Simple power supply. Chinese pulse adapters - power supplies Scheme of a 5 volt 2 ampere power supply

Everyone is well aware that the nominal on-board voltage of passenger cars is 12 volts. Maybe in some cases it can be 24 volts, since batteries for this voltage are also found, but we don’t know about it :)…
However, 12 volts is not always suitable for many electronic devices that use digital logic. Historically, most logic chips operate at 5 volts. It is this voltage that is often provided in the car with the help of chargers, adapters, stabilizers... By the way, we have already talked about such a charger in one of our articles “5 volt charger for use in a car”. Moreover, in essence, this article is a kind of continuation of the article we cited above, with only one exception. All possible options for converting 12 volts to 5 volts will be collected here. That is, we will analyze relatively unpromising options using resistors and transistors and talk about microassemblies and circuits using PWM to implement voltage converters in a car from 12 to 5 volts. So, let's begin.

How to make 5 volts from 12 volts using resistors

Using a resistor to reduce the load supply voltage is one of the most thankless methods. This conclusion can be drawn even from the very definition of a resistor. A resistor is a passive element of an electrical circuit that has a certain resistance to electric current. The key word here is “passive”. Indeed, such passivity does not allow flexible response to voltage changes, providing stabilization of power supply to the load.
The second disadvantage of the resistor is its relatively low power. There is no point in using a resistor larger than 3-5 Watts. If it is necessary to dissipate a lot of power, then the resistor will be too large, and the current at the dissipated power is not difficult to calculate. I=P/U=3/12=0.25 A. That is 250 mA. This is clearly not enough for either a DVR or a navigator. At least with the proper reserve.
Still, for the sake of interest and for the sake of those who need a small current and unstabilized voltage, we will consider this option. So the voltage of the on-board network of the car (vehicle) is 14 volts, but 5 volts are needed. 14-5 = 9 volts that need to be reset. The current, let's say the load current will be the same 0.25 A with a 3 Watt resistor. R=9/0.25=36 Ohm. That is, you can take a 36 Ohm resistor with a load current consumption of 250 mA and it will produce a supply voltage of 5 volts.
Now let's talk about more “civilized” options for a voltage converter from 12 to 5 volts.

How to make 5 volts from 12 volts using a transistor

This transistor circuit is not the easiest to manufacture, but it is the simplest in functionality. Now we are talking about the fact that the circuit is not protected from short circuits or overheating. The lack of such protection is a disadvantage. The relevance of this scheme can be attributed to those times when there were no microassemblies (microcircuits) or converters. Fortunately, there are a lot of options now and this option, like the previous one, can also be considered as one of the possible, but not preferable. The biggest advantage regarding the option with resistors will be the active change in resistance due to the zener diode and transistor used. It is these radioelements that can provide stabilization. Now about everything in more detail.

Initially, the transistor is closed and does not pass voltage. But after the voltage passes through resistor R1 and the zener diode VD1, it opens to a level corresponding to the voltage of the zener diode. After all, it is the zener diode that provides the reference voltage for the base of the transistor. As a result, the transistor is always open (closed) in direct proportion to the input voltage. This is how the voltage is reduced and stabilized. Capacitors act as some kind of “electrical buffers” in case of sudden surges and dips. This gives the circuit more stability. So, the transistor circuit is quite functional and applicable. The current to power the load will be much greater here. So let's say for the transistor indicated in the KT815 circuit, this is a current of 1.5 A. This is already quite enough to connect a navigator, tablet or video recorder, but not all at once!

How to make 5 volts from 12 volts using a microcircuit

Microcircuits have replaced transistor assemblies. Their advantages are obvious. Here you don’t even need to be an electronics engineer; you can assemble everything without any idea of ​​how and what works. Although even a specialist will not say what the manufacturer of this or that microcircuit has sewn into the case, of which there are a great many on our market. This actually works to our advantage; we can choose the best for less money. Also, the advantages of microassemblies will be the use of all kinds of protections that were not available in previous versions. This is protection against short circuit and overheating. Typically this is the default. Now let's look at similar examples.

The use of such micro-assemblies is justified if you need to power one of the devices, since the supply current is comparable to the previous option, about 1.5 A. However, the current will also depend on the body of the assembly. Below are the same microcircuits, but in different types of packages. In these cases, the supply current will be about 100 mA. This is an option for low-power consumers. In any case, we install radiators on the microcircuits.

So, if you connect several devices, you will have to connect the microassemblies in parallel, one chip for each device. Agree, this is not a completely correct option. Here it is better to follow the path of increasing the output supply current and increasing efficiency. This is precisely the option that PWM microcircuits offer us. More about him...

How to make 5 volts from 12 volts using a PWM chip

We will talk very briefly and unprofessionally about pulse width modulation. Its whole essence boils down to the fact that power is supplied not by direct current, but by pulses. The frequency of the pulses and their range are selected in such a way that the supply load receives power as if the current is constant, that is, there are no deviations in operation, shutdowns, blinking, etc. However, due to the fact that the current is pulsed, and due to the fact that it is intermittent, all elements of the circuit already work with peculiar “rest breaks”. This allows you to save on consumption and also relieve the load on the working elements of the circuit. It is because of this that switching power supplies and converters are so small and so “remote”. Using PWM allows you to increase the efficiency of the circuit to 95-98 percent. Believe me, this is a very good indicator. So, here is a diagram for a converter from 12 to 5 volts using PWM.

This is what she looks like "live".

More details about this option can be found in the same article about the 5 volt charger that we mentioned earlier.

Summarizing the voltage converter from 12 to 5 volts

All the circuits and converter options that we told you about in this article have the right to life. The simplest option with a resistor will be indispensable for the option when you need to connect something low-power and not requiring a stabilized voltage. Let's say a pair of LEDs connected in series. By the way, you can learn about connecting LEDs to 12 volts from the article “How to connect an LED to 12 volts”.
The second option will be appropriate when you need a converter now, but do not have the time or opportunity to go to the store. You can find a transistor and a zener diode in almost any equipment for write-off.
The use of microcircuits is one of the most common options today. Well, microcircuits with PWM are what it’s all about. This is exactly how the most promising and profitable options for voltage converters from 12 to 5 volts are seen.
Lastly, in terms of the chronology of the article, but not in terms of information content, we wanted to remind you how power should be connected to USB connectors, be it mini or micro connectors.

Now you can not only select and assemble the converter version you need, but also connect it to your electronic device via a USB connector, focusing on accepted power standards.

5 volts is one of the most widely used voltages. Most programmable and non-programmable microcontrollers, all kinds of indicators and testers are powered from this voltage. In addition, 5 volts is used to charge all kinds of gadgets: phones, tablets, players, and so on. I'm sure every radio amateur can come up with many uses for this voltage. And in this regard, I have prepared for you three good, in my opinion, options for power supplies with a stabilized output voltage of 5 volts.

The first option is the simplest.

This option is distinguished by a minimal number of parts used, extreme ease of assembly and incredible ‘survivability’ - the block is almost impossible to kill. So let's move on to the diagram.

This circuit is copied from an inexpensive phone charger, has stabilization of the output voltage and is capable of delivering a current of up to 0.5 A. In fact, the unit can output more, but as the current at the output increases, the overload protection begins to operate and the output voltage begins to decrease. Protection against overloads and short circuits is implemented on a 10 ohm resistor in the emitter circuit of the power transistor and a low-power transistor s9014. When the current through the primary winding of the transformer increases, a voltage drop is created on the emitter resistor sufficient to open s9014, which in turn pulls the base of the power transistor to negative, thereby closing it and reducing the duration of the pulses through the primary winding. By changing the value of this resistor, you can increase or decrease the protection operation current. You should not increase it too much, as this will entail an increase in heating of the power transistor and increase the likelihood of the latter failing.

Stabilization is performed using a common optocoupler pc817 and on the zener diode 3.9 V (by changing the value of which you can change the output voltage). When the output voltage is exceeded, the optocoupler LED begins to glow brighter, causing an increase in the current through the optocoupler transistor to the s9014 base and, as a result, closing the power switch. When the output voltage decreases, on the contrary, the optocoupler transistor will begin to close and s9014 will not interrupt the pulses based on the power switch, thereby increasing their duration and, accordingly, increasing the output voltage.

Particular attention should be paid to winding the transformer. This is often a factor that pushes beginners away from switching power supplies. So, since the block is single-ended, we will need a transformer with a non-magnetic gap between the core halves. The gap is needed to quickly demagnetize the core and to prevent the ferrite from entering saturation. The calculation of the transformer should ideally be carried out in special programs, but for those who do not want to do this, I will say that in such low-power power supplies the primary winding consists of 190-220 turns of 0.08-0.1mm wire. Roughly speaking, the larger the core, the fewer turns. The base winding is wound on top of the primary in the same direction. It consists of 7 - 15 turns of the same wire. And at the end the secondary is wound with a thicker wire. The number of turns is 5-7. It is extremely important to wind all the windings in the same direction and remember where the beginning and end are. On the diagram and on the board (which you can download here), the dots indicate the beginning of the windings.

There is nothing more to add regarding the scheme; it is quite simple and does not require any special skills for assembly. All components can be changed within 25%, the unit will work perfectly. The power transistor can be installed with any reverse conductivity corresponding to the power and with a calculated collector voltage of at least 400 volts. The base transistor is any low-power NPN with the same pinout as s9014.

This unit can be powerfully used where high current is not needed, but compactness is needed, for example, for powering Arduino or for charging devices with small-capacity batteries. The advantages of this power supply include its compactness, the presence of protection and stabilization and, of course, ease of assembly. The only downside is, perhaps, the low output power, which, by the way, can be increased by increasing the capacity of the input filter capacitor.

By the way, the block looks like this:

The second option is more powerful.

This option is very similar to the previous one, but more powerful. The block has improved feedback and, therefore, better stabilization. Let's take a look at the diagram.

The circuit is a standby power supply unit for a computer power supply. Unlike the previous circuit, this one has a more powerful power transistor, a larger input filter capacitor and, most importantly, a transformer with a larger overall power. All this just affects the output power. Also in this circuit, unlike the first, normal stabilization is done on the TL431 - the reference voltage source.

The principle of operation here is the same as the previous option. An initial bias voltage is applied through a 560 kOhm resistor to the base of the power switch, it opens slightly and current begins to flow through the primary winding. An increase in current in the primary causes an increase in current in all other windings, which means that the current arising in the base winding will open the transistor even more, and this process will continue until the transistor is completely open. When it opens, the current through the primary will stop changing, which means the secondary will stop flowing and the transistor will close and the cycle will repeat.

I spoke in detail about the operation of current protection and stabilization above and see no point in repeating myself, since everything works exactly the same here.

Since this power supply is made on the basis of a computer unit, I used a ready-made transformer and did not rewind it. Transformer EEL-19B. Estimated overall power 15 – 20 W.

As in the previous circuit, the component values ​​can be deviated within 25%, since in different computer power supplies this circuit works perfectly with different components. This instance, thanks to the output current of 2 A, can be used as a charger for phones and tablets or for other consumers requiring high current. One of the advantages of this design is the ease of obtaining radio components, because everyone probably has a non-working power supply from an old computer or TV, and there the elementary base is enough for 3 - 4 such power supplies. Also a plus can be considered a considerable output current and good stabilization. Of the minuses, we can rightly note the size of the board (it is quite high due to the transformer) and the possibility of whistling during idle. The whistle may appear due to a malfunction of some element, or simply due to the conversion frequency being too low at idle. Under load the frequency increases.

The third option is the most powerful.

This option is for those who need enormous power and excellent stabilization. If you don't mind sacrificing compactness, this unit is especially for you. So, let's look at the diagram.

Unlike the previous two options, this one uses a specialized PWM controller UC3843, which, unlike transistors, can somehow change the pulse width and is specially made for use in single-cycle power supplies. Also, with UC, the frequency does not change depending on the load and it can be clearly calculated in specialized calculators.

So the principle of operation. The initial power is supplied through a 300 kOhm resistor to the 7th leg of the microcircuit, it starts up and begins to generate pulses that come out from the 6th leg and go to the field device. The frequency of these same pulses depends on the elements Rt and Ct. With the specified components, the output frequency is 78.876 kHz. By the way, here is the device of the microcircuit:

This microcircuit is very convenient to implement current protection; it has a special output for this – current sense. If the voltage is more than 1 volt, the protection will work on this leg and the controller will reduce the duration of the pulses. Stabilization here is done using the built-in error amplifier current sense comparator. Since we have 0 volts at pin 2, the amplifier is error amp. It always produces a logical one and it goes to the input of the current sense comparator amplifier, thereby forming a reference voltage of 1 volt at its inverting input. When the voltage at the output of the power supply is exceeded, the phototransistor of the optocoupler opens and shunts 1 pin of the microcircuit to minus. In this case, the voltage at the inverting input of the current sense comparator decreases, and since the voltage at its non-inverting transistor at the moment of opening increases, at some point it will exceed the voltage at the inverting input (the same thing happens during a short circuit) and the current sense comparator will produce a logical unit, which in turn will lead to a decrease in the pulse duration and, ultimately, to a decrease in the voltage at the output of the power supply. The stabilization in this power supply is very good, so that you understand how good it is, when you connect a 1 Ohm resistor to the output, the voltage drops by only 0.06 volts, while 25 W of heat is dissipated on it and it burns out in a couple of seconds. In general, this unit can output both 30 W and 35 W, since a field-effect transistor is used here as a key. The diagram shows 4n60, but I used irf840 since I have a lot of them. The microcircuit can supply a current of up to 1 A to control the field switch, which makes it possible to control fairly powerful field switches without an additional driver.

Good day!

Today, I would like to touch on the topic of power supply for electronic devices.

So, the firmware is ready, the microcontroller has been purchased, the circuit has been assembled, all that remains is to connect the power, but where can I get it? Let's assume that the AVR microcontroller and the circuit are powered by 5 volts.

The following diagrams will help us get 5v:

On-chip linear voltage regulatorL 7805

This method is the simplest and cheapest. We will need:

  1. Microcircuit L 7805 or its analogues.
  2. Krona 9v or any other power source (charger for phone, tablet, laptop).
  3. 2 capacitors (for l 7805 this is 0.1 and 0.33 microFarad).
  4. Radiator.

Let's put together the following diagram:

This stabilizer bases its operation on the l 7805 microcircuit, which has the following characteristics:

    Maximum current: 1.5A

    Input voltage: 7-36V

    Output voltage: 5V

Capacitors are used to smooth out ripples. However, the voltage drop occurs directly on the chip. That is, if we supply 9 volts to the input, then 4 volts (the difference between the input voltage and the stabilization voltage) will drop on the l 7805 microcircuit. This will lead to heat generation on the microcircuit, the amount of which can be easily calculated using the formula:

(Input voltage – stabilization voltage)* current through the load.

That is, if we supply 12 volts to the stabilizer with which we power a circuit that consumes 0.1 Ampere, l 7805 will dissipate (12-5)*0.1=0.7 watts of heat. Therefore, the microcircuit must be mounted on a radiator:

The advantages of this stabilizer:

  1. Cheap (Excluding radiator).
  2. Simplicity.
  3. Easily assembled by hanging installation, i.e. There is no need to manufacture a printed circuit board.

Minuses:

  1. The need to place the chip on the radiator.
  2. There is no possibility of adjusting the stabilized voltage.

This stabilizer is perfect as a voltage source for simple, undemanding circuits.

Switching voltage stabilizer

For assembly we need:

  1. Microcircuit LM 2576S -5.0 (You can take an analogue, but the wiring will be different, check the documentation specifically for your microcircuit).
  2. Diode 1N5822.
  3. 2 capacitors (For LM 2576S -5.0, 100 and 1000 microFarad).
  4. Choke (Inductors) 100 microHenry.

The connection diagram is as follows:

The LM 2576S -5.0 chip has the following characteristics:

  • Maximum current: 3A
  • Input voltage:7-37V
  • Output voltage: 5V

It is worth noting that this stabilizer requires a larger number of components (as well as the presence of a printed circuit board, for more accurate and convenient installation). However, this stabilizer has a huge advantage over its linear counterpart - it does not heat up, and the maximum current is 2 times higher.

The advantages of this stabilizer:

  1. Less heating (No need to buy a radiator).
  2. Higher maximum current.

Minuses:

  1. More expensive than a linear stabilizer.
  2. Difficulty in hanging installation.
  3. There is no possibility of changing the stabilized voltage (When using the LM 2576S -5.0 microcircuit).

To power simple amateur circuits on AVR microcontrollers, the stabilizers presented above are sufficient. However, in the following articles, we will try to assemble a laboratory power supply that will allow you to quickly and conveniently configure the power parameters of the circuits.

Thank you for your attention!

The at 5 volts can be used to power a low-power load, for example, an electronic thermometer, a microcalculator, an electronic watch.

Technical parameters of a switching power supply

  • Input voltage - 220 ±15% V;
  • Conversion frequency - 35 kHz;
  • Maximum load power - 3 W;
  • Efficiency - up to 75%;

The basic module of this switching power supply is a voltage converter on transformer T1 and transistors VT1, VT2, built using a half-bridge circuit. The diode bridge rectifies the alternating voltage of the network. A parametric stabilizer is built on radioelements R1, VD2 - VD4, which, together with capacitors C2 - C4, creates a voltage divider.

To power the master oscillator, the voltage removed from VD2 is used. Resistance R1 plays a dual role: on the one hand, it acts as a ballast in the stabilizer, thereby forming a voltage boost for capacitance C8, and on the other hand, it reduces the current consumption from the mains at the moment of an accidental short circuit at the output of a switching power supply.

Operational amplifier DD1 connected according to a multivibrator circuit forms a master oscillator. Capacitance C7 provides galvanic isolation between the master oscillator and VT2.

Transformer T1 is assembled on a ferrite ring of grade 2000NM and size K12x8x3. Its windings contain: I – 500 vit. enameled wire PEV-2 with a diameter of 0.15 mm, II - 50 vit. (for 5 volts) of the same wire with a diameter of 0.31 with a tap in the middle.

Setting up a switching power supply consists of selecting resistances R1 and R9 for a certain load current value. Resistance R9 is selected based on the need to saturate transistor VT1, which is determined using an oscilloscope.

The value of R1 must be selected such that, under normal load, the current flowing through the zener diodes VD3 and VD4 is more than 5 mA. To reduce voltage ripple at the output, the values ​​of capacitances C3, C4 must be doubled. In addition, it is still possible to reduce the magnitude of the ripple by adding a 50...100 µF oxide capacitor in parallel with capacitance C6 for a rated voltage of 10 V.

Those beginners who are just starting to study electronics are in a hurry to build something supernatural, like microbugs for wiretapping, a laser cutter from a DVD drive, and so on... and so on... What about assembling a power supply with an adjustable output voltage? This power supply is an essential item in every electronics enthusiast's workshop.

Where to start assembling the power supply?

First, you need to decide on the required characteristics that the future power supply will satisfy. The main parameters of the power supply are the maximum current ( Imax), which it can supply to the load (powered device) and the output voltage ( U out), which will be at the output of the power supply. It’s also worth deciding what kind of power supply we need: adjustable or unregulated.

Adjustable power supply is a power supply whose output voltage can be changed, for example, from 3 to 12 volts. If we need 5 volts - we turned the regulator knob - we got 5 volts at the output, we need 3 volts - we turned it again - we got 3 volts at the output.

An unregulated power supply is a power supply with a fixed output voltage - it cannot be changed. For example, the well-known and widely used “Electronics” power supply D2-27 is unregulated and has an output voltage of 12 volts. Also unregulated power supplies are all kinds of chargers for cell phones, adapters for modems and routers. All of them, as a rule, are designed for one output voltage: 5, 9, 10 or 12 volts.

It is clear that for a novice radio amateur it is the regulated power supply that is of greatest interest. It can power a huge number of both homemade and industrial devices designed for different supply voltages.

Next you need to decide on the power supply circuit. The circuit should be simple, easy to repeat by beginning radio amateurs. Here it is better to stick to a circuit with a conventional power transformer. Why? Because finding a suitable transformer is quite easy both in radio markets and in old consumer electronics. Making a switching power supply is more difficult. For a switching power supply, it is necessary to produce quite a lot of winding parts, such as a high-frequency transformer, filter chokes, etc. Also, switching power supplies contain more electronic components than conventional power supplies with a power transformer.

So, the circuit of the regulated power supply proposed for repetition is shown in the picture (click to enlarge).

Power supply parameters:

    Output voltage ( U out) – from 3.3...9 V;

    Maximum load current ( Imax) – 0.5 A;

    The maximum amplitude of output voltage ripple is 30 mV;

    Overcurrent protection;

    Protection against overvoltage at the output;

    High efficiency.

It is possible to modify the power supply to increase the output voltage.

The circuit diagram of the power supply consists of three parts: a transformer, a rectifier and a stabilizer.

Transformer. Transformer T1 reduces the alternating mains voltage (220-250 volts), which is supplied to the primary winding of the transformer (I), to a voltage of 12-20 volts, which is removed from the secondary winding of the transformer (II). Also, “part-time”, the transformer serves as a galvanic isolation between the electrical network and the powered device. This is a very important function. If the transformer suddenly fails for any reason (voltage surge, etc.), then the mains voltage will not be able to reach the secondary winding and, therefore, the powered device. As you know, the primary and secondary windings of a transformer are reliably isolated from each other. This circumstance reduces the risk of electric shock.

Rectifier. From the secondary winding of power transformer T1, a reduced alternating voltage of 12-20 volts is supplied to the rectifier. This is already a classic. The rectifier consists of a diode bridge VD1, which rectifies alternating voltage from the secondary winding of the transformer (II). To smooth out voltage ripples, after the rectifier bridge there is an electrolytic capacitor C3 with a capacity of 2200 microfarads.

Adjustable pulse stabilizer.

The pulse stabilizer circuit is assembled on a fairly well-known and affordable DC/DC converter microcircuit - MC34063.

To make it clear. The MC34063 chip is a specialized PWM controller designed for pulsed DC/DC converters. This chip is the core of the adjustable switching regulator used in this power supply.

The MC34063 chip is equipped with a protection unit against overload and short circuit in the load circuit. The output transistor built into the microcircuit is capable of delivering up to 1.5 amperes of current to the load. Based on a specialized chip, the MC34063 can be assembled as step-up ( Step-Up), and downward ( Step-Down) DC/DC converters. It is also possible to build adjustable pulse stabilizers.

Features of pulse stabilizers.

By the way, switching stabilizers have a higher efficiency compared to stabilizers based on KR142EN series microcircuits ( CRANKS), LM78xx, LM317, etc. And although power supplies based on these chips are very simple to assemble, they are less economical and require the installation of a cooling radiator.

The MC34063 chip does not require a cooling radiator. It is worth noting that this chip can often be found in devices that operate autonomously or use backup power. The use of a switching stabilizer increases the efficiency of the device, and, consequently, reduces power consumption from the battery or battery. Due to this, the autonomous operating time of the device from a backup power source increases.

I think it’s now clear why a pulse stabilizer is good.

Parts and electronic components.

Now a little about the parts that will be required to assemble the power supply.


Power transformers TS-10-3M1 and TP114-163M

A TS-10-3M1 transformer with an output voltage of about 15 volts is also suitable. You can find a suitable transformer in radio parts stores and radio markets, the main thing is that it meets the specified parameters.

Chip MC34063 . The MC34063 is available in DIP-8 (PDIP-8) for conventional through-hole mount and SO-8 (SOIC-8) for surface mount. Naturally, in the SOIC-8 package the chip is smaller in size, and the distance between the pins is about 1.27 mm. Therefore, it is more difficult to make a printed circuit board for a microcircuit in the SOIC-8 package, especially for those who have only recently begun to master printed circuit board manufacturing technology. Therefore, it is better to take the MC34063 chip in a DIP package, which is larger in size, and the distance between the pins in such a package is 2.5 mm. It will be easier to make a printed circuit board for a DIP-8 package.

Chokes. Chokes L1 and L2 can be made independently. To do this, you will need two ring magnetic cores made of 2000HM ferrite, size K17.5 x 8.2 x 5 mm. The standard size is deciphered as follows: 17.5 mm. – outer diameter of the ring; 8.2 mm. - inner diameter; a 5 mm. – height of the ring magnetic circuit. To wind the choke you will need a PEV-2 wire with a cross section of 0.56 mm. 40 turns of such wire must be wound on each ring. The turns of the wire should be distributed evenly over the ferrite ring. Before winding, the ferrite rings must be wrapped in varnished cloth. If you don’t have varnished fabric at hand, you can wrap the ring with three layers of tape. It is worth remembering that ferrite rings may already be painted - covered with a layer of paint. In this case, there is no need to wrap the rings with varnished cloth.

In addition to homemade chokes, you can also use ready-made ones. In this case, the process of assembling the power supply will speed up. For example, as chokes L1, L2 you can use the following surface-mount inductors (SMD - inductor).


As you can see, on the top of their case the inductance value is indicated - 331, which stands for 330 microhenry (330 μH). Also, ready-made chokes with radial leads for conventional installation in holes are suitable as L1, L2. This is what they look like.


The amount of inductance on them is marked either with a color code or with a number. For the power supply, inductances marked 331 (i.e. 330 μH) are suitable. Taking into account the tolerance of ±20%, which is allowed for elements of household electrical equipment, chokes with an inductance of 264 - 396 μH are also suitable. Any inductor or inductor is designed for a certain direct current. As a rule, its maximum value ( I DC max) is indicated in the datasheet for the throttle itself. But this value is not indicated on the body itself. In this case, you can approximately determine the value of the maximum permissible current through the inductor based on the cross-section of the wire with which it is wound. As already mentioned, to independently manufacture chokes L1, L2, you need a wire with a cross-section of 0.56 mm.

Throttle L3 is homemade. To make it, you need a magnetic core made of ferrite. 400HH or 600HH with a diameter of 10 mm. You can find this in antique radios. There it is used as a magnetic antenna. You need to break off a piece 11 mm long from the magnetic circuit. This is quite easy to do; ferrite breaks easily. You can simply tightly clamp the required section with pliers and break off the excess magnetic circuit. You can also clamp the magnetic core in a vice, and then sharply hit the magnetic core. If you fail to carefully break the magnetic circuit the first time, you can repeat the operation.

Then the resulting piece of magnetic circuit must be wrapped with a layer of paper tape or varnished cloth. Next, we wind 6 turns of PEV-2 wire folded in half with a cross-section of 0.56 mm onto the magnetic circuit. To prevent the wire from unwinding, wrap it with tape on top. Those wire leads from which winding of the inductor began are subsequently soldered into the circuit in the place where the points are shown in image L3. These points indicate the beginning of winding the coils with wire.

Additions.

Depending on your needs, you can make certain changes to the design.

For example, instead of a VD3 zener diode type 1N5348 (stabilization voltage - 11 volts), you can install a protective diode - a suppressor - in the circuit 1.5KE10CA.

A suppressor is a powerful protective diode, its functions are similar to a zener diode, however, its main role in electronic circuits is protective. The purpose of the suppressor is to suppress high-voltage pulse noise. The suppressor has a high speed and is able to extinguish powerful impulses.

Unlike the 1N5348 zener diode, the 1.5KE10CA suppressor has a high response speed, which will undoubtedly affect the performance of the protection.

In technical literature and among radio amateurs, a suppressor can be called differently: protective diode, limiting zener diode, TVS diode, voltage limiter, limiting diode. Suppressors can often be found in switching power supplies - there they serve as protection against overvoltage of the powered circuit in the event of faults in the switching power supply.

You can learn about the purpose and parameters of protective diodes from the article about suppressor.

Suppressor 1.5KE10 C A has a letter WITH in the name and is bidirectional - the polarity of its installation in the circuit does not matter.

If there is a need for a power supply with a fixed output voltage, then the variable resistor R2 is not installed, but replaced with a wire jumper. The required output voltage is selected using a constant resistor R3. Its resistance is calculated using the formula:

Uout = 1.25 * (1+R4/R3)

After the transformations, we obtain a formula that is more convenient for calculations:

R3 = (1.25 * R4)/(U out – 1.25)

If you use this formula, then for U out = 12 volts you will need a resistor R3 with a resistance of about 0.42 kOhm (420 Ohm). When calculating, the value of R4 is taken in kilo-ohms (3.6 kOhm). The result for resistor R3 is also obtained in kilo-ohms.

To more accurately set the output voltage U out, you can install a trimming resistor instead of R2 and set the required voltage using the voltmeter more accurately.

It should be taken into account that a zener diode or suppressor should be installed with a stabilization voltage 1...2 volts higher than the calculated output voltage ( U out) power supply. So, for a power supply with a maximum output voltage equal to, for example, 5 volts, a 1.5KE suppressor should be installed 6V8 CA or similar.

Manufacturing of printed circuit board.

A printed circuit board for a power supply can be made in different ways. Two methods for making printed circuit boards at home have already been discussed on the pages of the site.

    The fastest and most comfortable way is to make a printed circuit board using a printed circuit board marker. Marker used Edding 792. He showed himself at his best. By the way, the signet for this power supply was made with just this marker.

    The second method is suitable for those who have a lot of patience and a steady hand. This is a technology for making a printed circuit board using a correction pencil. This is a fairly simple and affordable technology that will be useful to those who could not find a marker for printed circuit boards, but do not know how to make boards with LUT or do not have a suitable printer.

    The third method is similar to the second, only it uses tsaponlak - How to make a printed circuit board using tsaponlak?

In general, there is plenty to choose from.

Setting up and checking the power supply.

To check the functionality of the power supply, you first need to turn it on, of course. If there are no sparks, smoke or pops (this is quite possible), then the power supply is most likely working. At first, keep some distance from him. If you made a mistake when installing electrolytic capacitors or set them to a lower operating voltage, they can “pop” and explode. This is accompanied by electrolyte splashing in all directions through the protective valve on the body. So take your time. You can read more about electrolytic capacitors. Don’t be lazy to read this – it will come in handy more than once.

Attention! The power transformer is under high voltage during operation! Don't put your fingers near it! Don't forget about safety rules. If you need to change something in the circuit, then first completely disconnect the power supply from the mains, and then do it. There is no other way - be careful!

At the end of this whole story, I want to show you a finished power supply that I made with my own hands.

Yes, it does not yet have a housing, a voltmeter and other “goodies” that make it easier to work with such a device. But, despite this, it works and has already managed to burn out an awesome three-color flashing LED because of its stupid owner, who loves to twist the voltage regulator recklessly. I wish you, novice radio amateurs, to collect something similar!