A protection design for any type of power supply is presented. This protection circuit can work together with any power supplies - mains, switching and batteries direct current. The schematic decoupling of such a protection unit is relatively simple and consists of several components.

Power supply protection circuit

Power part - powerful field-effect transistor- does not overheat during operation, therefore it does not need a heat sink either. The circuit is at the same time a protection against power overload, overload and short circuit at the output, the protection operation current can be selected by selecting the resistance of the shunt resistor, in my case the current is 8 Amperes, 6 resistors of 5 watts 0.1 Ohm connected in parallel were used. The shunt can also be made from resistors with a power of 1-3 watts.

The protection can be more accurately adjusted by selecting the resistance of the trimming resistor. Power supply protection circuit, current limit regulator Power supply protection circuit, current limit regulator

~~~In the event of a short circuit and overload of the unit output, the protection will instantly operate, turning off the power source. Will notify you when the protection is triggered led indicator. Even if the output short-circuits for a couple of tens of seconds, the field-effect transistor remains cold

~~~The field-effect transistor is not critical; any switches with a current of 15-20 Amps or higher and an operating voltage of 20-60 Volts will do. Keys from the IRFZ24, IRFZ40, IRFZ44, IRFZ46, IRFZ48 line or more powerful ones - IRF3205, IRL3705, IRL2505 and the like are ideal.

~~~This circuit is also excellent as charger protection for car batteries, if the connection polarity is suddenly mixed up, then charger nothing bad will happen, the protection will save the device in such situations.

~~~Thanks fast work protection, it can be successfully used for pulse circuits, in the event of a short circuit, the protection will work faster than the power switches have time to burn out pulse block nutrition. The circuit is also suitable for pulse inverters, as current protection. If there is an overload or short circuit in the secondary circuit of the inverter, the inverter's power transistors instantly fly out, and such protection will prevent this from happening.

Comments
Short circuit protection, polarity reversal and overload are assembled on a separate board. The power transistor was used in the IRFZ44 series, but if desired, it can be replaced with a more powerful IRF3205 or with any other power switch that has similar parameters. You can use keys from the IRFZ24, IRFZ40, IRFZ46, IRFZ48 line and other keys with a current of more than 20 Amps. During operation, the field-effect transistor remains icy. therefore it does not need a heat sink.

The second transistor is also not critical; in my case, a high-voltage one was used bipolar transistor MJE13003 series, but there is a large selection. The protection current is selected based on the shunt resistance - in my case, 6 0.1 Ohm resistors in parallel, the protection is triggered at a load of 6-7 Amps. You can set it more precisely by rotating the variable resistor, so I set the operating current to around 5 Amps.

The power of the power supply is quite decent, the output current reaches 6-7 Amps, which is quite enough to charge a car battery.
I chose shunt resistors with a power of 5 watts, but 2-3 watts is also possible.

If everything is done correctly, the unit starts working immediately, close the output, the protection LED should light up, which will light up as long as the output wires are in short-circuit mode.
If everything works as it should, then we proceed further. Assembling the indicator circuit.

The circuit is copied from a battery screwdriver charger. The red indicator indicates that there is output voltage at the output of the power supply, a green indicator shows the charging process. With this arrangement of components, the green indicator will gradually go out and finally go out when the voltage on the battery is 12.2-12.4 Volts; when the battery is disconnected, the indicator will not light up.

The term “short circuit” in electrical engineering refers to the emergency operation of voltage sources. It occurs when there is a violation technological processes transmission of electricity when the output terminals of an operating generator or chemical element are short-circuited (shorted).

In this case, the entire power of the source is instantly applied to the short circuit. Huge currents flow through it, which can burn equipment and cause electrical injuries to nearby people. To stop the development of such accidents, special protections are used.

What are the types of short circuits?

Natural electrical anomalies

They appear during lightning discharges accompanied by.

The sources of their formation are high potentials of static electricity of various signs and values ​​accumulated by clouds when they are moved by the wind over vast distances. As a result of natural cooling when rising to altitude, moisture vapor inside the cloud condenses, forming rain.

A humid environment has low electrical resistance, which creates a breakdown of the air insulation for the passage of current in the form of lightning.

An electrical discharge jumps between two objects with different potentials:

• on approaching clouds;

• between a thundercloud and the ground.

The first type of lightning is dangerous for aircraft, and a discharge to the ground can destroy trees, buildings, industrial facilities, and overhead power lines. To protect against it, lightning rods are installed, which consistently perform the following functions:

1. receiving, attracting lightning potential to a special catcher;

2. passing the resulting current through the current conductor to the grounding loop of the building;

3. discharging the high-voltage discharge with this circuit to the ground potential.

Short circuits in DC circuits

Galvanic voltage sources or rectifiers create a difference of positive and negative potentials at the output contacts, which under normal conditions ensures the operation of the circuit, for example, the glow of a light bulb from a battery, as shown in the figure below.

The electrical processes occurring in this case are described by a mathematical expression.

The electromotive force of the source is distributed to create a load in the internal and external circuits by overcoming their resistances “R” and “r”.

In emergency mode, a short circuit with very low electrical resistance occurs between the battery terminals “+” and “-”, which practically eliminates the flow of current in the external circuit, rendering this part of the circuit inoperable. Therefore, in relation to the nominal mode, we can assume that R=0.

All current circulates only in the internal circuit, which has low resistance, and is determined by the formula I=E/r.

Since the magnitude of the electromotive force has not changed, the value of the current increases very sharply. Such a short circuit flows through the shorted conductor and the internal circuit, causing enormous heat generation inside them and subsequent structural failure.

Short circuits in AC circuits

All electrical processes here are also described by Ohm’s law and occur according to a similar principle. Features on their passage are imposed:

the use of single-phase or three-phase network diagrams of various configurations;

presence of a ground loop.

Types of short circuits in alternating voltage circuits

Short circuit currents can occur between:

phase and ground;

two different phases;

two different phases and ground;

three phases;

three phases and earth.

To transmit electricity via overhead power lines, power supply systems can use different neutral connection schemes:

1. isolated;

2. solidly grounded.

In each of these cases, short circuit currents will form their own path and have different magnitudes. Therefore, all of the listed assembly options electrical diagram and the possibility of short circuit currents occurring in them are taken into account when creating the current protection configuration for them.

A short circuit can also occur inside electrical consumers, such as an electric motor. In single-phase structures, the phase potential can break through the insulation layer to the housing or neutral conductor. In three-phase electrical equipment, a fault may additionally occur between two or three phases or between their combinations with the frame/ground.

In all these cases, as with a short circuit in DC circuits, a very large short circuit current will flow through the resulting short circuit and the entire circuit connected to it up to the generator, causing an emergency mode.

To prevent it, protection is used that automatically removes voltage from equipment exposed to high currents.

How to choose the operation limits of short circuit protection

All electrical appliances are designed to consume a certain amount of electricity in their voltage class. It is customary to evaluate the workload not by power, but by current. It is easier to measure, control and create protection on it.

The picture shows graphs of currents that can arise in different modes equipment operation. The parameters for setting up and adjusting protective devices are selected for them.

The graph in brown shows the sine wave of the nominal mode, which is selected as the initial one when designing an electrical circuit, taking into account the power of electrical wiring, and selecting current protective devices.

The frequency of an industrial sinusoid in this mode is always stable, and the period of one complete oscillation occurs in 0.02 seconds.

The operating mode sine wave in the picture is shown in blue. It is usually less than the nominal harmonic. People rarely fully use all the reserves of power allocated to them. As an example, if there is a five-arm chandelier hanging in a room, then for lighting they often turn on one group of light bulbs: two or three, and not all five.

In order for electrical appliances to operate reliably at rated load, a small current reserve is created for setting up protections. The amount of current at which they are set to turn off is called the setting. When it is reached, the switches remove voltage from the equipment.

In the range of sinusoid amplitudes between the nominal mode and the set point, the electrical circuit operates in a slight overload mode.

The possible time characteristic of the fault current is shown in black on the graph. Its amplitude exceeds the protection setting, and the oscillation frequency has changed sharply. Usually it is aperiodic in nature. Each half-wave varies in magnitude and frequency.

Any short circuit protection includes three main stages of operation:

1. constant monitoring of the state of the controlled current sinusoid and determining the moment when a malfunction occurs;

2. analysis of the current situation and issuance of a command by the logical part to the executive body;

3. Relieve voltage from equipment using switching devices.

Many devices use another element - introducing a time delay for operation. It is used to ensure the principle of selectivity in complex, branched circuits.

Since the sinusoid reaches its amplitude in 0.005 seconds, at least this period is necessary for its measurement by protections. The next two stages of work also do not happen instantly.

For these reasons, the total operating time of the fastest current protections is slightly less than the period of one harmonic oscillation of 0.02 seconds.

Design features of short circuit protection

Electric current passing through any conductor causes:

thermal heating of the conductor;

induction of magnetic field.

These two actions are taken as the basis for the design of protective devices.

Protection based on the principle of thermal influence of current

The thermal effect of current, described by the scientists Joule and Lenz, is used for protection by fuses.

Fuse protection

It is based on installing a fuse-link inside the current path, which optimally withstands the rated load, but burns out when it is exceeded, breaking the circuit.

The higher the magnitude of the emergency current, the faster a circuit break is created - voltage relief. If the current is slightly exceeded, shutdown may occur after a long period of time.

Fuses successfully operate in electronic devices, electrical equipment of automobiles, household appliances, and industrial devices up to 1000 volts. Some of their models are used in high-voltage equipment circuits.

Protection based on the principle of electromagnetic influence of current

The principle of inducing a magnetic field around a current-carrying conductor has made it possible to create a huge class of electromagnetic relays and circuit breakers that use a trip coil.

Its winding is located on a core - a magnetic circuit, in which the magnetic fluxes from each turn are added up. The moving contact is mechanically connected to the armature, which is the swinging part of the core. It is pressed against a permanently fixed contact by spring force.

A nominal current passing through the turns of the trip coil creates a magnetic flux that cannot overcome the spring force. Therefore, the contacts are constantly in a closed state.

When emergency currents occur, the armature is attracted to the stationary part of the magnetic circuit and breaks the circuit created by the contacts.

One of the types of circuit breakers operating on the basis of electromagnetic voltage removal from the protected circuit is shown in the picture.

It uses:

automatic shutdown of emergency modes;

electric arc extinguishing system;

manual or automatic switching on to work.

Digital short circuit protection

All the protections discussed above work with analog values. Besides them in Lately In industry and especially in the energy sector, digital technologies based on the operation of static relays are beginning to be actively introduced. The same devices with simplified functions are produced for household purposes.

The magnitude and direction of the current passing through the protected circuit is measured by a built-in step-down current transformer of a high accuracy class. The signal measured by it is digitized by superposition using the principle of amplitude modulation.

Then it goes to the logical part of the microprocessor protection, which works according to a certain, pre-configured algorithm. Whenever emergency situations The device logic issues a command to the actuator disconnecting mechanism to remove voltage from the network.

To operate the protection, a power supply is used that takes voltage from the network or autonomous sources.

Digital short circuit protection has big amount functions, settings and capabilities up to recording the pre-emergency state of the network and its shutdown mode.

This is an incredibly useful device that will protect your home from short circuits when testing any appliances being tested. There are times when it is necessary to check an electrical device for the absence of a short circuit, for example, after repair. And in order not to expose your network to danger, to play it safe and avoid unpleasant consequences, this very simple device will help.

Will need

• Overhead socket.
• Key switch, overhead.
• Incandescent light bulb 40 - 100 W with socket.
• Two-core wire in double insulation 1 meter.
• The fork is removable.
• Self-tapping screws.

All parts will be attached to a wooden square made of chipboard or other material.

It is better to use a wall socket for a light bulb, but if you don’t have one, we make a clamp for the girth from thin sheet metal.

And we roll out a square of thick wood.

It will be attached like this.

Assembling a socket with short circuit protection

Diagram of the entire installation.

As you can see, all elements are connected in series.
First of all, we assemble the plug by connecting the wire to it.

Since the socket and switch are wall-mounted, use a round file to make cuts on the side for the wire. This can be done with a sharp knife.

We screw the wooden square to the base with self-tapping screws. Choose ones that won't go right through.

We screw the lamp socket with a bracket to a wooden square.

We disassemble the socket and switch. Screw it to the base with self-tapping screws.

We connect the wires to the socket.

For complete reliability, all wires are soldered. That is: we clean it, bend the ring, solder it with a soldering iron with solder and flux.

We fix the power cord with nylon ties.

The circuit is assembled, the installation is ready for testing.

To test, insert the charger into the socket from cell phone. We press the switch - the lamp does not light. This means there is no short circuit.

Then we take a more powerful load: a power supply from a computer. Turn it on. The incandescent lamp first flashes and then goes out. This is normal, since the unit contains powerful capacitors, which initially become infected.

We simulate a short circuit - insert tweezers into the socket. Turn it on, the lamp lights up.

This is such a wonderful and very necessary device.

This installation is suitable not only for low-power devices, but also for powerful ones. Certainly washing machine or an electric stove will not work, but by the brightness of the glow you can understand that there is no short circuit.
Personally, I have been using a similar device almost my entire life, testing all newly assembled ones on it.

Almost everyone has experienced a short circuit in their life. But most often it happened like this: flash, clap and that’s it. This happened only because there was short circuit protection.

Short circuit protection device

The device may be electronic, electromechanical, or a simple fuse. Electronic devices are mainly used in complex electronic devices, and we will not consider them in this article. Let's focus on fuses and electromechanical devices. Fuses were first used to protect household electrical circuits. We are used to seeing them in the form of “plugs” in the electrical panel.

There were several types, but all the protection boiled down to the fact that inside this “plug” there was a thin copper wire that burned out when a short circuit occurred. It was necessary to run to the store, buy a fuse, or store at home a supply of fuses that might not be needed soon. It was inconvenient. And automatic switches were born, which at first also looked like “traffic jams”.

It was the simplest electromechanical circuit breaker. They were produced for different currents, but the maximum value was 16 amperes. Soon higher values ​​were required, and technical progress allowed us to produce machines the way we now see them in most electrical panels of our homes.

How does a machine gun protect us?

It has two types of protection. One type is based on induction, the second on heating. A short circuit is characterized by a large current that flows through the short-circuited circuit. The machine is designed in such a way that current flows through a bimetallic plate and an inductor. So, when a large current flows through the machine, a strong magnetic flux arises in the coil, which sets the machine’s release mechanism in motion. Well, the bimetallic plate is designed to carry the rated current. When current flows through wires, it always causes heat. But we often don’t notice this, because the heat has time to dissipate and it seems to us that the wires are not heating up. A bimetallic strip consists of two metals with different properties. When heated, both metals deform (expand), but as one metal expands more than the other, the plate begins to bend. The plate is selected in such a way that when the nominal value of the machine is exceeded, due to bending, it activates the release mechanism. Thus, it turns out that one protection (inductive) works on short-circuit currents, and the second on currents flowing for a long time through the cable. Since short circuit currents are rapid in nature and flow in the network for a short period of time, the bimetallic plate does not have time to heat up to such an extent as to deform and turn off the circuit breaker.

Short circuit protection circuit

In fact, there is nothing complicated in this scheme. It is installed in the circuit, which disconnects either the phase wire or the entire circuit at once. But there are nuances. Let's look at them in more detail.

1. You cannot install separate machines in the phase circuit and the zero circuit. For one simple reason. If suddenly, due to a short circuit, the zero circuit breaker turns off, then the entire electrical network will be energized, because the phase circuit breaker will remain on.
   
2. You cannot install a wire with a smaller cross-section than the machine allows. Very often, in apartments with old wiring, in order to increase power, more powerful circuit breakers are installed... Alas, this is the most common cause of short circuits. This is what happens in such cases. Suppose, for clarity, there is a copper wire with a cross-section of 1.5 sq. mm, which is capable of withstanding a current of up to 16 A. A 25A machine is placed on it. We connect a load to this network, say 4.5 kW, and a current of 20.5 amperes will flow through the wire. The wire will start to get very hot, but the machine will not turn off the network. As you remember, the machine has two types of protection. The short circuit protection does not work yet because there is no short circuit, and the rated current protection will operate at a value greater than 25 amps. So it turns out that the wire gets very hot, the insulation begins to melt, but the machine does not work. In the end, an insulation breakdown occurs and a short circuit appears and the machine finally trips. But what do you get? The line can no longer be used and must be replaced. This is not difficult if the wires are laid openly. But what if they are hidden in the wall? New repairs are guaranteed to you.
3. If the aluminum wiring is more than 15 years old, and the copper wiring is more than 25 years old, and you are going to make repairs, definitely replace it with new wiring. Despite the investment it will save you money. Imagine that you have already made a repair, and there is a bad contact in some junction box? This is if we talk about copper wire (in which, as a rule, only the insulation ages or the joints oxidize or weaken over time, then begin to heat up, which leads to the destruction of the twist even faster). If we talk about aluminum wire, then everything is even worse. Aluminum is a very ductile metal. With temperature fluctuations, the compression and expansion of the wire is quite significant. And if there was a microcrack in the wire (manufacturing defect, technological defect), then over time it increases, and when it becomes quite large, which means the wire in this place is thinner, then when current flows, this area begins to heat up and cool down, which only speeds up the process . Therefore, even if it seems to you that everything is fine with the wiring: “It worked before!”, it’s better to change it anyway.
4. Junction boxes. There are articles about this, but I will briefly go through them here. NEVER DO SCROLLS!!! Even if you make them well, it's a twist. Metal tends to shrink and expand under the influence of temperature, and the twist weakens. Avoid using screw terminals for the same reason. Screw terminals can be used in open wiring. Then, by at least, you can periodically look into the boxes and check the condition of the wiring. Screw clamps of the “PPE” type or terminal connections of the “WAGO” type are best suited for this purpose; screw clamps of the “Nut” type are best suited for power wiring (such clamps have two plates that are held together with four screws, in the middle there is another plate, i.e. using such clamps you can connect copper and aluminum wires). Leave a reserve of at least 15 cm of stripped wire. This serves two purposes: if the twist contact is poor, the wire has time to dissipate heat, and you have the opportunity to redo the twist if something happens. Try to place the wires in such a way that there is no overlap between the phase and neutral wires with the ground wire. The wires can cross, but not lie on top of each other. Try to place the twists so that the phase wire is on one side, and the neutral and ground wires are on the other.

   

5. Do not connect copper and aluminum wires directly. Either use WAGO terminal blocks or Walnut clamps. This is especially true for wires intended for connecting electric stoves. Usually, when they make repairs and move a stove socket, they extend the cable. Very often these are aluminum wires that are extended with copper.
6. A little special. Do not skimp on switches and sockets (especially for electric stoves). The fact is that nowadays it’s quite difficult to find good sockets for electric stoves (I’m talking about small towns), so it’s best to either use the “Nut” U739M clamps or find a good socket.
7. When tightening the terminals on sockets, do it more tightly, but do not break the thread; if this happens, it is better to change the socket immediately, do not rely on “maybe”.
8. When laying a new electrical route, use the following standards: 10-15 cm from corners, ceilings, walls (along the floor), jambs, window frames, floor (along the wall). This will protect you when installing, for example, suspended ceilings or baseboards, which are secured using dowels for which you need to punch a hole. If the wire is located in the corner between the floor and the wall, it is very easy to get caught in the wire. All wires must be positioned strictly horizontally or vertically. This will make it easier for you to understand where you can make a new hole if you suddenly need to hang a shelf or a picture or a TV.
9. Do not daisy chain (from one to another) more than 4 sockets. In the kitchen, I generally do not recommend connecting more than two, especially where you plan to use an oven, kettle, dishwasher and microwave in one place.
10. It is best to lay it on the oven separate line or connect it to the line from which the hob is powered (because very often they consume about 3 kW.) Not every outlet can withstand such a load, and if another powerful consumer is connected to it (for example, a kettle), you risk getting short circuit due to strong heating of the connection in the socket by the cable.
11. Avoid using extension cords to power high-power electrical appliances, such as oil heaters, or use extension cords from reputable manufacturers rather than Chinese "no name" brands. Read carefully what power a given extension cord can handle, and do not use it if it has less power than you need to power. When using an extension cord, try to avoid stranded wire. If the wire just lies there, it has time to dissipate heat. If the wire is twisted, the heat does not have time to dissipate and the wire begins to heat up noticeably, which can also lead to a short circuit.
12. Do not connect several powerful consumers to one outlet (through a tee or an extension cord with several outlets). A load of 3.5 kW can be connected to a good outlet, and up to 2 kW to a not-so-good outlet. In houses with aluminum wiring, no more than 2 kW in any socket, and even better, do not include more than 2 kW in a group of sockets powered by one circuit breaker.
13. Before installing a heater in each room, make sure that the rooms are powered from different machines. As they say: “And sometimes a stick can shoot,” the same is with machine guns: “And sometimes a machine gun can fail to work,” and the consequences of this are quite cruel. Therefore, protect yourself and your loved ones.
14. Handle heating devices carefully, making sure that the wire does not come into contact with the heating elements.

Short circuit circuit breaker

Why did I make this a separate point? It's simple. It is the machine that provides short circuit protection. If you install, then you must install an automatic machine next, or install it immediately (this is a two-in-one device: an RCD and an automatic machine). Such a device turns off the network in case of a short circuit, and when the rated current value is exceeded, and when there is a leakage current, when, for example, you are under voltage and electric current begins to flow through you. Let me remind you again: the RCD DOES NOT PROTECT FROM SHORT CIRCUIT, the RCD protects you from damage electric shock. Of course, it may be that the RCD will turn off the network in the event of a short circuit, but it is not intended for this. The operation of an RCD during a short circuit is completely random. And all the wiring may burn out, everything may be in flames, but the RCD will not turn off the network.

Similar materials.

The devices require a power supply unit (PSU), which has adjustable output voltage and the ability to regulate the level of overcurrent protection over a wide range. When the protection is triggered, the load (connected device) should automatically turn off.

An Internet search yielded several suitable power supply circuits. I settled on one of them. The circuit is easy to manufacture and set up, consists of accessible parts, and fulfills the stated requirements.

The power supply proposed for manufacture is based on the LM358 operational amplifier and has the following characteristics:
Input voltage, V - 24...29
Output stabilized voltage, V - 1...20 (27)
Protection operation current, A - 0.03...2.0

Photo 2. Power supply circuit

Description of the power supply

Adjustable voltage stabilizer assembled on operational amplifier DA1.1. The amplifier input (pin 3) receives a reference voltage from the motor of the variable resistor R2, the stability of which is ensured by the zener diode VD1, and the inverting input (pin 2) receives the voltage from the emitter of the transistor VT1 through the voltage divider R10R7. Using variable resistor R2, you can change the output voltage of the power supply.
The overcurrent protection unit is made on the DA1.2 operational amplifier; it compares the voltages at the op-amp inputs. Input 5 through resistor R14 receives voltage from the load current sensor - resistor R13. The inverting input (pin 6) receives a reference voltage, the stability of which is ensured by diode VD2 with a stabilization voltage of about 0.6 V.

As long as the voltage drop created by the load current across resistor R13 is less than the exemplary value, the voltage at the output (pin 7) of op-amp DA1.2 is close to zero. If the load current exceeds the permissible set level, the voltage at the current sensor will increase and the voltage at the output of op-amp DA1.2 will increase almost to the supply voltage. At the same time, the HL1 LED will turn on, signaling an excess, and the VT2 transistor will open, shunting the VD1 zener diode with resistor R12. As a result, transistor VT1 will close, the output voltage of the power supply will decrease to almost zero and the load will turn off. To turn on the load you need to press the SA1 button. The protection level is adjusted using variable resistor R5.

PSU manufacturing

1. The basis of the power supply and its output characteristics are determined by the current source - the transformer used. In my case, a toroidal transformer from washing machine. The transformer has two output windings for 8V and 15V. By connecting both windings in series and adding a rectifier bridge using the KD202M medium power diodes on hand, I got a source DC voltage 23v, 2a for power supply.

Photo 3. Transformer and rectifier bridge.

2. Another defining part of the power supply is the device body. In this case, a children's slide projector hanging around in the garage found use. By removing the excess and processing the holes in the front part for installing an indicating microammeter, a blank power supply housing was obtained.

Photo 4. PSU body blank

3. Installation electronic circuit made on a universal mounting plate measuring 45 x 65 mm. The layout of the parts on the board depends on the sizes of the components found on the farm. Instead of resistors R6 (setting the operating current) and R10 (limiting the maximum output voltage), trimming resistors with a value increased by 1.5 times are installed on the board. After setting up the power supply, they can be replaced with permanent ones.

Photo 5. Circuit board

4. Assembling the board and remote elements of the electronic circuit in full for testing, setting and adjusting the output parameters.

Photo 6. Power supply control unit

5. Fabrication and adjustment of a shunt and additional resistance for using a microammeter as an ammeter or power supply voltmeter. Additional resistance consists of permanent and trimming resistors connected in series (pictured above). The shunt (pictured below) is included in the main current circuit and consists of a wire with low resistance. The wire size is determined by the maximum output current. When measuring current, the device is connected in parallel to the shunt.

Photo 7. Microammeter, shunt and additional resistance

Adjustment of the length of the shunt and the value of additional resistance is carried out with the appropriate connection to the device with control for compliance using a multimeter. The device is switched to the Ammeter/Voltmeter mode using a toggle switch in accordance with the diagram:

Photo 8. Control mode switching diagram

6. Marking and processing of the front panel of the power supply unit, installation of remote parts. In this version, the front panel includes a microammeter (toggle switch for switching the A/V control mode to the right of the device), output terminals, voltage and current regulators, and operating mode indicators. To reduce losses and due to frequent use, a separate stabilized 5 V output is additionally provided. Why is the voltage from the 8V transformer winding supplied to the second rectifier bridge and standard diagram on 7805 with built-in protection.

Photo 9. Front panel

7. PSU assembly. All power supply elements are installed in the housing. In this embodiment, the radiator of the control transistor VT1 is an aluminum plate 5 mm thick, fixed in the upper part of the housing cover, which serves as an additional radiator. The transistor is fixed to the radiator through an electrically insulating gasket.