Let's take a look at the device and purpose of the breadboards. What is their advantage over other types of assembly, and how to work with them, as well as what schemes you can quickly build on them for a beginner?
The first problem that a radio amateur face is not even a lack of theoretical knowledge, but a lack of means and knowledge about how to assemble electronic devices. If you do not know how this or that part works, it will not prevent you from connecting it according to the electrical principle, but you need printed circuit board to clearly and efficiently assemble the circuit. Most often they are made according to the LUT method, but not everyone has a laser printer. Our fathers and grandfathers painted boards by hand with nail polish or paint, and then they were etched.
Here the newcomer is overtaken by the second problem - the lack of reagents for etching. Yes, of course, ferric chloride is sold in every store of radio-electronic components, but at first, and so you need to buy a lot and learn that it is simply difficult to pay attention to the technology of etching boards made of foil textolite. And not only for beginners but also experienced radio amateurs, it sometimes makes no sense to slack off a fee and spend money on an unfinished product at the stages of its adjustment.
To avoid problems with the search for ferric chloride, textolite, printer and not get from the wife (mother) for the unauthorized use of the iron, you can practice mounting electronic devices on solderless development boards.
What is a solderless breadboard?
As the name implies, this is such a board on which you can assemble the device layout without using a soldering iron. The mockup - as it is called by the people - is present in stores of different sizes and the models differ somewhat in layout, but the principle of operation and their internal structure are the same.
The prototype board consists of an ABS plastic case, in which are detachable connections that resemble dual metal tires between which the conductor is clamped. On the front of the case of the hole, numbered and marked, they can be inserted into wires, legs of the microcircuit, transistors and other radio components in the housings with leads. Take a look at the picture below, on it I have depicted all this.
On the considered printed circuit board, the extreme two columns of holes on each of the sides were joined vertically with common tires, of which the positive-contact power supply bus and the negative (common bus) are usually formed. Usually indicated by a red and blue stripe on the edge of the board plus and minus, respectively.
The middle part of the board is divided into two parts, each of the parts being joined along the line of five holes in a row on this particular board.
The internal structure of the board is shown in the figure below. Dual tires clamp the conductors as illustrated. Bold lines indicate internal connections.
Such boards in the English-language environment are called Breadboards by just such a name you can find it on aliexpress and similar online stores.
How to work with it?
Simply insert the legs of the electronic components into the holes, interconnecting the parts along horizontal lines, and feeding the extreme vertical ones. If you need a jumper, often use special ones with thin plugs on the end, in stores, you can find them under the name “jumper dupont” or jumpers for Arduino, by the way, you can also insert it into such a layout and assemble your projects.
If you didn’t have enough sizes of one development board, you can combine several, it is like puzzles inserted into each other, pay attention to the first picture in the article, the scheme is assembled on two connected boards. On one of them there is a spike, and on the other a notch, beveled from the outer part to the board body, so that the design does not collapse.
Build simple circuits on a breadboard
It is important for a beginner radio amateur to quickly assemble a circuit to make sure it works and understand how it works. Let's take a look at how different layouts look on a breadboard.
The symmetric multivibrator circuit is recommended as the first for many beginners, it allows you to learn how to connect parts in series and in parallel, as well as to determine the pinout of transistors. It can be assembled by mounting or diluting a printed circuit board, but this requires soldering, and mounting, despite its simplicity, is in fact very difficult for beginners and is fraught with short circuits or poor contact.
See how simple it looks on a solderless breadboard.
By the way, note here that the Dupont jumpers were not used. In general, they can not always be found in radio stores, and especially in the shops of small towns. Instead, you can use the wires from the Internet cable (Twisted pair) they are isolated, and the core is not coated with varnish, which allows you to quickly expose the end of the cable by removing a small layer of insulation and insert it into the connector on the board.
You can connect the parts as you like, just to provide the desired chain, here is the same scheme, but assembled slightly differently.
By the way, to describe the connections, you can use the board marking, the columns are designated by letters, and the lines are numbers.
For your designs, there are such power supplies, they have plugs that are mounted in the solderless board by connecting to the tires "+" and "-". It is convenient, it has a switch and a linear low-noise voltage regulator. In general, you will not be difficult to dilute such a fee yourself and collect it.
This is how you can connect an LED, for example, to test it. The picture shows a more “advanced” version of the PCB with clamping terminals for connecting the power supply. The anode of the LED is connected to the power supply (red bus) and the cathode to the horizontal bus of the working area, where it is connected to the current-limiting resistor.
The power supply on a linear stabilizer type L7805, or any other chip series L78xx, where xx - you need the voltage.
The assembled scheme tweeters on logic. The correct name of such a circuit is the Pulse Generator on the logical elements of type 2 and not. First, read the electrical schematic diagram.
As a logical chip suitable domestic K155LA3 or foreign type 74HC00. The elements R and C set the operating frequency. Here is its implementation on the board without soldering.
On the right is a white paper taped over a buzzer. It can be replaced by an LED if you reduce the frequency.
The greater the resistance or capacity, the lower the frequency.
But this is what a typical Arduinschik project looks like at the testing and development stage (and sometimes in the final form, depending on how lazy it is).
Actually, thanks to the Arduino project, the popularity of “brainboards” has recently increased significantly. They allow you to quickly assemble the circuit and check their performance, as well as use as a connector when flashing chips in a DIP package, and in other buildings, if there is an adapter.
Restricted Breadboard Restrictions
Despite its simplicity and obvious advantages over soldering, solderless layouts have several disadvantages. The fact is that not all circuits work normally in such a design, let's take a closer look.
Overload and parasitic components
On solderless development boards, it is not recommended to assemble powerful converters, and especially pulse circuits. The first ones will not work normally due to the current capacity of the contact tracks. It is not necessary to climb for currents more than 1-2 Amperes, although there are also messages on the Internet that include 5 Amperes, draw your own conclusions and experiment.
Pulse circuits may not work at all due to a large number of parasitic capacitances and inductances in the circuit. The location of the tires is such that they run along with each other and have a fairly large area. This causes unnecessary pickups and does not improve the stability of the pulse and precision circuits.
Do not forget that high voltage is dangerous to life. Designing devices that work, for example, from 220 V is FORBIDDEN categorically. Although the findings are closed with a plastic panel, a bunch of conductors and jumpers can cause an accidental short circuit or electric shock!
A non-safety prototype board is suitable for simple circuits, analog circuits that do not make high demands on electrical connections and precision, automation and digital circuits that do not work at high speeds (GigaHerz and tens MegaHerz is too much). At the same time, high voltage and currents are dangerous, and for such purposes, it is better to use hinged mounting and printed circuit boards, while the beginner should not make hinged mounting of such circuits. The elements of solderless model boards are the simplest circuits of up to a dozen of elements and amateur projects on Arduino and other microcontrollers.
To check the health of the field-effect transistor, you can use any digital multimeter with the function of “dialing” diodes. This function works in such a way that allows you to measure the direct voltage drop at the pn-junction, which will be displayed on the display of the multimeter during testing.
During this test, the multimeter is able to pass a current within a few milliamperes through the circuit being tested, and if the voltage drop is too small, then if the device has an audible warning function, it will sound. And since pn-junctions are present in any field-effect transistor, you can count on a completely adequate result.
Before checking the field-effect transistor for serviceability, short-circuit all its leads with foil for a second in order to discharge a static charge in order to discharge all its transient capacitances, including the gate-source capacitance.
Check the built-in reverse diode
Practically in any modern field-effect transistor, with the exception of their special types, an internal “protective” diode is connected in parallel with the drain-source circuit.
The presence of this diode inside the field is due to the peculiarities of the production technology of high-power transistors. Sometimes it interferes, it is considered parasitic, but in most field-effect transistors it is impossible to do without it, as part of the integral structure of the electronic component. Therefore, in a serviceable field effect transistor, this diode must also be in good order. In an n-channel field-effect transistor, this diode is connected to the drain by the cathode, to the source by the anode, and to the drain by the anode to the drain, and to the source by the cathode.
Turn the multimeter into the dialing mode of the diodes. If the field-effect transistor is n-channel, then apply a red multimeter probe to its source (source) and a black one to the drain (drain).
Usually, the drain is in the middle and connected to the conductive substrate of the transistor, and the source is the right pin (check this in the datasheet). If the internal diode is in good condition, the multimeter will display a direct voltage drop across it - in the region of 0.4-0.7 volts. If now the position of the probes is reversed, the device will show infinity. If everything is so, then the internal diode is healthy.
Drain-source circuit test
The field effect transistor is controlled by the electric field of the gate. And if the gate-source capacity is charged, the conductivity in the direction of the drain-source will increase.
So, if the transistor is n-channel, attach the black probe to the gate (gate), and the red one to the source, and in a second change the location of the probes to the opposite — red to the gate, and black to the source. So we probably first discharged the bolt, and after - charged it. The shutter is usually on the left and the source is on the right (see datasheet).
Now move the red probe from the shutter to the drain, and let the black one remain at the source. If the transistor is intact, then as soon as you move the red probe from the gate to the drain, the multimeter will show that there is a voltage drop in the drain (not infinite, but may increase) - this means that the transistor has passed into a conducting state.
Now the red probe is at the source, and the black one is at the shutter (we discharge the shutter of opposite polarity), after which the red probe is again at the drain, and the black one is at the source. The device should show infinity - the transistor is closed. For a p-channel field effect transistor, the probes simply change places.
If the device stumbles
If at the stage of checking the drain-source the device squeals, this can be quite normal, because in modern field-effect transistors the drain-source resistance in the open state is very small. The main thing is that there should be no shutter-source and drain-source ringing, especially at that moment when the shutter is charged with the opposite polarity. Alternatively, you can connect the gate with the source and in this position call the drain-source (for n-channel red to drain, black to source), the device should show infinity.
DC / DC converters are widely used for powering various electronic equipment. They are used in computing devices, communication devices, various control, and automation schemes, etc.
Transformer Power Supplies
In traditional transformer power units, the supply voltage is transformed by the transformer, most often lowered, to the desired value. The reduced voltage is rectified by a diode bridge and smoothed by a capacitor filter. If necessary, a semiconductor stabilizer is placed after the rectifier.
Transformer power supplies, as a rule, are equipped with linear stabilizers. The advantages of such stabilizers are at least two: this is a small cost and a small number of parts in the harness. But these advantages are eaten 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 voltage conversion to the desired level is possible only with the help of DC / DC converters.
The idea is quite simple: DC voltage is converted to AC, usually with a frequency of several tens or even hundreds of kilohertz, rises (decreases), and then straightens and is fed to the load. Such converters are often called impulse.
As an example, we can take a boost converter from 1.5V to 5V, just the output voltage of a computer USB. Such a converter of low power is sold to Aliexpress.
Pulse converters are good because they have high efficiency, within 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.
Step-down or buck lowering
The output voltage of these converters, as a rule, is lower than the input one: without any special heat losses of the regulating transistor, you can get a voltage of only a few volts at an input voltage of 12 ... 50V. The output current of such converters depends on the needs of the load, which in turn determines the converter circuitry.
Another English name for the chopper down converter. One of the translations for this word is a chopper. In technical literature, a down converter is sometimes called a “chopper.” For now, just remember this term.
Boost, in English terminology step-up or boost
The output voltage of these converters is higher than the input. For example, at an input voltage of 5V, the output can receive voltages up to 30V, moreover, it may be smoothly regulated and stabilized. Quite often, up-converters are called boosters.
Universal Converters - SEPIC
The output voltage of these converters is held at a predetermined level at an input voltage both above the input and below. It is recommended in cases where the input voltage can vary significantly. For example, in a car, the battery voltage may vary within 9 ... 14V and a stable voltage of 12V is required.
Inverting converters - inverting converter
The main function of these converters is to obtain at the output voltage of reverse polarity relative to the power supply. It is very convenient in those cases when bipolar power is required, for example, to power an opamp.
All of the mentioned converters can be stabilized or unstabilized, the output voltage can be galvanically connected to the input or be galvanically isolated from the voltages. It all depends on the specific device in which the converter will be used.
In order to proceed to the further story about DC / DC converters, you should at least in general terms understand the theory.
Chopper down converter - buck type converter
Its functional diagram is shown in the figure below. The arrows on the wires show the direction of the currents.
The input voltage Uin is fed to the input filter - capacitor Cin. The transistor VT is used as a key element; it performs high-frequency switching of the current. This may be a MOSFET transistor, IGBT structure or a conventional bipolar transistor. In addition to these parts, the circuit contains a bit diode VD and an output filter - LCout, from which the voltage enters the load RL.
It is easy to see that the load is connected in series with the elements VT and L. Therefore, the circuit is sequential. How does the voltage drop?
Pulse Width Modulation - PWM
The control circuit generates rectangular pulses with a constant frequency or a constant period, which is essentially the same. These pulses are shown in Figure 3.
Here ti is the pulse time, the transistor is open, tn is the pause time, the transistor is closed. The ratio ti / T is called the duty cycle, denoted by the letter D and expressed in %% or simply in numbers. For example, when D is 50%, it turns out that D = 0.5.
Thus, D can vary from 0 to 1. When D = 1, the key transistor is in the state of full conductivity, and when D = 0, in the cutoff state, simply speaking, it is closed. It is not hard to guess that at D = 50% the output voltage will be equal to half the input.
It is obvious that the regulation of the output voltage occurs due to a change in the width of the control pulse t and, in fact, a change in the coefficient D. This regulation principle is called pulse-width modulation PWM. Practically in all switching power supply units, 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, it may be a smooth start of the output voltage, remote switching on or protection of the converter from a short circuit.
In general, the converters are so widely used that the manufacturers of electronic components have established the release of PWM controllers for all occasions. The range is so large that just in order to list them you will need a whole book. Therefore, collecting converters on discrete elements, or as they often say on the “wastage”, does not occur to anyone.
Moreover, ready-made low-power converters can be bought on Aliexpress or Ebay for a small price. At the same time, for installation in the amateur construction, it is enough to solder the wires to the board for input and output and set the required output voltage.
But back to our picture 3. In this case, the coefficient D determines how long the key transistor will be open (phase 1) or closed (phase 2). For these two phases, it is possible to present a diagram in two figures. The figures do not show those elements that are not used in this phase.
When the transistor is open, the current from the power source (galvanic cell, battery, rectifier) passes through inductive choke L, load Rн, and charging capacitor Cout. In this case, a current flows through the load, the capacitor Cout and the choke L accumulate energy. The current iL GRADUALLY GROWTH is affected by the influence of the inductor inductance. This phase is called pumping.
After the voltage on the load reaches a predetermined value (determined by the setting of the control device), the transistor VT closes and the device switches to the second phase - the discharge phase. The closed transistor in the figure is not shown at all, as if it is not. But this only means that the transistor is closed.
When the transistor VT is closed, energy is not replenished in the choke because the power supply is disconnected. Inductance L tends to prevent a change in the magnitude and direction of the current (self-induction) of the choke flowing through the winding.
Therefore, the current can not instantly stop and closes through the "diode-load" circuit. Because of this, the diode VD was named bit. Typically, this is a high-speed Schottky diode. After the control period expires, phase 2 of the circuit switches to phase 1, the process is repeated again. The maximum voltage at the output of the considered circuit can be equal to the input, and no more. To get the output voltage greater than the input, step-up converters are used.
It should be noted that in reality everything is not as simple as it is written above: it is assumed that all components are ideal, i.e. on and off occurs without delay, and the resistance is zero. In the practical manufacture of such schemes, many nuances have to be taken into account, since very much depends on the quality of the components used and the parasitic mounting capacity. Only about such a simple detail as a choke (well, just a bundle of wire!) You can write more than one article.
So far it should only be recalled of the inductance itself, which determines the two modes of operation of the chopper. With insufficient inductance, the converter will operate in the mode of discontinuous currents, which is completely unacceptable for power supplies.
If the inductance is large enough, then the work takes place in the mode of continuous currents, which allows using the output filters to obtain a constant voltage with an acceptable level of ripple. In the mode of continuous currents work and step-up converters, which will be discussed below.
For a certain increase in efficiency, the discharge diode VD is replaced by 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 converter power is large enough.
Step-up or boost converters
Boost converters are used mainly with low-voltage power supply, for example, from two to three batteries, and some components of the design require a voltage of 12 ... 15 V with low current consumption. Quite often, the boost converter is briefly and clearly called the word "booster."
The input voltage Uin is applied to the input filter Cin and is applied to the series-connected inductor L and the switching transistor VT. A diode VD is connected to the connection point of the coil and drain of the transistor. To another pin of the diode, the load Rh and the shunt capacitor Cout are connected.
The VT transistor is controlled by a control circuit that produces a stable frequency control signal with an adjustable duty cycle D, just as described above in describing the chopper circuit (Fig. 3). Diode VD at the right time blocks the load from the key transistor.
When the key transistor is open, right according to the scheme, the output of the coil L is connected to the negative pole of the power source Uin. The increasing current (the effect of inductance effects) from the power source flows through the coil and the open transistor, energy is accumulated in the coil.
At this time, the diode VD blocks the load and the output capacitor from the key circuit, thereby preventing the discharge of the output capacitor through the open transistor. The load at this moment is powered by the energy stored in the capacitor Cout. Naturally, the voltage on the output capacitor drops.
As soon as the output voltage is slightly lower than the preset (determined by the settings of the control circuit), the key transistor VT closes and the energy stored in the inductor through the diode VD charges the capacitor Cout, which feeds 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 accumulation phase.
Universal converters - SEPIC (single-ended primary-inductor converter or converter with asymmetrically loaded primary inductance).
Such converters are used mainly when the load has a negligible power, and the input voltage changes relative to the output up or down.
It is very similar to the boost converter circuit shown in Figure 6, but it has additional elements: a capacitor C1 and a coil L2. It is these elements that ensure the operation of the converter in the voltage reduction mode.
SEPIC converters are used in cases where the input voltage varies widely. As an example, 4V-35V to 1.23V-32V Boost Buck Voltage Step Up / Down Converter Regulator. It is under this name in Chinese stores that a converter is sold, the circuit of which is shown in Figure 8 (click on image to enlarge).
Figure 9 shows the appearance of the board with the designation of the main elements.
The figure shows the main parts in accordance with Figure 7. Attention should be paid to the presence of two coils L1 L2. On this basis, it is possible to determine that this is the SEPIC converter.
The input voltage of the board can be within 4 ... 35V. In this case, the output voltage can be adjusted in the range of 1.23 ... 32V. The operating frequency of the inverter is 500 KHz. In the case of small dimensions of 50 x 25 x 12 mm, the board provides power up to 25 W. Maximum output current up to 3A.
But here it is necessary to make a remark. 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 allowable power or do not go beyond the limits of the allowable current.