A simple and reliable do-it-yourself power supply at the current level of development element base electronic components can be made very quickly and easily. It does not require knowledge of electronics and electrical engineering to high level. You will soon see this.
Making your first power supply is quite an interesting and memorable event. Therefore, an important criterion here is the simplicity of the circuit, so that after assembly it will immediately work without any advanced settings and tweaks.
It should be noted that almost every electronic, electrical device or device needs power. The difference is only in the main parameters - the magnitude of voltage and current, the product of which gives power.
Making a power supply with your own hands is a very good first experience for beginner electronics engineers, because it allows you to feel (not on yourself) the various values \u200b\u200bof the currents flowing in devices.
The modern market for power supplies is divided into two categories: transformer and transformerless. The first are quite simple to manufacture for beginner radio amateurs. The second indisputable advantage is the relatively low level of electromagnetic radiation, and, accordingly, interference. A significant drawback by modern standards is the significant weight and dimensions caused by the presence of a transformer - the heaviest and most bulky element in the circuit.
Transformerless power supplies are deprived of the last drawback due to the lack of a transformer. Rather, it is there, but not in the classical representation, but works with a high frequency voltage, which makes it possible to reduce the number of turns and the size of the magnetic circuit. As a result, the overall dimensions of the transformer are reduced. The high frequency is formed by semiconductor switches, in the process of switching on and off according to a given algorithm. As a result, strong electromagnetic interference occurs, therefore, such sources are subject to mandatory shielding.
We will assemble a transformer power supply that will never lose its relevance, since it is still used in audio equipment high class, due to the minimum level of noise generated, which is very important for obtaining high-quality sound.
The device and principle of operation of the power supply
The desire to get the finished device as compact as possible led to the emergence of various microcircuits, inside which there are hundreds, thousands and millions of individual electronic elements. Therefore, almost any electronic device contains a microcircuit, the standard power supply of which is 3.3 V or 5 V. Auxiliary elements can be powered from 9 V to 12 V DC. However, we are well aware that the socket has an alternating voltage of 220 V with a frequency of 50 Hz. If it is applied directly to a microcircuit or any other low-voltage element, they will instantly fail.
From this it becomes clear that the main task network block power supply (BP) consists in reducing the voltage to an acceptable level, as well as converting (rectifying) it from AC to DC. In addition, its level must remain constant regardless of fluctuations in the input (in the outlet). Otherwise, the device will be unstable. Therefore, another important function of the PSU is the stabilization of the voltage level.
In general, the structure of the power supply consists of a transformer, a rectifier, a filter and a stabilizer.
In addition to the main nodes, a number of auxiliary ones are also used, for example, indicator LEDs, which indicate the presence of the supplied voltage. And if the PSU provides for its adjustment, then naturally there will be a voltmeter, and possibly also an ammeter.
Transformer
In this circuit, a transformer is used to reduce the voltage in a 220 V outlet to the required level, most often 5 V, 9 V, 12 V or 15 V. At the same time, galvanic isolation of high-voltage and low-voltage circuits is also carried out. Therefore, in any emergency situations, the voltage on the electronic device will not exceed the value of the secondary winding. Also, galvanic isolation increases the safety of the operating personnel. In case of touching the device, a person will not fall under the high potential of 220 V.
The design of the transformer is quite simple. It consists of a core that acts as a magnetic circuit, which is made of thin, well-conductive magnetic flux plates, separated by a dielectric, which is a non-conductive varnish.
At least two windings are wound on the core rod. One primary (also called network) - 220 V is supplied to it, and the second - secondary - reduced voltage is removed from it.
The principle of operation of the transformer is as follows. If a voltage is applied to the mains winding, then, since it is closed, an alternating current will begin to flow in it. Around this current, an alternating magnetic field arises, which is collected in the core and flows through it in the form of a magnetic flux. Since there is another winding on the core - the secondary one, then under the action of an alternating magnetic flux one can see in it electromotive force(EMF). When this winding is shorted to a load, an alternating current will flow through it.
Radio amateurs in their practice most often use two types of transformers, which mainly differ in the type of core - armored and toroidal. The latter is more convenient to use in that it is quite easy to wind it up on it. right amount turns, thereby obtaining the necessary secondary voltage, which is directly proportional to the number of turns.
The main two parameters of the transformer for us are the voltage and current of the secondary winding. We will take the current value equal to 1 A, since we will take the zener diodes for the same value. About what a little further.
We continue to assemble the power supply with our own hands. And the next ordinal element in the circuit is a diode bridge, also known as a semiconductor or diode rectifier. It is intended to convert the alternating voltage of the secondary winding of the transformer into a constant, or rather, into a rectified pulsating one. This is where the name "rectifier" comes from.
There are various rectification schemes, but the bridge circuit has received the most use. Its principle of operation is as follows. In the first half-cycle of the alternating voltage, the current flows along the path through the VD1 diode, the R1 resistor and the VD5 LED. Next, the current returns to the winding through the open VD2.
A reverse voltage is applied to the diodes VD3 and VD4 at this moment, so they are locked and the current does not flow through them (in fact, it only flows at the moment of switching, but this can be neglected).
In the next half-cycle, when the current in the secondary winding changes its direction, the opposite will happen: VD1 and VD2 will close, and VD3 and VD4 will open. In this case, the direction of current flow through the resistor R1 and the LED VD5 will remain the same.
The diode bridge can be soldered from four diodes connected according to the diagram above. And you can buy ready-made. They come in horizontal and vertical versions in different cases. But in any case, they have four conclusions. The two leads are supplied with AC voltage, they are indicated by the sign "~", both of the same length and the shortest.
The rectified voltage is removed from the other two conclusions. They are designated "+" and "-". The “+” terminal has the longest length among the others. And on some cases, a bevel is made near it.
Condenser filter
After the diode bridge, the voltage has a pulsating character and is still unsuitable for powering microcircuits, and even more so microcontrollers, which are very sensitive to various kinds of voltage drops. Therefore, it needs to be smoothed out. To do this, you can use a choke or a capacitor. In the circuit under consideration, it is enough to use a capacitor. However, it must have a large capacity, so an electrolytic capacitor should be used. Such capacitors often have polarity, so it must be observed when connected to the circuit.
The negative terminal is shorter than the positive one and a “-” sign is applied on the case near the first one.
Voltage regulator LM 7805, LM 7809, LM 7812
You probably noticed that the voltage in the outlet is not equal to 220 V, but varies within certain limits. This is especially noticeable when connecting a powerful load. If you do not apply special measures, then it will also change at the output of the power supply in a proportional range. However, such fluctuations are highly undesirable, and sometimes unacceptable for many electronic elements. Therefore, the voltage after the capacitor filter is subject to mandatory stabilization. Depending on the parameters of the powered device, two stabilization options are used. In the first case, a zener diode is used, and in the second, an integrated voltage regulator. Let's consider the use of the latter.
In amateur radio practice, voltage stabilizers of the LM78xx and LM79xx series have been widely used. Two letters indicate the manufacturer. Therefore, instead of LM, there may be other letters, such as CM. The marking consists of four digits. The first two - 78 or 79 mean respectively positive or negative voltage. The last two digits, in this case, instead of them two x's: xx, indicate the value of the output U. For example, if there are 12 in the position of two x's, then this stabilizer outputs 12 V; 08 - 8 V, etc.
For example, let's decipher the following markings:
LM7805 → 5V positive voltage
LM7912 → 12V negative U
Integral stabilizers have three outputs: input, common and output; rated for 1A.
If the output U significantly exceeds the input and at the same time a limiting current of 1 A is consumed, then the stabilizer gets very hot, so it should be installed on a radiator. The design of the case provides for this possibility.
If the load current is much lower than the limit, then you can not install a radiator.
The classic power supply circuit includes: a mains transformer, a diode bridge, a capacitor filter, a stabilizer and an LED. The latter acts as an indicator and is connected through a current-limiting resistor.
Since in this circuit the LM7805 stabilizer is the limiting element flow (permissible value is 1 A), all other components must be rated for a current of at least 1 A. Therefore, the secondary winding of the transformer is selected for a current of one ampere. Its voltage should not be lower than the stabilized value. And for good, it should be chosen from such considerations that after rectification and smoothing, U should be 2–3 V higher than the stabilized one, i.e. the input of the stabilizer should be fed a couple of volts more than its output value. Otherwise, it will not work correctly. For example, for LM7805 input U = 7 - 8 V; for LM7805 → 15 V. However, it should be borne in mind that if the U value is too high, the microcircuit will heat up very much, since the “extra” voltage is quenched on its internal resistance.
The diode bridge can be made from diodes of the 1N4007 type, or you can take it ready for a current of at least 1 A.
The smoothing capacitor C1 should have a large capacitance of 100 - 1000 uF and U = 16 V.
Capacitors C2 and C3 are designed to smooth out the high frequency ripple that occurs when operating the LM7805. They are installed for greater reliability and are advisory in nature from manufacturers of stabilizers of this type. Without such capacitors, the circuit also works fine, but since they cost practically nothing, it is better to put them on.
Do-it-yourself power supply for 78 L 05, 78 L 12, 79 L 05, 79 L 08
It is often necessary to power only one or a pair of microcircuits or low-power transistors. In this case, it is not rational to use a powerful power supply. Therefore, the best option would be to use stabilizers of the 78L05, 78L12, 79L05, 79L08 series, etc. They are designed for a maximum current of 100 mA = 0.1 A, but at the same time they are very compact and no larger than a conventional transistor in size, and also do not require installation on a radiator.
The marking and connection diagram are similar to those of the LM series discussed above, only the pin arrangement differs.
For example, the connection diagram of the stabilizer 78L05 is shown. It is also suitable for LM7805.
The scheme for switching on negative voltage stabilizers is shown below. The input is -8V and the output is -5V.
As you can see, making a power supply with your own hands is very simple. Any voltage can be obtained by installing the appropriate stabilizer. You should also remember about the parameters of the transformer. Next, we will look at how to make a voltage regulated power supply.
I recently came across a curious circuit diagram of a simple but pretty good entry-level power supply capable of delivering 0-24 V at a current of up to 5 amperes. The power supply provides protection, that is, limiting the maximum current in case of overload. The attached archive contains a printed circuit board and a document that describes the settings for this unit, and a link to the author's website. Please read the description carefully before assembling.
Here is a photo of my PSU version, a view of the finished board, and you can see how to roughly apply the case from an old computer ATX. The adjustment is made 0-20 V 1.5 A. Capacitor C4 for such a current is set to 100 uF 35 V.
In the event of a short circuit, the maximum limited current is issued and the LED lights up, brought the limiter resistor to the front panel.
Power supply indicator
I conducted an audit, found a couple of simple M68501 arrowheads for this PSU. I spent half a day creating a screen for it, but still drew it and fine-tuned it to the required output voltages.
The resistance of the indicator head used and the applied resistor are indicated in the attached file on the indicator. I spread the front panel of the block, if anyone needs a case from an ATX power supply to remake, it will be easier to rearrange the inscriptions and add something than to create from scratch. If other voltages are required, the scale can simply be recalibrated, this will be easier. Here is the finished view of the regulated power supply:
Film - self-adhesive type "bamboo". The indicator has a backlight Green colour. Red LED Attention indicates that the overload protection has been activated.
Additions from BFG5000
The maximum limiting current can be made more than 10 A. On the cooler - a roll of 12 volts plus a temperature speed controller - from 40 degrees it starts to increase speed. The circuit error does not particularly affect the operation, but judging by the measurements during a short circuit, an increase in the transmitted power appears.
The power transistor installed 2n3055, everything else is also foreign analogues, except for BC548 - I installed KT3102. It turned out really indestructible BP. For beginner radio amateurs, that's it.
The output capacitor is set to 100 uF, the voltage does not jump, the adjustment is smooth and without visible delays. I set the calculation as indicated by the author: 100 microfarads of capacity per 1 A of current. The authors: Igoran and BFG5000.
Discuss the article POWER SUPPLY WITH CURRENT AND VOLTAGE REGULATION
Quite often, during testing, you have to power various crafts or devices. And using batteries, choosing the appropriate voltage, was no longer a joy. Therefore, I decided to assemble an adjustable power supply. Of the several options that came to mind, namely: remake a power supply from a computer ATX, or assemble a linear one, or purchase a KIT kit, or assemble it from ready-made modules - I chose the latter.
I liked this assembly option because of undemanding knowledge in the field of electronics, assembly speed, and in which case, quick replacement or addition of any of the modules. The total cost of all components came out to be about $15, and the power in the end turned out to be ~ 100 watts, with a maximum output voltage of 23V.
To create this adjustable power supply you will need:
- Switching power supply 24V 4A
- Step-down converter for XL4015 4-38V to 1.25-36V 5A
- Volt-ammeter 3 or 4 characters
- Two step-down converters on LM2596 3-40V to 1.3-35V
- Two 10K potentiometers and knobs for them
- Two terminals for bananas
- On/off button and 220V power socket
- Fan 12V, in my case 80mm slim
- Corps, whatever
- Racks and bolts for fixing boards
- The wires I used are from a dead ATX power supply.
After finding and acquiring all the components, we proceed to the assembly according to the scheme below. According to it, we will get an adjustable power supply with a voltage change from 1.25V to 23V and a current limit of up to 5A, plus additional opportunity charging devices via USB ports, the amount of current consumed, which will be displayed on the V-A meter.
We pre-mark and cut holes for the volt-ammeter, potentiometer knobs, terminals, USB outputs on the front side of the case.
In the form of a platform for attaching modules, we use a piece of plastic. It will protect against an unwanted short circuit to the case.
We mark and drill the location of the holes in the boards, after which we screw the racks.
We fasten the plastic pad to the body.
We solder the terminal on the power supply, and solder three wires to + and -, pre-cut length. One pair will go to the main converter, the second to the converter for powering the fan and the volt-ammeter, the third to the converter for USB outputs.
We install a 220V power connector and an on / off button. We solder the wires.
We fasten the power supply and connect 220V wires to the terminal.
We figured out the main power source, now we move on to the main converter.
We solder the terminals and trimmer resistors.
We solder the wires to the potentiometers responsible for adjusting the voltage and current, and to the converter.
Solder the thick red wire from V-A meters and output plus from the main probe to the output positive terminal.
Preparing USB output. We connect the date + and - for each USB separately so that the connected device can be charged, and not synchronized. Solder the wires to the paralleled + and - power contacts. Wires are better to take thicker.
We solder the yellow wire from the V-A meter and the negative wire from the USB outputs to the output negative terminal.
We connect the power wires of the fan and the V-A meter to the outputs of the additional converter. For the fan, you can assemble a thermostat (diagram below). You will need: a power MOSFET transistor (N channel) (I got it from the processor power supply harness on motherboard), trimmer 10 kOhm, NTC temperature sensor with a resistance of 10 kOhm (thermistor) (I got it from a broken ATX power supply). We fix the thermistor with hot glue to the microcircuit of the main converter, or to the radiator on this microcircuit. We adjust the trimmer to a certain temperature of the fan operation, for example, 40 degrees.
We solder to the output plus of another, additional converter plus USB outputs.
We take one pair of wires from the power supply and solder it to the input of the main converter, then the second to the input of the additional one. converter to USB, to provide incoming voltage.
We fasten the fan with a lattice.
We solder the third pair of wires from the power supply to the additional. fan converter and V-A meter. We fasten everything to the site.
We connect the wires to the output terminals.
We fasten the potentiometers to the front side of the case.
We fix the USB outputs. For reliable fixation, a U-shaped mount was made.
Set the output voltage to converters: 5.3V, taking into account the voltage drop when the load is connected to USB, and 12V.
We tighten the wires for a neat interior look.
We close the case with a lid.
We glue the legs for stability.
The regulated power supply is ready.
Video version of the review:
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We select the details. If you have a radiator with a cooler from an old or faulty computer, then we don’t miss such a chance - this will reduce the dimensions of the device, while at the same time facilitating the thermal regime of the stabilizer.
Microcircuits of 5-volt stabilizers are better to take imported ones in a plastic case - in this case, additional electrical insulation is not required.
The KT819 transistor can be replaced with a KT853 with a slight decrease in the power reserve, but this will not be displayed during operation of the device - the KT853 series transistors are designed for a maximum direct current of up to 7.5 A. When using a lower power transformer, you can get by with less powerful transistors, for example, series KT805, KT817, D2396, etc.
Schottky diodes of the S10C40 or KD270BS series can be used as rectifier diodes by installing them on a common radiator with a regulating transistor - electrical insulation between their cases is not required.
The filter capacitor C1 must have a capacitance of at least 8000 uF. If this is not the case, then this capacity can be filled with several capacitors - for example, as in the photo, 4 pcs. at 2200 uF. The operating voltage of the capacitors C1, C3 and C5 is selected equal to 35 V or slightly higher.
Those beginners who are just starting to learn 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 ... But what about assembling a power supply with adjustable output voltage? Such a power supply is an essential item in the workshop of every electronics lover.
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 give to the load (powered device) and output voltage (U out), which will be at the output of the power supply. It is also worth deciding which power supply we need: adjustable or unregulated.
Adjustable power supply - this is a power supply, the output voltage of which can be changed, for example, in the range from 3 to 12 volts. If we need 5 volts - we turned the knob of the regulator - 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 fixed output voltage power supply that cannot be changed. So, for example, the well-known and widespread power supply unit "Electronics" D2-27 is unregulated and has an output of 12 volts of voltage. Also, unregulated power supplies are all kinds of chargers for cell phones, modem and router adapters. 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 adjustable power supply that is of greatest interest. They can power a huge number of both home-made 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 novice radio amateurs. Here it is better to dwell on the circuit with a conventional power transformer. Why? Because finding a suitable transformer is easy enough both in radio markets and in old consumer electronics. Making a switching power supply is more difficult. For impulse block power supply, it is necessary to manufacture 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 scheme of the adjustable 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 ripples is 30 mV;
Overcurrent protection;
Protection against the appearance of overvoltage at the output;
High efficiency.
It is possible to modify the power supply in order 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 lowers 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, in combination, the transformer serves as a galvanic isolation between the mains and the powered device. This is very important function. If suddenly the transformer fails for any reason (power surge, etc.), then the mains voltage will not be able to get to the secondary winding and, therefore, to the powered device. As you know, the primary and secondary windings of the transformer are reliably isolated from each other. This circumstance reduces the risk of electric shock.
Rectifier. From the secondary winding of the power transformer T1, a reduced alternating voltage of 12-20 volts is supplied to the rectifier. It's already a classic. The rectifier consists of a diode bridge VD1, which rectifies the 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 switching stabilizer.
Scheme switching regulator assembled on a fairly well-known and affordable DC / DC converter chip - MC34063.
To be clear. The MC34063 is a dedicated PWM controller designed for switching DC/DC converters. This chip is the core of the adjustable switching regulator that is used in this power supply.
The MC34063 is equipped with an overload and short circuit protection unit 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. On the base specialized microcircuit MC34063 can be built as boosters ( step-up), and lowering ( step-down) DC/DC converters. It is also possible to build adjustable pulse stabilizers.
Features of impulse stabilizers.
By the way, switching regulators have a higher efficiency compared to stabilizers based on KR142EN series microcircuits ( Krenki), LM78xx, LM317, etc. And although power supplies based on these microcircuits are very easy to assemble, they are less economical and require the installation of a cooling radiator.
The MC34063 does not require a heatsink. It is worth noting that this microcircuit can be quite often found in devices that work autonomously or use backup power. The use of a switching regulator increases the efficiency of the device, and, consequently, reduces power consumption from the battery or battery. Due to this, it increases offline time device operation from backup source nutrition.
I think now it’s clear what a good pulse stabilizer is.
Details and electronic components.
Now a little about the details 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. In radio parts stores and radio markets, you can find a suitable transformer, as long as it meets the specified parameters.
Chip MC34063 . The MC34063 is available in DIP-8 (PDIP-8) conventional through hole mount and SO-8 (SOIC-8) surface mount packages. Naturally, in the SOIC-8 package, the microcircuit is smaller, and the distance between the pins is about 1.27 mm. So make printed circuit board for a microcircuit in a SOIC-8 package, it is more difficult, especially for those who have only recently begun to master the technology of manufacturing printed circuit boards. 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 the DIP-8 package.
Chokes. Chokes L1 and L2 can be made independently. This will require two ring magnetic cores made of 2000HM ferrite, size K17.5 x 8.2 x 5 mm. The standard size stands for: 17.5 mm. - outer diameter of the ring; 8.2 mm. - inner diameter; and 5 mm. is the height of the ring magnetic circuit. To wind the inductor, you need a PEV-2 wire with a cross section of 0.56 mm. 40 turns of such a wire must be wound on each ring. The turns of the wire should be evenly distributed over the ferrite ring. Before winding, ferrite rings must be wrapped with varnished cloth. If there is no varnished cloth at hand, then you can wrap the ring with tape in three layers. It is worth remembering that ferrite rings can already be painted - covered with a layer of paint. In this case, it is not necessary 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 these surface-mounted inductances (SMD - choke).
As you can see, on the top of their case, the inductance value is indicated - 331, which stands for 330 microhenries (330 μH). Also, as L1, L2, ready-made chokes with radial leads for conventional mounting in holes are suitable. They look like this.
The inductance value on them is marked either with a color code or a numerical one. For the power supply, inductances marked 331 (i.e. 330 uH) are suitable. Given 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 ( IDC max) is indicated in the datasheet for the throttle itself. But this value is not indicated on the body itself. In this case, it is possible to roughly determine the value of the maximum allowable current through the inductor according to the cross section of the wire with which it is wound. As already mentioned, for self-manufacturing chokes L1, L2 requires a wire with a cross section of 0.56 mm.
Choke L3 homemade. For its manufacture, a ferrite magnetic circuit is required. 400HH or 600HH 10 mm in diameter. You can find this in vintage radios. There it is used as a magnetic antenna. From the magnetic circuit you need to break off a piece 11 mm long. This is easy enough to do, ferrite breaks easily. You can simply tightly clamp the required segment with pliers and break off the excess magnetic circuit. You can also clamp the magnetic circuit in a vise, and then sharply hit the magnetic circuit. If the first time it is not possible to carefully break the magnetic circuit, then you can repeat the operation.
Then the resulting piece of the magnetic circuit must be wrapped with a layer of paper tape or varnished cloth. Next, we wind 6 turns of the PEV-2 wire folded in half with a cross section of 0.56 mm onto the magnetic circuit. In order to prevent the wire from unwinding, we wrap it on top with tape. Those wire leads from which the winding of the inductor began, are subsequently soldered into the circuit in the place where the points are shown in the image L3. These points indicate the beginning of the winding of the coils with wire.
Additions.
Depending on the needs, certain changes can be made to the design.
For example, instead of a VD3 zener diode of type 1N5348 (stabilization voltage - 11 volts), a protective diode can be installed in the circuit - a suppressor 1.5KE10CA.
A suppressor is a powerful protective diode, similar in function to a zener diode, however, its main role in electronic circuits is protective. The purpose of the suppressor is to suppress high-voltage impulse 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 the technical literature and in the communication environment of radio amateurs, a suppressor can be called differently: a protective diode, a limiting zener diode, a TVS diode, a voltage limiter, a limiting diode. Suppressors can often be found in switching power supplies - there they serve as overvoltage protection for the powered circuit in case of malfunctions of the switching power supply.
You can learn about the purpose and parameters of protective diodes from the article about the suppressor.
Suppressor 1,5KE10 C A has a letter FROM 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 desired output voltage is selected using a constant resistor R3. Its resistance is calculated by the formula:
U out \u003d 1.25 * (1 + R4 / R3)
After transformations, a formula is obtained that is more convenient for calculations:
R3 \u003d (1.25 * R4) / (U out - 1.25)
If use this formula, then for U out \u003d 12 volts, a resistor R3 with a resistance of about 0.42 kOhm (420 Ohm) is required. When calculating, the value of R4 is taken in kiloohms (3.6 kOhm). The result for the resistor R3 is also obtained in kilo-ohms.
For a more accurate setting of the output voltage U out, instead of R2, you can install a tuning resistor and set the required voltage more accurately using the voltmeter.
In this case, it should be noted that a zener diode or suppressor should be installed with a stabilization voltage of 1 ... 2 volts more 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.
PCB manufacturing.
The printed circuit board for the power supply can be made different ways. Two methods for manufacturing printed circuit boards at home have already been described on the pages of the site.
The fastest and most comfortable way is to make a PCB using a PCB marker. Marker applied Edding 792. He showed himself from the best side. By the way, the signet for this power supply is made with just this marker.
The second method is suitable for those who have a lot of patience and a steady hand in reserve. This is a technology for making a printed circuit board with a correction pencil. This, a fairly simple and affordable technology, will come in handy for those who could not find a marker for printed circuit boards, but do not know how to make boards with a LUT or do not have a suitable printer.
The third method is similar to the second, only it uses zaponlak - How to make a printed circuit board with zaponlak?
In general, there are plenty to choose from.
Setting up and testing the power supply.
To check the performance of the power supply, you must first, of course, turn it on. If there are no sparks, smoke and pops (this is quite real), then the PSU is more likely to work. At first, keep some distance from him. If you made a mistake when installing electrolytic capacitors or set them to a lower operating voltage, then they can “pop” - 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. Do not be lazy to read it - it will come in handy more than once.
Attention! During operation, the power transformer must be under high voltage! Don't stick your fingers in it! Do not forget about safety regulations. If you need to change something in the circuit, then first completely disconnect the power supply from the mains, and then do it. No other way - be careful!
Toward the close of this whole story, I want to show a finished power supply that was made by myself.
Yes, he still does not have a case, a voltmeter and other "buns" that make it easier to work with such a device. But, despite this, it works and has already managed to burn an awesome three-color flashing LED because of its stupid owner, who likes to turn the voltage regulator recklessly. I wish you, novice radio amateurs, to assemble something similar!
