DC step down converter simple circuit. High voltage DC-DC converter

As you know, in order to light up white and blue LEDs you need at least 3V, unlike red ones which can glow from 1.2 to 1.5 volts depending on the type.

In order for the white LED to start glowing from one 1.5 volt battery, you need to build electronic circuit called . These devices are typically used to produce a higher output voltage compared to the direct current (DC) input.

In circuits with alternating current this function. To obtain a higher output voltage, it is enough that the ratio of the number of turns of the secondary winding to the number of the primary winding is greater than 1 (transformation ratio > 1).

Description of the operation of the LED converter

Coming back to our DC/DC converter, there are many various options implementations of DC-DC conversion, many of which are quite complex. In our case, the goal is to create a simple and efficient converter circuit to step up the voltage from 1.5 V to 3.5 V. Below is a circuit diagram of a similar DC-DC converter for LEDs.

To wind the inductor, you need ferrite, the shape and size of which can be any, but it is better to use a “ring” (or torus) type core 1...1.5 cm in diameter. This is typically used as a filter on power supply wires (the black block next to the connector), and can also be found in pulsed sources power supplies, VCRs, scanners, etc. The winding is made of PEV-2 wire with a diameter of 0.4 mm and contains 30 turns.

The electronic circuit is very simple: it consists of a coil, two transistors, one capacitor and two resistors. The set isn't impressive, but it gets the job done. Current consumption is 25 mA, which is equivalent to approximately 50 hours of continuous operation of an AA battery. The circuit works quite well, providing intermediate level LED glow.

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 pulse 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 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

1. Stabilized voltage source
2. Converter circuit
3. Datasheet
4. USB charger based on LM2596
5. Current stabilizer
6. Use in homemade devices
7. Adjustment of output current and voltage
8. 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 given 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, 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 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 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?

1. 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 5V voltage, 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 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.

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 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 the usual 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 would 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

Input voltages up to 61 V, output voltages from 0.6 V, output currents up to 4 A, the ability to externally synchronize and adjust the frequency, as well as adjust the limiting current, adjust the soft start time, comprehensive load protection, a wide operating temperature range - all these features of modern sources power supplies are achievable using the new line of DC/DC converters produced by .

Currently, the range of switching regulator microcircuits produced by STMicro (Figure 1) allows you to create power supplies (PS) with input voltages up to 61 V and output currents up to 4 A.

The task of voltage conversion is not always easy. Each specific device has its own requirements for the voltage regulator. Sometimes main role Price (consumer electronics), size (portable electronics), efficiency (battery-powered devices), or even the speed of product development play a role. These requirements often contradict each other. For this reason, there is no ideal and universal voltage converter.

Currently, several types of converters are used: linear (voltage stabilizers), pulsed DC/DC converters, charge transfer circuits, and even power supplies based on galvanic insulators.

However, the most common are linear voltage regulators and step-down switching DC/DC converters. The main difference in the functioning of these schemes is evident from the name. In the first case, the power switch operates in linear mode, in the second - in key mode. The main advantages, disadvantages and applications of these schemes are given below.

Features of the linear voltage regulator

The operating principle of a linear voltage regulator is well known. The classic integrated stabilizer μA723 was developed back in 1967 by R. Widlar. Despite the fact that electronics have come a long way since then, the operating principles have remained virtually unchanged.

A standard linear voltage regulator circuit consists of a number of basic elements (Figure 2): power transistor VT1, a reference voltage source (VS), and a compensation feedback circuit on an operational amplifier (OPA). Modern regulators may contain additional functional blocks: protection circuits (from overheating, from overcurrent), power management circuits, etc.

The operating principle of such stabilizers is quite simple. The feedback circuit on the op-amp compares the value of the reference voltage with the voltage of the output divider R1/R2. At the op-amp output, a mismatch is formed that determines the gate-source voltage of power transistor VT1. The transistor operates in linear mode: the higher the voltage at the output of the op-amp, the lower the gate-source voltage, and the greater the resistance of VT1.

This circuit allows you to compensate for all changes in input voltage. Indeed, suppose that the input voltage Uin has increased. This will cause the following chain of changes: Uin increased → Uout will increase → the voltage on the divider R1/R2 will increase → the output voltage of the op-amp will increase → the gate-source voltage will decrease → the resistance VT1 will increase → Uout will decrease.

As a result, when the input voltage changes, the output voltage changes slightly.

When the output voltage decreases, reverse changes in voltage values ​​occur.

Features of operation of a step-down DC/DC converter

A simplified circuit of a classic step-down DC/DC converter (type I converter, buck-converter, step-down converter) consists of several main elements (Figure 3): power transistor VT1, control circuit (CS), filter (Lph-Cph), reverse diode VD1.

Unlike the linear regulator circuit, transistor VT1 operates in switching mode.

The operating cycle of the circuit consists of two phases: the pump phase and the discharge phase (Figures 4...5).

In the pumping phase, transistor VT1 is open and current flows through it (Figure 4). Energy is stored in the coil Lf and capacitor Cf.

During the discharge phase, the transistor is closed, no current flows through it. The Lf coil acts as a current source. VD1 is a diode that is necessary for reverse current to flow.

In both phases, a voltage equal to the voltage on the capacitor Sph is applied to the load.

The above circuit provides regulation of the output voltage when the pulse duration changes:

Uout = Uin × (ti/T)

If the inductance value is small, the discharge current through the inductance has time to reach zero. This mode is called the intermittent current mode. It is characterized by an increase in current and voltage ripple on the capacitor, which leads to a deterioration in the quality of the output voltage and an increase in circuit noise. For this reason, the intermittent current mode is rarely used.

There is a type of converter circuit in which the “inefficient” diode VD1 is replaced with a transistor. This transistor opens in antiphase with the main transistor VT1. Such a converter is called synchronous and has greater efficiency.

Advantages and disadvantages of voltage conversion circuits

If one of the above schemes had absolute superiority, then the second would be safely forgotten. However, this does not happen. This means that both schemes have advantages and disadvantages. Analysis of schemes should be carried out according to a wide range of criteria (Table 1).

Table 1. Advantages and disadvantages of voltage regulator circuits

Electrical characteristics. For any converter, the main characteristics are efficiency, load current, input and output voltage range.

The efficiency value for linear regulators is low and is inversely proportional to the input voltage (Figure 6). This is due to the fact that all the “extra” voltage drops across the transistor operating in linear mode. The transistor's power is released as heat. Low efficiency leads to the fact that the range of input voltages and output currents of the linear regulator is relatively small: up to 30 V and up to 1 A.

The efficiency of a switching regulator is much higher and less dependent on the input voltage. At the same time, it is not uncommon for input voltages of more than 60 V and load currents of more than 1 A.

If a synchronous converter circuit is used, in which the inefficient freewheeling diode is replaced by a transistor, then the efficiency will be even higher.

Accuracy and stability of output voltage. Linear stabilizers can have extremely high accuracy and stability of parameters (fractions of a percent). The dependence of the output voltage on changes in the input voltage and on the load current does not exceed a few percent.

According to the principle of operation, a pulse regulator initially has the same sources of error as a linear regulator. In addition, the deviation of the output voltage can be significantly affected by the amount of current flowing.

Noise characteristics. The linear regulator has a moderate noise response. There are low-noise precision regulators used in high-precision measuring technology.

The switching stabilizer itself is a powerful source of interference, since the power transistor operates in switch mode. Generated noise is divided into conducted (transmitted through power lines) and inductive (transmitted through non-conducting media).

Conducted interference is eliminated using low-pass filters. The higher the operating frequency of the converter, the easier it is to get rid of interference. In measuring circuits, a switching regulator is often used in conjunction with a linear stabilizer. In this case, the level of interference is significantly reduced.

It is much more difficult to get rid of the harmful effects of inductive interference. This noise originates in the inductor and is transmitted through air and non-conducting media. To eliminate them, shielded inductors and coils on a toroidal core are used. When laying out the board, they use a continuous fill of earth with a polygon and/or even select a separate layer of earth in multilayer boards. In addition, the pulse converter itself is as far away from the measuring circuits as possible.

Performance characteristics. From the point of view of simplicity of circuit implementation and printed circuit board layout, linear regulators are extremely simple. In addition to the integrated stabilizer itself, only a couple of capacitors are required.

A switching converter will require at least an external L-C filter. In some cases, an external power transistor and an external freewheeling diode are required. This leads to the need for calculations and modeling, and the topology of the printed circuit board becomes significantly more complicated. Additional complexity of the board occurs due to EMC requirements.

Price. Obviously, due to the large number of external components, a pulse converter will have a high cost.

As a conclusion, the advantageous areas of application of both types of converters can be identified:

• Linear regulators can be used in low power, low voltage circuits with high accuracy, stability and low noise requirements. An example would be measurement and precision circuits. In addition, the small size and low cost of the final solution can be ideal for portable electronics and low-cost devices.
• Switching regulators are ideal for high-power low- and high-voltage circuits in automotive, industrial and consumer electronics. High efficiency often makes the use of DC/DC no alternative for portable and battery-powered devices.

Sometimes it becomes necessary to use linear regulators at high input voltages. In such cases, you can use stabilizers produced by STMicroelectronics, which have operating voltages of more than 18 V (Table 2).

Table 2. STMicroelectronics Linear Regulators with High Input Voltage

If a decision is made to build a pulsed power supply, then a suitable converter chip should be selected. The choice is made taking into account a number of basic parameters.

Main characteristics of step-down pulse DC/DC converters

Let us list the main parameters of pulse converters.

Input voltage range (V). Unfortunately, there is always a limitation not only on the maximum, but also on the minimum input voltage. The value of these parameters is always selected with some margin.

Output voltage range (V). Due to restrictions on the minimum and maximum pulse duration, the range of output voltage values ​​is limited.

Maximum output current (A). This parameter is limited by a number of factors: the maximum permissible power dissipation, the final value of the resistance of the power switches, etc.

Converter operating frequency (kHz). The higher the conversion frequency, the easier it is to filter the output voltage. This makes it possible to combat interference and reduce the values ​​of the external L-C filter elements, which leads to an increase in output currents and a reduction in size. However, an increase in the conversion frequency increases switching losses of power switches and increases the inductive component of interference, which is clearly undesirable.

Efficiency (%) is an integral indicator of efficiency and is given in the form of graphs for various voltages and currents.

The remaining parameters (channel resistance of integrated power switches (mOhm), self-current consumption (µA), thermal resistance of the housing, etc.) are less important, but they should also be taken into account.

The new converters from STMicroelectronics have high input voltage and efficiency, and their parameters can be calculated using the free eDesignSuite software.

Line of pulsed DC/DC from ST Microelectronics

STMicroelectronics' DC/DC portfolio is constantly expanding. New converter microcircuits have an extended input voltage range up to 61 V ( / / ), high output currents, output voltages from 0.6 V ( / / ) (Table 3).

Table 3. New DC/DC STMicroelectronics

All new pulse converter microcircuits have soft start, overcurrent and overheating protection functions.

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

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

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

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

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

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

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

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

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

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

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

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In this homemade product, AKA KASYAN will make a universal step-down and step-up voltage converter.

The author recently assembled a lithium battery. And today he will reveal the secret for what purpose he made it.

The supply voltages for these gadgets have a very wide range.
For example, smartphones need only 5 V, laptops 18, some even 24 V.
The battery manufactured by the author is designed for an output voltage of 14.8 V.
Therefore, a converter capable of both increasing and decreasing the initial voltage is required.

Therefore, the scheme is universal. The parameters depend on the capacitance of the capacitors, the parameters of the inductor, the diode rectifier and the characteristics of the field switch.

The output voltage is set by resistor R3