Which Stirling engine has the best design with maximum efficiency. Which Stirling engine has the best design with maximum efficiency Devices with very high circuit efficiency

Single-ended converters with high efficiency, 12/220 volts

Some common household electrical appliances, such as a lamp daylight, photo flash and a number of others, sometimes it is convenient to use in a car.

Since most devices are designed to be powered from a network with an operating voltage of 220 V, a step-up converter is needed. An electric razor or a small fluorescent lamp consumes no more than 6...25 W of power. Moreover, such a converter is often not required alternating voltage on the way out. The above household electrical appliances operate normally when powered by direct or unipolar pulsating current.

The first version of a single-cycle (flyback) pulsed DC voltage converter 12 V/220 V is made on an imported UC3845N PWM controller chip and a powerful N-channel field-effect transistor BUZ11 (Fig. 4.10). These elements are more affordable than their domestic counterparts, and make it possible to achieve high efficiency from the device, including due to the low source-drain voltage drop across an open field-effect transistor (the efficiency of the converter also depends on the ratio of the width of the pulses transmitting energy to the transformer to the pause).

The specified microcircuit is specially designed for single-cycle converters and has all the necessary components inside, which allows reducing the number of external elements. It has a high-current quasi-complementary output stage specifically designed for direct power control. M-channel field-effect transistor with insulated gate. The operating pulse frequency at the output of the microcircuit can reach 500 kHz. The frequency is determined by the ratings of the elements R4-C4 and in the above circuit is about 33 kHz (T = 50 μs).

Rice. 4.10. Circuit of a single-cycle pulse converter that increases voltage

The chip also contains a protection circuit to shut down the converter when the supply voltage drops below 7.6 V, which is useful when powering devices from a battery.

Let's take a closer look at the operation of the converter. In Fig. Figure 4.11 shows voltage diagrams that explain the ongoing processes. When positive pulses appear at the gate of the field-effect transistor (Fig. 4.11, a), it opens and resistors R7-R8 will receive the pulses shown in Fig. 4.11, c.

The slope of the top of the pulse depends on the inductance of the transformer winding, and if at the top there is a sharp increase in the voltage amplitude, as shown by the dotted line, this indicates saturation of the magnetic circuit. At the same time, conversion losses increase sharply, which leads to heating of the elements and deteriorates the operation of the device. To eliminate saturation, you will need to reduce the pulse width or increase the gap in the center of the magnetic circuit. Usually a gap of 0.1...0.5 mm is sufficient.

When the power transistor is turned off, the inductance of the transformer windings causes voltage surges to appear, as shown in the figures.

Rice. 4.11. Voltage diagrams at circuit control points

With proper manufacturing of transformer T1 (sectioning the secondary winding) and low-voltage power supply, the surge amplitude does not reach a value dangerous for the transistor and therefore, in this circuit, special measures in the form of damping circuits in the primary winding of T1 are not used. And in order to suppress surges in the current signal feedback, coming to the input of the DA1.3 chip, a simple RC filter is installed from elements R6-C5.

The voltage at the converter input, depending on the condition of the battery, can vary from 9 to 15 V (which is 40%). To limit the change in output voltage, input feedback is removed from the divider of resistors R1-R2. In this case, the output voltage at the load will be maintained in the range of 210...230 V (Rload = 2200 Ohm), see table. 4.2, i.e. it changes by no more than 10%, which is quite acceptable.

Table 4.2. Circuit parameters when changing supply voltage

Stabilization of the output voltage is carried out by automatically changing the width of the pulse that opens transistor VT1 from 20 μs at Upit = 9 V to 15 μs (Upit = 15 V).

All elements of the circuit, except for capacitor C6, are placed on a single-sided printed circuit board made of fiberglass with dimensions of 90x55 mm (Fig. 4.12).

Rice. 4.12. Topology printed circuit board and arrangement of elements

Transformer T1 is mounted on the board using an M4x30 screw through a rubber gasket, as shown in Fig. 4.13.

Rice. 4.13 Mounting type of transformer T1

Transistor VT1 is installed on the radiator. Plug design. XP1 must prevent erroneous supply of voltage to the circuit.

The T1 pulse transformer is made using the widely used BZO armor cups from the M2000NM1 magnetic core. At the same time, in the central part they should have a gap of 0.1...0.5 mm.

The magnetic core can be purchased with an existing gap or it can be made using coarse sandpaper. It is better to select the gap size experimentally when tuning so that the magnetic circuit does not enter the saturation mode - this is convenient to control by the shape of the voltage at the source VT1 (see Fig. 4.11, c).

For transformer T1, winding 1-2 contains 9 turns of wire with a diameter of 0.5-0.6 mm, windings 3-4 and 5-6 each contain 180 turns of wire with a diameter of 0.15...0.23 mm (wire type PEL or PEV). In this case, the primary winding (1-2) is located between two secondary windings, i.e. First, winding 3-4 is wound, and then 1-2 and 5-6.

When connecting the transformer windings, it is important to observe the phasing shown in the diagram. Incorrect phasing will not damage the circuit, but it will not work as intended.

The following parts were used during assembly: adjusted resistor R2 - SPZ-19a, fixed resistors R7 and R8 type S5-16M for 1 W, the rest can be of any type; electrolytic capacitors C1 - K50-35 for 25 V, C2 - K53-1A for 16 V, C6 - K50-29V for 450 V, and the rest are of the K10-17 type. Transistor VT1 is installed on a small (by the size of the board) radiator made of duralumin profile. Setting up the circuit consists of checking the correct phrasing of connecting the secondary winding using an oscilloscope, as well as setting resistor R4 to the desired frequency. Resistor R2 sets the output voltage at the XS1 sockets when the load is on.

The given converter circuit is designed to work with a previously known load power (6...30 W - permanently connected). At idle, the voltage at the circuit output can reach 400 V, which is not acceptable for all devices, as it can lead to damage due to insulation breakdown.

If the converter is intended to be used in operation with a load of different power, which is also turned on during operation of the converter, then it is necessary to remove the voltage feedback signal from the output. A variant of such a scheme is shown in Fig. 4.14. This not only allows you to limit the output voltage of the circuit to idling 245 V, but will also reduce power consumption in this mode by about 10 times (Ipotr = 0.19 A; P = 2.28 W; Uh = 245 V).

Rice. 4.14. Single-cycle converter circuit with maximum no-load voltage limitation

Transformer T1 has the same magnetic circuit and winding data as in the circuit (Fig. 4.10), but contains an additional winding (7-4) - 14 turns of PELSHO wire with a diameter of 0.12.0.18 mm (it is wound last). The remaining windings are made in the same way as in the transformer described above.

To manufacture a pulse transformer, you can also use square cores of the series. KV12 made of M2500NM ferrite - the number of turns in the windings in this case will not change. To replace armor magnetic cores (B) with more modern square ones (KB), you can use the table. 4.3.

The voltage feedback signal from winding 7-8 is supplied through a diode to the input (2) of the microcircuit, which makes it possible to more accurately maintain the output voltage in a given range, as well as provide galvanic isolation between the primary and output circuits. The parameters of such a converter, depending on the supply voltage, are given in table. 4.4.

Table 4.4. Circuit parameters when changing supply voltage

The efficiency of the described converters can be increased a little more if the pulse transformers are secured to the board with a dielectric screw or heat-resistant glue. A variant of the printed circuit board topology for assembling the circuit is shown in Fig. 4.15.

Rice. 4.15. PCB topology and arrangement of elements

Using such a converter you can power from on-board network car electric razors "Agidel", "Kharkov" and a number of other devices.