A simple and reliable do-it-yourself power supply at the current level of development of the element base of radio-electronic components can be made very quickly and easily. It does not require knowledge of electronics and electrical engineering at a 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 additional settings and adjustments.
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 dimensions 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 high-end audio equipment 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 of the mains power supply (PSU) is to reduce 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 that signal the presence of the applied 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 a variable magnetic flux, an electromotive force (EMF) is seen in it. 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 the required number of turns on it, 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 heats up very much, 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 flow of the elements (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 U 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.
We all know that power supplies are an integral part of a large number of electrical appliances and lighting systems today. Without them, our life is unreal, especially since energy saving contributes to the operation of these devices. Basically, power supplies have an output voltage of 12 to 36 volts. In this article, I would like to deal with one question, is it possible to make a 12V power supply with your own hands? In principle, no problems, because this device actually has a simple design.
What can you build a power supply from?
So, what parts and devices are needed to assemble a homemade power supply? At the heart of the design are only three components:
- Transformer.
- Capacitor.
- Diodes, from which you will have to assemble a diode bridge with your own hands.
As a transformer, you will have to use a conventional step-down device that will reduce the voltage from 220 V to 12 V. Such devices are sold in stores today, you can use an old unit, you can convert, for example, a transformer with a decrease to 36 volts into a device with a decrease of up to 12 volt. In general, there are options, use any.
As for the capacitor, the best option for a homemade unit is a 470 microfarad capacitor with a voltage of 25V. Why with such a voltage? The thing is that the output voltage will be higher than planned, that is, more than 12 volts. And this is normal, because under load the voltage will drop to 12V.
Assembling the diode bridge
And now a very important point, which concerns the question of how to make a 12V power supply with your own hands. First, let's start with the fact that a diode is a bipolar element, like, in principle, a capacitor. That is, it has two outputs: one is a minus, the other is a plus. So, the plus on the diode is indicated by a strip, which means that without a strip it is a minus. Diode connection sequence:
- First, two elements are connected to each other according to the plus or minus scheme.
- The other two diodes are connected in the same way.
- After that, two paired structures must be connected to each other according to the plus with plus and minus with minus scheme. The main thing here is not to make a mistake.
At the end, you should get a closed structure, which is called a diode bridge. She has four connecting points: two "plus-minus", one "plus-plus" and one more "minus-minus". You can connect elements on any board of the required device. The main requirement here is a high-quality contact between the diodes.
Secondly, the diode bridge is, in fact, a conventional rectifier that rectifies the alternating current coming from the secondary winding of the transformer.
Complete instrument assembly
Everything is ready, you can proceed to the assembly of the final product of our idea. First you need to connect the transformer leads to the diode bridge. They are connected to the plus-minus connection points, the remaining points remain free.
Now you need to connect the capacitor. Please note that it also has marks that determine the polarity of the device. Only on it everything is the other way around than on diodes. That is, a negative contact is usually marked on the capacitor, which is connected to the “minus-minus” point of the diode bridge, and the opposite pole (positive) is connected to the “minus-minus” point.
It remains only to connect two power wires. For this, it is best to choose colored wires, although this is not necessary. You can use one-color ones, but on condition that they have to be marked in some way, for example, make a knot on one of them or wrap the end of the wire with electrical tape.
So, the power wires are connected. We will connect one of them to the “plus-plus” point on the diode bridge, the other to the “minus-minus” point. Everything, a 12-volt step-down power supply is ready, you can test it. In idle mode, it usually shows a voltage in the range of 16 volts. But as soon as a load is applied to it, the voltage drops to 12 volts. If there is a need to set the exact voltage, then you will have to connect a stabilizer to a home-made device. As you can see, making a power supply with your own hands is not very difficult.
Of course, this is the simplest circuit, power supplies can be with different parameters, where there are two main ones:
As an addition, a function can be used that distinguishes between regulated (pulse) and unregulated (stabilized) power supply models. The first are indicated by the ability to change the output voltage in the range from 3 to 12 volts. That is, the more complex the design, the more opportunities the units as a whole have.
And the last. Homemade power supplies are not entirely safe devices. So when testing them, it is recommended to move a certain distance and only after that to turn on the 220 volt network. If you calculated something inaccurately, for example, you chose the wrong capacitor, then there is a high probability that this element will simply explode. An electrolyte is poured into it, which, during an explosion, is sprayed over a decent distance. In addition, do not replace or solder when the power supply is on. There is a lot of voltage going on the transformer, so don't play with fire. All alterations must be carried out only with the device turned off.
Hello to all radio amateurs, in this article I want to introduce you to a power supply with voltage regulation from 0 to 12 volts. It is very easy to set the desired voltage on it, even in millivolts. The scheme does not contain any purchased parts - all this can be pulled out of old equipment, both imported and Soviet.
PSU schematic diagram (reduced)
The case is made of wood, a 12 volt transformer is screwed in the middle, a 1000 microfarad x 25 volt capacitor and a board that regulates the voltage.
Capacitor C2 must be taken with a large capacity, for example, to connect an amplifier to the power supply and so that the voltage does not fall at low frequencies.
Transistor VT2 is better to install on a small radiator. Because during long-term operation it can heat up and burn out, I have already burned out 2 pieces until I installed a decent-sized radiator.
Resistor R1 can be set constant, it does not play a big role. On top of the case there is a variable resistor that regulates the voltage, and a red LED that shows if there is voltage at the PSU output.
At the output of the device, in order not to constantly fasten the wires to something, I soldered the crocodiles - it is very convenient with them. The circuit does not require any settings and works reliably and stably, any radio amateur can really make it. Thank you for your attention, good luck everyone! .
How to assemble a simple power supply and a powerful voltage source yourself.
Sometimes you have to connect various electronic devices, including homemade ones, to a 12 volt DC source. The power supply is easy to assemble on your own during half a day off. Therefore, there is no need to purchase a ready-made block, when it is more interesting to make the necessary thing for your laboratory yourself. 
Anyone who wants to be able to make a 12-volt unit on their own, without much difficulty.
Someone needs a source to power the amplifier, and someone needs to power a small TV or radio ...
Step 1: What parts are needed to assemble the power supply...
To assemble the block, prepare in advance the electronic components, parts and accessories from which the block itself will be assembled....
-Circuit board.
- Four diodes 1N4001, or similar. The bridge is diode.
- Voltage stabilizer LM7812.
- Low-power step-down transformer for 220 V, the secondary winding should have 14V - 35V AC voltage, with a load current of 100 mA to 1A, depending on how much power you need to get at the output.
- Electrolytic capacitor with a capacity of 1000uF - 4700uF.
- 1uF capacitor.
-Two 100nF capacitors.
- Cut wires.
-Radiator, if needed.
If you need to get the maximum power from the power supply, you need to prepare the appropriate transformer, diodes and heatsink for the chip.
Step 2: Tools....
For the manufacture of the block, tools for installation are required:
-Soldering iron or soldering station
-Nippers
- Mounting tweezers
-Wire strippers
- Solder suction device.
-Screwdriver.
And other tools that you might find useful.
Step 3: Schematic and more... 
To get a 5 volt stabilized power supply, you can replace the LM7812 stabilizer with the LM7805.
To increase the load capacity by more than 0.5 amperes, you will need a heatsink for the microcircuit, otherwise it will fail from overheating.
However, if you need to get a few hundred milliamps (less than 500 mA) from the source, then you can do without a heatsink, heating will be negligible.
In addition, an LED is added to the circuit to visually verify that the power supply is working, but you can do without it.
Power supply circuit 12v 30A.
When using one 7812 stabilizer as a voltage regulator and several powerful transistors, this power supply is capable of providing an output load current of up to 30 amperes.
Perhaps the most expensive part of this circuit is the power step-down transformer. The voltage of the secondary winding of the transformer must be a few volts more than the stabilized voltage of 12V in order to ensure the operation of the microcircuit. It must be borne in mind that one should not strive for a larger difference between the input and output voltage values, since at such a current the heat sink of the output transistors increases significantly in size.
In the transformer circuit, the diodes used must be designed for a large maximum forward current, approximately 100A. The maximum current flowing through the 7812 chip in the circuit will not exceed 1A.
Six composite Darlington type TIP2955 transistors connected in parallel provide a load current of 30A (each transistor is rated for a current of 5A), such a large current requires an appropriate size of the radiator, each transistor passes through itself one sixth of the load current.
A small fan can be used to cool the radiator.
Checking the power supply
When you first turn it on, it is not recommended to connect the load. We check the operation of the circuit: we connect a voltmeter to the output terminals and measure the voltage, it should be 12 volts, or the value is very close to it. Next, we connect a load resistor of 100 ohms, with a dissipation power of 3 W, or a similar load - such as an incandescent lamp from a car. In this case, the voltmeter reading should not change. If there is no 12 volt voltage at the output, turn off the power and check the correct installation and serviceability of the elements.
Before installation, check the serviceability of the power transistors, since with a broken transistor, the voltage from the rectifier goes directly to the output of the circuit. To avoid this, check the power transistors for a short circuit, to do this, measure the resistance between the collector and emitter of the transistors separately with a multimeter. This check must be carried out before installing them in the circuit.
Power supply 3 - 24v
The power supply circuit produces an adjustable voltage in the range from 3 to 25 volts, with a maximum load current of up to 2A, if you reduce the current-limiting resistor of 0.3 ohms, the current can be increased to 3 amperes or more.
Transistors 2N3055 and 2N3053 are installed on the corresponding heatsinks, the power of the limiting resistor must be at least 3 watts. Voltage regulation is controlled by the LM1558 or 1458 op amp. When using the 1458 op amp, it is necessary to replace the stabilizer elements that supply voltage from pin 8 to 3 op amps from a divider with 5.1 K resistors.
The maximum constant voltage for supplying the op-amps 1458 and 1558 is 36 V and 44 V, respectively. The power transformer must deliver at least 4 volts more than the stabilized output voltage. The power transformer in the circuit has an output voltage of 25.2 volts AC with a tap in the middle. When switching the windings, the output voltage decreases to 15 volts.
1.5 V power supply circuit
The power supply circuit for obtaining a voltage of 1.5 volts uses a step-down transformer, a bridge rectifier with a smoothing filter and an LM317 chip.
Regulated power supply circuit from 1.5 to 12.5 V
A power supply circuit with output voltage regulation to obtain a voltage from 1.5 volts to 12.5 volts, the LM317 microcircuit is used as a regulating element. It must be installed on the radiator, on an insulating gasket to prevent a short circuit to the case.
Fixed Output Voltage Power Supply Diagram
Power supply circuit with a fixed output voltage of 5 volts or 12 volts. The LM 7805 microcircuit is used as an active element, LM7812 is installed on a radiator to cool the heating of the case. The choice of transformer is shown on the left side of the plate. By analogy, you can make a power supply for other output voltages.
20 watt power supply circuit with protection
The circuit is for a small homemade transceiver by DL6GL. When developing the unit, the task was to have an efficiency of at least 50%, a nominal supply voltage of 13.8V, a maximum of 15V, for a load current of 2.7A.
According to what scheme: switching power supply or linear?
Switching power supplies turn out to be small-sized and the efficiency is good, but it is not known how it will behave in a critical situation, output voltage surges ...
Despite the shortcomings, a linear control scheme was chosen: a sufficiently large transformer, not high efficiency, cooling is necessary, etc.
Used parts from a homemade power supply from the 1980s: a heatsink with two 2N3055s. The only thing missing was the µA723/LM723 voltage regulator and a few small parts.
The voltage regulator is assembled on a microcircuit µA723/LM723 in standard inclusion. Output transistors T2, T3 type 2N3055 are mounted on radiators for cooling. Using the potentiometer R1, the output voltage is set within 12-15V. Using the variable resistor R2, the maximum voltage drop across the resistor R7 is set, which is 0.7V (between pins 2 and 3 of the microcircuit).
A toroidal transformer is used for the power supply (it can be any at your discretion).
On the MC3423 chip, a circuit is assembled that is triggered when the voltage (emissions) at the output of the power supply is exceeded, by adjusting R3, the threshold for the voltage operation on leg 2 is set from the divider R3 / R8 / R9 (2.6V reference voltage), voltage is supplied from output 8 to open the thyristor BT145, causing a short circuit leading to the operation of the fuse 6.3a.
To prepare the power supply for operation (fuse 6.3a is not involved yet), set the output voltage, for example, 12.0V. Load the unit with a load, for this you can connect a 12V / 20W halogen lamp. Set R2 so that the voltage drop is 0.7V (the current must be within 3.8A 0.7 = 0.185Ωx3.8).
We configure the operation of overvoltage protection, for this we smoothly set the output voltage to 16V and adjust R3 to actuate the protection. Next, we set the output voltage to normal and install the fuse (before that, we put a jumper).
The described power supply can be reconstructed for more powerful loads, for this, install a more powerful transformer, additional transistors, strapping elements, a rectifier at your discretion.
Homemade 3.3v power supply
If you need a powerful power supply, 3.3 volts, then it can be made by redoing the old power supply from the PC or using the above diagrams. For example, in a 1.5 V power supply circuit, replace a 47 ohm resistor of a higher rating, or put a potentiometer for convenience, adjusting it to the desired voltage.
Transformer power supply on KT808
Many radio amateurs still have old Soviet radio components that are lying around idle, but which can be successfully applied and they will serve you faithfully for a long time, one of the well-known UA1ZH circuits that walks around the Internet. Many spears and arrows have been broken on the forums when discussing what is better than a field-effect transistor or an ordinary silicon or germanium one, what temperature of crystal heating they can withstand and which one is more reliable?
Each side has its own arguments, but you can get the parts and make another simple and reliable power supply. The circuit is very simple, it is protected from current overload and, when three KT808s are connected in parallel, it can deliver a current of 20A, the author used such a block with 7 parallel transistors and gave 50A to the load, while the capacitance of the filter capacitor was 120,000 microfarads, the voltage of the secondary winding was 19v. It must be taken into account that the relay contacts must switch such a large current.
With proper installation, the output voltage drawdown does not exceed 0.1 volts
Power supply for 1000v, 2000v, 3000v
If we need to have a high voltage constant voltage source to power the lamp of the transmitter output stage, what should we use for this? There are many different power supply circuits for 600v, 1000v, 2000v, 3000v on the Internet.
First: for high voltage, circuits are used from transformers for both one phase and three phases (if there is a three-phase voltage source in the house).
Second: to reduce the size and weight, a transformerless power supply circuit is used, directly a 220 volt network with voltage multiplication. The biggest drawback of this circuit is that there is no galvanic isolation between the network and the load, as the output is connected to this voltage source, observing the phase and zero.
The circuit has a step-up anode transformer T1 (for the required power, for example, 2500 VA, 2400V, current 0.8 A) and a step-down incandescent transformer T2 - TN-46, TN-36, etc. To eliminate current surges when switching on and protecting diodes when charging capacitors, switching on through quenching resistors R21 and R22 is used.
The diodes in the high-voltage circuit are shunted by resistors in order to evenly distribute Uobr. Calculation of the nominal value according to the formula R (Ohm) \u003d PIVx500. C1-C20 to eliminate white noise and reduce surges. Bridges of the KBU-810 type can also be used as diodes by connecting them according to the indicated scheme and, accordingly, taking the right amount, not forgetting about shunting.
R23-R26 for discharging capacitors after a power outage. To equalize the voltage on series-connected capacitors, equalizing resistors are placed in parallel, which are calculated from the ratio for every 1 volt there are 100 ohms, but at a high voltage, the resistors turn out to be of sufficiently high power and you have to maneuver here, given that the open circuit voltage is 1 more, 41.
More on the topic
Do-it-yourself transformer power supply 13.8 volts 25 a for a HF transceiver.
Repair and refinement of the Chinese power supply to power the adapter.
A rectifier is a device for converting AC voltage to DC. It is one of the most common parts in electrical appliances, ranging from hair dryers to all types of power supplies with DC output voltage. There are different schemes of rectifiers, and each of them copes with its task to a certain extent. In this article we will talk about how to make a single-phase rectifier, and why you need it.
Definition
A rectifier is a device that converts AC to DC. The word "constant" is not entirely correct, the fact is that at the output of the rectifier, in the sinusoidal alternating voltage circuit, in any case, there will be an unstabilized pulsating voltage. In simple words: constant in sign, but changing in magnitude.
There are two types of rectifiers:
half wave. It rectifies only one half-wave of the input voltage. Strong ripples and low relative to the input voltage are characteristic.
full wave. Accordingly, two half-waves are straightened. The ripple is lower, the voltage is higher than at the rectifier input - these are the two main characteristics.
What does stabilized and unstabilized voltage mean?
A stabilized voltage is a voltage that does not change in magnitude regardless of either the load or the input voltage surges. For transformer power supplies, this is especially important, because the output voltage depends on the input voltage and differs from it by Ktransformation times.
Unstabilized voltage - varies depending on surges in the supply network and load characteristics. With such a power supply, due to drawdowns, the connected devices may malfunction or be completely inoperable and fail.
Output voltage
The main values \u200b\u200bof alternating voltage are the amplitude and effective value. When they say “in the 220V network,” they mean the current voltage.
If they talk about the amplitude value, then they mean how many volts are from zero to the top point of the half-wave of the sinusoid.
Omitting the theory and a number of formulas, we can say that 1.41 times less than the amplitude. Or:
The amplitude voltage in the 220V network is:
The first scheme is more common. It consists of a diode bridge - interconnected by a "square", and a load is connected to its shoulders. The bridge type rectifier is assembled according to the diagram below:
It can be connected directly to a 220V network, as done in, or to the secondary windings of a mains (50 Hz) transformer. Diode bridges according to this scheme can be assembled from discrete (separate) diodes or you can use a ready-made assembly of a diode bridge in a single package.
The second circuit - a mid-point rectifier cannot be connected directly to the network. Its meaning is to use a transformer with a tap from the middle.
In essence, these are two half-wave rectifiers connected to the ends of the secondary winding, the load is connected with one contact to the junction point of the diodes, and the second - to the tap from the middle of the windings.
Its advantage over the first circuit is a smaller number of semiconductor diodes. And the disadvantage is the use of a transformer with a midpoint or, as they also call it, a tap from the middle. They are less common than conventional non-tapped secondary transformers.
Ripple smoothing
Power supply with pulsating voltage is unacceptable for a number of consumers, for example, light sources and audio equipment. Moreover, the permissible light pulsations are regulated in state and industry regulations.
To smooth out ripples, they use a parallel-mounted capacitor, an LC filter, various P- and G-filters ...
But the most common and simplest option is a capacitor installed in parallel with the load. Its disadvantage is that in order to reduce ripples on a very powerful load, it will be necessary to install capacitors of a very large capacity - tens of thousands of microfarads.
Its principle of operation is that the capacitor is charged, its voltage reaches an amplitude, the supply voltage after the point of maximum amplitude begins to decrease, from that moment the load is powered by the capacitor. The capacitor discharges depending on the resistance of the load (or its equivalent resistance if it is not resistive). The larger the capacitance of the capacitor, the smaller the ripple will be when compared with a capacitor with a smaller capacitance connected to the same load.
In simple words: the slower the capacitor discharges, the less ripple.
The discharge rate of the capacitor depends on the current drawn by the load. It can be determined by the time constant formula:
where R is the load resistance and C is the capacitance of the smoothing capacitor.
Thus, from a fully charged state to a fully discharged capacitor, it will be discharged in 3-5 t. It charges at the same rate if the charge occurs through a resistor, so in our case it does not matter.
It follows from this that in order to achieve an acceptable level of ripple (it is determined by the requirements of the load on the power source), a capacitance is needed that will be discharged in a time many times greater than t. Since the resistances of most loads are relatively small, a large capacitance is needed, therefore, in order to smooth out ripples at the output of the rectifier, they are used, they are also called polar or polarized.
Please note that it is highly not recommended to confuse the polarity of an electrolytic capacitor, because this is fraught with its failure and even explosion. Modern capacitors are protected from explosion - they have a stamping in the form of a cross on the top cover, along which the case will simply crack. But a jet of smoke will come out of the condenser, it will be bad if it gets into your eyes.
The capacitance is calculated based on what ripple factor needs to be provided. In simple terms, the ripple coefficient shows by what percentage the voltage sags (pulses).
C=3200*In/Un*Kp,
Where In is the load current, Un is the load voltage, Kn is the ripple factor.
For most types of equipment, the ripple factor is taken as 0.01-0.001. Additionally, it is desirable to install as large a capacitance as possible to filter out high-frequency interference.
How to make a power supply with your own hands?
The simplest DC power supply consists of three elements:
1. Transformer;
3. Capacitor.
This is an unregulated DC power supply with a smoothing capacitor. The voltage at its output is greater than the alternating voltage of the secondary winding. This means that if you have a 220/12 transformer (primary at 220V and secondary at 12V), then you will get 15-17V DC at the output. This value depends on the capacitance of the smoothing capacitor. This circuit can be used to power any load, if it does not matter to it that the voltage can “float” with changes in the mains voltage.
A capacitor has two main characteristics - capacitance and voltage. We figured out how to select the capacitance, but not with the selection of voltage. The voltage of the capacitor must exceed the amplitude voltage at the output of the rectifier by at least half. If the actual voltage on the capacitor plates exceeds the nominal voltage, there is a high probability of its failure.
Old Soviet capacitors were made with a good voltage margin, but now everyone uses cheap electrolytes from China, where at best there is a small margin, and at worst, it will not withstand the specified nominal voltage. So don't skimp on reliability.
A stabilized power supply differs from the previous one only in the presence of a voltage (or current) stabilizer. The simplest option is to use L78xx or others, such as the domestic ROOL.
So you can get any voltage, the only condition when using such stabilizers is that the voltage to the stabilizer must exceed the stabilized (output) value by at least 1.5V. Consider what is written in the 12V datasheet of the L7812 stabilizer:
The input voltage should not exceed 35V, for stabilizers from 5 to 12V, and 40V for stabilizers at 20-24V.
The input voltage should exceed the output voltage by 2-2.5V.
Those. for a stabilized 12V power supply with an L7812 series stabilizer, it is necessary that the rectified voltage lies within 14.5-35V to avoid drawdowns, it would be an ideal solution to use a transformer with a 12V secondary winding.
But the output current is quite modest - only 1.5A, it can be amplified using a pass transistor. If you have , you can use this scheme:
It shows only the connection of a linear stabilizer. The "left" part of the circuit with a transformer and a rectifier is omitted.
If you have NPN transistors like KT803 / KT805 / KT808, then this one will do:
It is worth noting that in the second circuit, the output voltage will be less than the stabilization voltage by 0.6V - this is a drop at the emitter-base junction, we wrote more about this. To compensate for this drop, a diode D1 was introduced into the circuit.
It is possible to install two linear stabilizers in parallel, but it is not necessary! Due to possible deviations in manufacturing, the load will be unevenly distributed and one of them may burn out because of this.
Install both the transistor and the linear regulator on a heatsink, preferably on separate heatsinks. They get very hot.
Regulated power supplies
The simplest adjustable power supply can be made with an adjustable linear stabilizer LM317, its current is also up to 1.5 A, you can amplify the circuit with a pass transistor, as described above.
Here is a more visual diagram for assembling an adjustable power supply.
With a thyristor regulator in the primary winding, essentially the same regulated power supply.
By the way, a similar scheme regulates the welding current:
Conclusion
A rectifier is used in power supplies to produce direct current from alternating current. Without his participation, it will not be possible to power a DC load, such as an LED strip or a radio.
Also used in a variety of car battery chargers, there are a number of circuits using a transformer with a group of taps from the primary winding, which are switched by a jack switch, and only a diode bridge is installed in the secondary winding. The switch is installed on the high voltage side, since the current is several times lower there and its contacts will not burn from this.
According to the diagrams from the article, you can assemble the simplest power supply both for constant work with some kind of device, and for testing your electronic homemade products.
The circuits do not have high efficiency, but they produce a stabilized voltage without much ripple, you should check the capacitance of the capacitors and calculate for a specific load. They are perfect for low-power audio amplifiers, and will not create additional background. An adjustable power supply will be useful for motorists and auto electricians to test the generator voltage regulator relay.
An adjustable power supply is used in all areas of electronics, and if it is improved with short-circuit protection or a current stabilizer on two transistors, then you will get an almost full-fledged laboratory power supply.
