High voltage DC-DC converter. How pulse voltage converters work (27 schemes) Do-it-yourself dc voltage converter
Pulse DC-DC converters are designed for both increasing and decreasing voltage. With their help, you can convert 5 volts, for example, into 12, or 24, or vice versa, with minimal losses. There are also high-voltage DC-DC converters; they are capable of obtaining a very significant potential difference of hundreds of volts from a relatively low voltage (5-12 volts). In this article we will consider the assembly of just such a converter, the output voltage of which can be adjusted within 60-250 volts.
It is based on the common NE555 integrated timer. Q1 in the diagram is a field-effect transistor; you can use IRF630, IRF730, IRF740 or any others designed to operate with voltages above 300 volts. Q2 is a low-power bipolar transistor, you can safely install BC547, BC337, KT315, 2SC828. Choke L1 should have an inductance of 100 μH, however, if this is not at hand, you can install chokes in the range of 50-150 μH, this will not affect the operation of the circuit. It’s easy to make a choke yourself - wind 50-100 turns of copper wire on a ferrite ring. Diode D1 according to the FR105 circuit; instead, you can install UF4007 or any other high-speed diode with a voltage of at least 300 volts. Capacitor C4 must be high-voltage, at least 250 volts, more possible. The larger its capacity, the better. It is also advisable to install a small-capacity film capacitor in parallel with it for high-quality filtering of high-frequency interference at the output of the converter. VR1 is a trimming resistor with which the output voltage is regulated. The minimum supply voltage for the circuit is 5 volts, the most optimal is 9-12 volts.
Converter manufacturing
The circuit is assembled on a printed circuit board measuring 65x25 mm; a file with a drawing of the board is attached to the article. You can take a textolite larger than the drawing itself, so that there is room at the edges for attaching the board to the case. A few photos of the manufacturing process:
After etching, the board must be tinned and checked for short circuits. Because There is high voltage on the board; there should be no metal burrs between the tracks, otherwise a breakdown is possible. First of all, small parts are soldered onto the board - resistors, diode, capacitors. Then the microcircuit (it is better to install it in the socket), transistors, trimming resistor, inductor. To make it easier to connect wires to the board, I recommend installing screw terminal blocks; places for them are provided on the board.
Download the board:
(downloads: 240)
First launch and setup
Before starting, be sure to check the correct installation and ring the tracks. Set the trimming resistor to the minimum position (the slider should be on the side of resistor R4). After this, you can apply voltage to the board by connecting an ammeter in series with it. At idle, the current consumption of the circuit should not exceed 50 mA. If it fits within the norm, you can carefully turn the trimming resistor, controlling the output voltage. If everything is fine, connect a load, for example, a 10-20 kOhm resistor to the high-voltage output and test the operation of the circuit again, this time under load.The maximum current that such a converter can produce is approximately 10-15 mA. It can be used, for example, as part of lamp technology to power lamp anodes, or to light gas-discharge or luminescent indicators. The main application is a miniature stun gun, because the output voltage of 250 volts is noticeable to a person. Happy building!
Sometimes you need to get high voltage from low voltage. For example, for a high-voltage programmer powered by a 5-volt USB, you need somewhere around 12 volts.
What should I do? There are DC-DC conversion circuits for this. As well as specialized microcircuits that allow you to solve this problem in a dozen parts.
Principle of operation
So, how do you make, for example, five volts something more than five? You can come up with many ways - for example, charge capacitors in parallel, and then switch them in series. And so many many times per second. But there is a simpler way, using the properties of inductance, to maintain current strength.
To make it very clear, I will first show an example for plumbers.
Phase 1
The damper closes abruptly. The flow has nowhere else to go, and the turbine, being accelerated, continues to push the liquid forward, because cannot get up instantly. Moreover, it presses it with a force greater than the source can develop. Drives the slurry through the valve into the pressure accumulator. Where does part of it (already with increased pressure) go to the consumer? From where, thanks to the valve, it no longer returns.
Phase 3
And again the damper closes, and the turbine begins to violently push liquid into the battery. Making up for the losses that occurred there in phase 3.
Back to diagrams
We get out of the basement, take off the plumber's sweatshirt, throw the gas wrench into the corner and, with new knowledge, begin to construct the diagram.
Instead of a turbine, inductance in the form of a choke is quite suitable for us. An ordinary key (in practice, a transistor) is used as a damper, a diode is naturally used as a valve, and a capacitor takes on the role of a pressure accumulator. Who else but he is capable of accumulating potential. That's it, the converter is ready!
Phase 1
The key opens, but the coil cannot be stopped. The energy stored in the magnetic field rushes out, the current tends to be maintained at the same level as it was at the moment the key was opened. As a result, the voltage at the output from the coil jumps sharply (to make way for the current) and, breaking through the diode, is packed into the capacitor. Well, part of the energy goes into the load.
Phase 3
The key opens and the energy from the coil again breaks through the diode into the capacitor, increasing the voltage that dropped during phase 3. The cycle is completed.
As can be seen from the process, it is clear that due to the greater current from the source, we increase the voltage at the consumer. So the equality of power here must be strictly observed. Ideally, with a converter efficiency of 100%:
U source *I source = U consumption *I consumption
So if our consumer requires 12 volts and consumes 1A, then from a 5 volt source into the converter you need to feed as much as 2.4A. At the same time, I did not take into account the losses of the source, although usually they are not very large (the efficiency is usually about 80-90%).
If the source is weak and is not able to supply 2.4 amperes, then at 12 volts there will be wild ripples and a drop in voltage - the consumer will eat the contents of the capacitor faster than the source will throw it there.
Circuit design
There are a lot of ready-made DC-DC solutions. Both in the form of microblocks and specialized microcircuits. I won’t split hairs and, to demonstrate my experience, I’ll give an example of a circuit on the MC34063A that I already used in the example.
- SWC/SWE pins of the transistor switch of the chip SWC is its collector, and SWE is its emitter. The maximum current it can draw is 1.5A of input current, but you can also connect an external transistor for any desired current (for more details, see the datasheet for the chip).
- DRC - compound transistor collector
- Ipk - current protection input. There, the voltage is removed from the shunt Rsc; if the current is exceeded and the voltage on the shunt (Upk = I*Rsc) becomes higher than 0.3 volts, the converter will stall. Those. To limit the incoming current to 1A, you need to install a 0.3 Ohm resistor. I didn’t have a 0.3 ohm resistor, so I put a jumper there. It will work, but without protection. If anything, it will kill my microcircuit.
- TC is the input of the capacitor that sets the operating frequency.
- CII is the comparator input. When the voltage at this input is below 1.25 volts, the key generates pulses and the converter operates. As soon as it gets bigger, it turns off. Here, through a divider on R1 and R2, the feedback voltage from the output is applied. Moreover, the divider is selected in such a way that when the voltage we need appears at the output, there will be exactly 1.25 volts at the input of the comparator. Then everything is simple - is the output voltage lower than necessary? We're threshing. Did you get what you needed? Let's switch off.
- Vcc - Circuit Power
- GND - Ground
All formulas for calculating denominations are given in the datasheet. I will copy from it here the most important table for us:
Etched, soldered...
Just like that. A simple scheme, but it allows you to solve a number of problems.
Today we are reviewing the famous DC-DC boost voltage converter based on the MT3608 chip. The board is popular among those who like to create something with their own hands. It is used in particular for building homemade external chargers (power banks).
Today we will conduct a very detailed review, study all the advantages and find out the disadvantages
Such a board costs only $0.5, knowing that during the review there would be tough tests that could result in failure of the boards, I bought several of them at once.
The board is of very good quality, the installation is double-sided, to be more precise, almost the entire reverse side is mass, and at the same time plays the role of a heat sink. Overall dimensions 36 mm * 17 mm * 14 mm
The manufacturer specifies the following parameters
1). Maximum output current - 2A
2). Input voltage: 2V~24V
3). Maximum output voltage: 28 V
4). Efficiency: ≤93%
Product size: 36mm * 17mm * 14mm
And the diagram is presented below.
The board has a tuning multi-turn resistor with a resistance of 100 kOhm, designed to adjust the output voltage. Initially, for the converter to work, you need to rotate the variable 10 steps counterclockwise, only after this the circuit will begin to increase the voltage, in other words, the variable turns idle until halfway.
The input and output are marked on the board, so there will be no connection problems.
Let's move directly to the tests.
1) The declared maximum voltage is 28 Volts, which corresponds to the real value
2) The minimum voltage at which the board starts working is 2 Volts, I will say that this is not entirely true, the board remains operational at this voltage, but starts working at 2.3-2.5 Volts
3) The maximum value of the input voltage is 24 Volts, I will say that one of the 8 boards I purchased could not withstand such an input voltage, the rest passed the exam perfectly.
4) Output short circuit mode. The laboratory power supply from which the source is powered is equipped with a current limiting system; in case of a short circuit at the output, the consumption from the laboratory power supply is 5 A (this is the maximum that the LPS can provide). Based on this, we conclude that if you connect an inverter, for example, to a battery, then in the event of a short circuit, the latter will instantly burn out - it has no protection against short circuits. There is also no overload protection.
6) What happens if the connection polarity is reversed. This test is clearly visible in the video, the board simply burns up with smoke, and it’s the microcircuit that burns out.
7) The no-load current is only 6mA, a very good result.
8) Now the output current. A voltage of 12 Volts is supplied to the input, and 14 Volts at the output, i.e. the input-output difference is only 2 Volts, the best operating conditions are ensured, and if with this situation the circuit does not produce 2 Amperes, then with other input-output values it cannot provide this.
Temperature tests
P.S. During the tests, the throttle began to smell of varnish and therefore it was replaced with a better one, at least the diameter of the wire of the new throttle is 2 times thicker than that of the original one.
In the case of these tests, a voltage of 12 Volts is applied to the input of the board, and 14 Volts is set at the output
Heat generation on the throttle, the throttle has already been replaced
Heat dissipation on the diode
Heat dissipation on the chip
As you can see, the temperature in some cases is above 100 degrees, but is stable.
It should also be pointed out that under such operating conditions the output parameters deteriorate significantly, which is to be expected.
As we can see, with an output current of 2A, the voltage sags, so I recommend using the board at currents of 1-1.2 Amps maximum; at higher values, the stability of the output voltage is lost, and the microcircuit, inductor and output rectifier diode overheat.
9) Oscillogram of the output voltage, where we observe ripples.
The situation can be improved if an electrolyte (35-50 Volts) is soldered parallel to the output, the capacity is from 47 to 220 μF (up to 470 is possible, there is no point anymore)
Generator operating frequency is about 1.5 MHz
Test error is no more than 5%
are electronic devices that produce an output voltage different from the input voltage.
Regulated power modules (DC-DC converters) are used to build power buses in galvanically isolated circuits. They are widely used to power a wide variety of electronic devices and can also be found in control circuits, communications and computing devices.
Principle of operation
The principle of operation is contained in the name itself. Direct voltage is converted to alternating voltage. After this, it is raised or lowered, followed by straightening and feeding to the device. DC-DC converters operating on the above principle are called pulse converters. The advantage of pulse converters is their high efficiency: around 90%.
Types of DC-DC converters
Buck DC/DC converters
The output voltage of these converters is lower than the input. For example, with an input voltage of 12-50 V, using such DC-DC converters you can get a voltage of several volts at the output.
The output voltage of these converters is higher than the input. For example, with a 5V input voltage, you can expect up to 30V output.
Voltage converters also differ in design. They can be:
Modular
This is the most common type of DC-DC converters, including a huge number of different models. The converter is placed in a metal or plastic case, excluding access to internal elements.
For PCB mounting
These converters are designed specifically for mounting on a printed circuit board. They differ from modular ones in that they do not have a housing.
Main characteristics
Operating Parameters
→ The input voltage range implies such input voltage parameters at which the converter will operate in normal mode in accordance with its declared functionality.
→ The output voltage range includes the parameters that the DC-DC converter is capable of producing at the output during normal operation.
→ The coefficient of performance (efficiency) is the ratio of the input and output power values. Efficiency depends on a number of conditions, but the highest efficiency is achieved at the maximum permissible load. The greater the difference between the input and output voltage, the lower the efficiency.
→Output current limitation. This protection is available in most modern stabilizer models. It works as follows: as soon as the output current reaches the set value, the input voltage drops. Once the output current is within the acceptable range, the voltage supply is resumed.
Accuracy parameters
→ Ripple. Even under ideal conditions, certain “noises” are present, so it is impossible to completely eliminate them. The units of measurement are mV. Sometimes the manufacturer puts “rr” next to it, which means the range of ripple voltage - from the minimum of the negative peak to the maximum of the positive.
Let's consider and compare the operation of several adjustable voltage converters of different price categories. Let's start from simple to complex.
Description
This model is an inexpensive miniature DC-DC converter that can be used to charge small batteries. Maximum output current: 2.5 A, so this converter will take a long time to charge batteries with a capacity of more than 20 ampere-hours.
This device is best suited for beginners who, based on it, will be able to assemble a power supply with an output voltage from 0.8 V to 20 V and an output current of up to 2 A. In this case, it is possible to adjust both the output voltage and the output current.
This stabilizer can hold up to 5 A, however, in practice, at this current value it will require a heat sink. Without a heat sink, the stabilizer can withstand up to 3 A.
Functional
The XL4005 voltage converter is not called “regulated” for nothing. It has several adjustments. One of the most valuable is the ability to limit the output current. For example, you can set the output current limit to 2.5 A, and the current will never reach this value, since otherwise it will immediately lead to a voltage drop. This protection is especially important when charging batteries.
The presence of LEDs also indicates that the presented stabilizer is perfect for charging purposes. There is an LED that lights up when the stabilizer is operating in current limiting mode, that is, when output overload protection is turned on. There are two more LEDs on the bottom side: one works when the charge is in progress, the other lights up when the charge is finished.
It is worth noting that this is a very affordable and easy-to-use model that fully corresponds to the declared functionality.
Now let's look at a more expensive and functional converter, which is perfect for more complex and serious projects.
Description
This model is an adjustable step-down voltage converter with digital control. It is characterized by high efficiency. Digital control means that parameters are adjusted using buttons. The module itself can be divided into several parts: DC-DC converter, power supply for the digital part, measuring part and digital part.
The input voltage of this device is from 6 V to 32 V. The output voltage is adjustable from 0 V to 30 V. The voltage adjustment step is 0.01 V. The output current is adjustable from 0 A to 6 A. The adjustment step is 0.001 A. Converter efficiency is up to 92% . To secure the wires on the converter, special clamps are installed. Also on the board there are inscriptions: input +, input -, output -, output +. The power part is built on the XL4016E1 PWM controller. A powerful ten-amp diode MBR1060 is used. Everything is controlled by an 8-bit microcontroller STM8S003F3. The digital part has a UART connector.
LEDs
In addition to the buttons and indicator, this device has three LEDs.
The first (red, out) lights up when the converter supplies voltage to the output. The second LED (yellow, CC - Constant Current) lights up when the output current limitation is triggered. The third LED (green, CV - Constant Voltage) lights up when the converter enters voltage limit mode.
Controls
The controls are represented by four buttons.
If we look at them from right to left, then the first button is “OK”, the second is “up”, the third is “down” and the fourth is “SET”.
The converter is started by pressing the “OK” button, which enters the menu. If you do not release the “OK” button, you can see how the numbers change: 0-1-2. These are the three programs that this converter has.
Program “0”: immediately after voltage is applied to the input, power is turned on at the output.Program “1”: allows you to save the necessary parameters.
Program "2": Automatically displays parameters after power on.
To select the desired program, you must release the “OK” button at the moment the desired number is displayed.
This device displays voltage relatively accurately. Possible error in voltage +/-0.035 V, in current +/- 0.006 A. Adjustment is made either by pressing the buttons once or by holding them down.
It is possible to display current current parameters. When you press the “OK” button again, the power is displayed on the indicator. If you press the “OK” button again, you can see the capacity that the converter gave.
This converter is accurate and powerful, and will cope well with serious tasks.
How to choose a voltage converter
Today there are a large number of models of various DC-DC converters on the market. The most popular among them are pulse converters. But their choice is so great that it’s easy to get confused. What should you pay special attention to?
♦ Efficiency and temperature rangeSome converters require a heatsink to operate properly and achieve their stated power. Otherwise, although the device is able to function, its efficiency decreases. As a rule, a conscientious seller indicates this point in notes and footnotes, which should not be neglected.
♦ Soldering temperature of surface mount converters
This information is usually indicated in the technical documentation.
And although a regular microcircuit should withstand temperatures up to 280°C, it is better to clarify this point.♦ Converter dimensions
A small converter cannot have very high power. And although modern technologies continue to improve, their capabilities are not unlimited. The converter needs certain dimensions to keep the components cool and to withstand the load.
Today there are a huge number of different miniature adjustable converters, with and without indication, with and without additional functions and programs. Such DC-DC converters can be used for a variety of purposes, depending on the imagination of the developer. Modern technologies make it possible to combine power, accuracy, miniature size and affordable price.
A push-pull pulse generator, in which, due to proportional current control of transistors, switching losses are significantly reduced and the efficiency of the converter is increased, is assembled on transistors VT1 and VT2 (KT837K). The positive feedback current flows through windings III and IV of transformer T1 and the load connected to capacitor C2. The role of diodes that rectify the output voltage is performed by the emitter junctions of the transistors.
A special feature of the generator is the interruption of oscillations when there is no load, which automatically solves the problem of power management. Simply put, such a converter will turn on itself when you need to power something from it, and turn off when the load is disconnected. That is, the power battery can be constantly connected to the circuit and practically not be consumed when the load is off!
For given input UВx. and output UBix. voltages and the number of turns of windings I and II (w1), the required number of turns of windings III and IV (w2) can be calculated with sufficient accuracy using the formula: w2=w1 (UOut. - UBx. + 0.9)/(UBx - 0.5 ). Capacitors have the following ratings. C1: 10-100 µF, 6.3 V. C2: 10-100 µF, 16 V.
Transistors should be selected based on acceptable values base current (it should not be less than the load current!!!) And reverse voltage emitter - base (it must be greater than twice the difference between the input and output voltages!!!) .
I assembled the Chaplygin module in order to make a device for recharging my smartphone while traveling, when the smartphone cannot be charged from a 220 V outlet. But alas... The maximum that I was able to squeeze out using 8 batteries connected in parallel is about 350-375 mA charging current at 4.75 V. output voltage! Although my wife’s Nokia phone can be recharged with this device. Without load, my Chaplygin Module produces 7 V with an input voltage of 1.5 V. It is assembled using KT837K transistors.
The photo above shows the pseudo-Krona, which I use to power some of my devices that require 9 V. Inside the case from the Krona battery there is an AAA battery, a stereo connector through which it is charged, and a Chaplygin converter. It is assembled using KT209 transistors.
Transformer T1 is wound on a 2000NM ring with dimensions K7x4x2, both windings are wound simultaneously in two wires. To avoid damaging the insulation on the sharp outer and inner edges of the ring, dull them by rounding off the sharp edges with sandpaper. First, windings III and IV (see diagram) are wound, which contain 28 turns of wire with a diameter of 0.16 mm, then, also in two wires, windings I and II, which contain 4 turns of wire with a diameter of 0.25 mm.
Good luck and success to everyone who decides to replicate the converter! :)
