Buck-boost voltage converter. DC voltage converter circuit and operation. Increasing, in English terminology step-up or boost

Battery-powered devices will no longer surprise anyone; there are dozens of all kinds of toys and gadgets powered by batteries in every home. Meanwhile, few people have thought about the number of different converters that are used to obtain the necessary voltages or currents from standard batteries. These same converters are divided into several dozen different groups, each with its own characteristics, but at this point in time we are talking about step-down and step-up voltage converters, which are most often called AC/DC and DC/DC converters. In most cases, to build such converters, specialized microcircuits are used, which make it possible to build a converter of a certain topology with a minimum amount of wiring; fortunately, there are a great many power supply microcircuits on the market now.

You can consider the features of using these microcircuits for an infinitely long time, especially taking into account the entire library of datasheets and appnotes from manufacturers, as well as countless number of conditionally advertising reviews from representatives of competing companies, each of which tries to present their product as the highest quality and most versatile. This time we will use discrete elements on which we will assemble several simple step-up DC/DC converters that serve to power a small low-power device, for example, an LED, from 1 battery with a voltage of 1.5 volts. These voltage converters can easily be considered a weekend project and are recommended for assembly by those who are taking their first steps into the wonderful world of electronics.

This diagram shows a relaxation self-oscillator, which is a blocking oscillator with counter-connection of the transformer windings. The principle of operation of this converter is as follows: when turned on, the current flowing through one of the windings of the transformer and the emitter junction of the transistor opens it, as a result of which it opens and more current begins to flow through the second winding of the transformer and the open transistor. As a result, an EMF is induced in the winding connected to the base of the transistor, which turns off the transistor and the current through it is interrupted. At this moment, the energy stored in the magnetic field of the transformer, as a result of the phenomenon of self-induction, is released and a current begins to flow through the LED, causing it to glow. Then the process is repeated.

The components from which this simple step-up voltage converter can be assembled can be completely different. A circuit assembled without errors is highly likely to work correctly. We even tried using the MP37B transistor - the converter functions perfectly! The most difficult thing is to make a transformer - it must be wound with a double wire on a ferrite ring, while the number of turns does not play a special role and ranges from 15 to 30. Less does not always work, more does not make sense. Ferrite - any, it doesn’t make much sense to take an N87 from Epcos, just like looking for a domestically produced M6000NN. The currents flowing in the circuit are negligible, so the size of the ring can be very small; an outer diameter of 10 mm will be more than enough. A resistor with a resistance of about 1 kilo ohm (no difference was found between resistors with a nominal value of 750 ohms and 1.5 kohms). It is advisable to choose a transistor with a minimum saturation voltage; the lower it is, the more discharged the battery can be used. The following were tested experimentally: MP 37B, BC337, 2N3904, MPSH10. LED - any available one, with the caveat that a powerful multi-chip one will not glow at full strength.

The assembled device looks like this:

The board size is 15 x 30 mm, and can be reduced to less than 1 square centimeter using SMD components and a small enough transformer. Without a load, this circuit does not work.

The second circuit is a typical step-up converter made with two transistors. The advantage of this circuit is that during its manufacture there is no need to wind the transformer, but just take a ready-made inductor, but it contains more parts than the previous one.

The operating principle boils down to the fact that the current through the inductor is periodically interrupted by transistor VT2, and the self-induction energy is directed through the diode to capacitor C1 and transferred to the load. Again, the circuit is workable with completely different components and element values. Transistor VT1 can be BC556 or BC327, and VT2 BC546 or BC337, diode VD1 can be any Schottky diode, for example, 1N5818. Capacitor C1 - any type, with a capacity from 1 to 33 μF, no longer makes sense, especially since you can do without it altogether. Resistors - with a power of 0.125 or 0.25 W (although you can also supply powerful wire-wound ones, about 10 watts, but this is more wasteful than necessary) of the following ratings: R1 - 750 Ohm, R2 - 220 KOhm, R3 - 100 KOhm. At the same time, all resistor values ​​can be completely freely replaced with those available within 10-15% of those indicated; this does not affect the performance of a correctly assembled circuit, but it does affect the minimum voltage at which our converter can operate.

The most important part is inductor L1, its rating can also differ from 100 to 470 μH (values ​​up to 1 mH have been experimentally tested - the circuit works stably), and the current for which it should be designed does not exceed 100 mA. Any LED, again taking into account the fact that the output power of the circuit is very small. A correctly assembled device starts working immediately and does not need to be configured.

The output voltage can be stabilized by installing a zener diode of the required value in parallel with capacitor C1, however, it should be remembered that when connecting a consumer, the voltage may sags and become insufficient.ATTENTION! Without load, this circuit can produce voltages of tens or even hundreds of volts! If used without a stabilizing element at the output, capacitor C1 will be charged to the maximum voltage, which, if the load is subsequently connected, can lead to its failure!

The converter is also made on a 30 x 15 mm board, which allows it to be attached to an AA size battery compartment. The PCB layout looks like this:

Both simple boost converter circuits can be made with your own hands and can be successfully used in camping conditions, for example in a lantern or lamp for lighting a tent, as well as in various electronic homemade products, for which the use of a minimum number of batteries is critical.

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.

DC/DC converters are widely used to power various electronic equipment. They are used in computer devices, communication devices, various control and automation circuits, etc.

Transformer power supplies

In traditional transformer power supplies, the voltage of the supply network is converted, most often reduced, to the desired value using a transformer. The reduced voltage is smoothed out by a capacitor filter. If necessary, a semiconductor stabilizer is installed after the rectifier.

Transformer power supplies are usually equipped with linear stabilizers. Such stabilizers have at least two advantages: low cost and a small number of parts in the harness. But these advantages are eroded by low efficiency, since a significant part of the input voltage is used to heat the control transistor, which is completely unacceptable for powering portable electronic devices.

DC/DC converters

If the equipment is powered from galvanic cells or batteries, then voltage conversion to the required level is possible only with the help of DC/DC converters.

The idea is quite simple: direct voltage is converted into alternating voltage, usually with a frequency of several tens or even hundreds of kilohertz, increased (decreased), and then rectified and supplied to the load. Such converters are often called pulse converters.

An example is a boost converter from 1.5V to 5V, just the output voltage of a computer USB. A similar low-power converter is sold on Aliexpress.

Rice. 1. 1.5V/5V converter

Pulse converters are good because they have high efficiency, in the range of 60..90%. Another advantage of pulse converters is a wide range of input voltages: the input voltage can be lower than the output voltage or much higher. In general, DC/DC converters can be divided into several groups.

Classification of converters

Lowering, in English terminology step-down or buck

The output voltage of these converters, as a rule, is lower than the input voltage: without any significant heating losses of the control transistor, you can get a voltage of only a few volts with an input voltage of 12...50V. The output current of such converters depends on the load demand, which in turn determines the circuit design of the converter.

Another English name for a step-down converter is chopper. One of the translation options for this word is interrupter. In technical literature, a step-down converter is sometimes called a “chopper”. For now, let's just remember this term.

Increasing, in English terminology step-up or boost

The output voltage of these converters is higher than the input voltage. For example, with an input voltage of 5V, the output voltage can be up to 30V, and its smooth regulation and stabilization is possible. Quite often, boost converters are called boosters.

Universal converters - SEPIC

The output voltage of these converters is maintained at a given level when the input voltage is either higher or lower than the input voltage. Recommended in cases where the input voltage can vary within significant limits. For example, in a car, the battery voltage can vary within 9...14V, but you need to get a stable voltage of 12V.

Inverting converters

The main function of these converters is to produce an output voltage of reverse polarity relative to the power source. Very convenient in cases where bipolar power is required, for example.

All of the mentioned converters can be stabilized or unstabilized; the output voltage can be galvanically connected to the input voltage or have galvanic voltage isolation. It all depends on the specific device in which the converter will be used.

To move on to a further story about DC/DC converters, you should at least understand the theory in general terms.

Step-down converter chopper - buck converter

Its functional diagram is shown in the figure below. The arrows on the wires show the directions of the currents.

Fig.2. Functional diagram of chopper stabilizer

The input voltage Uin is supplied to the input filter - capacitor Cin. The VT transistor is used as a key element; it carries out high-frequency current switching. It can be either. In addition to the indicated parts, the circuit contains a discharge diode VD and an output filter - LCout, from which the voltage is supplied to the load Rн.

It is easy to see that the load is connected in series with elements VT and L. Therefore, the circuit is sequential. How does voltage drop occur?

Pulse width modulation - PWM

The control circuit produces rectangular pulses with a constant frequency or constant period, which is essentially the same thing. These pulses are shown in Figure 3.

Fig.3. Control pulses

Here t is the pulse time, the transistor is open, t is the pause time, and the transistor is closed. The ratio ti/T is called the duty cycle duty cycle, denoted by the letter D and expressed in %% or simply in numbers. For example, with D equal to 50%, it turns out that D=0.5.

Thus, D can vary from 0 to 1. With a value of D=1, the key transistor is in a state of full conduction, and with D=0 in a cutoff state, simply put, it is closed. It is not difficult to guess that at D=50% the output voltage will be equal to half the input.

It is quite obvious that the output voltage is regulated by changing the width of the control pulse t and, in fact, by changing the coefficient D. This regulation principle is called (PWM). In almost all switching power supplies, it is with the help of PWM that the output voltage is stabilized.

In the diagrams shown in Figures 2 and 6, the PWM is “hidden” in rectangles labeled “Control circuit,” which performs some additional functions. For example, this could be a soft start of the output voltage, remote switching on, or short circuit protection of the converter.

In general, converters have become so widely used that manufacturers of electronic components have started producing PWM controllers for all occasions. The assortment is so large that just to list them you would need a whole book. Therefore, it never occurs to anyone to assemble converters using discrete elements, or as they often say in “loose” form.

Moreover, ready-made low-power converters can be purchased on Aliexpress or Ebay for a low price. In this case, for installation in an amateur design, it is enough to solder the input and output wires to the board and set the required output voltage.

But let's return to our Figure 3. In this case, the coefficient D determines how long it will be open (phase 1) or closed (phase 2). For these two phases, the circuit can be represented in two drawings. The figures DO NOT SHOW those elements that are not used in this phase.

Fig.4. Phase 1

When the transistor is open, the current from the power source (galvanic cell, battery, rectifier) ​​passes through the inductive choke L, the load Rн, and the charging capacitor Cout. At the same time, current flows through the load, capacitor Cout and inductor L accumulate energy. The current iL GRADUALLY INCREASES, due to the influence of the inductance of the inductor. This phase is called pumping.

After the load voltage reaches the set value (determined by the control device settings), the VT transistor closes and the device moves to the second phase - the discharge phase. The closed transistor in the figure is not shown at all, as if it does not exist. But this only means that the transistor is closed.

Fig.5. Phase 2

When the VT transistor is closed, there is no replenishment of energy in the inductor, since the power source is turned off. Inductance L tends to prevent changes in the magnitude and direction of the current (self-induction) flowing through the inductor winding.

Therefore, the current cannot stop instantly and is closed through the “diode-load” circuit. Because of this, the VD diode is called a discharge diode. As a rule, this is a high-speed Schottky diode. After the control period, phase 2, the circuit switches to phase 1, and the process repeats again. The maximum voltage at the output of the considered circuit can be equal to the input, and nothing more. To obtain an output voltage greater than the input, boost converters are used.

For now, we just need to remind you about the amount of inductance, which determines the two operating modes of the chopper. If the inductance is insufficient, the converter will operate in the breaking current mode, which is completely unacceptable for power supplies.

If the inductance is large enough, then operation occurs in the continuous current mode, which makes it possible, using output filters, to obtain a constant voltage with an acceptable level of ripple. Boost converters, which will be discussed below, also operate in the continuous current mode.

To slightly increase the efficiency, the discharge diode VD is replaced with a MOSFET transistor, which is opened at the right moment by the control circuit. Such converters are called synchronous. Their use is justified if the power of the converter is large enough.

Step-up or boost converters

Boost converters are used mainly for low-voltage power supply, for example, from two or three batteries, and some design components require a voltage of 12...15V with low current consumption. Quite often, a boost converter is briefly and clearly called the word “booster”.

Fig.6. Functional diagram of a boost converter

The input voltage Uin is applied to the input filter Cin and supplied to the series-connected L and switching transistor VT. A VD diode is connected to the connection point between the coil and the drain of the transistor. The load Rн and the shunt capacitor Cout are connected to the other terminal of the diode.

The VT transistor is controlled by a control circuit that produces a control signal of a stable frequency with an adjustable duty cycle D, just as was described just above when describing the chopper circuit (Fig. 3). The VD diode blocks the load from the key transistor at the right times.

When the key transistor is open, the right output of the coil L according to the diagram is connected to the negative pole of the power source Uin. An increasing current (due to the influence of inductance) from the power source flows through the coil and the open transistor, and energy accumulates in the coil.

At this time, the diode VD blocks the load and output capacitor from the switching circuit, thereby preventing the output capacitor from discharging through the open transistor. The load at this moment is powered by the energy accumulated in the capacitor Cout. Naturally, the voltage across the output capacitor drops.

As soon as the output voltage drops slightly below the set value (determined by the settings of the control circuit), the key transistor VT closes, and the energy stored in the inductor, through the diode VD, recharges the capacitor Cout, which energizes the load. In this case, the self-induction emf of the coil L is added to the input voltage and transferred to the load, therefore, the output voltage is greater than the input voltage.

When the output voltage reaches the set stabilization level, the control circuit opens the transistor VT, and the process repeats from the energy storage phase.

Universal converters - SEPIC (single-ended primary-inductor converter or converter with an asymmetrically loaded primary inductance).

Such converters are mainly used when the load has insignificant power, and the input voltage changes relative to the output voltage up or down.

Fig.7. Functional diagram of the SEPIC converter

Very similar to the boost converter circuit shown in Figure 6, but with additional elements: capacitor C1 and coil L2. It is these elements that ensure the operation of the converter in the voltage reduction mode.

SEPIC converters are used in applications where the input voltage varies widely. An example is 4V-35V to 1.23V-32V Boost Buck Voltage Step Up/Down Converter Regulator. It is under this name that the converter is sold in Chinese stores, the circuit of which is shown in Figure 8 (click on the figure to enlarge).

Fig.8. Schematic diagram of SEPIC converter

Figure 9 shows the appearance of the board with the designation of the main elements.

Fig.9. Appearance of the SEPIC converter

The figure shows the main parts according to Figure 7. Note that there are two coils L1 L2. Based on this feature, you can determine that this is a SEPIC converter.

The input voltage of the board can be within 4...35V. In this case, the output voltage can be adjusted within 1.23...32V. The operating frequency of the converter is 500 KHz. With small dimensions of 50 x 25 x 12 mm, the board provides power up to 25 W. Maximum output current up to 3A.

But a remark should be made here. If the output voltage is set at 10V, then the output current cannot be higher than 2.5A (25W). With an output voltage of 5V and a maximum current of 3A, the power will be only 15W. The main thing here is not to overdo it: either do not exceed the maximum permissible power, or do not go beyond the permissible current limits.

Thanks to the development of modern electronics, specialized current and voltage stabilizer microcircuits are produced in large quantities. They are divided according to functionality into two main types, DC DC step-up voltage converter and step-down converter. Some combine both types, but this does not affect the efficiency for the better.

Once upon a time, many radio amateurs dreamed of pulse stabilizers, but they were rare and in short supply. The assortment in Chinese stores is especially pleasing.

• 1. Application
• 2. Popular conversions
• 3. Boost voltage converters
• 4. Examples of boosters
• 5. Tusotek
• 6. For XL4016
• 7. On XL6009
• 8.MT3608
• 9. High voltage at 220
• 10. Powerful converters

Application

I recently purchased many different LEDs in 1W, 3W, 5W, 10W, 20W, 30W, 50W, 100W. All of them are of low quality, to compare them with high quality ones. To connect and power this whole bunch, I have 12 V and 19 V power supplies from laptops. I had to actively look through Aliexpress in search of low-voltage LED drivers.

Modern step-up voltage converters DC DC and step-down voltage converters were purchased, 1-2 Amperes and powerful ones 5-7 Amperes. In addition, they are perfect for connecting a laptop to 12V in a car; they will pull 80-90 watts. They are quite suitable as a charger for 12V and 24V car batteries.

In Chinese online stores, voltage stabilizers are a little more expensive.

Popular microcircuits for step-up switching stabilizers are:

1. LM2577, obsolete with low efficiency;
2. XL4016, 2 times more efficient than 2577;
3. XL6009;
4. MT3608.

Stabilizers are designated thus AC-DC, DC-DC. AC is alternating current, DC is direct current. This will make the search easier if you specify it in the request.

It is not rational to make a DC DC boost converter with your own hands; I will spend too much time on assembly and configuration. You can buy it from the Chinese for 50-250 rubles, this price includes delivery. For this amount I will receive an almost finished product that can be finalized as quickly as possible.

These switching ICs are used in conjunction with others, wrote the characteristics and datasheet for popular ICs for power supply,.

Popular conversions

Stabilizers-boosters are classified into low-voltage and high-voltage from 220 to 400 volts. Of course, there are ready-made blocks with a fixed boost value, but I prefer custom ones, they have wider functionality.

The most commonly requested transformations are:

1. 12V - 19V;
2. 12 - 24 Volts;
3. 5 - 12V;
4. 3 - 12V
5. 12 - 220V;
6. 24V - 220V.

Boosters are called car inverters.

Boost Voltage Converters

My laboratory power supply runs from a laptop unit at 19V 90W, but this is not enough to test series-connected LEDs. A series LED string requires 30V to 50V. Buying a ready-made unit for 50-60 Volts and 150W turned out to be a bit expensive, about 2000 rubles. Therefore, I ordered the first step-up stabilizer for 500 rubles. with an increase to 50V. After checking, it turned out that it reaches a maximum of 32V, because there are 35V capacitors at the input and output. I convincingly wrote to the seller about my indignation, and a couple of days later they returned my money.

I ordered a second one up to 55V under the Tusotek brand for 280 rubles, the booster turned out to be excellent. From 12V it easily increases to 60V, I didn’t turn the construction resistor higher, it would suddenly burn out. The radiator is glued with heat-conducting glue, so it was not possible to see the markings of the microcircuit. The cooling is done a little incorrectly, the heat sink pad of the Schottky diode and the controller is attached to the board, and not to the heatsink.

Examples of boosters

XL4016

..

Let's look at the 4 models that I have in stock. I didn’t waste time on photos; I took the sellers too.

Characteristics.

	Tusotek	XL4016	Driver	MT3608
Input, V	6 – 35V	6 – 32V	5 – 32V	2-24V
Input current	up to 10A	up to 10A	—	—
Output, V	6 – 55V	6 – 32V	6 – 60V	up to 28V
Output current	5A, max 7A	5A, max 8A	max 2A	1A, max 2A
Price	260rub	250rub	270rub	55rub

I have a lot of experience working with Chinese goods, most of them have shortcomings right away. Before use, I inspect and modify them to increase the reliability of the entire structure. These are mainly assembly problems that arise when quickly assembling products. I am finalizing LED spotlights, lamps for the home, car low and high beam lamps, controllers for controlling daytime running lights (DRL). I recommend that everyone do this; with a minimum of time spent, the service life can be doubled.

Be careful, not all have protection against short circuit, overheating, overload and improper connection.

The actual power depends on the mode; the specifications indicate the maximum. Of course, the characteristics of each manufacturer will be different; they install different diodes, and wind the inductor with wires of different thicknesses.

Tusotek

In my opinion, the best of all boosting stabilizers. Some elements do not have a reserve of characteristics or they are lower than those of PWM microcircuits, which is why they cannot provide even half of the promised current. Tusotek has a 1000mF 35V capacitor at the input and 470mF 63V at the output. The heat sink side with a metal plate is soldered to the board. But they are soldered poorly and askew, only one edge lies on the board, there is a gap under the other. Without looking at it, it is not clear how well they are sealed. If it’s really bad, then it’s better to dismantle them and put this side on the radiator; cooling will improve by 2 times.

A variable resistor sets the required number of volts. It will remain unchanged if you change the input voltage, it does not depend on it. For example, I set 50V at the output, increased it from 5V to 12V at the input, the set 50V did not change.

On XL4016

This converter has such a feature that it can only boost up to 50% of the input volts. If you connect 12V, then the maximum increase will be 18V. The description stated that it can be used for laptops that are powered by a maximum of 19V. But its main purpose turned out to be working with laptops from a car battery. Probably the 50% limitation can be removed by changing the resistors that set this mode. The output volts directly depend on the number of inputs.

Heat removal is much better, the radiators are installed correctly. Only instead of thermal paste there is a heat-conducting gasket to avoid electrical contact with the radiator. At the input there is a capacitor of 470mF 50V, at the other end 470mF at 35V.

On XL6009

A representative of modern efficient converters, like outdated models on the LM2596, is available in several options, from miniature to models with voltage indicators.

Efficiency example:

• 92% when converting 12V to 19V, 2A load.

The datasheet immediately indicates the scheme for using as power supply for a laptop in a car from 10V to 30V. Also on the XL6009 it is easy to implement bipolar power supply at +24 and -24V. As with most converters, the efficiency decreases the higher the voltage difference and the greater the ampere.

MT3608

Miniature model with good efficiency up to 97%, PWM frequency 1.2 MHz. Efficiency increases as input voltage increases and decreases as current increases. On the MT3608 boost converter you can count on a small current, internally limited to 4A in case of a short circuit. In terms of volts, it is advisable not to exceed 24.

High voltage at 220

Conversion units from 12.24 volts to 220 are widespread among car enthusiasts like. Used to connect devices powered by 220V. The Chinese mainly sell 7-10 models of such modules, the rest are ready-made devices. Price from 400 rub. Separately, I would like to note that if, for example, 500W is indicated on a finished unit, then this will often be a short-term maximum power. Real long-term will be about 240W.

Powerful converters

For special cases, powerful DC-DC boost converters of 10-20A and up to 120V are needed. I will show you several popular and affordable models. They mostly do not have markings or the seller hides them so as not to buy them elsewhere. I haven’t personally tested them; in terms of voltage, they coexist according to the promised characteristics. But the ampere will be a little less. Although products in this price category always hold the stated load, I bought similar devices only with LCD screens.

600W

Powerful #1:

1. power 600W;
2. 10-60V converts to 12-80V;
3. price from 800 rub.

You can find it by searching for “600W DC 10-60V to 12-80V Boost Converter Step Up”

400W

Powerful #2:

1. power 400W;
2. 6-40V converts to 8-80V;
3. output up to 10A;
4. price from 1200 rub.

To search, enter in the search engine “DC 400W 10A 8-80V Boost Converter Step-Up”

B900W

Powerful #3:

1. power 900W;
2. 8-40V converts to 10-120V;
3. output up to 15A.
4. price from 1400 rub.

The only unit that is designated as B900W and can be easily found.

I came across a very interesting step-down voltage converter in the open spaces of Ali, with such a set of characteristics.

Here's what the seller stated:
1.Input voltage range:5-36VDC
2.Output voltage range:1.25-32VDC adjustable
3.Output current: 0-5A
4.Output power: 75W
5.High efficiency up to 96%
6.Built in thermal shutdown function
7.Built in current limit function
8.Built in output short protection function
9.L x W x H =68.2x38.8x15mm

The seller either did not mention the most interesting features of this converter or did not draw attention to them. And the features are very interesting.

1. Built-in input and output voltage voltmeter, ammeter and wattmeter, with reading calibration function. The calibration function for voltage and current operates independently. The actual accuracy of the readings after calibration is around ~0.05v. But more on that below.

2. This step-down converter can operate in both voltage stabilization mode and current stabilization mode. In fact, this is the smallest and cheapest laboratory power supply with a built-in multimeter. To which you just need to attach a battery crib to get a ready-made charger for any type of battery.

The idea was to use this converter as a powerful converter capable of utilizing the full power of a solar battery with a voltage of 6v. Since the solar battery is planned to be used far from civilization, where there is no extra multimeter with you, I really wanted to find a converter with a built-in voltmeter-ammeter.

Step-down converters with a current stabilization function that are not afraid of short circuits, with a built-in voltmeter-ammeter, are not at all a big offer. Closest competitors:

In general, we couldn’t find anything better, and this converter was purchased. A month later the package was waiting at the post office.

The first tests of this converter were disappointing. It turned out that although the converter itself starts to work at input voltages above 3.2v, there was a problem with the voltmeter. The voltmeter was lying by SEVERAL VOLT!!! Therefore, the first thing to do was calibration. But it turned out that calibration does not help. If you calibrate the voltmeter at 5v, then problems began with readings at 12v and vice versa.

Later, experiments showed that the voltmeter shows correct values ​​only if the input voltage is above 6.5v. When the input voltage dropped below 6.5v, the voltmeter began to lie. Moreover, absolutely all readings were distorted at low input voltage. Even the output voltage readings began to “float”, although in fact they were stable. It was extremely unpleasant to observe when, when the input voltage decreased from 6.5v to 4.2v, the built-in voltmeter began to show that the input voltage was increasing. Here is an example of numbers, input voltage and voltage on the built-in voltmeter.

6.74v – 6.6v
6.25v – 6.7v
5.95v – 6.7v
5.55v – 6.8v
5.07v – 7.2v
4.61v – 7.5v
4.33v – 7.8v

When the input voltage dropped below 4.2v, the voltmeter turned off altogether.

A dispute was created, but the seller turned out to be normal and did not resist; he immediately returned 50% of the price.

If you forget about the voltmeter, or assume that the supply voltage will always be greater than 7v, then we can assume that the converter is working perfectly. But for my case, when the main operating voltage range was 4v-8v, this could be considered a complete fiasco.

But then autumn came, long gloomy evenings, and it became interesting to see if something could be done.

Photo of the main elements of the converter

It turned out that a number of important elements were hidden under the display, which I didn’t want to unsolder unless absolutely necessary. Therefore, it was not possible to draw a complete circuit of the converter. Moreover, despite its apparent simplicity, the scheme is not so simple. Having poked the working converter with a multimeter, it became clear that all the problems begin when a separate power bus, with a stabilized voltage of 5v for the voltmeter and other “brains,” begins to sag. The LM317 chip is responsible for stable 5v. And as soon as the voltage at its input begins to be insufficient to produce stable 5v, problems begin for the voltmeter.

The problem became clear, but its solution did not seem so simple. In theory, you need to replace LM317 with some kind of analogue that can not only lower the voltage, but also increase it. Analogue of SEPIC converter or similar. There are such chips, but they will definitely not be pin-compatible, they will definitely require additional wiring, and the prices for such chips are usually not reasonable. And then an idea came. What if you add a boost converter board in front of LM317. Moreover, the current consumed by the “brains” is very small. The MT3608 converter, reviews of which are either available, was ideal for such a board. Another undeniable advantage of the MT3608 is its price. Now on Ali the price of MT3608 starts at $0.35 and tends to become even cheaper.

In addition to the price, the good news is that for modification you need to make a minimum of changes on the board. It is enough to cut one track (1) and solder three wires to the MT3608 +Vin (2), -Vin (3) and +Vout (4).


Additionally, several layers of electrical tape were wound over the MT3608 inductor to align the height with the trimmer resistor. Plus, on the MT3608 board itself, a jumper was added to expand the range of adjustments with the potentiometer, and a 10 uF ceramic capacitor was added at the output. The result looked like this:

The result exceeded all expectations:

1. The accuracy of voltmeter-ammeter readings has increased significantly at input voltages below 6.5v. Simply put, the voltmeter began to work as it should immediately. Taking into account the calibration, you can set the readings in the desired range around 0.05v. Although it should still be noted that if you accurately set the region to 5v, in the region of 12v the voltmeter will lie in the region of 0.3v.

2. The voltmeter now turns on at 1.9v. Now you can see on the built-in voltmeter the moment the power part of the converter is turned on when the input voltage increases above 3.2v.

3. Now, in the event of a source overload, this is when the converter tries to take more from the power source than it can give, the converter has become much more stable. When overloaded, the power section drops the input voltage to somewhere around 3.45v, which is quite enough to power the “brains” of the converter. The converter does not enter a kind of flickering mode when the voltage is not enough to start the “brains”.

This modification also has a couple of disadvantages:

1. The board has become higher, so in order not to damage the “sandwich”, screws were screwed in, allowing the board to be installed on a flat surface without risk.

2. The operating range of input voltages has decreased. Previously, the input voltage could reach 35v. Now the upper limit has been reduced to 20v due to the MT3608 input voltage limitation. But in my case this is absolutely not critical.