Power amplifier without power transformer. Scheme, description

Transformer is a device for transferring energy from one circuit to another through electrical induction. It is intended for converting current and voltage values, for galvanic separation of electrical circuits, for converting resistance in magnitude and for other purposes.

A transformer can consist of two or more windings. We will consider a transformer made of two separated windings without a ferromagnetic core (air transformer), the diagram of which is shown in Fig. 5.12.

The winding with terminals 1-1’ connected to the power source is the primary winding, the winding to which the load resistance is connected is the secondary. Primary winding resistance , secondary resistance – .

The transformer equations with the accepted polarity of the coils and the direction of the currents have the form:

- for the primary winding

For secondary winding

Transformer input impedance

Let us denote the active resistance of the secondary circuit

then the equations can be rewritten

(5.22)

Transformer input impedance. Considering that and substituting into the first equation (5.21), we obtain that

Thus, the input resistance of the transformer from the side of the primary terminals consists of two terms: – the resistance of the primary winding without taking into account mutual induction, which appears due to the phenomenon of mutual induction. Resistance is, as it were, added (introduced) from the secondary coil and is therefore called introduced resistance.

Input impedance of an ideal transformer.

An ideal transformer (theoretical concept) is a transformer in which the conditions are met

(5.24)

Moreover, with a certain error, such conditions can be met in a transformer with a core with high magnetic permeability, on which wires with low active resistance are wound.

The input impedance of this transformer is

(5.25)

Consequently, an ideal transformer connected between the load and the energy source changes the load resistance in proportion to the square of the transformation ratio n.

The property of a transformer to convert resistance values ​​is widely used in various fields of electrical engineering, communications, radio engineering, automation and, above all, for the purpose of matching the resistance of the source and load.

Transformer equivalent circuit

The circuit of a two-winding transformer without a ferromagnetic core can be depicted as shown in Fig. 5.14. The current distribution in it is the same as in the circuit in Fig. 5.12 without a common point between the windings.

Let's do it in the diagram in Fig. 5.14 decoupling of inductive couplings. In this case, we obtain a transformer equivalent circuit (Fig. 5.15), in which there are no magnetic connections.

Energy processes in inductively coupled coils

Differential equations of an air transformer (Fig. 5.15):

(5.25)

Let's multiply the first equation by and the second by :

(5.26)

Adding these equations, we obtain the total instantaneous power that is consumed from the source and consumed in the primary and secondary windings of the transformer and in the load

(5.27)

where is the instantaneous power at the load, ;

– instantaneous power spent on heat in the windings of the transformer, ;

– energy magnetic field transformer windings, .

Three-phase generators.

A three-phase circuit (system) is understood as a combination of a three-phase source (generator), load and connecting wires.

It is known that when a conductor rotates in a uniform magnetic field, an emf is induced in it

. (1.1)

Let us rigidly fix three identical coils (windings) on one axis, displaced relative to each other in space by (120°) and begin to rotate them in a uniform magnetic field with an angular velocity w (Fig. 1.1).

In this case, coil A will be induced

The same EMF values ​​will appear in coils B and C, but respectively 120° and 240° after the start of rotation, i.e.

(1.3)

A set of three coils (windings) rotating on the same axis with an angular velocity w, in which EMFs are induced, equal in magnitude and shifted from each other by an angle of 120°, is called a symmetrical three-phase generator. Each generator coil is a generator phase. In the generator in Fig. 1.1 phase B “follows” phase A, phase C follows phase B. This sequence of phase alternation is called direct sequence. When changing the direction of rotation of the generator, a reverse phase sequence will occur. The direct sequence based on relations (1.2, 1.3) corresponds to the EMF vector diagram shown in Fig. 1.2, a, for the reverse – vector diagram of the EMF in Fig. 1.2, b.

In the future, all discussions on the calculation of three-phase circuits will concern only three-phase systems with a direct sequence of generator EMFs.

The graph of changes in instantaneous EMF values ​​at y = 90° is shown in Fig. 1.3. At every instant, the algebraic sum of the emf is zero.

The extreme points of the coils (windings) are called end and beginning. The beginnings of the coils are designated A, B, C, the ends are X, Y, Z, respectively (Fig. 1.4, a).

The phase windings of a three-phase generator can be depicted as EMF sources (Fig. 1.4, b).

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 or headphone amplifiers, replacing the classic power supply high voltage on transformers. 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.

Nowadays there is a lot of small-sized equipment in the house that requires constant power. These include watches with LED displays, thermometers, small-sized receivers, etc. In principle, they are designed for batteries, but they run out at the most inopportune moment. A simple way out is to power them from network power supplies. But even a small-sized network (step-down) transformer is quite heavy and takes up quite a bit of space, and switching power supplies are still complex, requiring certain experience and expensive equipment to manufacture.

A solution to this problem, if certain conditions are met, can be a transformerless power supply with a quenching capacitor. These conditions:

• complete autonomy of the powered device, i.e. no external devices should be connected to it (for example, a tape recorder to the receiver for recording a program);
• dielectric (non-conducting) housing and the same control knobs for the power supply itself and the device connected to it.

This is due to the fact that when powered from a transformerless unit, the device is under network potential, and touching its non-insulated elements can “shake” well. It is worth adding that when setting up such power supplies, you should follow safety rules and caution.

If necessary, use an oscilloscope for setup, the power supply must be connected via an isolation transformer.

In its simplest form, the circuit of a transformerless power supply has the form shown in Fig. 1.

To limit the inrush current when connecting the unit to the network, resistor R2 is connected in series with capacitor C1 and rectifier bridge VD1, and resistor R1 is connected in parallel to it to discharge the capacitor after disconnection.

In general, a transformerless power supply is a symbiosis of a rectifier and a parametric stabilizer. Capacitor C1 for alternating current is a capacitive (reactive, i.e., not consuming energy) resistance Xc, the value of which is determined by the formula:

where ( - network frequency (50 Hz); C - capacitance of capacitor C1, F.

Then the output current of the source can be approximately determined as follows:

where Uc is the network voltage (220 V).

The input part of another power supply (Fig. 2a) contains a ballast capacitor C1 and a bridge rectifier made of diodes VD1, VD2 and zener diodes VD3, VD4. Resistors R1, R2 play the same role as in the first circuit. The oscillogram of the block's output voltage is shown in Fig. 2b (when the output voltage exceeds the stabilization voltage of the zener diodes, otherwise it works like a regular diode).

From the beginning of the positive half-cycle of the current through capacitor C1 to moment t1, the zener diode VD3 and diode VD2 are open, and the zener diode VD4 and diode VD1 are closed. In the time interval t1...t3, the zener diode VD3 and the diode VD2 remain open, and a stabilization current pulse passes through the opened zener diode VD4. The voltage at the output Uout and at the zener diode VD4 is equal to its stabilization voltage Ust.

The pulse stabilization current, which is through for a diode-zener diode rectifier, bypasses the RH load, which is connected to the bridge output. At time t2 the stabilization current reaches its maximum, and at time t3 it is zero. Until the end of the positive half-cycle, the zener diode VD3 and diode VD2 remain open.

At moment t4 the positive half-cycle ends and the negative half-cycle begins, from the beginning of which to moment t5 the zener diode VD4 and diode VD1 are already open, and the zener diode VD3 and diode VD2 are closed. In the time interval t5-t7, the zener diode VD4 and the diode VD1 continue to remain open, and a through stabilization current pulse passes through the zener diode VD3 at voltage UCT, the maximum at time t6. Starting from t7 and until the end of the negative half-cycle, the zener diode VD4 and diode VD1 remain open. The considered cycle of operation of the diode-zener diode rectifier is repeated in the following periods of mains voltage.

Thus, a rectified current passes through the zener diodes VD3, VD4 from the anode to the cathode, and a pulsed stabilization current passes in the opposite direction. In the time intervals t1...t3 and t5...t7, the stabilization voltage changes by no more than a few percent. The value of the alternating current at the input of the bridge VD1...VD4 is, to a first approximation, equal to the ratio of the network voltage to the capacitance of the ballast capacitor C1.

The operation of a diode-zener diode rectifier without a ballast capacitor, which limits the through current, is impossible. Functionally, they are inseparable and form a single whole - a capacitor-zener diode rectifier.

The spread in the UCT values ​​of zener diodes of the same type is approximately 10%, which leads to additional ripples in the output voltage with the frequency of the supply network; the amplitude of the ripple voltage is proportional to the difference in the Ust values ​​of zener diodes VD3 and VD4.

When using powerful zener diodes D815A...D817G, they can be installed on a common radiator if their type designation contains the letters "PP (zener diodes D815APP...D817GPP have reverse polarity of the terminals). Otherwise, the diodes and zener diodes must be swapped.

Transformerless power supplies are usually assembled according to the classical scheme: quenching capacitor, AC voltage rectifier, filter capacitor, stabilizer. A capacitive filter smoothes out output voltage ripples. The greater the capacitance of the filter capacitors, the less ripple and, accordingly, the greater the constant component of the output voltage. However, in some cases you can do without a filter, which is often the most cumbersome component of such a power source.

It is known that a capacitor connected to a circuit alternating current, shifts its phase by 90°. A phase-shifting capacitor is used, for example, when connecting a three-phase motor to a single-phase network. If you use a phase-shifting capacitor in the rectifier, which ensures mutual overlap of half-waves of the rectified voltage, in many cases you can do without a bulky capacitive filter or significantly reduce its capacitance. The circuit of such a stabilized rectifier is shown in Fig. 3.

The three-phase rectifier VD1.VD6 is connected to an alternating voltage source through active (resistor R1) and capacitive (capacitor C1) resistances.

The output voltage of the rectifier stabilizes the zener diode VD7. Phase-shifting capacitor C1 must be designed for operation in alternating current circuits. Here, for example, capacitors of the K73-17 type with an operating voltage of at least 400 V are suitable.

Such a rectifier can be used where it is necessary to reduce the dimensions of an electronic device, since the dimensions of the oxide capacitors of a capacitive filter are, as a rule, much larger than those of a phase-shifting capacitor of a relatively small capacity.

Another advantage of the proposed option is that the current consumption is almost constant (in the case of a constant load), whereas in rectifiers with a capacitive filter, at the moment of switching on, the starting current significantly exceeds the steady-state value (due to the charge of the filter capacitors), which in some cases is extremely undesirable .

The described device can also be used with series voltage stabilizers that have a constant load, as well as with a load that does not require voltage stabilization.

A completely simple transformerless power supply (Fig. 4) can be built “on the knee” in literally half an hour.

In this embodiment, the circuit is designed for an output voltage of 6.8 V and a current of 300 mA. The voltage can be changed by replacing the zener diode VD4 and, if necessary, VD3. And by installing transistors on radiators, you can increase the load current. Diode bridge - any one designed for a reverse voltage of at least 400 V. By the way, you can also remember about the “ancient” diodes. D226B.

In another transformerless source (Fig. 5), the KR142EN8 microcircuit is used as a stabilizer. Its output voltage is 12 V. If adjustment of the output voltage is necessary, then pin 2 of the DA1 microcircuit is connected to the common wire through variable resistor, for example, type SPO-1 (with a linear characteristic of resistance change). Then the output voltage can vary in the range of 12...22 V.

As a DA1 microcircuit, to obtain other output voltages, you need to use the appropriate integrated stabilizers, for example, KR142EN5, KR1212EN5, KR1157EN5A, etc. Capacitor C1 must have an operating voltage of at least 300 V, brand K76-3, K73-17 or similar (non-polar , high voltage). Oxide capacitor C2 acts as a power supply filter and smoothes out voltage ripples. Capacitor C3 reduces high frequency interference. Resistors R1, R2 are MLT-0.25 type. Diodes VD1...VD4 can be replaced with KD105B...KD105G, KD103A, B, KD202E. Zener diode VD5 with a stabilization voltage of 22...27 V protects the microcircuit from voltage surges when the source is turned on.

Despite the fact that theoretically capacitors in an AC circuit do not consume power, in reality they can generate some heat due to losses. You can check the suitability of a capacitor as a damping capacitor for use in a transformerless source by simply connecting it to the mains and assessing the temperature of the case after half an hour. If the capacitor manages to warm up noticeably, it is not suitable. Special capacitors for industrial electrical installations practically do not heat up (they are designed for large reactive power). Such capacitors are usually used in fluorescent lamps, in ballasts of asynchronous electric motors, etc.

In a 5-volt source (Fig. 6) with a load current of up to 0.3 A, a capacitor voltage divider is used. It consists of a paper capacitor C1 and two oxide capacitors C2 and C3, forming the lower (according to the circuit) non-polar arm with a capacity of 100 μF (counter-series connection of capacitors). The polarizing diodes for the oxide pair are bridge diodes. With the indicated ratings of the elements, the short circuit current at the output of the power supply is 600 mA, the voltage on capacitor C4 in the absence of load is 27 V.

The power supply unit for the portable receiver (Fig. 7) easily fits into its battery compartment. The diode bridge VD1 is designed for operating current, its maximum voltage is determined by the voltage provided by the zener diode VD2. Elements R3, VD2. VT1 form an analogue of a powerful zener diode. The maximum current and power dissipation of such a zener diode are determined by transistor VT1. It may require a heatsink. But in any case, the maximum current of this transistor should not be less than the load current. Elements R4, VD3 - circuit indicating the presence of output voltage. At low load currents, it is necessary to take into account the current consumed by this circuit. Resistor R5 loads the power circuit with a low current, which stabilizes its operation.

Quenching capacitors C1 and C2 are KBG type or similar. You can also use K73-17 with an operating voltage of 400 V (250 V is also suitable, since they are connected in series). The output voltage depends on the resistance of the quenching capacitors to alternating current, the actual load current and the stabilization voltage of the zener diode.

To stabilize the voltage of a transformerless power supply with a quenching capacitor, you can use symmetrical dinistors (Fig. 8).

When the filter capacitor C2 is charged to the opening voltage of the dinistor VS1, it turns on and bypasses the input of the diode bridge. The load at this time receives power from capacitor C2. At the beginning of the next half-cycle, C2 is again recharged to the same voltage, and the process is repeated. The initial discharge voltage of capacitor C2 does not depend on the load current and network voltage, therefore the stability of the unit’s output voltage is quite high.

The voltage drop across the dinistor when turned on is small, the power dissipation, and therefore its heating, is significantly less than that of a zener diode. The maximum current through the dinistor is about 60 mA. If this value is not enough to obtain the required output current, you can “power up the dinistor with a triac or thyristor (Fig. 9). The disadvantage of such power supplies is the limited choice of output voltages, determined by the switching voltages of the dinistors.

A transformerless power supply with adjustable output voltage is shown in Fig. 10a.

Its feature is the use of adjustable negative feedback from the output of the unit to the transistor stage VT1, connected in parallel with the output of the diode bridge. This stage is a regulatory element and is controlled by a signal from the output of a single-stage amplifier to VT2.

The output signal VT2 depends on the difference in voltage supplied from the variable resistor R7, connected in parallel with the output of the power supply, and the reference voltage source on the diodes VD3, VD4. Essentially, the circuit is an adjustable parallel regulator. The role of the ballast resistor is played by the quenching capacitor C1, the parallel controlled element is played by the transistor VT1.

This power supply works as follows.

When connected to the network, transistors VT1 and VT2 are locked, and the storage capacitor C2 is charged through the diode VD2. When the base of transistor VT2 reaches a voltage equal to the reference voltage on diodes VD3, VD4, transistors VT2 and VT1 are unlocked. Transistor VT1 shunts the output of the diode bridge, and its output voltage drops, which leads to a decrease in the voltage on the storage capacitor C2 and to the blocking of transistors VT2 and VT1. This, in turn, causes an increase in voltage on C2, unlocking VT2, VT1 and repeating the cycle.

Due to the negative feedback operating in this way, the output voltage remains constant (stabilized) both with the load on (R9) and without it (at idle). Its value depends on the position of the potentiometer R7.

The upper (according to the diagram) position of the engine corresponds to a higher output voltage. The maximum output power of the given device is 2 W. The output voltage adjustment limits are from 16 to 26 V, and with a short-circuited diode VD4 - from 15 to 19.5 V. The level of ripple on the load is no more than 70 mV.

Transistor VT1 operates in alternating mode: when there is a load - in linear mode, at idle - in pulse-width modulation (PWM) mode with a voltage pulsation frequency on capacitor C2 of 100 Hz. In this case, the voltage pulses on the VT1 collector have flat edges.

The criterion for the correct choice of capacitance C1 is to obtain the required maximum voltage at the load. If its capacity is reduced, then the maximum output voltage at the rated load is not achieved. Another criterion for choosing C1 is the constancy of the voltage oscillogram at the output of the diode bridge (Fig. 10b).

The voltage oscillogram has the form of a sequence of rectified sinusoidal half-waves of the mains voltage with limited (flattened) peaks of positive half-sine waves; the amplitude of the peaks is a variable value, depending on the position of the R7 slider, and changes linearly as it rotates. But each half-wave must necessarily reach zero; the presence of a constant component (as shown in Fig. 10b by the dotted line) is not allowed, because in this case, the stabilization regime is violated.

The linear mode is lightweight, transistor VT1 heats up little and can operate practically without a heatsink. Slight heating occurs in the lower position of the R7 engine (at minimum output voltage). At idle, the thermal regime of transistor VT1 worsens in the upper position of the R7 engine. In this case, transistor VT1 should be installed on a small radiator, for example, in the form of a “flag” made of a square aluminum plate with a side of 30 mm and a thickness of 1...2 mm.

Regulating transistor VT1 is of medium power, with a high transmission coefficient. Its collector current must be 2...3 times greater than the maximum load current, the permissible collector-emitter voltage must be no less than the maximum output voltage of the power supply. Transistors KT972A, KT829A, KT827A, etc. can be used as VT1. Transistor VT2 operates in low current mode, so any low-power pnp transistor is suitable - KT203, KT361, etc.

Resistors R1, R2 are protective. They protect the control transistor VT1 from failure due to current overload during transient processes when the unit is connected to the network.

The transformerless capacitor rectifier (Fig. 11) operates with auto-stabilization of the output voltage. This is achieved by changing the connection time of the diode bridge to the storage capacitor. Transistor VT1, operating in switch mode, is connected parallel to the output of the diode bridge. The VT1 base is connected through a zener diode VD3 to a storage capacitor C2, separated by direct current from the bridge output by a diode VD2 to prevent rapid discharge when VT1 is open. As long as the voltage at C2 is less than the stabilization voltage VD3, the rectifier operates as usual. When the voltage on C2 increases and VD3 opens, transistor VT1 also opens and shunts the output of the rectifier bridge. The voltage at the bridge output decreases abruptly to almost zero, which leads to a decrease in the voltage at C2 and the zener diode and the key transistor are turned off.

Next, the voltage on capacitor C2 increases again until the zener diode and transistor are turned on, etc. The process of auto-stabilization of the output voltage is very similar to the operation of a pulse voltage stabilizer with pulse-width regulation. Only in the proposed device the pulse repetition rate is equal to the voltage ripple frequency at C2. To reduce losses, the key transistor VT1 must have a high gain, for example, KT972A, KT829A, KT827A, etc. You can increase the output voltage of the rectifier by using a higher-voltage zener diode (a chain of low-voltage ones connected in series). With two zener diodes D814V, D814D and a capacitance of capacitor C1 of 2 μF, the output voltage across a load with a resistance of 250 Ohms can be 23...24 V.

Similarly, you can stabilize the output voltage of a half-wave diode-capacitor rectifier (Fig. 12).

For a rectifier with a positive output voltage, an n-p-n transistor is connected in parallel with the diode VD1, controlled from the output of the rectifier through a zener diode VD3. When capacitor C2 reaches a voltage corresponding to the moment the zener diode opens, transistor VT1 also opens. As a result, the amplitude of the positive half-wave voltage supplied to C2 through the diode VD2 is reduced to almost zero. When the voltage on C2 decreases, transistor VT1 closes thanks to the zener diode, which leads to an increase in the output voltage. The process is accompanied by pulse-width regulation of the pulse duration at input VD2, therefore, the voltage on capacitor C2 is stabilized.

In a rectifier with a negative output voltage, a pnp transistor KT973A or KT825A must be connected in parallel with the diode VD1. The output stabilized voltage on a load with a resistance of 470 Ohms is about 11 V, the ripple voltage is 0.3...0.4 V.

In both options, the zener diode operates in a pulsed mode at a current of a few milliamps, which is in no way related to the rectifier load current, the variation in the capacitance of the quenching capacitor and fluctuations in the network voltage. Therefore, losses in it are significantly reduced, and it does not require a heat sink. The key transistor also does not require a radiator.

Resistors R1, R2 in these circuits limit the input current during transient processes at the moment the device is connected to the network. Due to the inevitable “bouncing” of the contacts of the power plug, the switching process is accompanied by a series of short-term short circuits and open circuits. During one of these short circuits, the quenching capacitor C1 can be charged to the full amplitude value of the network voltage, i.e. up to approximately 300 V. After a break and subsequent closure of the circuit due to “bouncing”, this and the mains voltage can add up and amount to a total of about 600 V. This is the worst case, which must be taken into account to ensure reliable operation of the device.

Another version of the key transformerless power supply circuit is shown in Fig. 13.

Mains voltage, passing through the diode bridge on VD1.VD4, is converted into a pulsating amplitude of about 300 V. Transistor VT1 is a comparator, VT2 is a switch. Resistors R1, R2 form a voltage divider for VT1. By adjusting R2 you can set the response voltage of the comparator. Until the voltage at the output of the diode bridge reaches the set threshold, the transistor VT1 is closed, the gate VT2 has an unlocking voltage and is open. Capacitor C1 is charged through VT2 and diode VD5.

When the set operating threshold is reached, transistor VT1 opens and bypasses the gate VT2. The key closes and will open again when the voltage at the bridge output becomes less than the comparator operating threshold. Thus, a voltage is set at C1, which is stabilized by the integrated stabilizer DA1.

With the ratings shown in the diagram, the source provides an output voltage of 5 V at a current of up to 100 mA. The setting consists of setting the response threshold VT1. You can use IRF730 instead. KP752A, IRF720, BUZ60, 2N6517 is replaced by KT504A.

A miniature transformerless power supply for low-power devices can be built on the HV-2405E chip (Fig. 14), which directly converts alternating voltage to direct voltage.

The input voltage range of the IC is -15...275 V. The output voltage range is 5...24 V with a maximum output current of up to 50 mA. Available in a flat plastic housing DIP-8. The structure of the microcircuit is shown in Fig. 15a, the pinout is shown in Fig. 15b.

In the source circuit (Fig. 14) Special attention you need to pay attention to resistors R1 and R2. Their total resistance should be around 150 Ohms, and the dissipated power should be at least 3 W. The input high-voltage capacitor C1 can have a capacitance from 0.033 to 0.1 μF. Varistor Rv can be used in almost any type with an operating voltage of 230.250 V. Resistor R3 is selected depending on the required output voltage. In its absence (outputs 5 and 6 are closed), the output voltage is slightly more than 5 V; with a resistance of 20 kOhm, the output voltage is about 23 V. Instead of a resistor, you can turn on a zener diode with the required stabilization voltage (from 5 to 21 V). There are no special requirements for other parts, except for the choice of operating voltage electrolytic capacitors(calculation formulas are shown in the diagram).

Considering the potential danger of transformerless sources, in some cases a compromise option may be of interest: with a quenching capacitor and a transformer (Fig. 16).

A transformer with a high-voltage secondary winding is suitable here, since the required rectified voltage is set by selecting the capacitance of capacitor C1. The main thing is that the transformer windings provide the required current.

To prevent the device from malfunctioning when the load is disconnected, a D815P zener diode should be connected to the output of the VD1...VD4 bridge. In normal mode, it does not work, since its stabilization voltage is higher than the operating voltage at the bridge output. Fuse FU1 protects the transformer and stabilizer in case of breakdown of capacitor C1.

In sources of this type, voltage resonance may occur in a circuit of series-connected capacitive (capacitor C1) and inductive (transformer T1) resistances. This should be remembered when setting them up and monitoring the voltages with an oscilloscope.

See other articles section.

Inverters from 220 to 12 volts are produced in different shapes and sizes. There are transformer and pulse types. Transformer converter 220 to 12 volts The design, as the name suggests, is based on a step-down transformer.

Types of converters and their design

A transformer is a product consisting of two main parts:

• a core assembled from electrical steel;
• windings made in the form of turns of conductor material.

Its work is based on the appearance of electromotive force in a closed conductive circuit. When alternating current flows through the primary winding, alternating lines of magnetic flux are formed. These lines penetrate the core and all windings on which electromotive force appears. When the secondary winding is under load, current begins to flow under the influence of this force.

The value of the potential difference will be determined by the ratio of the number of turns of the primary winding and the secondary. Thus, by changing this ratio, you can get any value.

To reduce the voltage value, the number of turns in the secondary winding is made smaller. It is worth noting that the above only works when AC is applied to the primary winding. Using direct current a constant magnetic flux is created, which does not induce an EMF and energy will not be transferred.

Transformerless converter from 220 to 12 volts

Such power devices are called switching power devices. The main part Such a device is usually a specialized microcircuit (pulse width modulator).

Inverting 220 to 12 volts occurs as follows. The mains voltage is supplied to the rectifier circuit, and then smoothed out by a capacitance with a nominal value of 300-400 volts. Then the rectified signal is converted into high-frequency signals using transistors square pulses with the required duty cycle. The pulse-type converter, due to the use of an inverting circuit, produces a stable voltage at the output. In this case, the conversion occurs both with galvanic isolation from the output circuits and without it.

In the first case, a pulse transformer is used, which receives a high-frequency signal up to 110 kHz.

Ferromagnets are used in the manufacture of the core, which leads to a reduction in weight and size. The second uses a low-pass filter instead of a transformer.

The advantages of pulsed sources are as follows:

1. light weight;
2. improved efficiency;
3. cheapness;
4. presence of built-in protection.

The disadvantages include the fact that using in work high frequency pulses, the device itself creates interference. This requires elimination and brings complications to electrical circuits.

How to make 12 volts from 220 volts yourself

The easiest way is to make an analog device based on a torus transformer. This device is easy to make yourself. To do this, you will need any transformer with a primary winding rated for 220 volts. The secondary winding is calculated according to simple formulas or selected practically.

For selection you may need:

• voltage measuring device;
• insulating tape;
• keeper tape;
• copper wire;
• soldering iron;
• disassembly tool (nippers, screwdrivers, pliers, knife, etc.).

First of all, it is necessary to determine on which side of the transformer being converted the secondary winding is located. Carefully remove the protective layer to gain access. Using a tester, measure the voltage at the terminals.

In case of lower voltage, solder the wire to either end of the winding, carefully insulating the connection point. Using this wire make ten turns and measure the voltage again. Depending on how much the voltage has increased, calculate the additional number of turns.

If the voltage exceeds the required, reverse actions are taken. Ten turns are unwound, the voltage is measured and it is calculated how many of them need to be removed. After this, the excess wire is cut off and soldered to the terminal.

It should be noted that when using a diode bridge, the output potential difference will rise by an amount equal to the product of the alternating voltage and the value of 1.41.

The main advantage of transformer conversion is simplicity and high reliability. The downside is the size and weight.

Self-assembly of pulse inverters is possible only with a good level of training and knowledge of electronics. Although you can buy ready-made KIT kits. This kit contains a printed circuit board and electronic components. The set also includes electrical diagram And drawing with detailed arrangement of elements. All that remains is to carefully unsolder everything.

Using pulse technology, you can also make a converter from 12 to 220 volts. Which is very useful when used in cars. A striking example may serve as a source uninterruptible power supply made from stationary equipment.