SU1746502A1 - Push-pull inverter - Google Patents

Abstract

Usage: voltage-to-voltage conversion. SUMMARY OF THE INVENTION: Switching Conductors 14. 15, being recharged in series through diode 16 (17) and the base-emitter junction of one of the additional transistors 21 (20), provide a delay in the rise of voltage on a closing power transistor 3 (4) . At the same time, an open additional transistor 21 (20) shunts the base-emitter junction of the power transistor 4 (3) of the other arm. As a result, dynamic power losses are reduced when the power transistor 3 is turned off (4) and the overlapping of processes is eliminated when they are switched. 3 hp ff, 4 il g // cl

Description

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The invention relates to electrical engineering and can be used in the secondary power supply sources of electronic equipment, converters of induction heating installations.

An inverter is known that contains a transformer, the primary winding of which is connected to the first input terminal by a midpoint and the extreme points to the collectors of power transistors shunted by reverse diodes and emitters connected to the second input terminal, and the feedback winding through the current limiting resistor is turned on between the base terminals of the power transistors. Between the extreme terminals of the transformer primary winding, a capacitor is connected, to the windings of which two opposite terminals of a diode-capacitor bridge are connected. Each of the two other opposite pins of the bridge is connected to the base pins of the power transistors through locking diode circuits.

In the device, when switching power transistors, part of the magnetizing current of the transformer flows through the locking circuits, keeps the power transistors in the closed state during the recharge of the capacitor connected to the extreme terminals of the primary winding, which reduces the rate of voltage variation on the transformer windings and transistors and eliminates switching overvoltages. For normal operation of the device, it is necessary for the part of the magnetizing current flowing through the locking circuits to exceed the base current of the opening transistor. inverter applications.

Also known is a high-voltage high-frequency voltage converter, made according to the two-stroke inverter circuit with a middle point of a transformer, containing power transistors, a transformer, a pulse driver, logic gates And, comparators, power cables, diodes, voltage divider.

In the converter, the voltage at the power transistors is measured by means of comparators, and when switching, the opening of the power transistors is carried out at a decrease in the voltage across them below the threshold voltage. The most effective use of the device is in high-voltage converters, the transformers of which are characterized by a large value of the capacity of the secondary winding. With the transformation ratio of the output transformer close to one and the step-down transformers, the rate of change of voltage across the transistors is high, which causes switching overvoltages and high levels of electromagnetic interference.

The closest technical solution is a constant-voltage transistor converter containing an output transformer having primary, output, and base windings; power transistors, in which the collectors are connected to the extreme terminals of the primary winding, and the emitters are connected to the minus terminal of the power source, an additional rectifier connected between the base windings and one of the inputs of the inhibit node, the second input of which is connected to the clock generator; an amplifier, a control input connected to the output of the inhibit node and one output to the positive power bus; two RCD chains connected between the second output of the amplifier and the base terminals of the power transistors, two matching transistors, shunted by the counter diodes, the transistor bases connected to the generator outputs, and the collectors to the connection points of resistors and capacitors of the RCD chains, two additional transistors, in which the collectors are connected to the bases, and the emitters are connected to the common connection points of the emitters of the power transistors and the bases are connected to the cathodes of the threshold elements of the RCD chains, an RC filter, one output of which is connected It is connected to the negative terminal of the power supply, and the second output is connected via an auxiliary rectifier to the base windings of the output transformer, a switching capacitor connected to the extreme terminals of the primary winding of the output transformer; two decoupling diodes, anodes connected to the junction of the resistor and the threshold element of the RD-chains, and the cathodes to the collectors of the power transistors; output rectifier with capacitive filter.

In the device, when switching the base-emitter junctions of the power transistors are shunted by additional transistors for the time of recharging the capacitor connected to the extreme outputs of the primary winding of the output transformer. The closure of additional transistors occurs when the voltage on the power transistors decreases.

In this case, it is necessary that the moment of locking the additional transistor coincides with the end of the reloading of the switching capacitor, when the voltage on the power transistor decreases to zero. Otherwise, the dose of the switching capacitor through the opening power transistor occurs, which causes an increase in its current loading. To eliminate this phenomenon, careful individual selection of resistors and threshold elements is required. However, due to the change in the parameters of the elements depending on the change in operating temperature and temporal aging, the working point is shifted from the initial setting area of the converter and, consequently, an increase in dynamic losses when the power transistors are turned on.

The purpose of the invention is to increase efficiency and reliability by reducing the dynamic power losses in power transistors when they are turned on.

The goal is achieved in that a two-stroke inverter containing an output transformer, the primary winding of which is withdrawn from the midpoint, is connected to the first output terminal of the inverter, and the extreme leads is connected to collectors of power transistors, the emitters of which are combined and connected to the second input terminal of the inverter, the first switching capacitor connected by the first output to the collector of the first power transistor, two additional transistors, each of which is connected to the base of the corresponding forces transistor and shunted on the base-emitter circuit by the first resistor, and the control unit, the paraphase outputs of which are connected to the bases of the power transistors, has a second switching capacitor connected by the first output to the collector of the second power transistor, the second output of each switching capacitor is connected to the emitter of the corresponding additional transistor and through the corresponding input diode, with the emitters of the power transistors with which the bases of the additional transistors are connected.

In addition, the above connection of the bases of additional transistors with the emitters of power transistors is made directly.

In addition, the connection of the bases of each of the additional transistors with the emitters of the power transistors is made through the input of the second resistor, and the input threshold element is connected in parallel with each diode.

FIG. 1 shows the scheme of the proposed push-pull inverter; in fig. 2 time diagrams for his work; in fig. 3 and 4.- inverter circuit.

The push-pull inverter (Fig. 1) contains an output transformer 1, the primary winding 2 of which is connected to the collectors of power transistors 3 and 4 by the extreme terminals of sub0, emitters through a current sensor 5 connected to the negative terminal of the power supply 6. The middle point of the primary winding 2 is connected through the switching node 7 and the choke 8, shunted by the diode 9, connected to the positive power terminal 6. To the secondary winding 10 of the output transformer 1 is connected active-inductive load 11.

0 Parallel to the power transistors 3 and 4, counter-diodes 12 and 13 and capacitors 14 and 15 are connected through diodes 16 and 17. In parallel to diodes 16 and 17, resistors 18 and 19 and base-emitter transitions of additional transistors 20 and 21 are connected, whose collector outputs are connected with the base terminals of the power transistors 3 and 4.

The outputs of the control unit 22, power

0 which is provided from the source 6, is connected to the control input of the switching unit 7 and through the current-limiting resistors 23 and 24 to the base terminals of the power transistors 3 and 4.

5B a push-pull inverter (Fig. 3) parallel to diode 16 and 17 are connected threshold elements 26 and 27, and the base-emitter transitions of transistors 20 and 21, shunted by resistors 18 and 19, are connected in parallel to diodes 16 and 17 through resistors 28 and 29.

In the inverter (Fig. 4) parallel to the primary winding 2 of the output transformer 1, a choke 25 is connected.

5 Push-pull inverter works as follows.

When power supply 6 is connected, voltage is applied to control unit 22, which is started after

0 mode produces a control pulse of switching unit 7, connecting the power to the midpoint of the primary winding 2 of the output transformer 1. The charging current of one of the capacitors 14 or 15 connected parallel to the power transistor closed at this moment is limited by the choke 8.

Timing diagrams of switching of the power transistors of the inverter are shown in FIG. 2. The control unit 22 produces control pulses of the power transistors 3 and 4 of the Uuprz and Uynp4 (figs, 2a, b), shifted between themselves by 180 el.grad. with a delay ti-t2, t4-ts, equal to the turn-off time of the power transistors.

Suppose that in the initial state, up to time tt, the power transistor 4 is open (Fig. 2h). The power supply voltage is applied to section 2.2 of the primary winding 2 of the output transformer 1 (the polarity of the voltage in Fig. 1 is shown without brackets). Capacitor 14 is charged to double voltage supply (Fig. 2d), and capacitor 15 is discharged {Fig. 2e). Transistors 20 and 21 are closed, because their base-emitter junctions are shunted by resistors 18 and 19..

At time ti, the opening signal is removed from the control input of the transistor 4 (Fig. 26). The transistor 4 is closed, and the current in it during the turn-off time of the transistor drops to zero (the absorption time is not taken into account). The primary current 2 of transformer 1, equal to the sum of the reduced load current (Fig. 2g) and magnetizing current (Fig. 2m), is closed in the following circuit: end of section 2.2 - capacitor 15 - diode 17 - base - emitter junction of transistor 20 - capacitor 14 - beginning of section 2.1. In this case, the capacitor 15 is charged (Fig. 2e), and the capacitor 14 is charged (Fig. 2e), the voltage on the windings of transformer 1 varies in accordance with the change in voltage on the capacitors 14 and 15. Since the discharge current the capacitor 14 flows through the base-emitter junction of the transistor 20 (Fig. 2k), the latter opens and shunts the base-emitter junction of the transistor of the power transistor 3 (Fig. 2c). Thus, the power transistor 3 remains closed until the end of the recharge of capacitors 14 and 15 (time interval t2-ts).

The voltage across the transistor 4 (Fig. 2h) increases in accordance with the voltage across the capacitor 15 (Fig. 2e). By selecting the appropriate capacitance of the capacitor 14 and 15, a safe path for switching off the power transistors is provided.

By the time point, the t3-capacitor 15 is charged to double the supply voltage (Fig. 2e, polarity in brackets), and the capacitor 14 is discharged to zero (Fig. 2e). The current through the base-emitter junction of the transistor 20 is stopped, the latter is closed, and the power transistor 3 is opened (Fig. 2c, i). In this case, the opening of the transistor occurs at zero voltage across it, which ensures a safe switching path of the power transistors B

over time, the power transistor 3 is open; a supply voltage is applied to section 2.1 of the primary winding of the transformer 1 (polarity in brackets).

At time t4, the opening signal is removed from the control input of the power transistor 3 (Fig. 2a). Transistor 3 closes, and the current in it in the time interval drops to zero (Fig. 2i). The primary current 2 of the transformer 1 is closed along the circuit: the beginning of section 2.1 - capacitor 14 - diode 16 - base-emitter junction of transistor 21 - capacitor

15-end section 2.2. In this case, the capacitor 15 is discharged (Fig. 2e), and the capacitor 14 is charged (Fig. 2e).

Since the discharge current of the capacitor 15 flows through the base-emitter junction

transistor 21 (fig. 2l), the latter opens and shunts the control junction of the power transistor 4 (fig. 2d). Thus, the transistor 4 remains in the closed state for the time of recharging the capacitors 14 and 15 in the time interval.

At the time point te, transistor 4 opens (Fig. 2d, g), supply voltage is applied to section 2.2 of the primary winding of transformer 1 (polarity without brackets).

At time t, the opening signal is removed from the control input of the transistor 4, and the processes in the device are repeated.

Under load, the control unit 22, from a current sensor 5, removes the opening signals from the control inputs of transistors 3 and 4 and opens the key element 7.

The inductor 7 limits the increase in current at the time of protection operation.

In the inverter (Fig. 1) in the time intervals ti-ta, t4-te (Fig. 2), the current reduced to the primary winding 2 flows through

base-emitter junctions of transistors 20 and 21. In low-voltage power converters, the value of this current may be greater than the maximum allowable base current.

In the inverter (Fig. 3), the discharge circuit of the capacitors 14 and 15 includes threshold elements 26 and 27, which consist, for example, of series-connected diodes. Voltage drops on elements 26 and 28

time intervals, t4-te through the resistors 28 and 29 are applied to the base-emitter transitions of the transistors 20 and 21, the selection of the voltage of the threshold elements 26 and 27 and the resistors 28 and 29 provide the nominal modes of the transistors 20 and 21

With the inverter load disconnected, the recharging of the capacitors 14 and 15 is carried out by the magnetizing current of the transformer 1 (Fig. 2m). If a serial transformer with a magnetizing current insufficient for recharging capacitors 14 and 15 is used, a choke 25 is connected parallel to the primary winding of the transformer 1 (Fig. 4).

In the proposed two-stroke inverter, the closure of additional transistors shunting the base-emitter junctions of the power transistors occurs at the time when the current of the switching of the switching capacitors ceases, which corresponds to the moment of the end of their recharging and decrease to zero voltage on the opening transistor. At the same time, there are no circuits measuring the voltage at the collector-emitter junction of power transistors and requiring careful selection of elements, which, compared with the known, increases the efficiency and reliability of the device.

Claims (4)

1. A push-pull inverter containing an output transformer, the primary winding of which is connected to the first input terminal of the inverter by tap from the middle point, and the extreme leads connected to the collectors of power transistors, the emitters of which are combined and connected to the second input terminal of the inverter, the first switching capacitor connected to the first output to the collector of the first power transistor, two additional transistors, each of which is connected to the base of the corresponding power transistor and shuntiro en the chain the first base-emitter resistor, and a control unit, the paraphase outputs of which are connected to the bases of the power transistors, characterized in that, in order to increase efficiency and reliability by reducing the dynamic power losses in the power transistors when they are turned on, a second switching capacitor connected to the collector of the second power transistor is inserted, the second output of each switch the capacitor is connected to the emitter of the corresponding additional transistor and through the corresponding input diode to the emitters of the power transistors with which the bases of the additional transistors. 2. The inverter according to claim 1, characterized in that said connection of the bases of the additional transistors with the emitters of the power transistors is performed directly. 3. Inverter pop. 1, characterized in that said connection of the bases of each of the additional transistors with the emitters of the power transistors is made through The introduced second resistor, and in addition to each diode, the introduced threshold element is switched on. 4. The inverter according to claim 1, characterized in that the input choke is connected parallel to the primary winding of the output transformer. t, 4 / s M) I / GC FIG. 2 0  I