Today we will look at several circuits of simple, one might even say simple, pulsed DC-DC voltage converters (converters of direct voltage of one value to constant voltage of another value)
What are the benefits of pulse converters? Firstly, they have high efficiency, and secondly, they can operate at an input voltage lower than the output voltage. Pulse converters are divided into groups:
- - bucking, boosting, inverting;
- - stabilized, unstabilized;
- - galvanically isolated, non-insulated;
- - with a narrow and wide range of input voltages.
To make homemade pulse converters, it is best to use specialized integrated circuits - they are easier to assemble and not capricious when setting up. So, here are 14 schemes for every taste:
This converter operates at a frequency of 50 kHz, galvanic isolation is provided by transformer T1, which is wound on a K10x6x4.5 ring made of 2000NM ferrite and contains: primary winding - 2x10 turns, secondary winding - 2x70 turns of PEV-0.2 wire. Transistors can be replaced with KT501B. Almost no current is consumed from the battery when there is no load.
Transformer T1 is wound on a ferrite ring with a diameter of 7 mm, and contains two windings of 25 turns of wire PEV = 0.3.
Push-pull unstabilized converter based on a multivibrator (VT1 and VT2) and a power amplifier (VT3 and VT4). The output voltage is selected by the number of turns of the secondary winding of the pulse transformer T1.
Stabilizing type converter based on the MAX631 microcircuit from MAXIM. Generation frequency 40…50 kHz, storage element - inductor L1.
You can use one of the two chips separately, for example the second one, to multiply the voltage from two batteries.
Typical circuit for connecting a pulse boost stabilizer on the MAX1674 microcircuit from MAXIM. Operation is maintained at an input voltage of 1.1 volts. Efficiency - 94%, load current - up to 200 mA.
Allows you to obtain two different stabilized voltages with an efficiency of 50...60% and a load current of up to 150 mA in each channel. Capacitors C2 and C3 are energy storage devices.
8. Switching boost stabilizer on the MAX1724EZK33 chip from MAXIM
Typical circuit diagram for connecting a specialized microcircuit from MAXIM. It remains operational at an input voltage of 0.91 volts, has a small-sized SMD housing and provides a load current of up to 150 mA with an efficiency of 90%.
A typical circuit for connecting a pulsed step-down stabilizer on a widely available TEXAS microcircuit. Resistor R3 regulates the output voltage within +2.8…+5 volts. Resistor R1 sets the short circuit current, which is calculated by the formula: Is(A)= 0.5/R1(Ohm)
Integrated voltage inverter, efficiency - 98%.
Two isolated voltage converters DA1 and DA2, connected in a “non-isolated” circuit with a common ground.
The inductance of the primary winding of transformer T1 is 22 μH, the ratio of turns of the primary winding to each secondary is 1: 2.5.
Typical circuit of a stabilized boost converter on a MAXIM microcircuit.
Buying a ready-made device will not be a problem– in auto stores you can find (pulse voltage converters) of various powers and prices.
However, the price of such a medium-power device (300-500 W) is several thousand rubles, and the reliability of many Chinese inverters is quite controversial. Making a simple converter with your own hands is not only a way to significantly save money, but also an opportunity to improve your knowledge in electronics. In case of failure, repairing a homemade circuit will be much easier.
Simple pulse converter
The circuit of this device is very simple, and most parts can be removed from an unnecessary computer power supply. Of course, it also has a noticeable drawback - the 220 volt voltage obtained at the output of the transformer is far from sinusoidal in shape and has a frequency significantly higher than the accepted 50 Hz. Electric motors or sensitive electronics must not be connected directly to it.
In order to be able to connect equipment containing switching power supplies (for example, a laptop power supply) to this inverter, an interesting solution was used - A rectifier with smoothing capacitors is installed at the output of the transformer. True, the connected adapter can only work in one position of the socket, when the polarity of the output voltage coincides with the direction of the rectifier built into the adapter. Simple consumers such as incandescent lamps or a soldering iron can be connected directly to the output of transformer TR1.
The basis of the above circuit is the TL494 PWM controller, the most common in such devices. The operating frequency of the converter is set by resistor R1 and capacitor C2; their values can be taken slightly different from those indicated without noticeable changes in the operation of the circuit.
For greater efficiency, the converter circuit includes two arms on power field-effect transistors Q1 and Q2. These transistors should be placed on aluminum radiators; if you intend to use a common radiator, install the transistors through insulating spacers. Instead of the IRFZ44 indicated in the diagram, you can use IRFZ46 or IRFZ48 that are similar in parameters.
The output choke is wound on a ferrite ring from the choke, also removed from the computer power supply. The primary winding is wound with a wire with a diameter of 0.6 mm and has 10 turns with a tap from the middle. A secondary winding containing 80 turns is wound on top of it. You can also take an output transformer from a broken uninterruptible power supply.
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Instead of high-frequency diodes D1 and D2, you can take diodes of types FR107, FR207.
Since the circuit is very simple, once turned on and installed correctly, it will start working immediately and will not require any configuration. It will be able to supply a current of up to 2.5 A to the load, but the optimal operating mode will be a current of no more than 1.5 A - and this is more than 300 W of power.
Ready-made inverter of such power would cost about three to four thousand rubles.This scheme is made with domestic components and is quite old, but this does not make it any less effective. Its main advantage is the output of full alternating current with a voltage of 220 volts and a frequency of 50 Hz.
Here the oscillation generator is made on the K561TM2 microcircuit, which is a dual D-trigger. It is a complete analogue of the foreign CD4013 microcircuit and can be replaced with it without changes in the circuit.
The converter also has two power arms based on KT827A bipolar transistors. Their main drawback compared to modern field ones is their higher resistance in the open state, which is why they heat up more for the same switched power.
Since the inverter operates at low frequency, the transformer must have a powerful steel core. The author of the diagram suggests using the common Soviet network transformer TS-180.
Like other inverters based on simple PWM circuits, this converter has an output voltage waveform quite different from the sinusoidal one, but this is somewhat smoothed out by the large inductance of the transformer windings and the output capacitor C7. Also, because of this, the transformer may emit a noticeable hum during operation - this is not a sign of a circuit malfunction.
Simple transistor inverter
This converter works on the same principle as the circuits listed above, but the square-wave generator (multivibrator) in it is built on bipolar transistors.
The peculiarity of this circuit is that it remains operational even on a heavily discharged battery: the input voltage range is 3.5...18 volts. But, since it does not have any stabilization of the output voltage, when the battery is discharged, the voltage across the load will simultaneously drop proportionally.
Since this circuit is also low-frequency, a transformer will be required similar to that used in the inverter based on K561TM2.
Improvements to inverter circuits
The devices presented in the article are extremely simple and have a number of functions. cannot compare with factory analogues. To improve their characteristics, you can resort to simple modifications, which will also allow you to better understand the principles of operation of pulse converters.
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Increased power output
All described devices operate on the same principle: through a key element (arm output transistor), the primary winding of the transformer is connected to the power input for a time specified by the frequency and duty cycle of the master oscillator. In this case, magnetic field pulses are generated, exciting common-mode pulses in the secondary winding of the transformer with a voltage equal to the voltage in the primary winding multiplied by the ratio of the number of turns in the windings.
Therefore, the current flowing through the output transistor is equal to the load current multiplied by the inverse turns ratio (transformation ratio). It is the maximum current that the transistor can pass through itself that determines the maximum power of the converter.
There are two ways to increase the power of the inverter: either use a more powerful transistor, or use parallel connection of several less powerful transistors in one arm. For a homemade converter, the second method is preferable, since it not only allows you to use cheaper parts, but also preserves the functionality of the converter if one of the transistors fails. In the absence of built-in overload protection, such a solution will significantly increase the reliability of a homemade device. The heating of the transistors will also decrease when they operate at the same load.
Using the last diagram as an example, it will look like this:
Automatic shutdown when battery is low
The absence of a device in the converter circuit that automatically turns it off when the supply voltage drops critically, can seriously let you down, if you leave such an inverter connected to the car battery. Supplementing a homemade inverter with automatic control will be extremely useful.
The simplest automatic load switch can be made from a car relay:
As you know, each relay has a certain voltage at which its contacts close. By selecting the resistance of resistor R1 (it will be about 10% of the resistance of the relay winding) you adjust the moment when the relay opens its contacts and stops supplying current to the inverter.
EXAMPLE: Let's take a relay with an operating voltage (U p) 9 volts and winding resistance (R o) 330 ohm. So that it works at a voltage above 11 volts (U min), a resistor with resistance must be connected in series with the windingR n, calculated from the condition of equalityU r /R o =(U min —U p)/R n. In our case, we will need a 73 ohm resistor, the nearest standard value is 68 ohms.Of course, this device is extremely primitive and is more of a workout for the mind. For more stable operation, it needs to be supplemented with a simple control circuit that maintains the shutdown threshold much more accurately:
Using this voltage converter you can get 220 volts from a battery with a voltage of 3.7 volts. The circuit is not complicated and all parts are accessible; these converters can be powered by an energy-saving or LED lamp. Unfortunately, it will not be possible to connect more powerful devices, since the converter is low-power and will not withstand heavy loads.
So, to assemble the converter we need:
- Transformer from an old phone charger.
- Transistor 882P or its domestic analogs KT815, KT817.
- Diode IN5398, an analogue of KD226, or any other diode designed for reverse current up to 10 volts of medium or high power.
- Resistor (resistance) 1 kOhm.
- Bread board.
Naturally, you will also need a soldering iron with solder and flux, wire cutters, wires and a multimeter (tester). You can, of course, make a printed circuit board, but for a circuit consisting of several parts, you should not waste time on developing the layout of the tracks, drawing them and etching foil PCB or getinax. Checking the transformer. Old charger board.
Carefully solder the transformer.
Next we need to check the transformer and find the terminals of its windings. Take a multimeter and switch it to ohmmeter mode. We check all the conclusions one by one, find those that “ring” in pairs and write down their resistance.
1. First 0.7 Ohm.
2. Second 1.3 Ohm.
3. Third 6.2 Ohm.
The winding with the greatest resistance was the primary winding, 220 V was supplied to it. In our device it will be the secondary, that is, the output. The rest were relieved of the reduced voltage. For us, they will serve as the primary (the one with a resistance of 0.7 ohms) and part of the generator (with a resistance of 1.3). The measurement results for different transformers may differ; you need to focus on their relationship to each other.
Device diagram
As you can see, it is the simplest. For convenience, we have marked the winding resistances. A transformer cannot convert direct current. Therefore, a generator is assembled on a transistor and one of its windings. It supplies a pulsating voltage from the input (battery) to the primary winding, a voltage of about 220 volts is removed from the secondary.
Assembling the converter
We take a breadboard.
We install the transformer on it. We choose a 1 kilo-ohm resistor. We insert it into the holes on the board, next to the transformer. We bend the leads of the resistor so as to connect them to the corresponding contacts of the transformer. We solder it. It is convenient to secure the board in some kind of clamp, as in the photo, so that the problem of a missing “third hand” does not arise. Soldered resistor. We bite off the excess length of the output. Board with bitten resistor leads. Next we take the transistor. We install it on the board on the other side of the transformer, as in the screenshot (I selected the location of the parts so that it would be more convenient to connect them according to the circuit diagram). We bend the terminals of the transistor. We solder them. Installed transistor. Let's take a diode. We install it on the board parallel to the transistor. Solder it. Our scheme is ready.
Solder the wires to connect constant voltage (DC input). And wires for picking up pulsating high voltage (AC output).
For convenience, we take 220 volt wires with “crocodiles”.
Our device is ready.
Testing the converter
In order to supply voltage, select a 3-4 volt battery. Although you can use any other power source.
Solder the low voltage input wires to it, observing the polarity. We measure the voltage at the output of our device. It turns out 215 volts.
Attention. It is not advisable to touch parts while the power is connected. This is not so dangerous if you do not have health problems, especially with the heart (although two hundred volts, the current is weak), but it can “pinch” unpleasantly.
We complete the testing by connecting a 220-volt energy-saving fluorescent lamp. Thanks to the "crocodiles" this is easy to do without a soldering iron. As you can see, the lamp is on.
Our device is ready.
Advice. You can increase the power of the converter by installing a transistor on the radiator.
True, the battery capacity will not last long. If you are going to use the converter constantly, then choose a higher-capacity battery and make a case for it.
It is a simple boost converter built on the NE555 m/s, which here performs the function of a pulse generator. The output voltage can vary between 110-220V (regulated by potentiometer).
Application area
The converter is ideal for powering Nixie clock tubes or low power amplifiers or headphone amplifiers, replacing the classic high voltage transformer power supply. The purpose of creating this device was to design a clock based on vacuum indicators in which the circuit acts as a high voltage power source. The converter is powered at 9 V and consumes a current of about 120 mA (at a 10 mA load).
Operating principle of the circuit
As you can see, this is a standard step-up voltage converter. The output frequency of the U1 chip (NE555) is determined by the ratings of the elements R1 (56k), R3 (10k), C2 (2.2 nF), and is about 45 kHz. The output from the generator directly drives mosfet transistor T1, which switches the current flowing through coil L1. During normal operation, coil L1 periodically stores and releases energy, increasing the output voltage.
555 inverter circuit
When transistor T1 (IRF740) turns on and supplies power to coil L1 (100 μH) (current flows from the power source to ground - this is the first stage. In the second stage, when the transistor is turned off, the current through the coil in accordance with the commutation law causes an increase in voltage on the anode of diode D1 (BA159) until it is polarized in the direction of conduction. The coil discharges into the capacitor C4 (2.2 uF). Thus, the voltage at C4 increases until the voltage at the output of the divider R5 (220k), P1 (1k) and R6 470R will not rise to a value of about 0.7 V. This will turn on transistor T2 (BC547) and turn off the 555 generator. When the output voltage drops, transistor T2 will be closed and the generator will turn on again. So the output voltage of the converter is regulated in magnitude.
Ready board for soldering Capacitor C1 (470uF) filters the circuit supply voltage. The output voltage is adjusted using potentiometer P1.
Assembly of a transformerless converter
Assembled 9-150 volt converter The converter can be soldered on a printed circuit board. PDF drawing of the board, including mirror image and location of parts - . Installation is simple and soldering of elements is free. It makes sense to use a socket for the U1 chip. The device should be powered with a voltage of 9V.
A very simple 50 kV converter, which essentially contains three elements. All components are available and can be easily found if desired.
The high voltage converter can be used for various experiments with high electricity, as an ionizer, insulation integrity tester, etc.
What you will need:
- Linear scan transformer from any TV with a kinescope.
- Field effect transistor IRFZ44 –
- Resistor 150 Ohm (1/2 W).
High voltage converter circuit
Let's assemble everything on a breadboard without soldering. I’ll just show you the work, and if you like it, you can transfer it to a more reliable board and solder all the elements.
Connecting a transistor, if anyone doesn’t know.
We need to wind the transformer winding. The high-voltage winding will be original. We take a regular, not very thin wire and wind it with 14-16 turns. We will make a tap in the middle of the winding.
Now we connect everything to our circuit. The last thing to do is connect the power. Be careful as you are working with high voltage. Do not put your hands near the switched on transformer.
Make a distance of approximately 1 cm between the high voltage output of the transformer and the terminals of the other side. And only then serve food. If it sparks, it means the generator is excited and everything works fine.
If you will use it for a long time, it is advisable to install the transistor on the radiator. And if the spark is small, then you can increase the voltage to 10 or 15 V.
