SU1138911A1 - Inverter - Google Patents

Abstract

INVERTER, containing the output “yoi transformer, the primary winding of which is connected to the power transistors through the collector windings of the switching current transformer, ka, base; the windings of which are connected by extreme leads to the collectors of the control transistors, to the emitters of which the first leads of the shunt resistors are connected, and to the control to the junction transitions through resistors there are additional windings that are different in order to improve reliability by eliminating overloads during a short circuit in the load, others the extreme terminals of the base windings of the current transformer are connected to the bases of the power transistors, the control transitions of which are bridged by the inserted reverse diodes, and to the emitters are connected Control transistors are designed, the conductivity type of which is opposite to the conductivity type of the power transistors, the second terminals of the shunt HR resistors are connected to the taps of the base windings of the overcurrent current transformer, and the additional windings are located at the output trans with the formatter.

Description

111389

The invention relates to electrical engineering and technology, and to be used in computing devices, radio engineering and automation.

Inverters are known that contain an output transformer, the primary winding of which is connected to power transistors through the collector windings of a switching current transformer, whose basic windings are connected to control transistors of power transistors, as well as control transistors connected to the bases of power transformers lj and 2

- The drawbacks of the devices are low efficiency and reliability due to the deep saturation of switching, transistors, especially in the mode of low load currents.

The closest to the invention according to the technical essence is an inverter containing an output transformer, the primary winding of which is connected to the power transistors through the collector windings of a switching 25 current transformer, the base windings of which are connected to the collectors of the control transistors to the emitters of which are connected to the first shunt terminals resistors, and for control transitions through resistors - additional windings 3J.

A disadvantage of the known device is low reliability due to; transistor overload during a short circuit in the load.

. The purpose of the invention is to increase the reliability of the device by eliminating overloads during a short circuit in the load,. .

The goal is achieved by the fact that in the inverter containing the output transformer, the primary winding of which is connected to the power transistors through the collector windings of a switching current transformer, the basic windings of one fluorine are connected to the emitters of which are connected to the first terminals of the control transistors shunt resistors, and additional resistors are connected to control transitions through resistors, other extreme terminals of the base current transformer windings are connected 55 to the bases, O transistors, controlled transitions which guides shunted introduced wheeling diodes, and

12

emitters are connected to emitters of control transistors, the type of conductivity which is opposite to the type of conductivity of power transistors, the second leads of the shunt resistors are connected to the taps of the base windings of the switching transformer TOKa, i and the additional windings are located on the output transformer.

The drawing shows a diagram of the proposed inverter.

The inverter contains an output transformer 1 with primary, secondary and additional windings 2 and 3, which are connected through resistors 4 and 5 to the control transitions of control transistors 6 and 7, whose collectors are connected to the extreme terminals of the base windings 8 and 9 of the current switching transformer 10, others The extreme terminals of the base B windings 8 and 9 of which are connected to the bases of the power transistors 11 and 12, the control transitions of which are shunted by reverse diodes 13 and 14, as well as the shunt resistors 15 and 16.

Due to the proposed incorporation of elements, the functional structure of the inverter contains several feedback circuits, which are closed as follows.

Positive voltage feedback, which provides self-excitation of the inverter, is closed by a current transformer 10 — the voltage on its additional windings 2 and 3 maintains the open state of the power transistor in the inverter shoulder where the current flows and in the other shoulder. In addition, due to this, the negative link is closed due to the current of the power circuit (mainly according to the load current, since its value is predominant), which is provided by the current transformation mode.

Therefore, when the load current decreases and, accordingly, the inverter power, the current in the base-emitter circuits of the power transistors decreases proportionally, ensuring that their saturation coefficients remain constant, as well as the inverter efficiency constant as the load current decreases. Negative

31

feedback monitoring the load condition is closed through the control transistors 6 and 7. When a load is short-circuited, the voltage on the secondary windings of the output transformer decreases sharply, approaching zero, due to which the open-shoulder control transistor turns off, ensuring the transfer of the power transistor from the amplifier to the amplifying mode, due to which the oscillation autogeneration process and the possibility of returning power to the load when a short circuit is canceled.

The processes that determine the operation of the inverter, which is a relaxation generator with one inductive energy storage, are divided into two stages, and their features are determined by the functional structure of the device.

At the slow stage of operation, one of the power transistors, for example, transistor 11, is open and the other (respectively, transistor 12) is closed and is in cut-off mode, while the control transistor 6 is also open and transistor 7 is closed on the feedback circuit with voltages windings of the output transformer 1. The main process at this stage is the magnetization reversal of the core of the current transformer 10 under the action of, the difference between the current amperages — the magnetization of the I-die (the collector current of the force transistor 11) and the demagnetizing (current ba oic chain of the same transistor). The latter, developed in the base winding 8, flows through the base-emitter junction of the transistor 11 and the open transistor 6, while the voltage on the winding 8 is limited at the level of the total saturation voltage of these transitions. In accordance with this, the voltage on the winding 9 in the inverter's closed arm is also limited to the indicated value, therefore, the winding 9 developed on the part between the outlet and the upper output of the circuit is the voltage below the diode 14 cutoff level and there is no current in this circuit. In this connection, for the transformer 10, under normal load conditions, the current transformer mode is ensured. With this, the choice of the ratio of turns of the base windings

11 -4.

transformer 10 to collector, equal to the minimum value of the gain of the power transistors, provides a key mode of operation of the latter. In this respect, the voltage on the collector windings of the transformer 10 also decreases as compared to the voltage on the base, due to which the power consumption of the power circuit to maintain the open state of the power transistor is minimal.

When saturating the switching current transformer 10, the base current of the transistor 11c dramatically decreases at this point, the fast operation stage of the inverter, the shoulder switching stage, begins. With a decrease in the collector current of the transistor 11 in accordance with the general principle of operation of relaxation generators with an inductive drive, the magnetic field energy accumulated in the magnetizing inductance of the transformer 10 leads to the induction of opposite polarity on the secondary windings, resulting in the opening of transistor 12 (second inverter shoulder) and the transistor 11 is closed by reverse voltage. At a fast stage, the closing of the transistor 11 occurs by reducing the current in its main circuit (due to The current of magnetization of the magnetic circuit of the transformer 10 upon its transition to saturation) at its constant collector current. In this connection, the transition of the transistor to the off state occurs through the stage of its preliminary output from its full state to the linear mode. However, at the very first moment of the start of this mode, when the collector current begins to decrease, the polarities of the voltages on the windings of the code transformer 1 change, this causes the control transistor 6 to close and the opening of the transistor 7 creates the conditions for the flow of the full control (opening) current in the base current the transistor circuit 12, and the transistor 6 cuts off a similar circuit in the left shoulder, forcing the switching process. As a result, an avalanche-like switching process occurs and the diverter, creatures stogo constant feature of the process is predvarntel, derivation of power transistor 11 from the rich state to a linear mode, eventually nsklyuchavt through current mode circuit 13 when the power transistors pereklkgchenii in communication simultaneously with the exception of their open state. By switching the inverter arms, the fast stage of the processes in the circuit is completed, after which the slow stage, which differs from the previous one only by changing the polarity on all the windings of the transformers and starting from the magnetic reversal of their magnetic circuits, begins again. During a short circuit of the load circuit, the main difference between the processes and the inverter from those described is that the shunting of one of the secondary windings, which occurs at the same time, is extremely low, the load resistance dramatically reduces the voltage on all secondary windings of the output transformer 1, including its additional coils 2 and 3, in connection with which the transistors 6 and 7 of the control remain closed. In this case, the current circuit of the base circuit of nozzle transistors, for example, a transistor, is closed from the secondary winding through the shunt resistor 15 to the emitter terminal of the transistor (common wire of the circuit). At the same time, the current in the winding loop 9 from the winding through the resistor 16 also flows and diode 14. In this case, the transformer 10 operates in the voltage transformer mode, and the voltage switches of the resistor 15 and 16 are selected from the condition of providing close to linear mode of the power transistors 11 and 12 with a power lower than flax tolerance for this mode. The condition that ensures the stability of this mode is fulfilled by the presence of an internal load (in the form of a circuit 16 and 1 for the left shoulder and a circuit 15 and 13 for the right shoulder) for the newly organized structure of the inverter according to the classical circuit containing power transistors 11 and 12, torus 10 in voltage transformer mode with primary windings connected to collector circuits of switching transistors, and secondary windings formed part of windings 8 and 9 and connected to current limiting resistors 15 and 16 to scroll inputs switching transistors. This internal load circuit is a buffer that smoothes the technological variation and changes from environmental conditions of the parameters of the transformer 10 and the power transistors in a linear mode. When a load short circuit is developed on the secondary windings 2 and 3. The output voltage transformer opens the corresponding control transistor, due to which the inverter is switched to the power return mode to the load. Moreover, the transfer of an inverter from one mode to another (and vice versa) can occur in any phase of the processes occurring in it without disturbing the operation stability. The inverter is switched from the standby mode (i.e., short-circuit mode) to the power-to-load mode since the moment of clearing the short circuit, provided that in the holding mode, the power level of the amplifying mode of the power transistors is sufficient to develop on the windings 2 and 3 of transformer 1, the voltage exceeded the threshold value of the input of control transistors. The inverter is switched to standby mode when the current increases abruptly at the time of the occurrence of a load short circuit due to the fact that the pulse drop in voltage on the leakage inductances of the primary transformer windings: dramatically reduces the voltage on the inductance of the magnetization reversal of transformer 1, resulting in a voltage its windings 2 and 3 decrease below the threshold level of the input characteristic of the control transistors, the latter are turned off and the power transistors are switched to the amplifier mode. The ratio of turns in the base windings of the current transformer Tr2 - (between the winding parts separated by the output) is determined by the following considerations. The voltage on the winding 8 is limited at the level of the sum of the voltages of the base-emitter junction of the transistor 11 and ccd of the transistor 6. The latter is usually lower than the voltage of the base-emitter junction, therefore half of the total voltage does not exceed the cut-off voltage of the semiconductor diodes shunt the power transistors, in particular the diode 14. In this connection, when choosing a tap not more than half of the turns of the base winding (counted from the upper output), there is no current in the secondary (base) vol. Transformer 10 connected to the closed side of the inverter. This provides the transformer 10 with the current transformer mode, which is necessary for the normal functioning of the inverter. When using semiconductor devices made of various materials, when the ratio of the direct voltage for open transitions is different from that considered, the choice of the required diversion switch-on factor (auto-transformation factor-Kg) can be determined from the expression у - Цш4; . riJsW 3.oc ,, .- the number of turns of the upper half of the base winding (from the upper half according to the output circuit to the outlet); 8 total number of turns of the base winding. . The resistance of the resistors 15 and 16 is derived from the ratio between the components of the inverter currents in the short circuit mode. In this case, the structure of the inverter is formed according to the classical scheme and the current into the base of the power transistor, is determined by the voltage developing on the upper half of the base winding Ngg, and the resistance in koHType of this current (resistance of resistors 15 or 16). . % t where E is the supply voltage {k is the number of turns of the collector winding of the transformer 10j resistance of resistors 15 and 16. The load of the inverter in this mode is the current loop in the closed-circuit base circuit (internal load) due to the bypass diode 13, ( 14), connected in reverse direction to the control transition of the power transistor 11 (12). Thus, the total current of the base windings brought to the collector 11 18. . winding of the transformer 10, determines the main component of the collector current (component of the collector current, determined by the coercive current across the core of the transformer 10, almost always significantly lower than the specified component) as a single power transistor .b 2E% .1 , We make the transition from the number of turns of the upper half of the base winding,: to the total number of its turns 2t 2 T - I -, -, - l - .. Lu IK n at y, v - -, is.-ib From the resulting expression, learn that Ng 2W3., nWg. resistors resistors B - the minimal possible, the gain of transistors 11 and 12. From the latter expression that. due to real values of transistor amplification coefficients exceeding Vd, power transistors also operate in a key mode with a saturation factor equal to the ratio of the real value of B to k, (due to the presence of a component of the collector current caused by the coercive value of the transformer core 10, the coefficient is somewhat lower). Considering this. to exclude at the time of switching the occurrence of the current of the power of the transistors, higher than the maximum allowable (. Ij ,, i, j,), it is necessary to limit the selected value, K-AOP in the light of this, the final expression for determining the resistance R, 5, i6 looks like ( 6.16 Thus, the proposed inverter compared with the known

has a high efficiency value due to the elimination of power losses at the current-limiting elements of the base circuits of the power transistors, retains a high efficiency value with decreasing load current. In addition, there is no mode in the inverter.

the through currents and, accordingly, the current overload of the power transistors when they are switched, which significantly increases reliability and efficiency, and when a short circuit in the load circuit dramatically reduces the power consumed by the inverter.

Claims (1)

i INVERTER containing the output * th transformer, the primary winding of which is connected to power transistors through the collector windings of a switching transformer, the base windings of which are connected by the extreme leads to the collectors of the • control transistors, to the emitters of which the first leads of the shunt resistors are connected, and to control transitions through resistors - additional windings, characterized in that, in order to increase reliability by eliminating overloads during a short circuit in the load, other extreme e terminals of the base windings of the current transformer are connected to the bases of power transistors, the control transitions of which are shunted by the introduced reverse diodes, and emitters of control transistors are connected to the emitters, the conductivity type of which is opposite to the type of conductivity of the power transistors, and the second terminals of the shunting resistors are connected to the taps base windings of a switching current transformer, and additional windings are located on the output transformer.