DIY adjustable dc converter 10a. Switching voltage converters. Lowering, in English terminology step-down or buck
Probably many remember my epic with homemade laboratory block nutrition.
But I have been repeatedly asked for something similar, only simpler and cheaper.
In this review, I decided to show an alternative version of a simple adjustable block nutrition.
Come in, I hope it will be interesting.
I put off this review for a long time, I didn’t have time, but I finally got around to it.
This power supply has slightly different characteristics than .
The basis of the power supply will be a DC-DC step-down converter board with digital control.
But everything has its time, and now there are actually a few standard photographs.
The scarf arrived in a small box, not much larger than a pack of cigarettes. 
Inside, in two bags (pimply and antistatic) was the heroine herself this review, converter board. 
The board has quite simple design, a power section and a small board with a processor (this board is similar to a board from another, less powerful converter), control buttons and an indicator. 
Characteristics of this board
Input voltage - 6-32 Volts
Output voltage - 0-30 Volts
Output current - 0-8 Amps
Minimum resolution of voltage setting/display - 0.01 Volt
Minimum discreteness of current installation/display - 0.001 Ampere
This board can also measure the capacitance that is transferred to the load and power.
The conversion frequency specified in the instructions is 150KHz, according to the controller datasheet - 300KHz, measured - about 270KHz, which is noticeably closer to the parameter indicated in the datasheet.
The main board contains power elements, a PWM controller, a power diode and inductor, filter capacitors (470 µF x 50 Volts), a PWM logic and operational amplifier power supply controller, operational amplifiers, current shunt, as well as input and output terminal blocks. 
There is practically nothing at the back, only a few power tracks. 
The additional board contains a processor, logic chips, a 3.3 Volt stabilizer for powering the board, an indicator and control buttons.
Processor -
Logic - 2 pieces
Power stabilizer - 
There are 2 operational amplifiers installed on the power board (the same opamps are installed in the ZXY60xx)
PWM power controller of the adj board itself 
A microcircuit acts as a power PWM controller. According to the datasheet, this is a 12 Ampere PWM controller, so it does not work here full force, which cannot but rejoice. However, it is worth considering that input voltage It’s better not to exceed it, it can also be dangerous.
The description for the board indicates a maximum input voltage of 32 Volts, the limit for the controller is 35 Volts.
More powerful converters use a low-current controller that controls a powerful field-effect transistor; here all this is done by one powerful PWM controller.
I apologize for the photos, I couldn't get good quality. 
The instructions I found on the Internet describe how to enter service mode, where you can change some parameters. To enter the service mode, you need to apply power while the OK button is pressed; the numbers 0-2 will sequentially switch on the screen; to switch the setting, you need to release the button while the corresponding number is displayed.
0 - Enables automatic supply of voltage to the output when power is applied to the board.
1 - Enable advanced mode, displaying not only current and voltage, but also the capacitance transferred to the load and output power.
2 - Automatic selection of measurements displayed on the screen or manual.
Also in the instructions there is an example of remembering the settings, since the board can set the limit for setting current and voltage and has a settings memory, but I didn’t go into this jungle anymore.
I also didn’t touch the contacts for the UART connector located on the board, because even if there was something there, I still couldn’t find a program for this board.
Summary.
pros.
1. Quite rich possibilities - setting and measuring current and voltage, measuring capacitance and power, as well as the presence of a mode for automatically supplying voltage to the output.
2. The output voltage and current range is sufficient for most amateur applications.
3. The workmanship is not that good, but without obvious flaws.
4. The components are installed with a reserve, PWM at 12 Amps at 8 declared, capacitors at 50 Volts at the input and output, at stated 32 Volts.
Minuses
1. The screen is very inconvenient; it can only display 1 parameter, for example -
0.000 - Current
00.00 - Voltage
P00.0 - Power
C00.0 - Capacity.
In the case of the last two parameters, the point is floating.
2. Based on the first point, the controls are quite inconvenient; a valcoder would be very helpful.
My opinion.
It’s quite a decent board for building a simple regulated power supply, but it’s better and easier to use a ready-made power supply.
I liked the review
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In this homemade product, AKA KASYAN will make a universal step-down and step-up voltage converter.
Recently the author collected lithium battery. And today he will reveal the secret for what purpose he made it.
Here is a new voltage converter, its operating mode is single-cycle.
The converter has small dimensions and quite high power.
Conventional converters do one of two things. They only increase or only decrease the voltage supplied to the input.
The version made by the author can both increase,
and lower the input voltage to the required value.
The author has various regulated power sources with which he tests assembled homemade products.
Charges batteries and uses them for various other tasks.
Not long ago, the idea of creating a portable power source appeared.
The problem statement was as follows: the device should be able to charge all kinds of portable gadgets.
From ordinary smartphones and tablets to laptops and video cameras, and even coped with powering the author’s favorite soldering iron TS-100.
Naturally, you can simply use universal chargers with power adapters.
But they are all powered by 220V
In the author’s case, what was needed was a portable source of various output voltages.
But the author did not find any of these for sale.
The supply voltages for these gadgets have a very wide range.
For example, smartphones need only 5 V, laptops 18, some even 24 V.
The battery manufactured by the author is designed for an output voltage of 14.8 V.
Therefore, a converter capable of both increasing and decreasing the initial voltage is required.
Please note that some of the values of the components indicated on the diagram differ from those installed on the board.
These are capacitors.
The diagram shows the reference values, and the author made the board to solve his own problems.
Firstly, I was interested in compactness.
Secondly, the author's power converter allows you to easily create an output current of 3 Amps.
AKA KASYAN nothing more is needed.
This is due to the fact that the capacity of the storage capacitors used is small, but the circuit is capable of delivering an output current of up to 5 A.
Therefore, the scheme is universal. The parameters depend on the capacitance of the capacitors, the parameters of the inductor, the diode rectifier and the characteristics of the field switch.
Let's say a few words about the scheme. It is a single-cycle converter based on the UC3843 PWM controller.
Since the voltage from the battery is slightly higher than the standard power supply of the microcircuit, a 12V 7812 stabilizer was added to the circuit to power the PWM controller.
This stabilizer was not indicated in the diagram above.
Assembly. About jumpers installed on the mounting side of the board.
There are four of these jumpers, and two of them are power ones. Their diameter must be at least a millimeter!
The transformer, or rather the choke, is wound on a yellow ring made of powdered iron.
Such rings can be found in the output filters of computer power supplies.
Dimensions of the core used.
External diameter 23.29mm.
Inner diameter 13.59mm.
Thickness 10.33mm.
Most likely, the thickness of the insulation winding is 0.3mm.
The choke consists of two equal windings.
Both windings are wound with copper wire with a diameter of 1.2 mm.
The author recommends using wire with a slightly larger diameter, 1.5-2.0 mm.
There are ten turns in the winding, both wires are wound at once, in the same direction.
Before installing the throttle, seal the jumpers with nylon tape.
The functionality of the circuit lies in the correct installation of the inductor.
It is necessary to solder the winding terminals correctly.
Simply install the throttle as shown in the photo.
Power N-channel field-effect transistor, almost any low voltage will do.
The transistor current is not lower than 30A.
The author used an IRFZ44N transistor.
The output rectifier is a YG805C dual diode in a TO220 package.
It is important to use Schottky diodes, as they give a minimal voltage drop (0.3V versus 0.7) at the junction, which affects losses and heating. They are also easy to find in the notorious computer units nutrition.
In blocks they are located in the output rectifier.
In one case there are two diodes, which in the author’s circuit are paralleled to increase the passing current.
The converter is stabilized and there is feedback.
The output voltage is set by resistor R3
It can be replaced with an external variable resistor for ease of operation.
The converter is also equipped with short circuit protection. Resistor R10 is used as a current sensor.
This is a low-resistance shunt, and the higher its resistance, the lower the protection response current. An SMD option is installed on the side of the tracks.
If short circuit protection is not needed, then we simply exclude this unit.
More protection. There is a 10A fuse at the input of the circuit.
By the way, the battery control board already has short circuit protection installed.
It is highly desirable to take capacitors used in the circuit with low internal resistance.
The stabilizer, field-effect transistor and diode rectifier are attached to an aluminum radiator in the form of a bent plate.
Be sure to isolate the transistor and stabilizer substrates from the radiator using plastic bushings and heat-conducting insulating pads. Don't forget about thermal paste. And the diode installed in the circuit already has an insulated housing.
Sometimes you have to get high voltage from low. For example, for a high-voltage programmer powered by a 5-volt USB, you need somewhere around 12 volts.
What should I do? For this there are DC-DC circuits transformations. As well as specialized microcircuits that allow you to solve this problem in a dozen parts.
Principle of operation
So, how do you make, for example, five volts something more than five? You can come up with many ways - for example, charge capacitors in parallel, and then switch them in series. And so many many times per second. But there is a simpler way, using the properties of inductance, to maintain current strength.
To make it very clear, I will first show an example for plumbers.
Phase 1
The damper closes abruptly. The flow has nowhere else to go, and the turbine, being accelerated, continues to push the liquid forward, because cannot get up instantly. Moreover, it presses it with a force greater than the source can develop. Drives the slurry through the valve into the pressure accumulator. Where does part of it (already with increased pressure) go to the consumer? From where, thanks to the valve, it no longer returns.
Phase 3
And again the damper closes, and the turbine begins to violently push liquid into the battery. Making up for the losses that occurred there in phase 3.
Back to diagrams
We get out of the basement, take off the plumber's sweatshirt, throw the gas wrench into the corner and, with new knowledge, begin to construct the diagram.
Instead of a turbine, inductance in the form of a choke is quite suitable for us. An ordinary key (in practice, a transistor) is used as a damper, a diode is naturally used as a valve, and a capacitor takes on the role of a pressure accumulator. Who else but he is capable of accumulating potential. That's it, the converter is ready!
Phase 1
The key opens, but the coil cannot be stopped. The energy stored in the magnetic field rushes out, the current tends to be maintained at the same level as it was at the moment the key was opened. As a result, the voltage at the output from the coil jumps sharply (to make way for the current) and, breaking through the diode, is packed into the capacitor. Well, part of the energy goes into the load.
Phase 3
The key opens and the energy from the coil again breaks through the diode into the capacitor, increasing the voltage that dropped during phase 3. The cycle is completed.
As can be seen from the process, it is clear that due to the greater current from the source, we increase the voltage at the consumer. So the equality of power here must be strictly observed. Ideally, with a converter efficiency of 100%:
U source *I source = U consumption *I consumption
So if our consumer requires 12 volts and consumes 1A, then from a 5 volt source into the converter you need to feed as much as 2.4A. At the same time, I did not take into account the losses of the source, although usually they are not very large (the efficiency is usually about 80-90%).
If the source is weak and is not able to supply 2.4 amperes, then at 12 volts there will be wild ripples and a drop in voltage - the consumer will eat the contents of the capacitor faster than the source will throw it there.
Circuit design
There are a lot of ready-made DC-DC solutions. Both in the form of microblocks and specialized microcircuits. I won’t split hairs and, to demonstrate my experience, I’ll give an example of a circuit on the MC34063A that I already used in the example.
- SWC/SWE pins of the transistor switch of the chip SWC is its collector, and SWE is its emitter. The maximum current it can draw is 1.5A of input current, but you can also connect an external transistor for any desired current (for more details, see the datasheet for the chip).
- DRC - compound transistor collector
- Ipk - current protection input. There, the voltage is removed from the shunt Rsc; if the current is exceeded and the voltage on the shunt (Upk = I*Rsc) becomes higher than 0.3 volts, the converter will stall. Those. To limit the incoming current to 1A, you need to install a 0.3 Ohm resistor. I didn’t have a 0.3 ohm resistor, so I put a jumper there. It will work, but without protection. If anything, it will kill my microcircuit.
- TC is the input of the capacitor that sets the operating frequency.
- CII is the comparator input. When the voltage at this input is below 1.25 volts, the key generates pulses and the converter operates. As soon as it gets bigger, it turns off. Here, through a divider on R1 and R2, voltage is applied feedback from the exit. Moreover, the divider is selected in such a way that when the voltage we need appears at the output, there will be exactly 1.25 volts at the input of the comparator. Then everything is simple - is the output voltage lower than necessary? We're threshing. Did you get what you needed? Let's switch off.
- Vcc - Circuit Power
- GND - Ground
All formulas for calculating denominations are given in the datasheet. I will copy from it here the most important table for us:
Etched, soldered...
Just like that. A simple scheme, but it allows you to solve a number of problems.
Pulse DC-DC converters Designed for both increasing and decreasing voltage. With their help, you can convert 5 volts, for example, into 12, or 24, or vice versa, with minimal losses. There are also high-voltage DC-DC converters; they are capable of obtaining a very significant potential difference of hundreds of volts from a relatively low voltage (5-12 volts). In this article we will consider the assembly of just such a converter, the output voltage of which can be adjusted within 60-250 volts.
It is based on the common integral timer NE555. Q1 in the diagram is a field-effect transistor; you can use IRF630, IRF730, IRF740 or any others designed to operate with voltages above 300 volts. Q2 – low power bipolar transistor, you can safely install BC547, BC337, KT315, 2SC828. Choke L1 should have an inductance of 100 μH, however, if this is not at hand, you can install chokes in the range of 50-150 μH, this will not affect the operation of the circuit. It’s easy to make a choke yourself - wind 50-100 turns copper wire on a ferrite ring. Diode D1 according to the FR105 circuit; instead, you can install UF4007 or any other high-speed diode with a voltage of at least 300 volts. Capacitor C4 must be high-voltage, at least 250 volts, more possible. The larger its capacity, the better. It is also advisable to install a small-capacity film capacitor in parallel with it for high-quality filtering of high-frequency interference at the output of the converter. VR1 is a trimming resistor with which the output voltage is regulated. The minimum supply voltage for the circuit is 5 volts, the most optimal is 9-12 volts.
Converter manufacturing
The circuit is assembled on printed circuit board dimensions 65x25 mm, a file with a drawing of the board is attached to the article. You can take a textolite larger than the drawing itself, so that there is room at the edges for attaching the board to the case. A few photos of the manufacturing process:
After etching, the board must be tinned and checked for short circuits. Because There is high voltage on the board; there should be no metal burrs between the tracks, otherwise a breakdown is possible. First of all, they are soldered onto the board small parts– resistors, diode, capacitors. Then the microcircuit (it is better to install it in the socket), transistors, trimming resistor, inductor. To make it easier to connect wires to the board, I recommend installing screw terminal blocks; places for them are provided on the board.
Download the board:
(downloads: 240)
First launch and setup
Before starting, be sure to check the correct installation and ring the tracks. Set the trimming resistor to the minimum position (the slider should be on the side of resistor R4). After this, you can apply voltage to the board by connecting an ammeter in series with it. At idle, the current consumption of the circuit should not exceed 50 mA. If it fits within the norm, you can carefully turn the trimming resistor, controlling the output voltage. If everything is fine, connect a load, for example, a 10-20 kOhm resistor to the high-voltage output and test the operation of the circuit again, this time under load.The maximum current that such a converter can produce is approximately 10-15 mA. It can be used, for example, as part of lamp technology to power lamp anodes, or to light gas-discharge or luminescent indicators. The main application is a miniature stun gun, because the output voltage of 250 volts is noticeable to a person. Happy building!
DC/DC converters are widely used to power various electronic equipment. They are used in devices computer technology, communication devices, various control and automation schemes, etc.
Transformer power supplies
In traditional transformer power supplies, the supply voltage is converted using a transformer, most often reduced, to desired value. 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. Converter 1.5V/5V
Pulse converters 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 buck 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 general outline understand the theory.
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 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 pulse blocks power supply, 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. B in this case 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 MOSFET transistor, which is opened at the right time 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 in Chinese stores A converter is sold, the circuit of which is shown in Figure 8 (click on the figure to enlarge).
Fig.8. Schematic diagram SEPIC converter
Figure 9 shows the appearance of the board with the designation of the main elements.
Fig.9. Appearance 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.