SU1741243A1 - D c / d c converter - Google Patents

Abstract

Use: secondary power supply systems. The essence of the invention: the converter contains transistors (1-4), diodes (5,6,22,23), a transformer (7), a choke (9) and a control unit (10). Two capacitors (11,12) are introduced, two pairs of diodes

Description

The invention relates to electrical engineering and can be used in secondary power supply systems for converting a constant voltage.

A DC / DC converter is known, comprising four transistors connected in a bridge circuit and shunted by reverse diodes, in which the dynamic switching losses are reduced by the introduction of a damping throttle. The stored energy of the choke with an additional diode is dissipated at the resistor, the stored energy of the capacitor connected through the diode parallel to the transistor is dissipated at the resistor when the transistor is open.

Such a converter has low efficiency and utilization of transistors for current and voltage, especially when

high levels of power supply voltage.

The closest to the proposed invention is a converter made according to a bridge circuit including four transistors shunted by reverse diodes. The bridge diagonal includes a damping capacitor and a parallel-connected current sensor, a power transformer and a damping choke parallel to it, and an additional choke is connected in parallel with the transformer and the damping choke. In addition, the converter includes a control circuit connected to the current sensor.

The main disadvantage of the converter is the low reliability associated with the over-current of the transistors when turned on. This is due to the fact that

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At the initial start-up of transforming the body, when the damping capacitor is discharged, it is charged through open transistors with a current determined by the internal resistance of the transistors. At the same time, the current sensor together with the load is shunted by a damping capacitor. Protective fuics of current control circuit are excluded. In this connection, obtaining high load powers is problematic. The limitation of output power control at higher frequencies is associated with the presence of a large pause between control pulses, determined by the recharge process of the damping capacitor through an additional choke and a load circuit whose resistance increases significantly with low load currents.

The purpose of the invention is to increase the reliability and extend the range of output power adjustment by improving the conditions for turning off the transistors of the converter.

The goal is achieved by the fact that in a known DC / DC converter, there are four transistors and a transformer with a series-connected choke, connected in a bridge circuit, four diodes, shunt transistors in the opposite direction, a control unit, two capacitors, two pairs of diodes, two are inserted restrictive chokes, and two additional windings are introduced into the transformer, while the capacitors are connected through the input diodes of the first pair in parallel to two transistors connected by the same pin, parallel to capacitors included in the chain of series-connected additional winding of the transformer, a diode limiting choke and a second pair of transistors are connected to the base terminals of the control unit.

In this case, the control pulses applied to the first transistor of each shoulder have a duration longer than the control pulse duration of the second transistor.

Transferring the stored energy of the damping capacitors to the load when the first transistors open state ensures their subsequent shutdown at low currents in the absence of constant voltage, increases the efficiency and reliability of the converter, and reduces electromagnetic radiation due to the formation of sinusoidal currents during switching.

Fig. 1 shows a constant voltage converter; Fig. 2 shows time diagrams of currents and voltages at characteristic points that show the operation of one transducer arm. The converter contains transistors 1-4, connected by a bridge circuit, the first transistors 1.3 are shunted by reverse diodes 5.6, the output transformer 7, the primary winding 8 of which is connected to the output of the transistor bridge (diagonal AC) through a damping choke 9. The control of transistors 1.3 and 2.4 is carried out by them5 pulses of different duration from the control unit 10. Transistors 1.3 are open for a longer time with respect to the open state of transistors 2.4. Parallel to the transistors 1.3, the decoupling capacitors 11, 12 are turned on, through the second diodes 13, 14. Parallel to the capacitors 11, 12, their charging circuits are connected in series from the additional winding 15, 16 of the transformer 7, the limiting chokes 17, 18, and the separation diodes 19, 20. In this case, the split diodes 19, 20 are included according to the second diodes 13, 14, and the additional windings 15, 16 are antiphase. A source

0, the power supply 21 is connected to the input of a transistor bridge (a diagonal of a constant voltage).

The formation of control voltages is possible by a wide variety of devices: programmable timers, delay lines, etc.

In Figure 2, the following notation is accepted: IKL 1k4, UKI, UK4, 1) B1, 11b4 - voltage and current of transistors 1.4; Uia - voltage on

0 capacitor 12; he - current drossel 18; IG - current through diode 6; tu is the nominal transistor control pulse duration 2.4; m3 is the time by which the open state of transistors 1 and 3 is delayed for

5 provide charge capacitors 11,12.

The Converter operates as follows. In the initial state, the transistors 1,2,3,4 are closed, the damping capacitors 11,12 are discharged. On transistors

0 1.4 synchronizing pulses Uei; U64, through the damping choke 9 and the primary winding 8, the current rises with a speed determined by the inductance of the damping throttle 9, by the parameters of the transformer 7 in the whole charge-load circuit. Simultaneously, the damping capacitor 12 is charged through separation diode 20, an additional limiting choke 18 from the additional secondary winding 16

transformer 7 being a voltage source. The ratio of the turns of the primary winding 8 of the transformer 7 to the turns of each additional winding 15,16 is equal to two or more. During the open state of the transistor 4, the resonant charge of the damping capacitor 12 occurs to almost double the voltage on the additional winding 16. When the voltage on the capacitor 12 is equal to the voltage of the power source 21, the excess energy stored in the limiting choke 18 is transferred to load on the circuit: diodes 20,14 - transistor 1 - choke 9 - primary winding 8 of transformer 7 - additional winding 16 - additional choke 18.

In this case, a voltage approximately equal to Eupite is applied to the winding 8, the voltage in the windings 15, 16 is about 1/2 Epip The charge of another damping capacitor 11 does not occur, since the reverse voltage from the winding 15 is applied to the diode 19. the control signal from transistor 4, the latter begins to turn off. The damping capacitor 12 is discharged through the still open transistor 1 to choke 9 and transformer 7 and is a source of voltage for the load. The discharge rate of the capacitor 12 determines the rate of increase of the voltage on the transistor 4. Considering the turn-off time of the transistor 4, it is possible to provide switching off at the minimum voltage on the transistor and, therefore, at low dynamic power losses in the transistor. After the capacitor 12 is discharged to zero, the stored energy in the damping choke 9 and the transformer 7 is closed through the diode 6 and the open transistor 1 and transferred to the load. After the transfer of the power of the drossel 9 to the load, the current in it decreases almost to zero, the control signal is removed from the transistor 1. The latter turns off at a low current determined by the magnetizing current of the transformer. The closure of the magnetizing circuit during a pause occurs through the corresponding diode circuits: 6.22 and 5.23. Since the circuits 16,18,20,12 are separated by a diode 14, the processes in them are determined by the parameters of the charge circuit formed by these elements.

mi The windings 15 and 16 are sources of voltage at a specific time for resonant charging of capacitors 11, 12

In the proposed converter, the maximum voltage across the transistor during switching is guaranteed to be equal to the voltage of the power source.

When applying control signals to another pair of transistors 3.2, the converter operation process is similar to that described above. At the same time, a charge circuit consisting of diode 19, throttles 17, additional winding 15, damping capacitor 11, diode 13, recovery circuit of excess energy of throttles 17, diodes 19,13, transistor 3, transformer 7, choke 9, additional winding 15 of the transformer 7. Thus, due to the separation in time of the transistors of each arm of the bridge and the organization of the conditions for turning off the transistors at low currents and voltages, overloads of the transistors during switching are eliminated, the maximum voltage is fixed, transistors when switching, equal to the voltage of the power source, and ensures safe working conditions of the transistors both during operation and during initial startup

Claims (1)

Claims A DC / DC converter containing four transistors and a transformer with a series-connected choke, connected in a bridge circuit, four diodes, shunting transistors in the reverse direction, a control unit, characterized in that, in order to increase reliability by improving the conditions for turning off the transistors , two capacitors, two pairs of diodes, two restrictive chokes, are introduced, and two additional windings are introduced into the transformer, and the capacitors through the diodes introduced are first two pairs of transistors are connected in parallel, connected homonymous pin parallel to capacitors included in the chain of series-connected additional winding transformer tion, a bounded choke and diode vvedenno1 second pair of transistors are connected to the base you Waters control unit.