RU2573647C1 - Semi-bridge self-maintained inverter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: semi-bridge self-maintained inverter comprises divider of input supply voltage at two in-series capacitors, two in-series field-effect transistors, transformer, load coil and control circuit supply coil, control element, current-limiting resistors, frequency-setting circuit, trigger circuit and rectifier with filter capacitor to supply the control circuit. Voltage comparator is used as the control element with balancing circuit connected additionally to its input. The field-effect transistors have different type of conductivity: n-type and p-type. Aforesaid elements are interconnected in such a way as pointed out in application materials.

EFFECT: enlarging functional capabilities; improving reliability and mounting flexibility of the device.

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Description

The invention relates to a conversion technique and can be used to power equipment for various purposes.

Half-bridge inverter circuits are widely used in the power range from tens of watts to units of kW. This is due to their advantage over single-cycle schemes - in terms of energy efficiency; in front of bridges - in terms of cost and the absence of problems associated with saturation of the power transformer; in front of the circuits with the midpoint of the power transformer - according to the lower installed voltage of the key elements and the guaranteed absence of overvoltage on them.

The main problems in the development of half-bridge inverters are associated with the control of the upper half-bridge key.

Several main types of half-bridge inverters are known.

Autogenerators with saturable power or additional switching transformers [1, 2]. These simple and cheap devices have low efficiency, the dependence of the operating frequency on the magnitude of the supply voltage, the inability to adjust the output parameters. Half-bridge inverters can be with the transmission of key management signals from an external control circuit via a pulse transformer to two n-channel [3] or n- and p-channel MOSFETs [4]. The main disadvantage of such devices is non-optimal key management. There are half-bridge inverters with galvanically isolated half-bridge drivers. These are optocoupled decoupled drivers from Agilent Technologies, IXYS, Analog Devices transformer decoupled drivers, and isolating barrier RF drivers from Silicon Labs. Drivers with optocoupler and RF isolation require an additional "floating" power source. Analog Devices drivers containing isolation transformers inside the microcircuit have a control signal power limitation. All such known devices are not practical due to the high cost and scarcity of the listed drivers themselves. The most widespread are half-bridge inverters controlled by half-bridge drivers with bootstrap power and a high-voltage pulse cascade for shifting the level of the upper key control signal. Such drivers are produced by most leading manufacturers of components for power electronics [5, 6]. These known simple and inexpensive devices also have a number of disadvantages listed below:

- a limited range of operating frequencies, which is associated with a finite duration of level shift pulses [3];

- restriction on the power of the upper key control;

- low noise immunity due to the method of transmitting the control signal to the upper key by means of short pulses;

- criticality to the installation topology in terms of pairing the driver output with the key inputs, especially at high power levels. This is due to the fact that the control signals of the transistor gates are unipolar [3]. The last two points indicate the low reliability of half-bridge inverters.

The listed well-known types of half-bridge inverters have another common significant drawback - they lack a symmetrization mechanism, i.e. automatic voltage equalization on the capacitors of the divider. The reasons for the asymmetry, even when the drivers work perfectly, may be differences in the parameters of the power switches, determined by the technological spread of the output parameters during the manufacturing process of these elements. In half-bridge inverters, asymmetry, although it does not lead to one-sided magnetization of the core of the power transformer, is undoubtedly the reason for the increased level of output voltage ripples at the operating frequency, as well as to unequal key loading in power, which negatively affects the reliability of the known device.

The closest in technical essence to the claimed invention (prototype) is the device presented in the source [7], Fig. 17, which is a half-bridge inverter controlled by the International Rectifiert IR215X driver in a typical inclusion, supplemented by a driver power supply circuit from the transformer winding. The IR215X driver is a self-oscillating type with bootstrap power and a high-voltage pulse cascade for shifting the level of the upper key control signal.

The known device comprises a capacitive divider of the input supply voltage Uin on capacitors C4, C5; two series-connected keys made on field-effect transistors with an insulated gate and an n-type channel (n-MOSFET) VT1, VT2, whose gates are connected via a current-limiting resistor R3, R4 to a control chip D1, a transformer Τ with a primary winding W1, a load winding Wн and the power winding of the Waux control circuit; rectifier VD2-VD5 with filter C1 to power the control circuit; R2 start chain frequency setting circuit R1C2 and bootstrap power supply circuit of the upper key VD1 C3. Thus, the known device is burdened by the presence of an additional bootstrap power circuit, a complex driver on the corresponding chip, and the absence of a symmetry circuit. Together, all this sets high requirements for the wiring, installation and commissioning of its elements, as well as for protective shields of the housing, especially when using the device in aggressive environments, in particular with a high level of electromagnetic and radiation radiation. As a result, the main disadvantages of the known device are limited functionality, low reliability, manufacturing complexity, which determines its low manufacturability.

The aim of the invention is to eliminate these drawbacks, namely, expanding functionality by expanding the range of operating frequencies and capacities, as well as increasing reliability by improving resistance to external influences, in particular to electromagnetic and radiation radiation, reducing structural requirements, which increases manufacturability of the installation of the device.

This goal is achieved by the fact that a half-bridge self-generating inverter containing an input voltage divider for two series-connected capacitors, two series-connected field-effect transistors, a transformer, the first output of the primary winding connected to the connection point of the transistors, and the second output to the connection point of the capacitors, also containing load winding and power winding of the control circuit, a control element, the output of which is connected via current limiting resistors to creates transistors frequency control circuit, the trigger circuit and a rectifier with a filter capacitor for the power control circuit, wherein the control element as applied voltage comparator, the inputs of which is further connected to a balun circuit; field-effect transistors are used with different conductivities, so that one of them is n-type and the second is p-type, the drain of the second transistor is connected to the negative bus, the source is connected to the source of the first transistor, and the gates of the transistors connected together through a current-limiting resistor are connected to the output control schemes; moreover, the transformation of the mountain winding of the power supply of the control circuit is made with a tap from the middle point and, together with the rectifier and two filtering capacitors, provides a bipolar, relative to the connection point of the transistor sources, power of the comparator.

The diagram shows a half-bridge self-generating inverter, where the numbers indicate:

1. The comparator.

2. The rectifier.

3. The transformer.

4. Retraction from the midpoint of the rectifier winding.

The drawing shows a schematic diagram of a half-bridge self-oscillating inverter, consisting of: a capacitive voltage divider on two series-connected capacitors C4 and C5, two series-connected field-effect transistors VT1 and VT2, a transformer with three windings 3, a current-limiting resistor R6, a frequency limiting circuit R1C1, a start-up circuit R4 , R5, rectifier 2, made with tap from the midpoint of the winding 4, with a filter capacitor C2, C3, comparator 1, the balancing circuit R2, R3.

The half-bridge self-generating inverter presented in the diagram works as follows.

When voltage Uvx is applied, the filtering capacitors C2, C3 through the resistors of the start circuit R4, R5 are charged to a total voltage sufficient for the control comparator, for example TLC3702, to enter the operating mode. Using a comparator with a balancing circuit, in this version of the inverter’s technical solution, avoids using a bootstrap powered driver, while the inverter has high noise immunity, high duty cycle, does not require complicated installation, a protective housing, etc. The output of the comparator appears voltage taken as positive. The transistor VT1 (n-MOSFET), for example FQD4N50, is unlocked, and VT2 (p-MOSFET), for example FQD3P50, for which the positive gate voltage is a gate, is locked accordingly. Such a control circuit of the half-bridge transistors, in the absence of bootstrap power supply circuits, determines the absence of fundamental restrictions on the power of control pulses, and the range of operating frequencies and device capacities is expanded. In this case, the sources of the upper and lower transistors are combined and form the output of the half-bridge inverter, to which the primary winding of the transformer 3 is connected, the drain of the p-type transistor VT2 is connected to the negative bus, and the gates connected together through the current-limiting resistor R6 are connected to the output of the control circuit. The power supply winding of the control circuit is tapped from the midpoint and together with the rectifier, for example, the BAV99S diode assembly, provides a bipolar relative to the connection point of the comparator power sources, which, in turn, increases the reliability of the claimed circuit. A potential negative with respect to the sources is established at the inverting input of the comparator through the R3R1 divider, and a full-fledged bipolar power of the comparator 1 appears at the output of the rectifier 2. At the capacitor C1 connected to the non-inverting input of the comparator, the voltage negative from the sources from the current flowing through R2 increases linearly. With equal potentials at the inputs of the comparator, it changes its state by closing VT1 and unlocking VT2. At the inverting input, a positive threshold potential is established, and at C1, the growth of positive voltage begins. With equal potentials at the inputs, comparator 1 returns to its previous state, closing VT2 and unlocking VT1. The process is then repeated. The same voltage-meander is applied to the control transitions of the transistors without any protective pauses, but due to the peculiarities of the input characteristics of the MOSFET, their switching occurs without through currents. Thus, the inventive device acquires two new qualities: the exact symmetry of the operating mode and an increase in reliability due to the fundamental absence of spurious through currents.

At R2 = R3 = R, the operating frequency is determined by the expression F = 1 / 4R1C1 and does not depend on Uin at least when it changes twice. Under the condition of Uinx / R >> lin.κomp., Which is easily performed for modern comparators, the device automatically provides a symmetrical mode, and both the comparator's own delays and transistor switching delays are compensated. The symmetrization mechanism is connected with the fact that in each half-cycle a voltage of one of the capacitors of the divider is applied to the frequency-setting circuit, as a result, the circuit monitors the difference of these voltages and seeks to make it equal to zero for the period.

The use of a comparator as a control element, bipolar control, the absence of differentiating links in the control circuit allow us to achieve the claimed technical result, namely, expanding functionality by expanding the range of operating frequencies and powers, as well as increasing reliability by improving resistance to external influences, in particular electromagnetic and radiation radiation, reducing design requirements, which increases the manufacturability of device installation but.

Industrial applicability

The inventive half-bridge self-generating inverter can be successfully used in aggressive environments, such as nuclear power plants or in space, and the available elemental base and ease of installation allow you to create the inventive inverter in enterprises with the usual set of standard equipment, parts and materials.

Information sources

1. Senkezich A.K., Aleshin A.F. Self-generating half-bridge inverter. Patent RU 2007830.

2. Gladyshev O.M. Half-bridge oscillator. Patent RU 2176847.

3. Laszio Balogh, translation by D. Makashov. Development and application of high-speed power field-effect transistor control circuits. Proceedings of the SEM-1400 UNITRODE Conference, 2001

4. Abdus Sattar. IXYS P-cannel Power MOSFET and Applications. Kyong-Wook Seok, IXAN0064.

5. Kosenkov D. Drivers MOSFET and IGBT. Modern Electronics, No.6, 2005

6. Kolpakov A. Characteristics and application features of the MOSFET / IGBT drivers. Components and technology. No 3, 2003

7. Volovich G. Drivers of power keys. Modern Electronics, No.8, 2007

Claims (1)

A half-bridge self-oscillating inverter containing an input voltage divider on two series-connected capacitors, two field-effect transistors in series, a transformer connected to the transistor connection point by the first output of the primary winding, and the capacitor connection point, which also contains the load winding and the power supply circuit of the second output control, a control element, the output of which through current-limiting resistors is connected to the gates of transistors, ep, trigger circuit and a rectifier with a filter capacitor for the power control circuit, characterized in that the control member is applied a voltage comparator, the inputs of which is further connected to a balun circuit; field-effect transistors are used with different conductivities, so that one of them is n-type and the second is p-type, the drain of the second transistor is connected to the negative bus, the source is connected to the source of the first transistor, and the gates of the transistors connected together through a current-limiting resistor are connected to the output control schemes; moreover, the transformer winding of the power supply of the control circuit is taped off from the midpoint and, together with the rectifier and two filtering capacitors, provides a bipolar, relative to the connection point of the transistor sources, power of the comparator.