters of the series transformers TP114(TP114-1, TP114-2,...,TP114-12). The maximum output power of these transformers is 13.2 W. The most suitable parameters for the transformer TP114-163M turned out to be TP114-12. The voltage on the secondary winding in idle mode is 19.4V, and under load - 16V. Rated load current - 0.82A.
I also had another transformer at my disposal, also of the TP114 series. Here it is.
Judging by the output voltage (~22.3V) and the laconic marking 9M, this is a modification of the transformer TP114-9. The parameters of TP114-9 are as follows: rated voltage - 18V; rated load current - 0.73A.
Based on the first transformer ( TP114-163M) I will be able to make an adjustable power supply of 1.2...24 volts, but this is without load. It is clear that when a load (current consumer) is connected, the voltage at the output of the transformer will drop, and the resulting voltage at the output of the DC-DC converter will also decrease by several volts. Therefore, this point must be taken into account and kept in mind.
Based on the second transformer ( TP114-9) you will now have an adjustable power supply of 1.2...28 volts. It's also load-free.
About the output current. The manufacturer stated that the maximum output current of the DC-DC converter is 5A. Judging by the reviews, maximum 2A. But, as you can see, I managed to find quite low-power transformers. Therefore, I’m unlikely to be able to squeeze out even 2 amperes, although it all depends on the output voltage of the DC-DC module. The smaller it is, the more current you can get.
For any low-power “razor” this power supply will be a great fit. Here is the powering of the “laughing ball” with a voltage of 9V and a current of about 100 mA.
And this is already powering a 12-volt LED strip about 1 meter long.
There is also a lightweight, Lite version of this DC-DC converter, which is also assembled on the XL4015E1 chip.
The only difference is the lack of a built-in voltmeter.
The parameters are similar: input voltage 4...38V, maximum current 5A (recommended no more than 4.5A). It is realistic to use it with an input voltage of up to 30V, 30V or more. Load current no more than 2...2.5A. If you load it more, it heats up noticeably and, naturally, the service life and reliability decrease.