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A powerful and fairly good step-up voltage converter can be built based on a simple multivibrator.
In my case, this inverter was built simply to review the work; a short video was also made with the operation of this inverter.

About the circuit as a whole - a simple push-pull inverter, it’s hard to imagine simpler. The master oscillator and at the same time the power part are powerful field-effect transistors (it is advisable to use switches like IRFP260, IRFP460 and similar) connected using a multivibrator circuit. As a transformer, you can use a ready-made trans from a computer power supply (the largest transformer).

For our purposes, we need to use 12 Volt windings and the middle point (braid, tap). At the output of the transformer, the voltage can reach up to 260 Volts. Since the output voltage is variable, it needs to be rectified with a diode bridge. It is advisable to assemble the bridge from 4 separate diodes; ready-made diode bridges are designed for network frequencies of 50 Hz, and in our circuit the output frequency is around 50 kHz.

Be sure to use pulsed, fast or ultra-fast diodes with a reverse voltage of at least 400 Volts and a permissible current of 1 Ampere or higher. You can use diodes MUR460, UF5408, HER307, HER207, UF4007, and others.
I recommend using the same diodes in the master circuit circuit.

The inverter circuit operates on the basis of parallel resonance, therefore, the operating frequency will depend on our oscillatory circuit - represented by the primary winding of the transformer and the capacitor parallel to this winding.
Regarding power and performance in general. A correctly assembled circuit does not require additional adjustment and works immediately. During operation, the keys should not heat up at all if the transformer output is not loaded. The idle current of the inverter can reach up to 300mA - this is the norm, higher is already a problem.

With good switches and a transformer, you can remove power in the region of 300 watts, in some cases even 500 watts, from this circuit without any problems. The input voltage rating is quite high, the circuit will work from a source of 6 Volts to 32 Volts, I didn’t dare to supply more.

Chokes - wound with a 1.2mm wire on yellow-white rings from the group stabilization choke in the computer power supply. The number of turns of each inductor is 7, both inductors are exactly the same.

Capacitors parallel to the primary winding may heat up slightly during operation, so I advise you to use high-voltage capacitors with an operating voltage of 400 Volts or higher.

The circuit is simple and fully operational, but despite the simplicity and accessibility of the design, this is not an ideal option. The reason is not the best field key management. The circuit lacks a specialized generator and control circuit, which makes it not entirely reliable if the circuit is intended for long-term operation under load. The circuit can power LDS and devices that have built-in SMPS.

An important link - the transformer - must be well wound and correctly phased, because it plays a major role in the reliable operation of the inverter.

The primary winding is 2x5 turns with a bus of 5 wires 0.8 mm. The secondary winding is wound with a 0.8 mm wire and contains 50 turns - this is in the case of self-winding of the transformer.

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; 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.