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 converting the voltage to the required level is only possible using DC/DC converters.
The idea is quite simple: constant pressure is converted into an alternating voltage, as a rule, with a frequency of several tens and even hundreds of kilohertz, increases (decreases), and then is rectified and fed 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 are good because they have high efficiency, ranging from 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 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 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 protection of the converter from short circuit.
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.
DC-DC converters (Converters)– modular electronic devices, intended for constructing power buses in circuits with galvanic isolation. The devices are ready-made devices that convert DC voltage to DC, made in sealed, protected housings with leads for mounting on a printed circuit board. Converters differ in their power, design, number of output channels, and range of input and output voltages.
The company presented a line of high-performance products TRACO ELECTRONIC And AIMTEC. The converters have high reliability and performance, operate in a wide range of input voltages, and provide the load with a high output current, both through one and two output channels. The small dimensions of product cases allow them to be used in modern microelectronics with high packing density. Product series TMA 0505 D, 0512 D, 0515 D are boost converters with a bipolar output voltage, and an output current sufficient to power the operational amplifiers of various portable battery-powered equipment.
A well-known Japanese company presented a range of high-tech DC / DC converters MURATA POWER, whose products are in great demand in various sectors of industrial electronics. Specialized compact products are produced both in closed, sealed cases and in open modular versions for mounting on a board. A special element of modular devices are stabilized, isolated DC / DC converters with fixed input and output voltage, especially in demand in medical technology and telecommunications equipment.
Features of the company's products PEAK Electronics are unique developments of miniature DC/DC converter modules for cost-effective portable electronics. Modular devices are produced in closed, sealed housings, with one or two non-isolated outputs, and bipolar output voltage, as well as modules operating in voltage multiplying mode, for example , P 10 CU -0512 ZLF, P 6 CU -0512 ZLF.
You can view and buy goods in our stores in the cities: Moscow, St. Petersburg, Volgograd, Voronezh, Yekaterinburg, Izhevsk, Kazan, Kaluga, Krasnodar, Krasnoyarsk, Minsk, Naberezhnye Chelny, Nizhny Novgorod, Novosibirsk, Omsk, Perm, Rostov-on-Don on-Don, Ryazan, Samara, Tver, Tomsk, Tula, Tyumen, Ufa, Chelyabinsk. Delivery of the order by mail, through the Pickpoint delivery system or through Euroset showrooms to the following cities: Tolyatti, Barnaul, Ulyanovsk, Irkutsk, Khabarovsk, Yaroslavl, Vladivostok, Makhachkala, Tomsk, Orenburg, Kemerovo, Novokuznetsk, Astrakhan, Penza, Lipetsk, Kirov, Cheboksary, Kaliningrad, Kursk, Ulan-Ude, Stavropol, Sochi, Ivanovo, Bryansk, Belgorod, Surgut, Vladimir, Nizhny Tagil, Arkhangelsk, Chita, Smolensk, Kurgan, Orel, Vladikavkaz, Grozny, Murmansk, Tambov, Petrozavodsk, Kostroma, Nizhnevartovsk , Novorossiysk, Yoshkar-Ola, etc.
You can buy products from the “DC-DC converters (Converters)” group wholesale and retail.
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. Based on this stabilizer it is easy to make pulse block power supply, I use it as a simple and reliable laboratory block 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 your car LED matrix at 10 watts, 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 batteries or rechargeable batteries, 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 large quantities in stock 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, good example this is shown 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 that when using the LM2596 as a step-down converter after the transformer and rectifier, the input capacitor (i.e. the one immediately after diode bridge) may have a small capacity (about 50-100 µF).
Output capacitor
Thanks to high frequency conversion, 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 task) - 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 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 car battery with a cigarette lighter connector - and switch 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.
Classical linear stabilizer current is 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 submit for it is our business.
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 in it both diodes are made within the same technological process and on one 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
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 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:
- LM2577, obsolete with low efficiency;
- XL4016, 2 times more efficient than 2577;
- XL6009;
- 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:
- 12V - 19V;
- 12 - 24 Volts;
- 5 - 12V;
- 3 - 12V
- 12 - 220V;
- 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'm 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 470mF 50V, at the other end 470mF at 35V.
On XL6009
Representative of modern efficient converters, like outdated models The LM2596 is available in several variants, 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:
- power 600W;
- 10-60V converts to 12-80V;
- price from 800 rub.
You can find it by searching “600W DC 10-60V to 12-80V Boost Converter Step Up”
400W
Powerful #2:
- power 400W;
- 6-40V converts to 8-80V;
- output up to 10A;
- price from 1200 rub.
To search, enter in the search engine “DC 400W 10A 8-80V Boost Converter Step-Up”
B900W
Powerful #3:
- power 900W;
- 8-40V converts to 10-120V;
- output up to 15A.
- price from 1400 rub.
The only unit that is designated as B900W and can be easily found.
DC voltage converter (12/24V - 5V 5A). Model 122405B25Z
This converter uses the latest high-frequency conversion technologies to achieve small size, high efficiency and reliability. The converter has a plastic housing. Suitable for use on cars, electric vehicles, autonomous power supply systems to power various 5V DC loads. Can be used for power or recharging mobile phones, smartphones, MP3 players, tablets (not all!), etc., which are powered by 5V DC.
Technical specifications
Peculiarities
- Aluminum housing with epoxy resin sealing - waterproof, dustproof;
- Lightweight, compact, easy to use and transport;
- Protection against overload, overheat, overvoltage, low voltage, output short circuit.
- Automatic recovery after protection is triggered