Power supply based on a ready-made adjustable DC-DC converter. Overview of adjustable voltage converters (stabilizers, DC-DC converters) DC-DC module control

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 price (consumer electronics), size (portable electronics), efficiency (battery-powered devices), or even the speed of product development play a major 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.

Standard scheme linear voltage regulator consists of a number of main elements (Figure 2): power transistor VT1, reference voltage source (VS), compensation circuit feedback on operational amplifier(OU). 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. A mismatch is formed at the op-amp output, which 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 characteristics. 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 powerful low- and high voltage circuits in automotive, industrial and consumer electronics. High efficiency often makes the use of DC/DC no alternative for portable devices 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 case, etc.) are less important, but they should also be taken into account.

New converters from STMicroelectronics have high input voltage and efficiency, and their parameters can be calculated using free program eDesignSuite.

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.

One of the most popular devices in the workshop of a novice radio amateur is an adjustable power supply. I have already talked about how to independently assemble an adjustable power supply using the MC34063 chip. But it also has limitations and disadvantages. Firstly, it's power. Secondly, the lack of output voltage indication.

Here I will talk about how to assemble an adjustable power supply of 1.2 - 32 volts and a maximum output current of up to 4 amperes with a minimum of time and effort.

To do this we need two very important elements:

Transformer, with output voltage up to ~25...26 volts. I will tell you further about how to pick it up and where to find it;

Ready module adjustable DC-DC converter with built-in voltmeter based on a microcircuit XL4015.

The most common and cheapest modules based on microcircuits XL4015 and LM2956. The cheapest option is a module without digital voltmeter. For myself, I bought several versions of such DC-DC converters, but most of all I liked the module based on the XL4015 chip with a built-in voltmeter. This is what we will talk about.

This is what he looks like. I bought it on Aliexpress, here is the link. You can choose the one that suits you by price and modification through the search.

Reverse side of the board and side view.

Main characteristics of the module:

Let's not forget that manufacturers like to inflate the characteristics of their products. Judging by the reviews, the most optimal option for using this DC-DC module is to operate with an input voltage of up to 30 volts and a current consumption of up to 2 amperes.

DC-DC module control.

On the printed circuit board of the DC-DC module there are two control buttons and an output voltage regulator - a conventional multi-turn variable resistor.

Short press of the button 1 disables/enables the voltmeter indication. A kind of dimmer. Convenient when powered by battery.

Short press the button 2 you can switch the operating mode of the voltmeter, namely, displaying the input or output voltage on the indicator. When used in conjunction with a battery, you can control the battery voltage and prevent deep discharge.

Calibration of voltmeter readings.

First, use button 2 to select which voltage to display on the voltmeter display (input or output). Then use a multimeter to measure the DC voltage (input or output) at the terminals. If it differs from the voltage displayed by the voltmeter, then we begin calibration.

Press the 2nd button for 3-4 seconds. The display should go dark. Let's release the button. In this case, the readings on the display will appear and begin to blink.

Next, by briefly pressing buttons 1 and 2, we decrease or increase the value of the displayed voltage in steps of 0.1V. If you need to increase the readings, for example, from 12.0V to 12.5V, then press button 2 5 times. If you need to decrease from 12V to 11.5V, then, accordingly, press button 1 5 times.

After the calibration is completed, press button 2 for 5 seconds. In this case, the readings on the voltmeter display will stop blinking - the calibration is completed. You can also do nothing and after 10 seconds the voltmeter will exit the calibration mode.

In order to assemble a power supply, in addition to the DC/DC module itself, we need a transformer, as well as a small circuit - a diode bridge and a filter.

Here is the diagram that we have to assemble.

(The picture is clickable. Click it to open in a new window)

I’ll talk about transformer T1 a little later, but now let’s look at the diode bridge VD1-VD4 and filter C1. I will call this part of the circuit rectifier. Next in the photo are the necessary parts for its assembly.

I drew the layout of future printed tracks on the board with a marker for printed circuit boards. Before this, I made a sketch of the arrangement of elements on the board and routed the connecting conductors. Then, using the template, I marked the drilling locations on the workpiece. I drilled before etching in ferric chloride, since if you drill after etching, nicks may remain around the holes and easily damage the edging around the holes.

Then I dried the workpiece after etching and washed off the protective layer of varnish from the marker with White Spirit. After that, I washed and dried the workpiece again, cleaned the copper tracks with fine sandpaper and tinned all the tracks with solder. This is what happened.

A little about the miscalculations. Since I did everything quickly and on my knees, there were, of course, some “jambs.” Firstly, I made the board double-sided, but it wasn’t necessary. The fact is that the holes are not metallized, and then soldering the same connector into such a double-sided printed circuit board is not an easy task. On one side you can solder the contacts without any problems, but on the other side of the board you can’t. So I got tired of it.

Ready straightener.

Instead of the mains switch, SA1 temporarily soldered a jumper. Installed input and output connectors, as well as a connector for connecting a transformer. I installed the connectors with modularity and ease of use in mind, so that in the future it would be possible to quickly and without soldering connect the rectifier unit with different DC-DC modules.

As fuse FU1 used ready-made with holder. Very comfortably. And the live contacts are covered, and replacing the fuse without soldering is not a problem. In theory, a fuse in any design and type of housing is suitable.

As diode bridge(VD1 - VD4) I used an RS407 assembly for a maximum forward current of 4 amperes. Analogues of the RS407 diode bridge are KBL10, KBL410. A diode bridge can also be assembled from separate rectifier diodes.

Here it is worth understanding that the adjustable DC-DC module itself is designed for a maximum current of 5 amperes, but it can withstand such a current only if a radiator is installed on the XL4015 chip, and for the SS54 diode on the board, the current is 5A - maximum!

Let’s also not forget that manufacturers tend to overestimate the capabilities of their products and their service life under such loads. Therefore, I decided for myself that such a module can be loaded with current up to 1 - 2 amperes. We are talking about a constant, long-term load, and not periodic (pulse).

In this situation, the diode bridge can be selected for a direct current of 3-4 amperes. This should be plenty to spare. Let me remind you that if you assemble a diode bridge from individual diodes, then each of the diodes included in the bridge must withstand the maximum current consumption. In our case it is 3-4 amperes. Diodes 1N5401 - 1N5408 (3A), KD257A (3A), etc. are quite suitable.

Also for assembly you will need an electrolytic capacitor C1 with a capacity of 470 - 2200 μF. It is better to choose a capacitor for an operating voltage of 63V, since the maximum input voltage of a DC-DC converter can be up to 36V, or even 38...40V. Therefore, it is wiser to install a capacitor at 63V. With reserve and reliability.

Here, again, it is worth understanding that everything depends on what voltage you will have at the input of the DC-DC module. If, for example, you plan to use the module to power a 12-volt LED strip, and the input DC-DC voltage of the module is only 16 volts, then the electrolytic capacitor can be supplied with an operating voltage of 25 volts or more.

I set it to the maximum, since I planned to use this module and the assembled rectifier with different transformers that have different output voltages. Therefore, in order not to solder the capacitor every time, I set it to 63V.

Any network transformer with two windings is suitable as transformer T1. The primary winding (Ⅰ) is network and must be designed for an alternating voltage of 220V, the secondary winding (Ⅱ) must produce a voltage of no more than 25 ~ 26 volts.

If you take a transformer whose output will be more than 26 volts AC voltage, then after the rectifier the voltage may already be more than 36 volts. And, as we know, the DC-DC converter module is designed for input voltage up to 36 volts. It is also worth considering the fact that in a 220V household power supply the voltage is sometimes slightly too high. Because of this, even if only briefly, a rather significant voltage “jump” can form at the output of the rectifier, which will exceed permissible voltage at 38...40 volts for our module.

Approximate calculation of output voltage U out after the diode rectifier and filter on the capacitor:

U out = (U T1 - (V F *2))*1.41.

Alternating voltage on the secondary winding of transformer T1 (Ⅱ) - U T1;

Voltage drop ( Forward Voltage Drop ) on rectifier diodes - V F. Since in a diode bridge the current flows through two diodes in each half-cycle, then V F multiply by 2. For the diode assembly the situation is the same.

So, for RS407 in the datasheet I found the following line: Maximum forward Voltage drop per bridge element at 3.0A peak- 1 Volt. This means that if a direct current of 3 amperes flows through any of the bridge diodes, then 1 volt of voltage will be lost across it ( per bridge element - for each element of the bridge). That is, we take the value V F= 1V and, as in the case of individual diodes, multiply the value V F by two, since in each half-cycle the current flows through two elements of the diode assembly.

In general, in order not to rack your brains, it is useful to know that V F for rectifier diodes it is usually about 0.5 volts. But this is with a small forward current. As it increases, the voltage drop also increases V F at the p-n junction of the diode. As we see, the value V F with a forward current of 3A for diodes of the RS407 assembly it is already 1V.

Since the peak value of the rectified (pulsating) voltage is released on the electrolytic capacitor C1, the final voltage that we get after the diode bridge ( U T1 - (V F*2)) must be multiplied by the square root of 2, namely √2 ~ 1.41 .

So with this simple formula we can determine the output voltage of the filter. Now all that's left to do is find a suitable transformer.

As a transformer I used the TP114-163M power armor transformer.

Unfortunately, I did not find accurate data on it. The output voltage on the secondary winding without load is ~19.4V. The approximate power of this transformer is ~7 W. I counted by .

In addition, I decided to compare the data obtained with the parameters of the series transformers TP114(TP114-1, TP114-2,...,TP114-12). The maximum output power of these transformers is 13.2 W. The most suitable parameters for the transformer TP114-163M turned out to be TP114-12. The voltage on the secondary winding in idle mode is 19.4V, and under load - 16V. Rated load current - 0.82A.

I also had another transformer at my disposal, also of the TP114 series. Here it is.

Judging by the output voltage (~22.3V) and the laconic marking 9M, this is a modification of the transformer TP114-9. The parameters of TP114-9 are as follows: rated voltage - 18V; rated load current - 0.73A.

Based on the first transformer ( TP114-163M) I will be able to make an adjustable power supply of 1.2...24 volts, but this is without load. It is clear that when a load (current consumer) is connected, the voltage at the output of the transformer will drop, and the resulting voltage at the output of the DC-DC converter will also decrease by several volts. Therefore, this point must be taken into account and kept in mind.

Based on the second transformer ( TP114-9) you will now have an adjustable power supply of 1.2...28 volts. It's also load-free.

About the output current. The manufacturer stated that the maximum output current of the DC-DC converter is 5A. Judging by the reviews, maximum 2A. But, as you can see, I managed to find quite low-power transformers. Therefore, I’m unlikely to be able to squeeze out even 2 amperes, although it all depends on the output voltage of the DC-DC module. The smaller it is, the more current you can get.

For any low-power “razor” this power supply will be a great fit. Here is the powering of the “laughing ball” with a voltage of 9V and a current of about 100 mA.

And this is already powering a 12-volt LED strip about 1 meter long.

There is also a lightweight, Lite version of this DC-DC converter, which is also assembled on the XL4015E1 chip.

The only difference is the lack of a built-in voltmeter.

The parameters are similar: input voltage 4...38V, maximum current 5A (recommended no more than 4.5A). It is realistic to use it with an input voltage of up to 30V, 30V or more. Load current no more than 2...2.5A. If you load it more, it heats up noticeably and, naturally, the service life and reliability decrease.

DC/DC converters are widely used to power various electronic equipment. They are used in computing devices, communication devices, various schemes control and automation, 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: direct voltage is converted into alternating voltage, usually with a frequency of several tens or even hundreds of kilohertz, increased (decreased), and then rectified and supplied to the load. Such converters are often called pulse converters.

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

Rice. 1. Converter 1.5V/5V

Pulse converters 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 the specific device in which the converter will be used.

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

Step-down converter chopper - buck converter

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

Fig.2. Functional diagram chopper stabilizer

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

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

Pulse width modulation - PWM

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

Fig.3. Control pulses

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

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

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

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

In general, converters have become so widely used that manufacturing companies electronic components launched the production of PWM controllers for all occasions. The assortment is so large that just to list them you would need a whole book. Therefore, collect converters on discrete elements, or as they often say in “rassypukh”, does not occur to anyone.

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

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

Fig.4. Phase 1

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

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

Fig.5. Phase 2

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

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

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

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

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

Step-up or boost converters

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

Fig.6. Functional diagram of a boost converter

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

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

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

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

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

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

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

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

Fig.7. Functional diagram of the SEPIC converter

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

SEPIC converters are used in applications where the input voltage varies widely. An example is 4V-35V to 1.23V-32V Boost Buck Voltage Step Up/Down Converter Regulator. It is under this name that the converter is sold in Chinese stores, the diagram 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 in accordance with 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.

Tony Armstrong Translation: Pavel Bashmakov active@site Vladimir Rentyuk

Introduction

The technical policy of telecommunications equipment manufacturers, in response to market demands, is aimed at constantly increasing the throughput and efficiency of the systems they produce, as well as improving their functionality and overall specifications. At the same time, the issues of reducing the overall energy consumption of manufactured systems also remain relevant. For example, a typical goal is to reduce overall power consumption by redirecting worker thread and moving workload to underutilized servers, allowing some servers that are currently freed to be shut down. To meet these requirements, it is necessary to know the power consumption of the end-user equipment. Thus, a properly designed digital power management system (DPSM) can provide the user with data on power consumption, which helps implement intelligent, or, as they say, “smart” solutions for managing overall energy consumption.

The main advantage and benefit of using DPSM technology is reduced development costs and reduced time to market for the final product. Complex multi-bus systems can be efficiently created using a comprehensive development environment with an intuitive graphical user interface (GUI). In addition, such systems simplify testing and debugging of the device, making it possible to make changes directly through the graphical interface instead of soldering jumpers. Another benefit is predicting power system failures and implementing preventive measures, which is made possible by the availability of real-time telemetry data. Perhaps most importantly, DC/DC converters with digital control capabilities enable designers to design green power systems that deliver the required performance with minimal power consumption at load points. Moreover, the benefits already exist at the installation level of such systems, reducing infrastructure costs and the overall cost of using the system over the entire life of the product.

Most telecommunications systems are powered via a 48V rail, which is then typically stepped down to an intermediate rail voltage, typically in the 12V to 3.3V voltage range, which directly powers the cards in the system racks. However, most auxiliary circuits or ICs on boards must operate at voltages ranging from less than 1 V to 3.3 V at currents ranging from tens of milliamps to hundreds of amps. As a result, DC/DC converters used in POL (Point-of-Load) technology must step down the intermediate bus voltage to the voltage required by these auxiliary circuits or microcircuits. Such buses are subject to very strict requirements for compliance with the switching sequence, voltage accuracy, margining and control (usually using the supervisor function).

There are up to fifty different POL buses in telecommunications systems, and system designers need a simple way to control these buses, both with respect to output voltage, the sequence of their activation and the level of maximum allowable load current. For example, some processors require that their I/O ports be supplied with voltage before the main voltage is applied to the core. Other solutions, in particular DSP (English DSP - Digital Signal Processor, digital signal processor), provide for the supply of its main voltage even before the voltage arrives at the input/output ports. Compliance with a certain procedure for relieving stress when turning off the power is also a prerequisite. In order to simplify the power design, the system designer needs an easy way to make all the necessary changes to optimize the system's performance while still maintaining the specific configuration required for each of its DC/DC converters.

In addition, to simultaneously meet the requirements for all the multiple power rails on the boards and to reduce the area of ​​the boards themselves, system designers must have relatively simple voltage converters, since voltage converters with a height of more than 2 mm cannot be placed on the back side of the boards, due to installation density, if it is performed in rack racks. Therefore, specialists really need such completely complete power supplies in a small form factor.

Solution

μModule companies present a complete complete so-called system in a package - SiP (English SiP - System in a Package). The use of such a design minimizes design time and makes it possible to reduce the area of ​​printed circuit boards and increase the layout density.

DC/DC converters type μModule is a complete power management solution with a built-in controller, power transistors, input and output capacitors, compensation circuit elements and inductors, housed in compact surface mount packages such as BGA or LGA. Designing with DC/DC converters such as μModules can significantly reduce development time. Thus, the time required to complete the design process, depending on the complexity of the design, can be reduced by up to 50%. The μModule family relieves the developer of the heavy burden of component selection, optimization and device layout, reducing total time system development and search possible malfunctions, and ultimately speeds up the product's time to market.

Solutions based on DC/DC converters μModule from company Linear Technology, Designed in a compact, IC-like form factor, they integrate all key components and are commonly used to replace power supplies on discrete components, signal circuits, and isolated structures. Thanks to careful control and rigorous testing by the company Linear Technology DC/DC converters family μModule are distinguished by high reliability, and the wide available range of such products simplifies their selection to optimize the design and placement of converters on a specific printed circuit board.

Product family μModule covers the widest range of applications, including PoL modules, charging device, LED drivers, power management chips (digitally controlled PMBus power supplies) and isolated converters. Line converters μModule Power solutions reduce design time and overcome space constraints while delivering high efficiency, reliability and, for some products, lower radiated electromagnetic interference (EMI) solutions that meet EN55022 Class B requirements.

Rice. 1. Low profile μModule line sources (less than 2mm height) can be placed on both sides of the PCB

Since, due to the increased complexity of the system, all its constituent structural elements are dispersed, and the design cycles themselves are shortened as much as possible, the issue of intellectual property of such a system as a whole comes to the fore. This often means that power system design cannot be left until the entire design cycle is completed. With little time and very limited resources, power system designers are often faced with the challenge of creating the most consistent, high-efficiency power system possible while occupying the smallest amount of PCB space. To solve precisely such problems, power supplies of the μModule line were created, combining the high efficiency of a pulse converter and the ease of use of LDO.

Careful design, correct PCB layout, careful selection of components - all this is an integral and time-consuming task when designing an effective power system. When time is extremely limited or experience in creating such systems is insufficient, ready-made modular power supplies from the μModule line will help save your time and eliminate the risk of missing project deadlines.

As an example, let's take a super-compact pulse DC/DC voltage regulator -. This is a dual-channel 2.5A per channel/single-channel 5-A step-down voltage regulator in a micromodular design in a tiny, super-thin LGA package of 6.25 x 6.25 x 1.82 mm. The profile of this source is comparable to the profile of a standard ceramic capacitor in the 1206 package, which allows this source to be placed on both the top and bottom sides of the printed circuit board, significantly reducing the footprint, which is especially important for PCIe format cards and mezzanine connection types (Fig. 1 ).

DC/DC converters family μModule companies Linear Technology also represent a solution that simultaneously provides high output power, and DPSM functionality.

Table. List of Low Profile Modular DC/DC Power Supplies from Linear Technology

Since many voltage stabilizers of the family μModule for high current loads can be connected in parallel, and with high precision matching in the distribution of currents (within a nominal deviation of 1% from each other), this reduces the risk of local overheating points. In addition, it is sufficient that only one of the connected voltage stabilizers μModule provided the ability to implement DPSM functionality, and it is he who is able to provide a complete digital interface, even if other μModule devices connected in parallel do not have the ability to implement the DPSM function. In Fig. Figure 2 shows a circuit for a solution for a current of 180 A plus the implementation of the DPSM function for PoL technology. This solution is based on one module LTM4677(μModule voltage regulator with DPSM function for current up to 36 A), connected in parallel with three LTM4650 (μModule voltage stabilizer for current up to 50 A without DPSM function).

Rice. 2. The combination of one LTM4677 DPSM μModule and three LTM4650 μModule family voltage regulators allows you to implement a power supply with an output voltage of 1 V and a current of 186 A from the input intermediate bus with a nominal input voltage of 12 V

Conclusion

With DPSM capability and ultra-thin profiles, power designers can easily implement modern systems meet design requirements and provide high 1V output power to power the latest sub-20nm application-specific integrated circuits (ASICs), GPU cores and FPGAs. When mounted on a PCB, the LTM4622 optimizes the use of space on the underside of the board thanks to its ultra-thin profile. Of course, this solution does not significantly save expensive space on the board, but it reduces General requirements cooling due to greater efficiency.

And in conclusion, I would like to remind you that the use of voltage stabilizers of the μModule family makes sense in those areas where it significantly reduces debugging time and helps to use the printed circuit board area more efficiently. The result is reduced infrastructure costs as well as total ownership costs over the life of the end product.

Samples and debugging tools can be requested at

Principle of operation

The principle of operation is contained in the name itself. Direct voltage is converted to alternating voltage. After this, it is raised or lowered, followed by straightening and feeding to the device. DC-DC converters operating on the above principle are called pulse converters. The advantage of pulse converters is their high efficiency: around 90%.

The output voltage of these converters is lower than the input. For example, with an input voltage of 12-50 V, using such DC-DC converters you can get a voltage of several volts at the output.

Voltage converters also differ in design. They can be:

Modular
This is the most common type of DC-DC converters, including a huge number of the most different models. The converter is placed in a metal or plastic case, excluding access to internal elements.
For PCB mounting

These converters are designed specifically for mounting on a printed circuit board. They differ from modular ones in that they do not have a housing.

→ The output voltage range includes the parameters that the DC-DC converter is capable of producing at the output during normal operation.

→ The coefficient of performance (efficiency) is the ratio of the input and output power values. Efficiency depends on a number of conditions, but the highest efficiency is achieved at the maximum permissible load. The greater the difference between the input and output voltage, the lower the efficiency.

→Output current limitation. This protection is available in most modern stabilizer models. It works as follows: as soon as the output current reaches the set value, the input voltage drops. Once the output current is within the acceptable range, the voltage supply is resumed.

Accuracy parameters

→ Ripple. Even under ideal conditions, certain “noises” are present, so it is impossible to completely eliminate them. The units of measurement are mV. Sometimes the manufacturer puts “rr” next to it, which means the range of ripple voltage - from the minimum of the negative peak to the maximum of the positive.

Controls
The controls are represented by four buttons.