DC boost circuits. How pulse voltage converters work (27 schemes). Pulse width modulation - PWM

Simple circuits of pulsed-DC voltage converters for powering amateur radio devices

Good afternoon, dear radio amateurs!
Today on the website “ “we will look at several simple schemes, one might even say simple, DC-DC pulse voltage converters(converters of DC voltage of one value to DC voltage of another value)

What are the benefits of pulse converters? Firstly, they have high efficiency, and secondly, they can operate at an input voltage lower than the output voltage.
Pulse converters are divided into groups:
– step-down, step-up, inverting;
– stabilized, unstabilized;
– galvanically isolated, non-insulated;
– with a narrow and wide range of input voltages.
To make homemade pulse converters, it is best to use specialized integrated circuits - they are easier to assemble and not capricious when setting up.

First scheme.
Unstabilized transistor converter:
This converter operates at a frequency of 50 kHz, galvanic isolation is provided by transformer T1, which is wound on a K10x6x4.5 ring made of 2000NM ferrite and contains: primary winding - 2x10 turns, secondary winding - 2x70 turns of PEV-0.2 wire. Transistors can be replaced with KT501B. Almost no current is consumed from the battery when there is no load.

Second scheme.

Transformer T1 is wound on a ferrite ring with a diameter of 7 mm, and contains two windings of 25 turns of wire PEV = 0.3.

Third scheme.
:

Push-pull unstabilized converter based on a multivibrator (VT1 and VT2) and a power amplifier (VT3 and VT4). The output voltage is selected by the number of turns of the secondary winding of the pulse transformer T1.

Fourth scheme.
Converter on a specialized chip:
Stabilizing type converter on a specialized microcircuit from MAXIM. Generation frequency 40...50 kHz, storage element – ​​inductor L1.

Fifth scheme.
Unstabilized two-stage voltage multiplier:

You can use one of the two chips separately, for example the second one, to multiply the voltage from two batteries.

Sixth scheme.
Pulse boost stabilizer on a MAXIM chip:
Typical circuit for connecting a pulse boost stabilizer on a MAXIM microcircuit. Operation is maintained at an input voltage of 1.1 volts. Efficiency – 94%, load current – ​​up to 200 mA.

Seventh scheme.
Two voltages from one power supply :
Allows you to obtain two different stabilized voltages with an efficiency of 50...60% and a load current of up to 150 mA in each channel. Capacitors C2 and C3 are energy storage devices.

Eighth scheme.
Pulse boost stabilizer on chip-2 from MAXIM:
Typical circuit diagram for connecting a specialized microcircuit from MAXIM. It remains operational at an input voltage of 0.91 volts, has a small-sized SMD housing and provides a load current of up to 150 mA with an efficiency of 90%.

Ninth scheme.
Pulse step-down stabilizer on a TEXAS chip:

A typical circuit for connecting a pulsed step-down stabilizer on a widely available TEXAS microcircuit. Resistor R3 regulates the output voltage within +2.8…+5 volts. Resistor R1 sets the short circuit current, which is calculated by the formula:
Ikz(A)= 0.5/R1(Ohm)

Tenth scheme.
Integrated voltage inverter on a chip from MAXIM:
Integrated voltage inverter, efficiency – 98%.

Eleventh scheme.
Two isolated converters on microcircuits from YCL Elektronics:
Two isolated voltage converters DA1 and DA2, connected in a “non-isolated” circuit with a common ground.

Input voltages up to 61 V, output voltages from 0.6 V, output currents up to 4 A, the ability to externally synchronize and adjust the frequency, as well as adjust the limiting current, adjust the soft start time, comprehensive load protection, a wide operating temperature range - all these features of modern sources power supplies are achievable using the new line of DC/DC converters produced by .

Currently, the range of switching regulator microcircuits produced by STMicro (Figure 1) allows you to create power supplies (PS) with input voltages up to 61 V and output currents up to 4 A.

The task of voltage conversion is not always easy. Each specific device has its own requirements for the voltage regulator. Sometimes price (consumer electronics), size (portable electronics), efficiency (battery-powered devices), or even the speed of product development play a major role. These requirements often contradict each other. For this reason, there is no ideal and universal voltage converter.

Currently, several types of converters are used: linear (voltage stabilizers), pulsed DC/DC converters, charge transfer circuits, and even power supplies based on galvanic insulators.

However, the most common are linear voltage regulators and step-down switching DC/DC converters. The main difference in the functioning of these schemes is evident from the name. In the first case, the power switch operates in linear mode, in the second - in key mode. The main advantages, disadvantages and applications of these schemes are given below.

Features of the linear voltage regulator

The operating principle of a linear voltage regulator is well known. The classic integrated stabilizer μA723 was developed back in 1967 by R. Widlar. Despite the fact that electronics have come a long way since then, the operating principles have remained virtually unchanged.

A standard linear voltage regulator circuit consists of a number of basic elements (Figure 2): power transistor VT1, a reference voltage source (VS), and a compensation feedback circuit on an operational amplifier (OPA). Modern regulators may contain additional functional blocks: protection circuits (from overheating, from overcurrent), power management circuits, etc.

The operating principle of such stabilizers is quite simple. The feedback circuit on the op-amp compares the value of the reference voltage with the voltage of the output divider R1/R2. A mismatch is formed at the op-amp output, which determines the gate-source voltage of power transistor VT1. The transistor operates in linear mode: the higher the voltage at the output of the op-amp, the lower the gate-source voltage, and the greater the resistance of VT1.

This circuit allows you to compensate for all changes in input voltage. Indeed, suppose that the input voltage Uin has increased. This will cause the following chain of changes: Uin increased → Uout will increase → the voltage on the divider R1/R2 will increase → the output voltage of the op-amp will increase → the gate-source voltage will decrease → the resistance VT1 will increase → Uout will decrease.

As a result, when the input voltage changes, the output voltage changes slightly.

When the output voltage decreases, reverse changes in voltage values ​​occur.

Features of operation of a step-down DC/DC converter

A simplified circuit of a classic step-down DC/DC converter (type I converter, buck-converter, step-down converter) consists of several main elements (Figure 3): power transistor VT1, control circuit (CS), filter (Lph-Cph), reverse diode VD1.

Unlike the linear regulator circuit, transistor VT1 operates in switch mode.

The operating cycle of the circuit consists of two phases: the pump phase and the discharge phase (Figures 4...5).

In the pumping phase, transistor VT1 is open and current flows through it (Figure 4). Energy is stored in the coil Lf and capacitor Cf.

During the discharge phase, the transistor is closed, no current flows through it. The Lf coil acts as a current source. VD1 is a diode that is necessary for reverse current to flow.

In both phases, a voltage equal to the voltage on the capacitor Sph is applied to the load.

The above circuit provides regulation of the output voltage when the pulse duration changes:

Uout = Uin × (ti/T)

If the inductance value is small, the discharge current through the inductance has time to reach zero. This mode is called the intermittent current mode. It is characterized by an increase in current and voltage ripple on the capacitor, which leads to a deterioration in the quality of the output voltage and an increase in circuit noise. For this reason, the intermittent current mode is rarely used.

There is a type of converter circuit in which the “inefficient” diode VD1 is replaced with a transistor. This transistor opens in antiphase with the main transistor VT1. Such a converter is called synchronous and has greater efficiency.

Advantages and disadvantages of voltage conversion circuits

If one of the above schemes had absolute superiority, then the second would be safely forgotten. However, this does not happen. This means that both schemes have advantages and disadvantages. Analysis of schemes should be carried out according to a wide range of criteria (Table 1).

Table 1. Advantages and disadvantages of voltage regulator circuits

Electrical characteristics. For any converter, the main characteristics are efficiency, load current, input and output voltage range.

The efficiency value for linear regulators is low and is inversely proportional to the input voltage (Figure 6). This is due to the fact that all the “extra” voltage drops across the transistor operating in linear mode. The transistor's power is released as heat. Low efficiency leads to the fact that the range of input voltages and output currents of the linear regulator is relatively small: up to 30 V and up to 1 A.

The efficiency of a switching regulator is much higher and less dependent on the input voltage. At the same time, it is not uncommon for input voltages of more than 60 V and load currents of more than 1 A.

If a synchronous converter circuit is used, in which the inefficient freewheeling diode is replaced by a transistor, then the efficiency will be even higher.

Accuracy and stability of output voltage. Linear stabilizers can have extremely high accuracy and stability of parameters (fractions of a percent). The dependence of the output voltage on changes in the input voltage and on the load current does not exceed a few percent.

According to the principle of operation, a pulse regulator initially has the same sources of error as a linear regulator. In addition, the deviation of the output voltage can be significantly affected by the amount of current flowing.

Noise characteristics. The linear regulator has a moderate noise response. There are low-noise precision regulators used in high-precision measuring technology.

The switching stabilizer itself is a powerful source of interference, since the power transistor operates in switch mode. Generated noise is divided into conducted (transmitted through power lines) and inductive (transmitted through non-conducting media).

Conducted interference is eliminated using low-pass filters. The higher the operating frequency of the converter, the easier it is to get rid of interference. In measuring circuits, a switching regulator is often used in conjunction with a linear stabilizer. In this case, the level of interference is significantly reduced.

It is much more difficult to get rid of the harmful effects of inductive interference. This noise originates in the inductor and is transmitted through air and non-conducting media. To eliminate them, shielded inductors and coils on a toroidal core are used. When laying out the board, they use a continuous fill of earth with a polygon and/or even select a separate layer of earth in multilayer boards. In addition, the pulse converter itself is as far away from the measuring circuits as possible.

Performance characteristics. From the point of view of simplicity of circuit implementation and printed circuit board layout, linear regulators are extremely simple. In addition to the integrated stabilizer itself, only a couple of capacitors are required.

A switching converter will require at least an external L-C filter. In some cases, an external power transistor and an external freewheeling diode are required. This leads to the need for calculations and modeling, and the topology of the printed circuit board becomes significantly more complicated. Additional complexity of the board occurs due to EMC requirements.

Price. Obviously, due to the large number of external components, a pulse converter will have a high cost.

As a conclusion, the advantageous areas of application of both types of converters can be identified:

• Linear regulators can be used in low power, low voltage circuits with high accuracy, stability and low noise requirements. An example would be measurement and precision circuits. In addition, the small size and low cost of the final solution can be ideal for portable electronics and low-cost devices.
• Switching regulators are ideal for high-power low- and high-voltage circuits in automotive, industrial and consumer electronics. High efficiency often makes the use of DC/DC no alternative for portable and battery-powered devices.

Sometimes it becomes necessary to use linear regulators at high input voltages. In such cases, you can use stabilizers produced by STMicroelectronics, which have operating voltages of more than 18 V (Table 2).

Table 2. STMicroelectronics Linear Regulators with High Input Voltage

If a decision is made to build a pulsed power supply, then a suitable converter chip should be selected. The choice is made taking into account a number of basic parameters.

Main characteristics of step-down pulse DC/DC converters

Let us list the main parameters of pulse converters.

Input voltage range (V). Unfortunately, there is always a limitation not only on the maximum, but also on the minimum input voltage. The value of these parameters is always selected with some margin.

Output voltage range (V). Due to restrictions on the minimum and maximum pulse duration, the range of output voltage values ​​is limited.

Maximum output current (A). This parameter is limited by a number of factors: the maximum permissible power dissipation, the final value of the resistance of the power switches, etc.

Converter operating frequency (kHz). The higher the conversion frequency, the easier it is to filter the output voltage. This makes it possible to combat interference and reduce the values ​​of the external L-C filter elements, which leads to an increase in output currents and a reduction in size. However, an increase in the conversion frequency increases switching losses of power switches and increases the inductive component of interference, which is clearly undesirable.

Efficiency (%) is an integral indicator of efficiency and is given in the form of graphs for various voltages and currents.

Other parameters (channel resistance of integrated power switches (mOhm), self-current consumption (µA), thermal resistance of the case, etc.) are less important, but they should also be taken into account.

The new converters from STMicroelectronics have high input voltage and efficiency, and their parameters can be calculated using the free eDesignSuite software.

Line of pulsed DC/DC from ST Microelectronics

STMicroelectronics' DC/DC portfolio is constantly expanding. New converter microcircuits have an extended input voltage range up to 61 V ( / / ), high output currents, output voltages from 0.6 V ( / / ) (Table 3).

Table 3. New DC/DC STMicroelectronics

All new pulse converter microcircuits have soft start, overcurrent and overheating protection functions.

Even before the New Year, readers asked me to review a couple of converters.
Well, in principle it’s not difficult for me, and I’m curious myself, I ordered it, received it, tested it.
True, I was more interested in a slightly different converter, but I never got around to it, so I’ll talk about it another time.
Well, today is a review of a simple DC-DC converter with a stated current of 10 Amps.

I apologize in advance for the long delay in publishing this review for those who have been waiting for it for a long time.

To begin with, the characteristics stated on the product page and a small explanation and correction.
Input voltage: 7-40V
1, Output voltage: continuously adjustable (1.25-35V)
2, Output Current: 8A, 10A maximum time within the (power tube temperature exceeds 65 degrees, please add cooling fan, 24V 12V 5A turn within generally be used at room temperature without a fan)
3, Constant Range: 0.3-10A (adjustable) module over 65 degrees, please add fan.
4, Turn lights Current: current value * (0.1) This version is a fixed 0.1 times (actually turn the lamp current value is probably not very accurate) is full of instructions for charging.
5, Minimum pressure: 1V
6, Conversion efficiency: up to about 95% (output voltage, the higher the efficiency)
7, Operating frequency: 300KHZ
8, Output Ripple: about the ripple 50mV (without noise) 20M bandwidth (for reference) Input 24V Output 12V 5A measured
9, Operating temperature: Industrial grade (-40℃ to +85℃)
10, No-load current: Typical 20mA (24V switch 12V)
11, Load regulation: ± 1% (constant)
12, Voltage Regulation: ± 1%
13, Constant accuracy and temperature: the actual test, the module temperature changes from 25 degrees to 60 degrees, the change is less than 5% of the current value (current value 5A)

I'll translate it a little into a more understandable language.
1. Output voltage adjustment range - 1.25-35 Volts
2. Output current - 8 Amps, 10 amperes possible but with additional cooling using a fan.
3. Current adjustment range 0.3-10 Amps
4. The threshold for turning off the charge indication is 0.1 of the set output current.
5. The minimum difference between input and output voltage is 1 Volt (presumably)
6. Efficiency - up to 95%
7. Operating frequency - 300 kHz
8. Output voltage ripple, 50 mV at a current of 5 Amps, input voltage 24 and output 12 Volts.
9. Operating temperature range - from - 40 ℃ to + 85 ℃.
10. Own current consumption - up to 20mA
11. Accuracy of current maintenance - ±1%
12. Voltage maintenance accuracy - ±1%
13. Parameters were tested in the temperature range of 25-60 degrees and the change was less than 5% at a load current of 5 Amps.

The order arrived in a standard plastic bag, generously wrapped with polyethylene foam tape. Nothing was damaged during the delivery process.
Inside was my experimental scarf.

There are no external comments. I just twisted it in my hands and there wasn’t really anything to complain about, it was neat, and if I replaced the capacitors with branded ones, I would say it was beautiful.
On one side of the board there are two terminal blocks, a power input and output.

On the second side there are two trimming resistors to adjust the output voltage and current.

So if you look at the photo in the store, the scarf seems quite large.
I deliberately took the previous two photos close-up. But the understanding of size comes when you put a matchbox next to it.
The scarf is really small, I didn’t look at the sizes when I ordered it, but for some reason it seemed to me that it was noticeably larger. :)
Board dimensions - 65x37mm
Transducer dimensions - 65x47x24mm

The board is two-layer, double-sided mounting.
There were also no comments regarding the soldering. Sometimes it happens that massive contacts are poorly soldered, but the photo shows that this is not the case here.
True, the elements are not numbered, but I think that’s okay, the diagram is quite simple.

In addition to the power elements, the board also contains an operational amplifier, which is powered by a 78L05 stabilizer, and there is also a simple reference voltage source assembled using a TL431.

The board has a powerful PWM controller, and it is even isolated from the heatsink.
I don’t know why the manufacturer isolated the chip from the heatsink, since this reduces heat transfer, perhaps for safety reasons, but since the board is usually built in somewhere, it seems unnecessary to me.

Since the board is designed for a fairly large output current, a fairly powerful diode assembly was used as a power diode, which was also installed on the radiator and also isolated from it.
In my opinion, this is a very good solution, but it could be improved a little if we used a 60 Volt assembly rather than 100.

The choke is not very large, but in this photo you can see that it is wound in two wires, which is not bad.

1, 2 There are two 470 µF x 50 V capacitors installed at the input, and two 1000 µF, but 35 V, at the output.
If you follow the list of declared characteristics, then the output voltage of the capacitors is quite close, but it is unlikely that anyone will lower the voltage from 40 to 35, not to mention the fact that 40 Volts for a microcircuit is generally the maximum input voltage.
3. The input and output connectors are labeled, albeit at the bottom of the board, but this is not particularly important.
4. But the tuning resistors are not marked in any way.
On the left is adjustment of the maximum output current, on the right - voltage.

Now let’s take a little look at the declared characteristics and what we actually have.
I wrote above that the converter uses a powerful PWM controller, or rather a PWM controller with a built-in power transistor.
I also quoted the stated characteristics of the board above, let’s try to figure it out.
Stated - Output voltage: continuously adjustable (1.25-35V)
There are no questions here, the converter will produce 35 Volts, even 36 Volts, in theory.
Stated - Output Current: 8A, 10A maximum
And here's the question. The chip manufacturer clearly indicates the maximum output current is 8 Amps. In the characteristics of the microcircuit there is actually a line - the maximum current limit is 10 Amperes. But this is far from the maximum operating limit; 10 Amps is the maximum.
Stated - Operating frequency: 300KHZ
300 kHz is of course cool, you can put the choke in smaller dimensions, but excuse me, the datasheet clearly says 180 kHz fixed frequency, where does 300 come from?
Stated - Conversion efficiency: up to about 95%
Well, everything is fair here, the efficiency is up to 95%, the manufacturer generally claims up to 96%, but this is in theory, at a certain ratio of input and output voltage.

And here is the block diagram of the PWM controller and even an example of its implementation.
By the way, it is clearly visible here that for 8 Amperes of current a choke of at least 12 Amps is used, i.e. 1.5 of the output current. I usually recommend using 2x stock.
It also shows that the output diode can be installed with a voltage of 45 Volts; diodes with a voltage of 100 Volts usually have a larger drop and, accordingly, reduce efficiency.
If there is a goal to increase the efficiency of this board, then from old computer power supplies you can pick up diodes of the type 20 Ampere 45 Volt or even 40 Ampere 45 Volt.

Initially, I didn’t want to draw a circuit; the board on top is covered with parts, a mask, and also silk-screen printing, but then I saw that it was quite possible to redraw the circuit and decided not to change traditions :)
I did not measure the inductance of the inductor, 47 μH was taken from the datasheet.
The circuit uses a dual operational amplifier, the first part is used to regulate and stabilize the current, the second for indication. It can be seen that the input of the second op-amp is connected through a divider of 1 to 11; in general, the description states 1 to 10, but I think that this is not fundamental.

The first test is at idle, the board is initially configured for an output voltage of 5 Volts.
The voltage is stable in the supply voltage range of 12-26 Volts, the current consumption is below 20 mA as it is not registered by the power supply ammeter.

The LED will glow red if the output current is greater than 1/10 (1/11) of the set current.
This indication is used to charge batteries, since if during the charging process the current drops below 1/10, then it is usually considered that the charge is complete.
Those. We set the charge current to 4 Amps, it glows red until the current drops below 400mA.
But there is a warning, the board only shows a decrease in current, the charging current does not turn off, but simply decreases further.

For testing, I assembled a small stand in which they took part.






Pen and paper, lost the link :)

But during the testing process, I eventually had to use an adjustable power supply, since it turned out that due to my experiments, the linearity of measuring/setting the current in the range of 1-2 Amps for a powerful power supply was disrupted.
As a result, I first carried out heating tests and assessed the ripple level.

Testing this time happened a little differently than usual.
The temperatures of the radiators were measured in places close to the power components, since the temperature of the components themselves was difficult to measure due to the dense installation.
In addition, operation in the following modes was tested.
Input - output - current
14V - 5V - 2A
28V - 12V - 2A
14V - 5V - 4A
Etc. up to current 7.5 A.

Why was testing done in such a cunning way?
1. I was not sure of the reliability of the board and increased the current gradually alternating between different operating modes.
2. The conversion of 14 to 5 and 28 to 12 was chosen because these are one of the most frequently used modes, 14 (approximate voltage of the on-board network of a passenger car) to 5 (voltage for charging tablets and phones). 28 (on-board voltage of a truck) to 12 (simply a frequently used voltage.
3. Initially, I had a plan to test until it turns off or burns out, but plans changed and I had some plans for components from this board. That’s why I only tested up to 7.5 Amps. Although in the end this did not in any way affect the correctness of the check.

Below are a couple of group photos where I will show the 5 Volt 2 Ampere and 5 Volt 7.5 Ampere tests, as well as the corresponding ripple level.
The ripples at currents of 2 and 4 Amperes were similar, and the ripples at currents of 6 and 7.5 Amps were also similar, so I do not give intermediate options.

Same as above, but 28 Volt input and 12 Volt output.

Thermal conditions when working with an input of 28 Volts and an output of 12.
It can be seen that there is no point in increasing the current further; the thermal imager already shows the temperature of the PWM controller at 101 degrees.
For myself, I use a certain limit: the temperature of the components should not exceed 100 degrees. In general, it depends on the components themselves. for example, transistors and diode assemblies can be safely operated at high temperatures, and it is better for microcircuits not to exceed this value.
Of course, it’s not very visible in the photo, the board is very compact, and in the dynamics it was visible a little better.

Since I thought that this board could be used as a charger, I figured out how it would work in a mode where the input is 19 Volts (typical laptop power supply voltage), and the output is 14.3 Volts and 5.5 Amps (typical parameters for charging a car battery).
Here everything went without problems, well, almost without problems, but more on that later.

I summarized the temperature measurement results in a table.
Judging by the test results, I would recommend not using the board at currents exceeding 6 Amps, at least without additional cooling.

I wrote above that there were some features, I’ll explain.
During the tests, I noticed that the board behaves a little inappropriately in certain situations.
1.2 I set the output voltage to 12 Volts, the load current to 6 Amps, after 15-20 seconds the output voltage dropped below 11 Volts, I had to adjust it.
3.4 The output was set to 5 Volts, the input was 14, the input was raised to 28 and the output dropped to 4 Volts. In the photo on the left the current is 7.5 Amperes, on the right 6 Amperes, but the current did not play a role; when the voltage rises under load, the board “resets” the output voltage.

After this, I decided to check the efficiency of the device.
The manufacturer provided graphs for different operating modes. I am interested in the graphs with output 5 and 12 Volts and input 12 and 24, as they are closest to my testing.
In particular, it is declared -

2A - 91%
4A - 88%
6A - 87%
7.5A - 85%

2A - 94%
4A - 94%
6A - 93%
7.5A - Not declared.

What followed was basically a simple check, but with some nuances.
The 5 Volt test passed without any problems.

But with the 12 volt test there were some peculiarities, I will describe them.
1. 28V input, 12V output, 2A, everything is fine
2. 28V input, 12V output, 4A, everything is fine
3. We raise the load current to 6 Amps, the output voltage drops to 10.09
4. We correct it by raising it again to 12 Volts.
5. We raise the load current to 7.5 Amperes, it drops again, and we adjust it again.
6. We lower the load current to 2 Amps without correction, the output voltage rises to 16.84.
Initially, I wanted to show how it rose to 17.2 without load, but I decided that this would be incorrect and provided a photo where there is a load.
Yes it's sad:(

Well, at the same time I checked the efficiency in the mode of charging a car battery from a laptop’s power supply.
But there are some peculiarities here too. At first the output was set to 14.3 V, I ran a heating test and put the board aside. but then I remembered that I wanted to check the efficiency.
I connect the cooled board and observe a voltage of about 14.59 Volts at the output, which dropped to 14.33-14.35 as it warmed up.
Those. In fact, it turns out that the board has instability in the output voltage. and if such a run-up is not so critical for lead-acid batteries, then lithium batteries cannot be charged with such a board categorically.

I completed two efficiency tests.
They are based on two measurement results, although in the end they do not differ very much.
P out - calculated output power, the value of current consumption is rounded, P out DCL - output power measured by the electronic load. Input and output voltages were measured directly at the board terminals.
Accordingly, two efficiency measurement results were obtained. But in any case, it is clear that the efficiency is approximately similar to the declared one, although slightly less.
I will duplicate what is stated in the datasheet
For 12 Volt input and 5 Volt output
2A - 91%
4A - 88%
6A - 87%
7.5A - 85%

For 24 Volt input and 12 Volt output.
2A - 94%
4A - 94%
6A - 93%
7.5A - Not declared.

And what happened in reality. I think that if you replace the powerful diode with its lower-voltage analogue and install a choke designed for a higher current, you would be able to extract a couple more percent.

That seems to be all, and I even know what the readers are thinking -
Why do we need a bunch of tests and incomprehensible photos, just tell us what in the end is good or not :)
And to some extent, readers will be right, by and large, the review can be shortened by 2-3 times by removing some of the photos with tests, but I’m already used to it, sorry.

And so the summary.
pros
Quite high quality production
Small size
Wide range of input and output voltages.
Availability of indication of end of charge (reduction of charging current)
smooth adjustment of current and voltage (without problems you can set the output voltage with an accuracy of 0.1 Volt
Great packaging.

Minuses.
For currents above 6 Amps, it is better to use additional cooling.
The maximum current is not 10, but 8 Amperes.
Low accuracy of maintaining the output voltage, its possible dependence on the load current, input voltage and temperature.
Sometimes the board began to “sound”, this happened in a very narrow adjustment range, for example, I change the output from 5 to 12 and at 9.5-10 Volts it beeps quietly.

Special reminder:
The board only displays the current drop; it cannot turn off the charge, it is just a converter.

My opinion. Well, honestly, when I first took the board in my hands and twisted it, examining it from all sides, I wanted to praise it. Made carefully, there were no special complaints. When I connected it, I also didn’t really want to swear, well, it’s heating up, that’s how they all heat up, this is basically normal.
But when I saw how the output voltage jumped from anything, I got upset.
I don't want to investigate these issues because that should be done by the manufacturer who makes money from it, but I will assume that the problem lies in three things
1. Long feedback path running almost along the perimeter of the board
2. Trimmer resistors installed close to the hot choke
3. The throttle is located exactly above the node where the “thin” electronics are concentrated.
4. Non-precision resistors are used in feedback circuits.

Conclusion - it’s quite suitable for an undemanding load, up to 6 Amps for sure, it works well. Alternatively, using the board as a driver for high-power LEDs will work well.
Use as a charger is highly questionable and in some cases dangerous. If lead-acid still reacts normally to such differences, then lithium cannot be charged, at least without modification.

That's all, as always, I'm waiting for comments, questions and additions.

The product was provided for writing a review by the store. The review was published in accordance with clause 18 of the Site Rules.