In this article I will talk about very commonplace things that have not changed for more than a decade, but they have not changed at all. Another thing is that since the principle of voltage reduction in a closed circuit due to resistance was studied, other principles of power supply to the load, due to PWM, have appeared, but this is a separate topic, although it deserves attention. Therefore, I will continue, nevertheless, in the order of the logical channel, when I talk about Ohm's law, then about its application for various radioelements involved in lowering the voltage, and after that we can already mention PWM.
Ohm's law when voltage drops
Actually, there was such an uncle Georg Ohm, who studied the flow of current in a circuit. He made measurements, made certain conclusions and conclusions. The result of his work was Ohm's formula, as they say Ohm's law. The law describes the dependence of voltage drop, current on resistance.
The law itself is very clear and is similar to the representation of such physical events as the flow of fluid through a pipeline. Where is the liquid, or rather its flow rate is the current, and its pressure is the voltage. Well, of course, any changes in the cross section or obstacles in the pipe for the flow, this will be resistance. In total, it turns out that the resistance "strangles" the pressure, when drops can simply drip from the pipe under pressure, and the flow rate immediately drops. Pressure and flow are highly dependent on each other, like current and voltage. In general, if we write everything down with a formula, it turns out like this:
R \u003d U / I; That is, the pressure (U) is directly proportional to the resistance in the pipe (R), but if the flow (I) is large, then there is no resistance as such ... And the increased flow should indicate a reduced resistance.
Very vague, but objective! It remains to say that this law, however, was obtained empirically, that is, the final factors of its change are not quite determined.
Now, armed with theoretical knowledge, we will continue our path in learning how to reduce our stress.
How to lower the voltage from 12 to 5 volts using a resistor
The simplest thing is to take and use an unstabilized circuit. That is, when we simply lower the voltage due to resistance and that's it. There is nothing special to talk about this principle, we just count using the formula above and that's it. Let me give you an example. Let's say we reduce it from 12 volts to 5.
R \u003d U / I. The tension is understandable, but look, we don't have enough data! Nothing is known about the "consumption", about the current consumption. That is, if you decide to calculate the resistance to lower the voltage, then you definitely need to know how much our load “wants to eat”.
You will need to look at this value on the device that you are going to power or in the instructions for it. Let's take conditionally a current consumption of 50 mA \u003d 0.05 A. It remains also to note that according to this formula we will select a resistance that will completely extinguish the voltage, but we need to leave 5 volts, then we substitute 12-5 \u003d 7 volts in the formula.
R \u003d 7 / 0.05 \u003d 140 Ohm, resistance is needed in order to get 5 from 12 volts, with a load current of 50 mA.
It remains to mention something equally important! The fact that any extinguishing of energy, and in this case voltage, is associated with the dissipated power, that is, our resistor will have to "withstand" the heat that will dissipate. The power of the resistor is calculated using the formula.
P \u003d U * I. We receive. P \u003d 7 * 0.05 \u003d 0.35 W must be the power of the resistor. No less. Now the calculation course for the resistor can be considered complete.
How to lower the voltage from 12 to 5 volts using a microcircuit
Nothing fundamentally changes in this case. If we compare this option of lowering through a microcircuit, with the option using a resistor. In fact, everything is one to one here, except that useful "intellectual" features of adjusting the internal resistance of the microcircuit based on the current consumption are added. That is, as we understood from the paragraph above, depending on the current consumption, the calculated resistance should "float". This is exactly what happens in the microcircuit, when the resistance adjusts to the load in such a way that the output of the microcircuit always has the same supply voltage! Well, the plus are such "useful buns" as protection against overheating and short circuits. As for the microcircuits, the so-called voltage stabilizers for 5 volts, these can be: LM7805, KREN142EN5A. The connection is also quite simple.
Of course for effective work microcircuits we put it on the radiator. The stabilization current is limited to 1.5-2 A.
These are the principles of lowering the voltage from 12 to 5 volts. Now, once you understand them, you can easily calculate what resistance you need to supply or how to choose a microcircuit to get any other lower voltage.
It remains to say a few words about PWM.
Pulse width modulation is a very promising and most importantly highly efficient method of powering the load, but again with its pitfalls. The whole point of PWM boils down to supplying pulses with such a supply voltage, which, in total, with the moments of no voltage, will give power and average voltage sufficient for the load to work. And there can be problems if you connect a power supply from one device to another. Well, the simplest problem is the lack of those characteristics that are stated. Interference, erratic operation is possible. In the worst case, the PWM power supply can completely burn out the device, for which it was not originally intended!
Immediately after the first voyage in a car with a family at sea, the idea arose to make a stationary distribution of USB sockets in the car for charging mobile devices. By the way, now new cars have already begun to be equipped with 220V inverters and, accordingly, 5V sockets.
I have never met such cars.
Yes, if there are adapters on sale for mobile PCs, then they are designed to charge one, maximum two devices, provided that the second device is not so powerful. I already have 3 adapters permanently connected in my car, but they are hidden under the fuse box.
Passengers use an adapter that sticks into the socket in the ashtray, which is not very convenient for me, since I constantly touch it when changing gears. After a day's journey, passengers usually have all their devices thinned out and the fuss begins with charging mobile phones. You even have to turn off your navigator to charge someone else's device.
It was possible to do, as many do, they buy a block for several adapters and snot wires stretch throughout the cabin. And so you need a device that produces the prescribed 5 volts and a power of 10 A. A lot? Let's estimate: 4 phones, consume about 1 A each, a tablet of about 2 A, a navigator is more than 0.5 A, a DVR is also 0.5 A and a radar detector is about 0.5 A. And that is 7.5 A.
In the process, 3 converters were assembled, but not one could withstand even 3 A for a long time. One of them burst into flames.
Only this scheme worked normally.
DC / DC converter circuit on MC34063
Device board
Assembly drawing
Yes, my pay is far from ideal, the ability to pay a board is comparable to talent. The field worker with the diode positioned it so that it was possible to attach almost any radiator, making the board a little longer, and the fasteners already in place. I did not specifically fit the board to the case due to the lack of such. All the details were found in the first raskurochenny computer power supply.
To make the device it took:
1. Ceramic capacitor C1 470 pF (1pc)
2. Electrolytic capacitor C3, C5, C6 1000 uF, 16V (3pcs)
3. Electrolytic capacitor C2 100 uF, 16V (1pc)
4. Electrolytic capacitor C4 470 uF, 25V is better than 50V (1pc)
5. Inductance DR1, DR2 dumbbell type (2pcs)
6. Pulse transformer DR3 ring (1pc)
7. Inductance type stump DR4 (1pc)
8. Screw terminal J1 (1pc)
9. Resistor R1 1.2 kOhm (1 piece)
10. Resistor R2 3.6 kOhm (1 piece)
11. Resistor R3 5.6 kOhm (1pc)
12. Resistor R4 2.2 kOhm (1 piece)
13. Resistor R5 2.2 kOhm or 1 kOhm for 1 watt (1 piece)
14. Microcontroller U1 MC34063
15. Diode VD1, VD3 FR155 (2pcs)
16. Diode VD2 SBL25L25CT (1pc)
17. Bipolar transistor VT1 2SC1846 (1pc)
18. Field-effect transistor IRL3302 (1pc)
19. Socket DIP8 (1pc)
20. Casing of arbitrary dimensions
Main components: this is the U1 microcircuit itself, a pulse transformer DR3, a powerful N channel field controller VT2 (can be anything used in power circuits) and a diode assembly VD2. The VD3 transformer was made from the same transformer from the same power supply unit. Ring made of yellow prespermaloy. 27mm. I stuffed the primary winding with a 2mm wire 22 turns, the secondary winding was wound with a wire thinner, 0.55 mm 44 turns.
Inductance DR1 DR2 type dumbbell took as is from the power supply. The DR4 stump inductance is the same. I placed the transistor and diode on the radiator from the same power supply unit.
I assembled everything on a PCB of my own design. In the course of laboratory tests, it was necessary to make changes to the scheme proposed by the author. The fact is that the author himself points out that the resistor R5 is heating up, even replacing it with a more powerful resistor does not solve the problem. Within an hour, this resistor turned black and charred.
I decided to try to increase the resistance to 2.2 kOhm and he stopped heating everything. Transistor VT1, reinsured, replaced with a more powerful one. The DR3 transformer also did not warm up much at first, rewound it, added the number of turns to the primary and secondary windings, it became 30 and 60.
I do not know what is there with the opening fronts of the field-effect transistor, but the circuit works fine, with a load of 2A, the device remains cold. Radiators on the transistor and diode can be omitted. I put a ferrite ring at the + 5V output to reduce interference.
Here's my first working test prototype.
Resistance test 1 Ohm resistance quickly warmed up the amperage in the photo.
And lastly, a 5V boiler is in operation. See the current in the photo. Yes, here the transistor with a diode has already begun to warm up.
I tested my 5A converter and worked almost all day so a little warm. Then I found an old power supply from the monitor which is no longer there. I put the board into analysis, fit my circuit into the case. The transistor and diode are located on the cooler from the old laptop. I drilled a series of holes on the opposite side of the box. Very much even nothing happened. Air will be pumped through the entire circuit.
Ready-made device for installation in a car.
I plan to embed the double sockets for USB into one in the front panel instead of a blank button and the second to the rear passengers in the armrest of the front seats. I also think of a single socket in the front left pillar panel and supply power to the DVR which is located by the mirror. According to this scheme, you can assemble a generally universal power supply, that is, add a conversion stage from 12V to 19V to power the laptop, which I plan in the future.
A stabilizer is a device that, regardless of fluctuations in the input characteristics, always outputs a stable nominal voltage at the output. And it may be needed not only for use in 220V networks, but also in 12V systems. For example - in a car, or where there is a need to use low-voltage equipment (lighting in wet rooms, etc.).
For example, connecting LED backlights in a car without a 12V voltage stabilizer chip is fraught with a quick failure of the diodes, since the auto generator cannot provide a stable voltage in the on-board network. However, it is not necessary to buy a ready-made device - you can assemble such a scheme yourself.
Varieties of 12V stabilizers
There are several variations of the circuits of such a device for 12 volts, but the most common are linear and pulse. How are they, in essence, different?
- A linear stabilizer is a conventional voltage divider by its properties, which receives the input voltage on one of the arms, and changes the resistance on the other, so that as a result, a given voltage is obtained at the output. If the input / output delta is too large, the efficiency of such a device drops sharply, since a significant part of the energy is dissipated in the form of heat - this leads to the need for cooling.
- In the pulsed version, the current enters the storage device (capacitor or inductor) by short pulses formed by the switch. When the electronic key is closed, the stored energy is supplied to the load, while the voltage value remains stable. The stabilization process itself takes place by controlling the pulse duration using PWM. This version of the device has a high efficiency, however, it induces impulse noise at the output, which is not always acceptable.
There are also autotransformer and ferroresonant devices used mainly for alternating current, but they are relatively complex.
Due to the presence of many electronic components and radio components on free sale, anyone, even a novice radio amateur, can, if necessary, assemble a 12 Volt voltage stabilizer for their needs at home - there would be a circuit.
How to make a 12V stabilizer
Stabilizer on LM317
The easiest way to get a working 12 Volt stabilizer at home is to purchase a ready-made microcircuit, for example, and, by adding a resistor, get a ready-made voltage equalizer. This option is perfect for triggering LEDs in conditions of constantly surging voltage.
A 120-130 Ohm resistor is soldered to the finished LM317 microcircuit, namely to the middle contact, the left contact is soldered to the output to the load immediately after the resistance, and the voltage from the source is applied to the right contact. For a better understanding, everything is shown in the picture below.
Scheme on the LD1084 chip
Also, a 12 Volt voltage regulator on the LD1084 chip is very simple. Thanks to smooth stabilization, such a device will help not only when using LEDs, but also, for example, to get rid of changes in the brightness of light in a car, which is always present due to the peculiarities of the on-board electrical system. A diagram of such a device is shown below.
Stabilizer on diodes and board L7812
Another version of the device at home can be a simple circuit based on L7812 and Schottky diodes. In addition to these parts, you will need a pair of capacitors, and wires for soldering. So, a diode and capacitors are soldered to the regulatory microcircuit according to the diagram. The diode must be between the + of the input power, and the left pin of the microcircuit. The right contact of the handkerchiefs is soldered to the + load. Medium - to the minuses of the capacities and the minus of the power supply. Thus, a simple and reliable voltage stabilization circuit is obtained.
The simplest stabilizer is the KREN board
Perhaps the simplest option for making a device at home is the KREN microcircuit, or rather KR142EN8B (this is its full name). In addition to the scarf itself, you will need a 1n4007 rectifying diode. By soldering these elements according to the diagram below, you can get the most elementary, but very reliable device.
Applying any of these stabilization schemes, you can quickly and inexpensively assemble a device that is able to provide the required output characteristics in 12V electrical networks.
If your knowledge of electronics does not allow you to solder and tinker, then the best option would be to purchase a factory device that is assembled in a factory environment, has a suitable case, a cooling system, and is assembled from a well-matched and matched element base.
The main points regarding the manufacture of a 12 Volt stabilizer are given in this video:
Once assembled, the simplest voltage regulator on one transistor was designed for a specific power supply and a specific consumer, of course it was not necessary to connect it anywhere else, but as always there comes a moment when we stop doing the right thing. The consequence of this is the hassle and thought of how to live and be further and the decision to restore what was created earlier or continue to create.
Scheme number 1
There was a stabilized switching power supply that gave an output voltage of 17 volts and a current of 500 milliamps. A periodic change in voltage was required in the range of 11 - 13 volts. And the well-known one transistor coped with this perfectly. From myself, I added only an indication LED and a limiting resistor to it. By the way, the LED here is not only a "firefly" signaling the presence of an output voltage. With a properly selected value of the limiting resistor, even a small change in the output voltage is reflected in the brightness of the LED, which gives additional information about its increase or decrease. The output voltage could be changed from 1.3 to 16 volts.
KT829 - a powerful low-frequency silicon composite transistor, was installed on a powerful metal radiator and it seemed that, if necessary, it could easily withstand a heavy load, but there was a short circuit in the consumer's circuit and it burned out. The transistor has a high gain and is used in low-frequency amplifiers - you can really see its place there and not in voltage regulators.
On the left, removed electronic components, on the right, prepared by him for replacement. The difference in quantity is two names, but in the quality of the schemes, the former and the one that it was decided to collect, it is incomparable. This begs the question - "Is it worth collecting a circuit with limited capabilities when there is a more advanced version" for the same money ", in the literal and figurative sense of this saying?
Scheme number 2
The new circuit also has a three-pin e-mail. component (but this is no longer a transistor) constant and variable resistors, an LED with its own limiter. Added only two electrolytic capacitors. Typically, typical circuits indicate the minimum values \u200b\u200bof C1 and C2 (C1 \u003d 0.1 μF and C2 \u003d 1 μF) that are necessary for the stable operation of the stabilizer. In practice, the capacitances range from tens to hundreds of microfarads. Capacities should be located as close to the microcircuit as possible. For large capacities, the condition C1 \u003e\u003e C2 is mandatory. If the capacitance of the output capacitor exceeds the capacitance of the input capacitor, then a situation arises in which the output voltage exceeds the input, which leads to damage to the stabilizer microcircuit. To exclude it, a protective diode VD1 is installed.
This scheme has completely different possibilities. Input voltage from 5 to 40 volts, output 1.2 - 37 volts. Yes, there is an input-output voltage drop of about 3.5 volts, but there are no roses without thorns. But the KR142EN12A microcircuit, called a linear adjustable voltage stabilizer, has good protection for exceeding the load current and short-term protection against short circuit at the output. Its operating temperature is up to + 70 degrees Celsius, it works with an external voltage divider. Output load current up to 1 A for continuous operation and 1.5 A for short-term operation. The maximum allowable power when operating without a heat sink is 1 W, if the microcircuit is installed on a radiator of sufficient size (100 cm2) then P max. \u003d 10 W.
What happened
The very process of the updated editing took no more time than the previous one. At the same time, not a simple voltage regulator was obtained, which is connected to a stabilized voltage power supply; the assembled circuit, when connected even to a network step-down transformer with a rectifier at the output, itself gives the necessary stabilized voltage. Naturally, the output voltage of the transformer must correspond to the permissible parameters of the input voltage of the KR142EN12A microcircuit. Instead, you can use an imported analogue integral stabilizer. Author Babay iz barnaula.
Discuss the article TWO SIMPLE VOLTAGE REGULATORS
According to the PUE, a voltage of no higher than 50 Volts should be used to power portable lighting, and when working in especially dangerous and confined spaces - 12 Volts (PUE 6.1.16-18). In this case, the power supply must be carried out through transformers. This is to prevent electric shock. And the output parameters of power supplies or batteries do not always allow connecting gadgets or other electronics. In this regard, we will tell you how to lower the DC and AC voltage to the value you need.
Lowering the AC voltage
Consider typical situations when you need to lower the voltage in order to connect a device that operates on AC, but its supply voltage does not correspond to the usual 220 Volts. It can be both various household appliances, tools, and the lamps mentioned above.
Connecting household appliances from the USA for 110 V to a 220 V network
Perhaps the most common situation arises when a person buys some kind of device from foreign online stores, and upon receiving it, determines that it is designed for power supply from 110 volts. The first option is to rewind the transformer supplying the device, but most devices operate from a switching power source, and to connect a power tool, it is better to do without rewinding at all. To do this, you need to use a step-down transformer. In addition, you can lower the voltage in the network using an autotransformer or a conventional transformer with 110-127V taps from the primary winding - these were often found in Soviet TVs and other electrical appliances.
However, when using such a transformer connection, if a part of the winding breaks after tapping 110 Volts (see figure below), all 220V will fit the device, and it will fail.
If we talk about ready-made devices, then we can pay attention to the “SHTIL” autotransformers.
Important! When buying transformers or autotransformers, consider the rated current of its windings and the power that it will withstand.
A more reliable solution to the problem would be to lower the voltage from 220 to 110V or from 220 to 127V using a transformer. There are many companies on the market that sell such products, mostly toroidal transformers. They come in metal boxes or smaller cases with a built-in socket, as well as adapters in plastic cases.
Let's summarize by listing the main requirements for a transformer for powering 110V devices:
- The output of the transformer should be 110V, and the input should be 220V.
- The power of the transformer must be at least 20% higher than the power of the connected device.
- It is advisable to protect the primary and secondary circuits with a fuse.
- Access to high voltage terminals should be limited and all connections insulated.
Lowering the voltage to power low-voltage lamps
At the beginning of the article, we mentioned that the portable lamp should be powered from reduced voltage. In everyday life, this issue will be especially relevant for motorists when repairing a car in the garage. The same lamps are also used as a local light source on machine tools (drilling, turning, sharpening and others).
In order to lower the voltage from 220 to 36V, you can use transformers of the brand:
- OSO 0.25 220 / 36V;
- OSM 0.063kW 220/36;
- OSZR 0.063kW 220 / 36V;
- Box with a step-down transformer YATP-0.25 220 36V (this is a ready-made solution in a metal case for indoor installation, protection class IP54).
To reduce the voltage from 220 to 12V, you can use transformers of the brand:
- OSO25 220 / 12V;
- TRS 300W AC 220 V-AC 12V (toroidal does not take up much space);
- 30VA, 230 / 12V, 2.5A INDEL TSZS30 / 005M (low power for mounting on DIN rail).
Reducing voltage in the house
Along with, there is often a problem with overvoltage and undervoltage. This leads to premature failure of heating devices, lamps and other devices at the consumer. Let's say you need to lower the voltage from 260 to 220V, then your choice is to use a voltage stabilizer. They are of different types, the cheapest of them is a relay one, in fact it is an autotransformer in which the relay automatically switches the taps from the winding.
If you need to protect a specific device, for example, a computer, use low-power models with a capacity of about 1000 VA (1 kVA), such as SVEN VR-L1000, its cost is 17-20 dollars. But keep in mind that their active output power is less than the indicated total in Volt-Ampere. For example, a 1 kVA model can supply loads up to 0.3-0.4 kW. Also look at the characteristics. The specified model can withstand up to 285 volts, but most models rest against 260 V.
To protect the whole house, in most cases, the RUCELF SRWII-12000-L model will suffice, its full power is 12000 VA, and the active power load capacity is 10000 W. It can handle input voltages up to 270V.
To learn more about how to choose a voltage stabilizer and what kind of stabilizers there are, we told in the articles:
Ballast capacitor for supplying low-power devices
To power low-power devices, you can do without a transformer - one capacitor. Such a circuit is called a transfluoromated power supply unit on a ballast capacitor. Its principle of operation is based on limiting the current using the reactance of the capacitor. Below you can see the options for its implementation.
The calculation of the capacity of the ballast capacitor for transformerless power supply is based on the current consumption of the load and its supply voltage.
Or according to this formula, they give approximately the same result:
By the way, the expression under the root as a result, when calculating capacitors for powering devices from 5-20V, gives about 220, or a value equal to Uinput.
Such a power source is suitable for connecting receivers, LEDs, night lights, charging small batteries and other low-power consumers.
Lowering the DC voltage
When designing electronics, it is often necessary to lower the voltage of an existing power supply. We will also look at a few typical situations.
If you work with microcontrollers, you may have noticed that some of them operate from 3 volts. Finding the right power supplies can be tricky, so you can use a phone charger. Then you need to lower its output from 5 to 3 volts (3.3V). This can be done by lowering the output voltage of the power supply by replacing the zener diode in the feedback circuit. You can achieve any voltage, both high and low, by setting the Zener diode of the desired rating. It can be determined by the selection method, in the diagram below it is highlighted with a red ellipse.
And on the board it looks like this:
On chargers of a more advanced design, an adjustable zener diode TL431 is used, then adjustment is possible by replacing the resistor or by the ratio of a pair of resistors, depending on the circuitry. They are marked in red in the diagram below.
In addition to replacing the zener diode on the memory board, you can lower the voltage using a resistor and a zener diode - this is called a parametric stabilizer.
Another option is to install a chain of diodes in the open circuit. Each silicon diode will drop about 0.6-0.7 volts. So you can lower the voltage to the desired level by dialing the required number of diodes.
Often it becomes necessary to connect the device to the vehicle's on-board network, it ranges from 12 to 14.3-14.7 volts. To lower the DC voltage from 12 to 9 volts, you can use a linear regulator type L7809, and to lower it from 12 to 5 volts, use the L7805. Or their analogues ams1117-5.0 or ams1117-9.0 or amsr-7805-nz and the like for any desired voltage. The connection diagram of such stabilizers is shown below.
To power more powerful consumers, it is convenient to use pulse converters to lower and regulate the voltage from the power source. An example of such devices are boards based on LM2596, and in English-language online stores they can be found by searching for "DC-DC step down" or "DC-DC buck converter".
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