As already noted, smoothing voltage pulses using an LC filter is necessary so that the filter cutoff frequency f 0 = 2/ was significantly lower than the repetition rate of voltage pulses. This condition allows you to choose the necessary capacitance and inductance of the filter. However, let's digress from the formulas and try to explain the principle of the filter in a simpler language.

At the moment when the power switch is open (transistor T 1 is open, transistor T 2 is closed), energy from the input source is transferred to the load through the inductance L in which energy is stored. The current flowing through the circuit does not change instantly, but gradually, since the EMF that occurs in the inductance prevents the current from changing. At the same time, the capacitor installed in parallel with the load is also charged.

After the power switch closes (transistor T 1 is closed, transistor T 2 is open), the current from the input voltage line does not flow into the inductance, but according to the laws of physics, the emerging induction EMF maintains the current direction. That is, during this period, the current is supplied to the load from the inductive element. In order for the circuit to close and the current to flow to the smoothing capacitor and to the load, the transistor T 2 opens, providing a closed circuit and current flow along the path inductance - capacitance and load - transistor T 2 - inductance.

As already noted, using such a smoothing filter, you can get a voltage at the load that is proportional to the duty cycle of the PWM control pulses. However, it is clear that with this method of smoothing output voltage will have supply voltage ripple relative to some average value (output voltage) - fig. 4. The magnitude of the voltage ripple at the output depends on the switching frequency of the transistors, the value of the capacitance and inductance.

Rice. 4. Voltage ripple after smoothing with an LC filter

Output voltage stabilization and PWM controller functions

As already noted, the output voltage depends (for a given load, frequency, inductance and capacitance) on the duty cycle of the PWM pulses. Since the current through the load changes dynamically, the problem arises of stabilizing the output voltage. This is done in the following way. PWM controller that generates transistor switching signals is connected to the load in a loop feedback and continuously monitors the output voltage at the load. Inside the PWM controller, a reference supply voltage is generated, which should be on the load. The PWM controller constantly compares the output voltage with the reference voltage, and if a mismatch occurs U, then this error signal is used to change (correct) the duty cycle of the PWM pulses, that is, the change in the duty cycle of the pulses ~ U. Thus, the stabilization of the output voltage is realized.

Naturally, the question arises: how does the PWM controller know about the required supply voltage? For example, if we talk about processors, then, as you know, the supply voltage different models processor may be different. In addition, even for the same processor, the supply voltage can dynamically change depending on its current load.

The PWM controller learns about the required nominal supply voltage by the VID (Voltage Identifier) ​​signal. For modern processors Intel Core i7 processors that support the VR 11.1 power specification, the VID signal is 8-bit, and for legacy processors that are compatible with the VR 10.0 specification, the VID signal was 6-bit. The 8-bit VID signal (a combination of 0 and 1) allows you to set 256 different levels of processor voltage.

Limitations of a single-phase switching supply voltage regulator

The single-phase circuit of the switching supply voltage regulator considered by us is simple in execution, but it has a number of limitations and disadvantages.

If we talk about the limitation of a single-phase switching supply voltage regulator, then it lies in the fact that MOSFETs, inductances (chokes), and capacitances have a limit on the maximum current that can be passed through them. For example, for most MOSFET transistors that are used in motherboard voltage regulators, the current limit is 30 A. At the same time, the processors themselves, with a supply voltage of about 1 V and a power consumption of more than 100 W, consume more than 100 A. It is clear that if at such a current strength a single-phase supply voltage regulator is used, then its elements will simply “burn out”.

If we talk about the disadvantage of a single-phase switching supply voltage regulator, then it lies in the fact that the output supply voltage has ripples, which is highly undesirable.

In order to overcome the current limitations of switching voltage regulators, as well as to minimize output voltage ripple, polyphase switching voltage regulators are used.

Multi-phase switching voltage regulators

In polyphase switching voltage regulators, each phase is formed by a MOSFET switching driver, a pair of MOSFETs themselves, and an LC smoothing filter. In this case, one multichannel PWM controller is used, to which several power phases are connected in parallel (Fig. 5).

Rice. 5. Structural scheme multiphase switching supply voltage regulator

The use of an N-phase supply voltage regulator allows you to distribute the current over all phases, and therefore, the current flowing through each phase will be in N times less than the load current (in particular, the processor). For example, if you use a 4-phase processor supply voltage regulator with a current limit of 30 A in each phase, then the maximum current through the processor will be 120 A, which is quite enough for most modern processors. However, if processors with a TDP of 130 W are used or the possibility of overclocking the processor is expected, then it is advisable to use not a 4-phase, but a 6-phase switching processor supply voltage regulator, or use chokes, capacitors and MOSFETs designed for a higher current in each phase of the supply .

To reduce the output voltage ripple in multi-phase voltage regulators, all phases operate in synchronism with the time s m shift relative to each other. If T is the switching period of the MOSFETs (PWM signal period) and is used N phases, then the time shift for each phase will be T/N(Fig. 6). The PWM controller is responsible for synchronizing the PWM signals for each phase with a time shift.

Rice. 6. Timing shifts of PWM signals in a polyphase voltage regulator

As a result of the fact that all phases work with time s m shift relative to each other, the ripple of the output voltage and current for each phase will also be shifted along the time axis relative to each other. The total current passing through the load will be the sum of the currents in each phase, and the resulting current ripple will be less than the current ripple in each phase (Fig. 7).

Rice. 7. Current per phase
and resulting load current
in a three-phase voltage regulator

So, the main advantage of multi-phase switching supply voltage regulators is that they allow, firstly, to overcome the current limit, and secondly, to reduce the output voltage ripple with the same capacitance and inductance of the smoothing filter.

Discrete Multi-Phase Voltage Regulators and DrMOS Technology

As we already noted, each power phase is formed by a control driver, two MOSFETs, a choke and a capacitor. At the same time, one PWM controller simultaneously controls several power phases. Structurally, on motherboards, all phase components can be discrete, that is, there is a separate driver chip, two separate MOSFET transistors, a separate inductor and capacitance. This discrete approach is used by most motherboard manufacturers (ASUS, Gigabyte, ECS, AsRock, etc.). However, there is a slightly different approach, when instead of using a separate driver chip and two MOSFET transistors, one chip is used that combines both power transistors and a driver. This technology has been developed by Intel and was named DrMOS, which literally means Driver + MOSFETs. Naturally, separate chokes and capacitors are also used in this case, and a multi-channel PWM controller is used to control all phases.

Currently, DrMOS technology is only used on MSI motherboards. It is rather difficult to talk about the advantages of DrMOS technology in comparison with the traditional discrete way of organizing power phases. Here, rather, everything depends on the specific DrMOS chip and its characteristics. For example, if we talk about new MSI boards for processors of the Intel Core i7 family, then they use the Renesas R2J20602 DrMOS chip (Fig. 8). For example, on MSI board Eclipse Plus uses a 6-phase processor voltage regulator (Fig. 9) based on an Intersil ISL6336A 6-channel PWM controller (Fig. 10) and Renesas R2J20602 DrMOS chips.

Rice. 8. DrMOS Chip Renesas R2J20602

Rice. 9. Six-phase processor voltage regulator
based on 6-channel PWM controller Intersil ISL6336A
and DrMOS ICs Renesas R2J20602 on MSI Eclipse Plus board

Rice. 10. Six-channel PWM controller
Intersil ISL6336A

The Renesas R2J20602 DrMOS IC supports MOSFET switching frequencies up to 2 MHz and is very efficient. With an input voltage of 12 V, an output of 1.3 V and a switching frequency of 1 MHz, its efficiency is 89%. The current limit is 40 A. It is clear that with a six-phase processor power supply, at least a twofold current reserve is provided for the DrMOS microcircuit. With a real current value of 25 A, the power consumption (released as heat) of the DrMOS chip itself is only 4.4 watts. It also becomes obvious that when using Renesas R2J20602 DrMOS chips, there is no need to use more than six phases in the processor voltage regulators.

Intel in its parent Intel board DX58S0 based Intel chipset X58 for Intel Core i7 processors also uses a 6-phase, but discrete processor voltage regulator. A 6-channel PWM controller ADP4000 from On Semiconductor is used to control the power phases, and ADP3121 microcircuits are used as MOSFET drivers (Fig. 11). The ADP4000 PWM controller supports the PMBus (Power Manager Bus) interface and is programmable for operation in 1, 2, 3, 4, 5 and 6 phases with the ability to switch the number of phases in real time. In addition, using the PMBus interface, you can read the current values ​​​​of the processor current, its voltage and power consumption. One can only regret that Intel did not implement these features of the ADP4000 chip in the processor status monitoring utility.

Rice. 11. Six-phase processor voltage regulator
based on ADP4000 PWM controller and ADP3121 MOSFET drivers
on an Intel DX58S0 board (two power phases shown)

Note also that each power phase uses On Semiconductor NTMFS4834N MOSFET power transistors with a current limit of 130 A. It is easy to guess that with such current limits, the power transistors themselves are not the bottleneck of the power phase. In this case, the current limit on the supply phase imposes a choke. In the voltage regulator circuit under consideration, PULSE PA2080.161NL chokes with a current limit of 40 A are used, but it is clear that even with such a current limit, six phases of the processor power supply are enough and there is a large margin for extreme overclocking of the processor.

Dynamic phase switching technology

Almost all motherboard manufacturers currently use the technology of dynamically switching the number of processor power phases (we are talking about motherboards for Intel processors). Actually, this technology is by no means new and was developed by Intel a long time ago. However, as it often happens, having appeared, this technology turned out to be unclaimed by the market and for a long time was in storage. And only when the idea of ​​reducing the power consumption of computers took possession of the minds of developers, they remembered the dynamic switching of the processor power phases. Motherboard manufacturers are trying to pass off this technology as their own and come up with various names for it. For example, at Gigabyte it is called Advanced Energy Saver (AES), ASRock - Intelligent Energy Saver (IES), ASUS - EPU, MSI - Active Phase Switching (APS). However, despite the variety of names, all these technologies are implemented in exactly the same way and, of course, are not proprietary. Moreover, the ability to switch the power phases of the processor is built into the Intel VR 11.1 specification, and all PWM controllers that are compatible with the VR 11.1 specification support it. Actually, motherboard manufacturers have little choice here. These are either PWM controllers from Intersil (for example, the 6-channel PWM controller Intersil ISL6336A), or PWM controllers from On Semiconductor (for example, the 6-channel PWM controller ADP4000). Controllers from other companies are used less frequently. Both Intersil and On Semiconductor VR 11.1 compliant controllers support dynamic power phase switching. The only question is how the motherboard manufacturer uses the capabilities of the PWM controller.

Naturally, the question arises: why is the technology of dynamic switching of power phases called energy-saving and what is the efficiency of its application?

Consider, for example, a motherboard with a 6-phase processor voltage regulator. If the processor is not heavily loaded, which means that the current consumed by it is small, it is quite possible to get by with two power phases, and the need for six phases arises when the processor is heavily loaded, when the current consumed by it reaches its maximum value. Indeed, it is possible to make the number of power phases involved correspond to the current consumed by the processor, that is, so that the power phases are dynamically switched depending on the processor load. But isn't it easier to use all six power phases at any processor current? To answer this question, you need to take into account that any voltage regulator itself consumes part of the electricity it converts, which is released in the form of heat. Therefore, one of the characteristics of a voltage converter is its efficiency, or energy efficiency, that is, the ratio of the power transferred to the load (to the processor) to the power consumed by the regulator, which is the sum of the power consumed by the load and the power consumed by the regulator itself. The energy efficiency of the voltage regulator depends on the current value of the processor current (its load) and the number of power phases involved (Fig. 12).

Rice. 12. Dependence of energy efficiency (efficiency) of the voltage regulator
on the processor current with a different number of power phases

The dependence of the energy efficiency of the voltage regulator on the processor current with a constant number of power phases is as follows. Initially, with an increase in the load current (processor), the efficiency of the voltage regulator increases linearly. Further, the maximum efficiency value is reached, and with a further increase in the load current, the efficiency gradually decreases. The main thing is that the value of the load current, at which the maximum efficiency value is reached, depends on the number of supply phases, and therefore, if the technology of dynamic switching of the supply phases is used, then the efficiency of the supply voltage regulator can always be maintained at the highest possible level.

Comparing the dependences of the energy efficiency of the voltage regulator on the processor current for a different number of power phases, we can conclude: at a low processor current (with a slight processor load), it is more efficient to use a smaller number of power phases. In this case, less energy will be consumed by the voltage regulator itself and released as heat. At high processor currents, the use of a small number of power phases leads to a decrease in the energy efficiency of the voltage regulator. Therefore, in this case, it is optimal to use a larger number of power phases.

From a theoretical point of view, the use of the technology of dynamic switching of the processor power phases should, firstly, reduce the overall power consumption of the system, and secondly, heat dissipation on the supply voltage regulator itself. Moreover, according to motherboard manufacturers, this technology can reduce system power consumption by as much as 30%. Of course, 30% is a number taken from the ceiling. In reality, the technology of dynamic switching of power phases can reduce the total power consumption of the system by no more than 3-5%. The fact is that this technology allows you to save electricity consumed only by the voltage regulator itself. However, the main consumers of electricity in a computer are the processor, video card, chipset and memory, and against the background of the total power consumption of these components, the power consumption of the voltage regulator itself is quite small. Therefore, no matter how you optimize the power consumption of the voltage regulator, it is simply impossible to achieve significant savings.

Marketing "chips" of manufacturers

Motherboard manufacturers go to great lengths to attract the attention of buyers to their products and motivatedly prove that they are better than those of competitors! One of these marketing "chips" is the increase in the power phases of the processor voltage regulator. If earlier six-phase voltage regulators were used on top motherboards, now they use 10, 12, 16, 18 and even 24 phases. Do you really need so many power phases, or is this just a marketing gimmick?

Of course, multi-phase supply voltage regulators have their own undeniable advantages but there is a reasonable limit to everything. For example, as we have already noted, a large number of power phases allows the use of low current components (MOSFETs, chokes and capacitances) in each power phase, which, of course, are cheaper than high current limiting components. However, now all motherboard manufacturers use solid polymer capacitors and ferrite core chokes, which have a current limit of at least 40 A. MOSFETs also have a current limit of at least 40 A (and recently there has been a trend towards MOSFETs). with a current limit of 75 A). It is clear that with such current limitations, it is sufficient to use six power phases on each phase of the wave. Such a voltage regulator is theoretically capable of providing a processor current of more than 200 A, and therefore a power consumption of more than 200 watts. It is clear that even in the extreme overclocking mode, it is almost impossible to achieve such current and power consumption values. So why do manufacturers make voltage regulators with 12 phases or more, if a six-phase voltage regulator can also provide power to the processor in any mode of its operation?

If we compare 6- and 12-phase voltage regulators, then theoretically, when using dynamic power phase switching technology, the energy efficiency of a 12-phase voltage regulator will be higher. However, the difference in energy efficiency will be observed only at high processor currents, which are unattainable in practice. But even if it is possible to achieve such a high current value at which the energy efficiency of 6- and 12-phase voltage regulators will differ, then this difference will be so small that it can be ignored. Therefore, for all modern processors with a power consumption of 130 W, even in the mode of their extreme overclocking, a 6-phase voltage regulator is enough for the wave. The use of a 12-phase voltage regulator does not provide any advantages even with dynamic phase switching technology. Why manufacturers started making 24-phase voltage regulators is anyone's guess. There is no common sense in this, apparently, they expect to impress technically illiterate users, for whom "the more the better."

By the way, it would be useful to note that today there are no 12- and even more so 24-channel PWM controllers that control the power phases. Maximum amount channels in PWM controllers is six. Therefore, when voltage regulators with more than six phases are used, manufacturers are forced to install several PWM controllers that work in synchrony. Recall that the PWM control signal in each channel has a certain delay relative to the PWM signal in the other channel, but these signal timing offsets are implemented within the same controller. It turns out that when using, for example, two 6-channel PWM controllers to organize a 12-phase voltage regulator, the supply phases controlled by one controller are combined in pairs with the supply phases controlled by another controller. That is, the first power phase of the first controller will operate synchronously (without time shift) with the first power phase of the second controller. The phases will be dynamically switched, most likely, also in pairs. In general, this is not an "honest" 12-phase voltage regulator, but rather a hybrid version of a 6-phase regulator with two channels in each phase.

Distinctive features:

• Smallest Dual Boost Converter: 16-pin QSOP
• efficiency 90%
• Start at 1.5V power supply
• Maximum total current consumption 85 μA
• Current consumption in off mode 1 μA
• Separate shutdown inputs
• Drives two N-channel SMD MOSFETs
• Low battery comparator input and output
• Can be used as a step-up or step-down converter

Areas of use:

• Portable equipment with 2- and 3-cell power supply
• Organizers
• Electronic translators
• Portable, portable instrumentation
• Portable computers
• Personal digital assistants(PDA)
• Dual power supplies (logic and LCD power)

Typical switching circuit:

Pin Arrangement:

Pin Description:

Description:

The MAX863 is a dual output DC/DC converter that contains two independent boost controllers in one compact package. The IC is made using Bi-CMOS technology and consumes only 85 uA when both controllers are running. The minimum input supply voltage is 1.5V, which allows using this IC in organizers, translators and other low-power portable equipment. MAX863 provides efficiency. 90% conversion at load current from 20 mA to 1A. This small-sized IC is available in 16-pin. package QSOP, which occupies the same dimensions as the 8-pin. SOIC package.

The IC adopts a current limiting pulse-frequency modulation architecture, which features low start-up current surge and low current consumption, thus ensuring high efficiency. transformations in a wide range of loading. Each controller drives a low cost, external, N-channel MOSFET, sized to suit any output current or voltage.

In more powerful systems, two MAX863s can be used to generate 5V, 3.3V, 12V, and 28V with just two or three batteries as a power source. To speed up design time, the MAX863EVKIT evaluation kit is available. If a single output controller is required, see the MAX608 and MAX1771 documentation.

With this lesson, I begin a series of articles on switching regulators, digital regulators, and output power control devices.

The goal that I set is the development of a controller for a refrigerator on a Peltier element.

We will do an analogue of my development, only implemented on the basis of the Arduino board.

• This development interested many, and letters rained down on me with requests to implement it on Arduino.
• The development is ideal for studying the hardware and software of digital controllers. In addition, it combines many of the tasks studied in previous lessons:
  • measurement of analog signals;
  • working with buttons;
  • connection of indication systems;
  • temperature measurement;
  • work with EEPROM;
  • connection with a computer;
  • parallel processes;
  • and much more.

I will develop the development sequentially, step by step, explaining my actions. What will be the result - I do not know. I hope for a full-fledged working project of the refrigerator controller.

I don't have a finished project. I will write lessons according to the current state, so during the tests it may turn out that at some stage I made a mistake. I will correct. This is better than me debugging the development and issuing ready-made solutions.

Differences between development and prototype.

The only functional difference from the prototype development on the PIC controller is the absence of a fast voltage regulator that compensates for the ripple of the supply voltage.

Those. this option The device must be powered by a stabilized power supply with a low level of ripple (no more than 5%). These requirements are met by all modern impulse blocks nutrition.

And the power supply option from an unstabilized power supply (transformer, rectifier, capacitive filter) is excluded. The speed of the Arduino system does not allow for a fast voltage regulator. I recommend reading about the power requirements of the Peltier element.

Development of the overall structure of the device.

At this stage, you need to understand in general terms:

• what elements the system consists of;
• on which controller to execute it;
• are there enough conclusions and functionality controller.

I imagine the controller as a “black box” or “garbage pit” and connect everything I need to it. Then I look if, for example, the board is suitable for these purposes. Arduino UNO R3.

In my interpretation it looks like this.

I drew a rectangle - the controller and all the signals necessary to connect the elements of the system.

I decided that I need to connect to the board:

• LCD indicator (for displaying results and modes);
• 3 buttons (for control);
• error indication LED;
• fan control key (to turn on the hot side radiator fan);
• switching stabilizer key (for adjusting the power of the Peltier element);
• analog input for measuring the load current;
• analog input for measuring load voltage;
• temperature sensor in the chamber (accurate 1-wire sensor DS18B20);
• radiator temperature sensor (have not yet decided which sensor, rather DS18B20 too);
• computer communication signals.

There were 18 signals in total. At arduino boards UNO R3 or Arduino NANO 20 conclusions. There are still 2 conclusions left in reserve. Maybe you want to connect another button, or an LED, or a humidity sensor, or a cold side fan ... We need 2 or 3 analog inputs, the board has 6. That is. everything suits us.

You can assign pin numbers immediately, you can during development. I appointed immediately. Connection occurs through connectors, you can always change. Keep in mind that pin assignments are not final.

impulse stabilizers.

For accurate temperature stabilization and the operation of the Peltier element in the optimal mode, it is necessary to adjust the power on it. Regulators are analog (linear) and pulse (key).

Analog regulators are a regulating element and a load connected in series to a power source. By changing the resistance of the regulating element, the voltage or current on the load is adjusted. As a regulating element, as a rule, a bipolar transistor is used.

The control element operates in linear mode. It is allocated "extra" power. At high currents, stabilizers of this type are very hot, have a low efficiency. A typical linear voltage regulator is the 7805 chip.

This option does not suit us. We will make a pulse (key) stabilizer.

Switching stabilizers are different. We need a step-down switching regulator. The load voltage in such devices is always lower than the supply voltage. The circuit of the step-down switching regulator looks like this.

And this is a diagram of the regulator.

Transistor VT operates in the key mode, i.e. it can only have two states: open or closed. The control device, in our case, the microcontroller, switches the transistor with a certain frequency and duty cycle.

• When the transistor is open, current flows through the circuit: power supply, transistor switch VT, inductor L, load.
• When the key is open, the energy stored in the inductor is supplied to the load. Current flows through the circuit: inductor, VD diode, load.

Thus, the constant voltage at the output of the regulator depends on the ratio of the time of the open (topen) and closed key (tclose), i.e. on the duty cycle of the control pulses. By changing the duty cycle, the microcontroller can change the voltage at the load. Capacitor C smooths out the output voltage ripple.

The main advantage of this method of regulation is high efficiency. The transistor is always on or off. Therefore, little power is dissipated on it - always either the voltage across the transistor is close to zero, or the current is 0.

This is a classic switching buck regulator circuit. In it, the key transistor is torn off from the common wire. The transistor is difficult to drive, requiring special bias circuits to the supply voltage rail.

So I changed the schema. In it, the load is disconnected from the common wire, but a key is attached to the common wire. This solution allows you to control the transistor switch from the microcontroller signal using a simple current driver-amplifier.

• When the key is closed, the current enters the load through the circuit: power supply, inductor L, key VT (the current path is shown in red).
• When the key is open, the energy accumulated in the inductor is returned to the load through the regenerative diode VD (the current path is shown in blue).

Practical implementation of the key regulator.

We need to implement a switching regulator node with the following functions:

• the actual key controller (key, choke, regenerative diode, smoothing capacitor);
• load voltage measurement circuit;
• regulator current measurement circuit;
• hardware overcurrent protection.

I, with virtually no changes, took the regulator circuit from.

Scheme of a switching regulator for working with an Arduino board.

I used MOSFET transistors IRF7313 as a power switch. In an article on increasing the power of the Peltier element controller, I wrote in detail about these transistors, about a possible replacement, and about the requirements for key transistors for this circuit. Here is a link to the technical documentation.

On transistors VT1 and VT2, a key MOSFET transistor driver is assembled. This is just a current amplifier, in terms of voltage it even attenuates the signal to about 4.3 V. Therefore, the key transistor must be low-threshold. There are different options for implementing drivers MOSFET transistors. Including using integrated drivers. This option is the easiest and cheapest.

To measure the voltage at the load, a divider R1, R2 is used. With such resistor values ​​and a reference voltage source of 1.1 V, the measurement range is 0 ... 17.2 V. The circuit allows you to measure the voltage at the second load terminal relative to the common wire. We calculate the voltage at the load, knowing the voltage of the power source:

Uload = Usupply - Umeasured.

It is clear that the measurement accuracy will depend on the stability of maintaining the voltage of the power source. But we do not need high accuracy in measuring voltage, current, load power. We need to accurately measure and maintain only the temperature. We will measure it with high accuracy. And if the system shows that the Peltier element has a power of 10 W, but in fact it will be 10.5 W, this will not affect the operation of the device in any way. This applies to all other energy parameters.

The current is measured using a resistor-current sensor R8. Components R6 and C2 form a simple low pass filter.

The simplest hardware protection is assembled on the R7 and VT3 elements. If the current in the circuit exceeds 12 A, then the voltage across resistor R8 will reach the transistor opening threshold of 0.6 V. The transistor will open and close the RES (reset) pin of the microcontroller to ground. Everything should turn off. Unfortunately, the threshold for such protection is determined by the base-emitter voltage of the bipolar transistor (0.6 V). Because of this, the protection only works at significant currents. You can use an analog comparator, but this will complicate the circuit.

The current will be measured more accurately with an increase in the resistance of the current sensor R8. But this will lead to the release of significant power on it. Even with a resistance of 0.05 ohms and a current of 5 A, 5 * 5 * 0.05 = 1.25 watts is dissipated on the resistor R8. Note that resistor R8 has a power of 2 watts.

Now, what current are we measuring. We measure the current consumption of the switching regulator from the power supply. The circuit for measuring this parameter is much simpler than the circuit for measuring the load current. Our load is “untied” from the common wire. For the system to work, it is necessary to measure the electric power on the Peltier element. We calculate the power consumed by the regulator by multiplying the power supply voltage by the current drawn. Let's assume that our regulator has an efficiency of 100% and decide that this is the power on the Peltier element. In fact, the efficiency of the regulator will be 90-95%, but this error will not affect the operation of the system in any way.

Components L2, L3, C5 are a simple RFI filter. It may not be necessary.

Calculation of the throttle of the key stabilizer.

The throttle has two parameters that are important to us:

• inductance;
• saturation current.

The required inductance of the inductor is determined by the PWM frequency and the allowable inductor current ripple. There is a lot of information on this topic. I will give the most simplified calculation.

We applied voltage to the inductor and the current through it began to increase the current. Increase, but did not appear, because some current was already flowing through the inductor at the moment I was turned on).

The transistor is open. The voltage is connected to the throttle:

Uchoke = Usupply - Uload.

The current through the inductor began to increase according to the law:

Ichoke = Uchoke * topen / L

• topen - pulse duration public key;
• L - inductance.

Those. the value of the ripple current of the inductor or how much the current has increased during the time of the open key is determined by the expression:

Ioff - Ion = Uchoke * topen / L

The load voltage may change. And it determines the voltage at the throttle. There are formulas that take this into account. But in our case, I would take the following values:

• supply voltage 12 V;
• minimum voltage on the Peltier element 5 V;
• means the maximum voltage on the throttle 12 - 5 \u003d 7 V.

The duration of the pulse of the public key topen is determined by the frequency of the PWM period. The higher it is, the less inductance the inductor needs. Maximum frequency PWM board Arduino 62.5 kHz. I will tell you how to get such a frequency in the next lesson. We will use it.

Let's take the worst case - PWM switches exactly in the middle of the period.

• Period duration 1/62500 Hz = 0.000016 sec = 16 µs;
• Public key duration = 8 µs.

Current ripple in such circuits is usually set to 20% of the average current. Not to be confused with output voltage ripple. They are smoothed out by capacitors at the output of the circuit.

If we allow a current of 5 A, then we take a current ripple of 10% or 0.5 A.

L = Uchoke * topen / Ipulsation = 7 * 8 / 0.5 = 112 μH.

Inductor saturation current.

Everything in the world has a limit. And the throttle too. At some current, it ceases to be an inductance. This is the saturation current of the inductor.

In our case, the maximum inductor current is defined as the average current plus ripple, i.e. 5.5 A. But it is better to choose the saturation current with a margin. If we want hardware protection to work in this version of the circuit, then it must be at least 12 A.

The saturation current is determined by the air gap in the inductor's magnetic core. In articles about Peltier element controllers, I talked about the design of the throttle. If I start to expand this topic in detail, then we will leave Arduino, programming, and I don’t know when we will return.

My throttle looks like this.

Naturally, the inductor winding wire must be of sufficient cross section. The calculation is simple - the determination of heat losses due to the active resistance of the winding.

Active winding resistance:

Ra = ρ * l / S,

• Ra is the active resistance of the winding;
• Ρ – resistivity of the material, for copper 0.0175 Ohm mm2/m;
• l is the length of the winding;
• S is the cross section of the winding wire.

Thermal losses on the active resistance of the inductor:

The key regulator draws a decent current from the power supply and this current should not be allowed to pass through the Arduino board. The diagram shows that the wires from the power supply are connected directly to the blocking capacitors C6 and C7.

The main pulse currents of the circuit pass through the circuit C6, load, L1, D2, R8. This chain must be closed by links with a minimum length.

The common wire and power bus of the Arduino board are connected to the blocking capacitor C6.

The signal wires between the Arduino board and the key regulator module must be of the minimum length. Capacitors C1 and C2 are best placed on the connectors to the board.

I have assembled the circuit board. Soldered only the necessary components. Looks assembled circuit I have so.

I set the PWM to 50% and checked the operation of the circuit.

• When powered from a computer, the board formed a given PWM.
• At self-powered From an external power supply, everything worked great. Pulses with good fronts were formed on the throttle, there was a constant voltage at the output.
• When I turned on the power from both the computer and the external power supply at the same time, the Arduino board burned out.

My stupid mistake. Let me tell you so no one will repeat it. In general, connecting outdoor unit supply must be accurate, ring all connections.

The following happened to me. There was no VD2 diode in the circuit. I added it after this trouble. I figured that the board can be powered from an external source through the Vin pin. He himself wrote in lesson 2 that the board can be powered from an external source through the connector (RWRIN signal). But I thought it was the same signal, only on different connectors.