RU2635364C2 - Push-pull dc/dc converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: push-pull DC/DC converter contains a main choke with a power winding; a transformer with the primary and the secondary windings; bridge transistorized (key) current switch of the primary transformer winding; the secondary winding current rectifier; an output filter capacitor; the first and the second diodes; an additional choke; an additional capacitor. In the push-pull DC/DC converter, an additional capacitor and the first diode are connected in series between the second and the first outleads of the power coil of the main choke; the connection of the common point of the additional capacitor and the first diode with the second power line is realized through a series circuit in form of the second diode and an additional choke winding; gate conductivities of the first and the second diodes match. In another embodiment of the circuit, the second winding is connected to the main choke magnetically coupled to its power winding and the second winding of the main choke is included in the mentioned series circuit and is connected in series with the winding of the additional choke.

EFFECT: decrease in the switching losses energy in the transistors of the current switch of the transformer primary winding in case of locking that increases reliability of their operation and contributes to the increase in energy efficiency of the energy conversion.

2 cl, 2 dwg

Description

The proposed device relates to power conversion technology and is a device that implements an energy-efficient pulsed method of regulating the power transmitted to the load.

A push-pull DC / DC converter, considered as a prototype [1, p. 87, Fig. 5.13], contains a main inductor with a power winding, a transformer with primary and secondary windings, a bridge transistor (key) switch for the current of the primary winding of the transformer, a rectifier of the secondary winding and a capacitor of the output filter, as well as the first and second diodes, an additional inductor and an additional capacitor.

The first output of the power winding of the main inductor is connected to the first power bus, and between the second output of this winding and the second power bus the input circuit of the bridge transistor switch is connected, to the output circuit of which the primary winding of the transformer is connected, and its secondary winding through the rectifier of the current of this winding is connected to the output condenser filter.

The operation of the circuit occurs in two steps.

In the first part of each of the cycles, all transistors of the primary current switch are closed. In this case, the primary winding is shorted through the output circuits of these transistors, and the supply voltage is applied to the power winding of the main inductor, due to which energy is accumulated in it.

In the second part of each cycle, two power transistors of the bridge switch are opened, and through two other transistors the primary winding of the transformer is connected between the end of the power winding of the main inductor and the second power bus. At the same time, the first pair of bridge transistors located in its opposite shoulders is working in a state of high conductivity for the first clock cycle, and the beginning of the transformer primary winding is connected to the end of the main winding of the main inductor, and the end of the primary winding is connected to the second power bus. In the second cycle, in a state of high conductivity, another pair of bridge transistors operating in its opposite shoulders is working, and the end of the primary winding of the transformer is connected to the end of the power winding of the main inductor, and the beginning of the primary winding is connected to the second power bus.

The presence of the power winding of the inductor, which is connected in series with the primary winding of the transformer through the transistors of the current switch of this winding, contributes to a rapid increase in voltage on the primary winding and on the transistor during its shutdown. As a result, significant switching losses occur.

In real-world transformers, there is leakage inductance. It prevents the instantaneous transfer of power by the transformer to its secondary winding, due to which short voltage surges occur on the primary winding. If the voltage amplitude at the power transistor, which has switched to a non-conducting state, reaches the value of the breakdown voltage, then additional transistor energy stored in the transformer inductance will be released in this transistor.

High switching losses in transistors reduce the reliability of their operation and, accordingly, the reliability of the device as a whole, as well as reduce the efficiency of electric energy conversion.

The aim of the proposal contained in this application is to increase the energy efficiency and reliability of the device.

The proposed device is presented in FIG. one.

The essential features of the proposed device, coinciding with similar features of the prototype, are that:

- A push-pull DC / DC converter contains a main inductor with a power winding, a transformer with primary and secondary windings, a bridge transistor (key) switch for the primary current of the transformer, a rectifier for the secondary winding, an output filter capacitor, the first and second diodes, an additional inductor and an additional capacitor.

- The first output of the power winding of the main inductor is connected to the first power bus, and between the second output of this winding and the second power bus the input circuit of the bridge transistor switch is connected, to the output circuit of which the primary winding of the transformer is connected.

- The secondary winding of the transformer through the rectifier of the current of this winding is connected to the capacitor of the output filter.

The salient features of the proposed device are that:

- Between the second and first terminals of the power winding of the main inductor, an additional capacitor and a first diode, respectively, are connected, which are connected in series.

- The common point of the additional capacitor and the first diode is connected to the second power bus through a serial circuit in the form of a second diode and an additional inductor winding.

- The gate conductivity of the first and second diodes connected in series coincide.

In FIG. 2 shows a variant of the circuit of the proposed device, which differs from the variant of the circuit in FIG. 1 by the fact that a second winding is magnetically coupled magnetically to its power winding, and this second winding of the main inductor is included in said series circuit and connected in series with the winding of the additional inductor.

In the device of FIG. 1, between the first power bus 1 and the second power bus 2, an energy source 3 is included as a voltage source. The first output terminal (beginning) of the power winding 4 of the main inductor is connected to the power bus 1.

The primary winding 5 of the transformer 6 is connected between the second terminal of the power winding 4 of the main inductor and the second power bus 2 through the bridge transistor switch 7 of the current of the primary winding 5 of the transformer 6. The input circuit of the bridge is connected between the second terminal of the power winding 4 of the main inductor and the second power bus 2, and the primary winding 5 of the transformer 6 is connected to the output circuit of the transistor bridge.

The secondary winding 8 of the transformer 6 through the rectifier 9 of the current of this winding is connected to the capacitor 10 of the output filter. Parallel to this capacitor, a load of 11 is connected.

Between the second and first terminals of the power winding 4 of the main inductor, an additional capacitor 12 and a first diode 13 are included, respectively, which are connected in series.

The common point of the additional capacitor 12 and the first diode 13 is connected to the second power bus 2 through a serial circuit in the form of a second diode 14 and an additional inductor winding 15, and the gate conductances of the first and second diodes are connected in series.

In the circuit of FIG. 2, the main inductor is supplemented by a second winding 16, which is magnetically connected to the power winding 4 of this inductor. The second winding 16 of the main inductor is introduced into the aforementioned series circuit and connected in series with the winding 15 of the additional inductor.

The objectives of the technical solution proposed in this application are achieved through the interaction of significant known and distinctive features of the device.

In the stationary mode of operation of a push-pull DC / DC converter, made according to the circuit in FIG. 1, in the first part of each cycle in a state of high conductivity are all the transistors of the bridge circuit. In this case, the primary winding 5 of the transformer 6 is shorted, a supply voltage is applied to the power winding 4 of the main inductor, and energy is accumulated in it.

In the second part of the first cycle, two transistors are locked, located in two opposite branches of the transistor bridge (for example, the second and third transistors), and the other two (first and fourth) continue to operate in a state of high conductivity. In this case, through the output circuits of the first and fourth transistors, the primary winding 5 of the transformer 6 is connected to the beginning of the second output of the power winding 4 of the main inductor, and the end to the second bus 2.

In the second part of the second cycle, two transistors are locked, located in two other opposite branches of the transistor bridge (the first and fourth transistors), and the remaining (second and third) continue to work in a state of high conductivity. In this case, through the output circuits of the second and third transistors, the primary winding 5 of the transformer 6 is connected end to the second output of the power winding 4 of the main inductor, and the beginning to the second bus 2.

Thus, alternating voltage occurs on the primary winding 5 of the transformer 6. Its value exceeds the supply voltage by the value of the voltage occurring on the winding 4 of the main inductor in the interval of output from it previously accumulated energy.

By the beginning of each new cycle of the circuit, the additional capacitor 12 is charged to a level that is equal to the difference between the potential arising on the second output of the power winding 4 of the main inductor and the supply voltage. In this case, the polarity of the voltage across the capacitor 12: plus - at the terminal that is connected to the second terminal of the power winding 4, and minus - at the terminal that is connected to the first diode 13.

At the beginning of each cycle, a charged capacitor 12 is discharged through the output circuits of the bridge power transistors, the second diode 14 and the winding 15 of the additional inductor. The discharge process is oscillatory in nature, and at the end of this process, the capacitor 12 is again charged almost to the same level that took place on the interval of the locked state of the two transistors of the bridge located in its opposite branches. However, now the voltage across the capacitor 12 has a reverse polarity: minus at the terminal that is connected to the second terminal of the power winding 4, and plus at the terminal that is connected to the first diode 13.

If the voltage of the opposite polarity on the capacitor 12 is less than the supply voltage, then at the beginning of the second part of each cycle, when the transistors of the bridge located in its opposite branches are locked, the voltage on them increases stepwise. This increase occurs to a level that is equal to the difference between the supply voltage and the reverse polarity voltage on the capacitor 12. Then, the voltage on the bridge transistors, which have switched to the locked state, begins to increase smoothly due to the process of overcharging the capacitor 12 with the current of the power winding 4 of the main inductor.

In the original circuit, when the transistor is locked, the voltage on it rises stepwise to a level equal to the sum of the supply voltage and the voltage that occurs on the power winding 4 of the main inductor in the interval of output of stored energy from it.

Thus, the application of the described technical solution allows to reduce the initial voltage jump on the transistors of the bridge, which went into a locked state, and then create the condition for a smooth increase in this voltage. This reduces the level of switching energy losses in the transistors of the bridge when they are locked and increases the reliability of their work. In general, this helps to increase the reliability of the DC / DC converter and increase the energy efficiency of the energy conversion process.

In the circuit of FIG. 2, an additional secondary winding 16 of the transformer 6 provides the conditions for the final voltage value on the capacitor 12 to be set at the level of the supply voltage in the oscillatory process of recharging the capacitor 12 in the high-conductivity interval of all transistors of the switch 7 made according to the bridge circuit. In this case, the first diode 13 is unlocked, and the excess energy stored in the additional inductor is returned to the power source.

If you set the transformation coefficient of the additional winding 16 equal to half, then by the time the transistors of the current switch 7 are locked according to the bridge circuit, the capacitor 12 will be charged to the supply voltage level, and this will take place regardless of the value of the converter output voltage. In this case, when the power transistors of the switch 7 are locked, there will be no initial voltage jump on them, and the voltage will gradually increase from almost zero level, which ensures a decrease in switching energy losses in the transistors during their shutdown.

Information sources

1. Meleshin V.I., Ovchinnikov D.A. Management of transistor power converters. - M .: Technosphere, 2011 .-- 576 p.

Claims (2)

1. A push-pull DC / DC converter containing a main inductor with a power winding, a transformer with primary and secondary windings, a bridge transistor (key) switch, a rectifier of the secondary winding and a capacitor of the output filter, as well as the first and second diodes, an additional inductor and an additional capacitor, the first output of the power winding of the main inductor is connected to the first power bus, and between the second output of this winding and the second power bus the input circuit of the bridge transistor switch is connected, to the output the ohmic circuit of which the primary winding of the transformer is connected, and its secondary winding through the rectifier of the current of this winding is connected to the output capacitor filter, characterized in that between the second and first terminals of the power winding of the main inductor are connected an additional capacitor and the first diode, respectively, which are connected in series, and their the common point is connected to the second power bus through a serial circuit in the form of a second diode and an additional inductor winding, and the valve conductivities coincide first and second diodes connected in series. 2. The device according to claim 1, characterized in that the second winding is connected magnetically to its power winding and the second winding of the main inductor is included in the series circuit and connected in series with the winding of the additional inductor.

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