LM2596 reduces the input voltage (to 40 V) - the output is regulated, the current is 3 A. Ideal for LEDs in a car. Very cheap modules - about 40 rubles in China.
Texas Instruments produces high-quality, reliable, affordable and cheap, easy-to-use DC-DC controllers LM2596. Chinese factories produce ultra-cheap pulsed stepdown converters based on it: the price of a module for LM2596 is approximately 35 rubles (including delivery). I advise you to buy a batch of 10 pieces at once - there will always be a use for them, and the price will drop to 32 rubles, and less than 30 rubles when ordering 50 pieces. Read more about calculating the circuitry of the microcircuit, adjusting the current and voltage, its application and some of the disadvantages of the converter.
The typical method of use is a stabilized voltage source. It is easy to make a switching power supply based on this stabilizer; I use it as a simple and reliable laboratory power supply that can withstand short circuits. They are attractive due to the consistency of quality (they all seem to be made at the same factory - and it’s difficult to make mistakes in five parts), and full compliance with the datasheet and declared characteristics.
Another application is a pulse current stabilizer for power supply for high-power LEDs. The module on this chip will allow you to connect a 10-watt automotive LED matrix, additionally providing short-circuit protection.
I highly recommend buying a dozen of them - they will definitely come in handy. They are unique in their own way - input voltage is up to 40 volts, and only 5 external components are required. This is convenient - you can increase the voltage on the smart home power bus to 36 volts by reducing the cross-section of the cables. We install such a module at the points of consumption and configure it to the required 12, 9, 5 volts or as needed.
Let's take a closer look at them.
Chip characteristics:
- Input voltage - from 2.4 to 40 volts (up to 60 volts in the HV version)
- Output voltage - fixed or adjustable (from 1.2 to 37 volts)
- Output current - up to 3 amperes (with good cooling - up to 4.5A)
- Conversion frequency - 150 kHz
- Housing - TO220-5 (through-hole mounting) or D2PAK-5 (surface mounting)
- Efficiency - 70-75% at low voltages, up to 95% at high voltages
- Stabilized voltage source
- Converter circuit
- Datasheet
- USB charger based on LM2596
- Current stabilizer
- Use in homemade devices
- Adjustment of output current and voltage
- Improved analogues of LM2596
History - linear stabilizers
To begin with, I’ll explain why standard linear voltage converters like LM78XX (for example 7805) or LM317 are bad. Here is its simplified diagram.
The main element of such a converter is a powerful bipolar transistor, switched on in its “original” meaning - as a controlled resistor. This transistor is part of a Darlington pair (to increase the current transfer coefficient and reduce the power required to operate the circuit). The base current is set by the operational amplifier, which amplifies the difference between the output voltage and the one set by the ION (reference voltage source), i.e. it is connected according to the classical error amplifier circuit.
Thus, the converter simply turns on the resistor in series with the load, and controls its resistance so that, for example, exactly 5 volts are extinguished across the load. It is easy to calculate that when the voltage decreases from 12 volts to 5 (a very common case of using the 7805 chip), the input 12 volts are distributed between the stabilizer and the load in the ratio “7 volts on the stabilizer + 5 volts on the load.” At a current of half an ampere, 2.5 watts are released at the load, and at 7805 - as much as 3.5 watts.
It turns out that the “extra” 7 volts are simply extinguished on the stabilizer, turning into heat. Firstly, this causes problems with cooling, and secondly, it takes a lot of energy from the power source. When powered from an outlet, this is not very scary (although it still causes harm to the environment), but when powered by a battery or rechargeable battery, this cannot be ignored.
Another problem is that it is generally impossible to make a boost converter using this method. Often such a need arises, and attempts to solve this issue twenty or thirty years ago are amazing - how complex the synthesis and calculation of such circuits was. One of the simplest circuits of this kind is a push-pull 5V->15V converter.
It must be admitted that it provides galvanic isolation, but it does not use the transformer efficiently - only half of the primary winding is used at any time.
Let's forget this like a bad dream and move on to modern circuitry.
Voltage source
Scheme
The microcircuit is convenient to use as a step–down converter: a powerful bipolar switch is located inside, all that remains is to add the remaining components of the regulator - a fast diode, an inductance and an output capacitor, it is also possible to install an input capacitor - only 5 parts.
The LM2596ADJ version will also require an output voltage setting circuit, these are two resistors or one variable resistor.
Step-down voltage converter circuit based on LM2596:
The whole scheme together:
Here you can download datasheet for LM2596.
Operating principle: a powerful switch inside the device, controlled by a PWM signal, sends voltage pulses to the inductance. At point A, x% of the time there is full voltage, and (1-x)% of the time the voltage is zero. The LC filter smooths out these oscillations by highlighting a constant component equal to x * supply voltage. The diode completes the circuit when the transistor is turned off.
Detailed job description
Inductance resists the change in current through it. When voltage appears at point A, the inductor creates a large negative self-induction voltage, and the voltage across the load becomes equal to the difference between the supply voltage and the self-induction voltage. The inductance current and voltage across the load gradually increase.
After the voltage disappears at point A, the inductor strives to maintain the previous current flowing from the load and the capacitor, and shorts it through the diode to ground - it gradually drops. Thus, the load voltage is always less than the input voltage and depends on the duty cycle of the pulses.
Output voltage
The module is available in four versions: with a voltage of 3.3V (index –3.3), 5V (index –5.0), 12V (index –12) and an adjustable version LM2596ADJ. It makes sense to use the customized version everywhere, since it is available in large quantities in the warehouses of electronic companies and you are unlikely to encounter a shortage of it - and it only requires an additional two penny resistors. And of course, the 5 volt version is also popular.
The quantity in stock is in the last column.
You can set the output voltage in the form of a DIP switch, a good example of this is given here, or in the form of a rotary switch. In both cases, you will need a battery of precision resistors - but you can adjust the voltage without a voltmeter.
Frame
There are two housing options: the TO-263 planar mount housing (model LM2596S) and the TO-220 through-hole housing (model LM2596T). I prefer to use the planar version of the LM2596S, since in this case the heatsink is the board itself, and there is no need to buy an additional external heatsink. In addition, its mechanical resistance is much higher, unlike the TO-220, which must be screwed to something, even to a board - but then it is easier to install the planar version. I recommend using the LM2596T-ADJ chip in power supplies because it is easier to remove a large amount of heat from its case.
Input voltage ripple smoothing
Can be used as an effective “smart” stabilizer after current rectification. Since the microcircuit directly monitors the output voltage, fluctuations in the input voltage will cause an inversely proportional change in the conversion coefficient of the microcircuit, and the output voltage will remain normal.
It follows from this that when using the LM2596 as a step-down converter after a transformer and rectifier, the input capacitor (i.e. the one located immediately after the diode bridge) may have a small capacitance (about 50-100 μF).
Output capacitor
Due to the high conversion frequency, the output capacitor also does not have to have a large capacity. Even a powerful consumer will not have time to significantly reduce this capacitor in one cycle. Let's do the calculation: take a 100 µF capacitor, 5 V output voltage and a load consuming 3 amperes. Full charge of the capacitor q = C*U = 100e-6 µF * 5 V = 500e-6 µC.
In one conversion cycle, the load will take dq = I*t = 3 A * 6.7 μs = 20 μC from the capacitor (this is only 4% of the total charge of the capacitor), and immediately a new cycle will begin, and the converter will put a new portion of energy into the capacitor.
The most important thing is not to use tantalum capacitors as the input and output capacitors. They write right in the datasheets - “do not use in power circuits”, because they very poorly tolerate even short-term overvoltages, and do not like high pulse currents. Use regular aluminum electrolytic capacitors.
Efficiency, efficiency and heat loss
The efficiency is not so high, since a bipolar transistor is used as a powerful switch - and it has a non-zero voltage drop, about 1.2V. Hence the drop in efficiency at low voltages.
As you can see, maximum efficiency is achieved when the difference between the input and output voltages is about 12 volts. That is, if you need to reduce the voltage by 12 volts, a minimal amount of energy will go into heat.
What is converter efficiency? This is a value that characterizes current losses - due to heat generation on a fully open powerful switch according to the Joule-Lenz law and to similar losses during transient processes - when the switch is, say, only half open. The effects of both mechanisms can be comparable in magnitude, so one should not forget about both loss paths. A small amount of power is also used to power the “brains” of the converter themselves.
Ideally, when converting voltage from U1 to U2 and output current I2, the output power is equal to P2 = U2*I2, the input power is equal to it (ideal case). This means that the input current will be I1 = U2/U1*I2.
In our case, the conversion has an efficiency below unity, so part of the energy will remain inside the device. For example, with efficiency η, the output power will be P_out = η*P_in, and losses P_loss = P_in-P_out = P_in*(1-η) = P_out*(1-η)/η. Of course, the converter will have to increase the input current to maintain the specified output current and voltage.
We can assume that when converting 12V -> 5V and an output current of 1A, the losses in the microcircuit will be 1.3 watts, and the input current will be 0.52A. In any case, this is better than any linear converter, which will give at least 7 watts of losses, and will consume 1 ampere from the input network (including for this useless thing) - twice as much.
By the way, the LM2577 microcircuit has a three times lower operating frequency, and its efficiency is slightly higher, since there are fewer losses in transient processes. However, it needs three times higher ratings of the inductor and output capacitor, which means extra money and board size.
Increasing output current
Despite the already fairly large output current of the microcircuit, sometimes even more current is required. How to get out of this situation?
- Several converters can be parallelized. Of course, they must be set to exactly the same output voltage. In this case, you cannot get by with simple SMD resistors in the Feedback voltage setting circuit; you need to use either resistors with an accuracy of 1%, or manually set the voltage with a variable resistor.
USB charger for LM2596
You can make a very convenient travel USB charger. To do this, you need to set the regulator to a voltage of 5V, provide it with a USB port and provide power to the charger. I use a radio model lithium polymer battery purchased in China that provides 5 amp hours at 11.1 volts. This is a lot - enough to 8 times charge a regular smartphone (not taking into account efficiency). Taking into account the efficiency, it will be at least 6 times.
Don't forget to short the D+ and D- pins of the USB socket to tell the phone that it is connected to the charger and the current transferred is unlimited. Without this event, the phone will think that it is connected to the computer and will be charged with a current of 500 mA - for a very long time. Moreover, such a current may not even compensate for the current consumption of the phone, and the battery will not charge at all.
You can also provide a separate 12V input from a car battery with a cigarette lighter connector - and switch the sources with some kind of switch. I advise you to install an LED that will signal that the device is on, so as not to forget to turn off the battery after full charging - otherwise the losses in the converter will completely drain the backup battery in a few days.
This type of battery is not very suitable because it is designed for high currents - you can try to find a lower current battery, and it will be smaller and lighter.
Current stabilizer
Output current adjustment
Only available with adjustable output voltage version (LM2596ADJ). By the way, the Chinese also make this version of the board, with regulation of voltage, current and all kinds of indications - a ready-made current stabilizer module on LM2596 with short-circuit protection can be bought under the name xw026fr4.
If you do not want to use a ready-made module, and want to make this circuit yourself, there is nothing complicated, with one exception: the microcircuit does not have the ability to control current, but you can add it. I'll explain how to do this, and clarify the difficult points along the way.
Application
A current stabilizer is a thing needed to power powerful LEDs (by the way - my microcontroller project high power LED drivers), laser diodes, electroplating, battery charging. As with voltage stabilizers, there are two types of such devices - linear and pulsed.
The classic linear current stabilizer is the LM317, and it is quite good in its class - but its maximum current is 1.5A, which is not enough for many high-power LEDs. Even if you power this stabilizer with an external transistor, the losses on it are simply unacceptable. The whole world is making a fuss about the energy consumption of standby light bulbs, but here the LM317 works with an efficiency of 30% This is not our method.
But our microcircuit is a convenient driver for a pulse voltage converter that has many operating modes. Losses are minimal, since no linear operating modes of transistors are used, only key ones.
It was originally intended for voltage stabilization circuits, but several elements turn it into a current stabilizer. The fact is that the microcircuit relies entirely on the “Feedback” signal as feedback, but what to feed it is up to us.
In the standard switching circuit, voltage is supplied to this leg from a resistive output voltage divider. 1.2V is a balance; if Feedback is less, the driver increases the duty cycle of the pulses; if it is more, it decreases it. But you can apply voltage to this input from a current shunt!
Shunt
For example, at a current of 3A you need to take a shunt with a nominal value of no more than 0.1 Ohm. At such a resistance, this current will release about 1 W, so that’s a lot. It is better to parallel three such shunts, obtaining a resistance of 0.033 Ohm, a voltage drop of 0.1 V and a heat release of 0.3 W.
However, the Feedback input requires a voltage of 1.2V - and we only have 0.1V. It is irrational to install a higher resistance (the heat will be released 150 times more), so all that remains is to somehow increase this voltage. This is done using an operational amplifier.
Non-inverting op-amp amplifier
Classic scheme, what could be simpler?
We unite
Now we combine a conventional voltage converter circuit and an amplifier using an LM358 op-amp, to the input of which we connect a current shunt.
A powerful 0.033 Ohm resistor is a shunt. It can be made from three 0.1 Ohm resistors connected in parallel, and to increase the permissible power dissipation, use SMD resistors in a 1206 package, place them with a small gap (not close together) and try to leave as much copper layer around the resistors and under them as possible. A small capacitor is connected to the Feedback output to eliminate a possible transition to oscillator mode.
We regulate both current and voltage
Let's connect both signals to the Feedback input - both current and voltage. To combine these signals, we will use the usual wiring diagram “AND” on diodes. If the current signal is higher than the voltage signal, it will dominate and vice versa.
A few words about the applicability of the scheme
You cannot adjust the output voltage. Although it is impossible to regulate both the output current and voltage at the same time - they are proportional to each other, with a coefficient of "load resistance". And if the power supply implements a scenario like “constant output voltage, but when the current exceeds, we begin to reduce the voltage,” i.e. CC/CV is already a charger.
The maximum supply voltage for the circuit is 30V, as this is the limit for the LM358. You can extend this limit to 40V (or 60V with the LM2596-HV version) if you power the op-amp from a zener diode.
In the latter option, it is necessary to use a diode assembly as summing diodes, since both diodes in it are made within the same technological process and on the same silicon wafer. The spread of their parameters will be much less than the spread of parameters of individual discrete diodes - thanks to this we will obtain high accuracy of tracking values.
You also need to carefully ensure that the op-amp circuit does not get excited and go into lasing mode. To do this, try to reduce the length of all conductors, and especially the track connected to pin 2 of the LM2596. Do not place the op amp near this track, but place the SS36 diode and filter capacitor closer to the LM2596 body, and ensure a minimum area of the ground loop connected to these elements - it is necessary to ensure a minimum length of the return current path “LM2596 -> VD/C -> LM2596”.
Application of LM2596 in devices and independent board layout
I spoke in detail about the use of microcircuits in my devices not in the form of a finished module in another article, which covers: the choice of diode, capacitors, inductor parameters, and also talked about the correct wiring and a few additional tricks.
Opportunities for further development
Improved analogues of LM2596
The easiest way after this chip is to switch to LM2678. In essence, this is the same stepdown converter, only with a field-effect transistor, thanks to which the efficiency rises to 92%. True, it has 7 legs instead of 5, and it is not pin-to-pin compatible. However, this chip is very similar and will be a simple and convenient option with improved efficiency.
L5973D– a rather old chip, providing up to 2.5A, and a slightly higher efficiency. It also has almost twice the conversion frequency (250 kHz) - therefore, lower inductor and capacitor ratings are required. However, I saw what happens to it if you put it directly into the car network - quite often it knocks out interference.
ST1S10- highly efficient (90% efficiency) DC–DC stepdown converter.
- Requires 5–6 external components;
ST1S14- high-voltage (up to 48 volts) controller. High operating frequency (850 kHz), output current up to 4A, Power Good output, high efficiency (no worse than 85%) and a protection circuit against excess load current make it probably the best converter for powering a server from a 36-volt source.
If maximum efficiency is required, you will have to turn to non-integrated stepdown DC–DC controllers. The problem with integrated controllers is that they never have cool power transistors - the typical channel resistance is no higher than 200 mOhm. However, if you take a controller without a built-in transistor, you can choose any transistor, even AUIRFS8409–7P with a channel resistance of half a milliohm
DC-DC converters with external transistor
Next part
Today we will look at several circuits of simple, one might even say simple, pulsed DC-DC voltage converters (converters of direct voltage of one value to constant voltage of another value)
What are the benefits of pulse converters? Firstly, they have high efficiency, and secondly, they can operate at an input voltage lower than the output voltage. Pulse converters are divided into groups:
- - bucking, boosting, inverting;
- - stabilized, unstabilized;
- - galvanically isolated, non-insulated;
- - with a narrow and wide range of input voltages.
To make homemade pulse converters, it is best to use specialized integrated circuits - they are easier to assemble and not capricious when setting up. So, here are 14 schemes for every taste:
This converter operates at a frequency of 50 kHz, galvanic isolation is provided by transformer T1, which is wound on a K10x6x4.5 ring made of 2000NM ferrite and contains: primary winding - 2x10 turns, secondary winding - 2x70 turns of PEV-0.2 wire. Transistors can be replaced with KT501B. Almost no current is consumed from the battery when there is no load.
Transformer T1 is wound on a ferrite ring with a diameter of 7 mm, and contains two windings of 25 turns of wire PEV = 0.3.
Push-pull unstabilized converter based on a multivibrator (VT1 and VT2) and a power amplifier (VT3 and VT4). The output voltage is selected by the number of turns of the secondary winding of the pulse transformer T1.
Stabilizing type converter based on the MAX631 microcircuit from MAXIM. Generation frequency 40…50 kHz, storage element - inductor L1.
You can use one of the two chips separately, for example the second one, to multiply the voltage from two batteries.
Typical circuit for connecting a pulse boost stabilizer on the MAX1674 microcircuit from MAXIM. Operation is maintained at an input voltage of 1.1 volts. Efficiency - 94%, load current - up to 200 mA.
Allows you to obtain two different stabilized voltages with an efficiency of 50...60% and a load current of up to 150 mA in each channel. Capacitors C2 and C3 are energy storage devices.
8. Pulse boost stabilizer on the MAX1724EZK33 chip from MAXIM
Typical circuit diagram for connecting a specialized microcircuit from MAXIM. It remains operational at an input voltage of 0.91 volts, has a small-sized SMD housing and provides a load current of up to 150 mA with an efficiency of 90%.
A typical circuit for connecting a pulsed step-down stabilizer on a widely available TEXAS microcircuit. Resistor R3 regulates the output voltage within +2.8…+5 volts. Resistor R1 sets the short circuit current, which is calculated by the formula: Is(A)= 0.5/R1(Ohm)
Integrated voltage inverter, efficiency - 98%.
Two isolated voltage converters DA1 and DA2, connected in a “non-isolated” circuit with a common ground.
The inductance of the primary winding of transformer T1 is 22 μH, the ratio of turns of the primary winding to each secondary is 1: 2.5.
Typical circuit of a stabilized boost converter on a MAXIM microcircuit.
Even before the New Year, readers asked me to review a couple of converters.
Well, in principle it’s not difficult for me, and I’m curious myself, I ordered it, received it, tested it.
True, I was more interested in a slightly different converter, but I never got around to it, so I’ll talk about it another time.
Well, today is a review of a simple DC-DC converter with a stated current of 10 Amps.
I apologize in advance for the long delay in publishing this review for those who have been waiting for it for a long time.
To begin with, the characteristics stated on the product page and a small explanation and correction.
Input voltage: 7-40V
1, Output voltage: continuously adjustable (1.25-35V)
2, Output Current: 8A, 10A maximum time within the (power tube temperature exceeds 65 degrees, please add cooling fan, 24V 12V 5A turn within generally be used at room temperature without a fan)
3, Constant Range: 0.3-10A (adjustable) module over 65 degrees, please add fan.
4, Turn lights Current: current value * (0.1) This version is a fixed 0.1 times (actually turn the lamp current value is probably not very accurate) is full of instructions for charging.
5, Minimum pressure: 1V
6, Conversion efficiency: up to about 95% (output voltage, the higher the efficiency)
7, Operating frequency: 300KHZ
8, Output Ripple: about the ripple 50mV (without noise) 20M bandwidth (for reference) Input 24V Output 12V 5A measured
9, Operating temperature: Industrial grade (-40℃ to +85℃)
10, No-load current: Typical 20mA (24V switch 12V)
11, Load regulation: ± 1% (constant)
12, Voltage Regulation: ± 1%
13, Constant accuracy and temperature: the actual test, the module temperature changes from 25 degrees to 60 degrees, the change is less than 5% of the current value (current value 5A)
I'll translate it a little into a more understandable language.
1. Output voltage adjustment range - 1.25-35 Volts
2. Output current - 8 Amps, 10 amperes possible but with additional cooling using a fan.
3. Current adjustment range 0.3-10 Amps
4. The threshold for turning off the charge indication is 0.1 of the set output current.
5. The minimum difference between input and output voltage is 1 Volt (presumably)
6. Efficiency - up to 95%
7. Operating frequency - 300 kHz
8. Output voltage ripple, 50 mV at a current of 5 Amps, input voltage 24 and output 12 Volts.
9. Operating temperature range - from - 40 ℃ to + 85 ℃.
10. Own current consumption - up to 20mA
11. Accuracy of current maintenance - ±1%
12. Voltage maintenance accuracy - ±1%
13. Parameters were tested in the temperature range of 25-60 degrees and the change was less than 5% at a load current of 5 Amps.
The order arrived in a standard plastic bag, generously wrapped with polyethylene foam tape. Nothing was damaged during the delivery process.
Inside was my experimental scarf. 
There are no external comments. I just twisted it in my hands and there wasn’t really anything to complain about, it was neat, and if I replaced the capacitors with branded ones, I would say it was beautiful.
On one side of the board there are two terminal blocks, a power input and output. 
On the second side there are two trimming resistors to adjust the output voltage and current. 
So if you look at the photo in the store, the scarf seems quite large.
I deliberately took the previous two photos close-up. But the understanding of size comes when you put a matchbox next to it.
The scarf is really small, I didn’t look at the sizes when I ordered it, but for some reason it seemed to me that it was noticeably larger. :)
Board dimensions - 65x37mm
Transducer dimensions - 65x47x24mm 
The board is two-layer, double-sided mounting.
There were also no comments regarding the soldering. Sometimes it happens that massive contacts are poorly soldered, but the photo shows that this is not the case here.
True, the elements are not numbered, but I think that’s okay, the diagram is quite simple. 
In addition to the power elements, the board also contains an operational amplifier, which is powered by a 78L05 stabilizer, and there is also a simple reference voltage source assembled using a TL431. 
The board has a powerful PWM controller, and it is even isolated from the heatsink.
I don’t know why the manufacturer isolated the chip from the heatsink, since this reduces heat transfer, perhaps for safety reasons, but since the board is usually built in somewhere, it seems unnecessary to me. 
Since the board is designed for a fairly large output current, a fairly powerful diode assembly was used as a power diode, which was also installed on the radiator and also isolated from it.
In my opinion, this is a very good solution, but it could be improved a little if we used a 60 Volt assembly rather than 100.
The choke is not very large, but in this photo you can see that it is wound in two wires, which is not bad. 
1, 2 There are two 470 µF x 50 V capacitors installed at the input, and two 1000 µF, but 35 V, at the output.
If you follow the list of declared characteristics, then the output voltage of the capacitors is quite close, but it is unlikely that anyone will lower the voltage from 40 to 35, not to mention the fact that 40 Volts for a microcircuit is generally the maximum input voltage.
3. The input and output connectors are labeled, albeit at the bottom of the board, but this is not particularly important.
4. But the tuning resistors are not marked in any way.
On the left is adjustment of the maximum output current, on the right - voltage. 
Now let’s take a little look at the declared characteristics and what we actually have.
I wrote above that the converter uses a powerful PWM controller, or rather a PWM controller with a built-in power transistor.
I also quoted the stated characteristics of the board above, let’s try to figure it out.
Stated - Output voltage: continuously adjustable (1.25-35V)
There are no questions here, the converter will produce 35 Volts, even 36 Volts, in theory.
Stated - Output Current: 8A, 10A maximum
And here's the question. The chip manufacturer clearly indicates the maximum output current is 8 Amps. In the characteristics of the microcircuit there is actually a line - the maximum current limit is 10 Amperes. But this is far from the maximum operating limit; 10 Amps is the maximum.
Stated - Operating frequency: 300KHZ
300 kHz is of course cool, you can put the choke in smaller dimensions, but excuse me, the datasheet clearly says 180 kHz fixed frequency, where does 300 come from?
Stated - Conversion efficiency: up to about 95%
Well, everything is fair here, the efficiency is up to 95%, the manufacturer generally claims up to 96%, but this is in theory, at a certain ratio of input and output voltage. 
And here is the block diagram of the PWM controller and even an example of its implementation.
By the way, it is clearly visible here that for 8 Amperes of current a choke of at least 12 Amps is used, i.e. 1.5 of the output current. I usually recommend using 2x stock.
It also shows that the output diode can be installed with a voltage of 45 Volts; diodes with a voltage of 100 Volts usually have a larger drop and, accordingly, reduce efficiency.
If there is a goal to increase the efficiency of this board, then from old computer power supplies you can pick up diodes of the type 20 Ampere 45 Volt or even 40 Ampere 45 Volt. 
Initially, I didn’t want to draw a circuit; the board on top is covered with parts, a mask, and also silk-screen printing, but then I saw that it was quite possible to redraw the circuit and decided not to change traditions :)
I did not measure the inductance of the inductor, 47 μH was taken from the datasheet.
The circuit uses a dual operational amplifier, the first part is used to regulate and stabilize the current, the second for indication. It can be seen that the input of the second op-amp is connected through a divider of 1 to 11; in general, the description states 1 to 10, but I think that this is not fundamental. 
The first test is at idle, the board is initially configured for an output voltage of 5 Volts.
The voltage is stable in the supply voltage range of 12-26 Volts, the current consumption is below 20 mA as it is not registered by the power supply ammeter. 
The LED will glow red if the output current is greater than 1/10 (1/11) of the set current.
This indication is used to charge batteries, since if during the charging process the current drops below 1/10, then it is usually considered that the charge is complete.
Those. We set the charge current to 4 Amps, it glows red until the current drops below 400mA.
But there is a warning, the board only shows a decrease in current, the charging current does not turn off, but simply decreases further. 
For testing, I assembled a small stand in which they took part.
Pen and paper, lost the link :)
But during the testing process, I eventually had to use an adjustable power supply, since it turned out that due to my experiments, the linearity of measuring/setting the current in the range of 1-2 Amps for a powerful power supply was disrupted.
As a result, I first carried out heating tests and assessed the ripple level. 
Testing this time happened a little differently than usual.
The temperatures of the radiators were measured in places close to the power components, since the temperature of the components themselves was difficult to measure due to the dense installation.
In addition, operation in the following modes was tested.
Input - output - current
14V - 5V - 2A
28V - 12V - 2A
14V - 5V - 4A
Etc. up to current 7.5 A.
Why was testing done in such a cunning way?
1. I was not sure of the reliability of the board and increased the current gradually alternating between different operating modes.
2. The conversion of 14 to 5 and 28 to 12 was chosen because these are one of the most frequently used modes, 14 (approximate voltage of the on-board network of a passenger car) to 5 (voltage for charging tablets and phones). 28 (on-board voltage of a truck) to 12 (simply a frequently used voltage.
3. Initially, I had a plan to test until it turns off or burns out, but plans changed and I had some plans for components from this board. That’s why I only tested up to 7.5 Amps. Although in the end this did not in any way affect the correctness of the check.
Below are a couple of group photos where I will show the 5 Volt 2 Ampere and 5 Volt 7.5 Ampere tests, as well as the corresponding ripple level.
The ripples at currents of 2 and 4 Amperes were similar, and the ripples at currents of 6 and 7.5 Amps were also similar, so I do not give intermediate options. 
Same as above, but 28 Volt input and 12 Volt output. 
Thermal conditions when working with an input of 28 Volts and an output of 12.
It can be seen that there is no point in increasing the current further; the thermal imager already shows the temperature of the PWM controller at 101 degrees.
For myself, I use a certain limit: the temperature of the components should not exceed 100 degrees. In general, it depends on the components themselves. for example, transistors and diode assemblies can be safely operated at high temperatures, and it is better for microcircuits not to exceed this value.
Of course, it’s not very visible in the photo, the board is very compact, and in the dynamics it was visible a little better. 
Since I thought that this board could be used as a charger, I figured out how it would work in a mode where the input is 19 Volts (typical laptop power supply voltage), and the output is 14.3 Volts and 5.5 Amps (typical parameters for charging a car battery).
Here everything went without problems, well, almost without problems, but more on that later. 
I summarized the temperature measurement results in a table.
Judging by the test results, I would recommend not using the board at currents exceeding 6 Amps, at least without additional cooling. 
I wrote above that there were some features, I’ll explain.
During the tests, I noticed that the board behaves a little inappropriately in certain situations.
1.2 I set the output voltage to 12 Volts, the load current to 6 Amps, after 15-20 seconds the output voltage dropped below 11 Volts, I had to adjust it.
3.4 The output was set to 5 Volts, the input was 14, the input was raised to 28 and the output dropped to 4 Volts. In the photo on the left the current is 7.5 Amperes, on the right 6 Amperes, but the current did not play a role; when the voltage rises under load, the board “resets” the output voltage. 
After this, I decided to check the efficiency of the device.
The manufacturer provided graphs for different operating modes. I am interested in the graphs with output 5 and 12 Volts and input 12 and 24, as they are closest to my testing.
In particular, it is declared -
2A - 91%
4A - 88%
6A - 87%
7.5A - 85%
2A - 94%
4A - 94%
6A - 93%
7.5A - Not declared. 
What followed was basically a simple check, but with some nuances.
The 5 Volt test passed without any problems. 
But with the 12 volt test there were some peculiarities, I will describe them.
1. 28V input, 12V output, 2A, everything is fine
2. 28V input, 12V output, 4A, everything is fine
3. We raise the load current to 6 Amps, the output voltage drops to 10.09
4. We correct it by raising it again to 12 Volts.
5. We raise the load current to 7.5 Amperes, it drops again, and we adjust it again.
6. We lower the load current to 2 Amps without correction, the output voltage rises to 16.84.
Initially, I wanted to show how it rose to 17.2 without load, but I decided that this would be incorrect and provided a photo where there is a load.
Yes it's sad:( 
Well, at the same time I checked the efficiency in the mode of charging a car battery from a laptop’s power supply.
But there are some peculiarities here too. At first the output was set to 14.3 V, I ran a heating test and put the board aside. but then I remembered that I wanted to check the efficiency.
I connect the cooled board and observe a voltage of about 14.59 Volts at the output, which dropped to 14.33-14.35 as it warmed up.
Those. In fact, it turns out that the board has instability in the output voltage. and if such a run-up is not so critical for lead-acid batteries, then lithium batteries cannot be charged with such a board categorically. 
I completed two efficiency tests.
They are based on two measurement results, although in the end they do not differ very much.
P out - calculated output power, the value of current consumption is rounded, P out DCL - output power measured by the electronic load. Input and output voltages were measured directly at the board terminals.
Accordingly, two efficiency measurement results were obtained. But in any case, it is clear that the efficiency is approximately similar to the declared one, although slightly less.
I will duplicate what is stated in the datasheet
For 12 Volt input and 5 Volt output
2A - 91%
4A - 88%
6A - 87%
7.5A - 85%
For 24 Volt input and 12 Volt output.
2A - 94%
4A - 94%
6A - 93%
7.5A - Not declared.
And what happened in reality. I think that if you replace the powerful diode with its lower-voltage analogue and install a choke designed for a higher current, you would be able to extract a couple more percent. 
That seems to be all, and I even know what the readers are thinking -
Why do we need a bunch of tests and incomprehensible photos, just tell us what in the end is good or not :)
And to some extent, readers will be right, by and large, the review can be shortened by 2-3 times by removing some of the photos with tests, but I’m already used to it, sorry.
And so the summary.
pros
Quite high quality production
Small size
Wide range of input and output voltages.
Availability of indication of end of charge (reduction of charging current)
smooth adjustment of current and voltage (without problems you can set the output voltage with an accuracy of 0.1 Volt
Great packaging.
Minuses.
For currents above 6 Amps, it is better to use additional cooling.
The maximum current is not 10, but 8 Amperes.
Low accuracy of maintaining the output voltage, its possible dependence on the load current, input voltage and temperature.
Sometimes the board began to “sound”, this happened in a very narrow adjustment range, for example, I change the output from 5 to 12 and at 9.5-10 Volts it beeps quietly.
Special reminder:
The board only displays the current drop; it cannot turn off the charge, it is just a converter.
My opinion. Well, honestly, when I first took the board in my hands and twisted it, examining it from all sides, I wanted to praise it. Made carefully, there were no special complaints. When I connected it, I also didn’t really want to swear, well, it’s heating up, that’s how they all heat up, this is basically normal.
But when I saw how the output voltage jumped from anything, I got upset.
I don't want to investigate these issues because that should be done by the manufacturer who makes money from it, but I will assume that the problem lies in three things
1. Long feedback path running almost along the perimeter of the board
2. Trimmer resistors installed close to the hot choke
3. The throttle is located exactly above the node where the “thin” electronics are concentrated.
4. Non-precision resistors are used in feedback circuits.
Conclusion - it’s quite suitable for an undemanding load, up to 6 Amps for sure, it works well. Alternatively, using the board as a driver for high-power LEDs will work well.
Use as a charger is highly questionable and in some cases dangerous. If lead-acid still reacts normally to such differences, then lithium cannot be charged, at least without modification.
That's all, as always, I'm waiting for comments, questions and additions.
The product was provided for writing a review by the store. The review was published in accordance with clause 18 of the Site Rules.
Planning to buy +121 Add to favorites I liked the review +105 +225Probably many remember my epic with a homemade laboratory power supply.
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 regulated power supply.
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 actual heroine of this review, the converter board. 
The board has a fairly 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, a 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 here it does not work at full capacity, which is good news. However, it is worth considering that it is better not to exceed the input voltage, as this 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
+123
+268
Sometimes you need to get high voltage from low voltage. For example, for a high-voltage programmer powered by a 5-volt USB, you need somewhere around 12 volts.
What should I do? There are DC-DC conversion circuits for this. 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, the feedback voltage from the output is applied. 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.