RU98651U1 - KEY POWER AMPLIFIER - Google Patents

Abstract

A key power amplifier is proposed for bridge semiconductor converters based on composite transistors composed of power and auxiliary bipolar transistors controlled from the transformer windings, the primary winding of which is connected via a bridge circuit between the preliminary and output amplification stages, and a bias source is connected between the collectors of the power and auxiliary transistors, and between the base of the auxiliary transistor and the collector of the power transistor two are connected in series with single diodes, and the said transformer is equipped with two additional windings, each of which is connected between the collectors of the power and auxiliary transistors.

The proposed amplifier dramatically simplifies the circuit with an adjustable saturation depth and reduces the value of "through" currents when switching. A variant of use in a single-phase converter is presented.

Description

The utility model relates to electrical engineering and can be used in the construction of semiconductor DC-to-AC converters, the main device of which is a key power amplifier, most of which are built according to bridge circuits. The main element of the bridge converter is a serial pair of power keys-rack. The most widely used are solid-state composite power amplifiers from field-effect and bipolar transistors, which are often called IGBT keys.

The disadvantage of these key amplifiers is that the voltage drop on such a key reaches 2-3 volts. With a supply voltage of about 500 V, this does not greatly reduce the efficiency, but with a supply of 27 V or even less than 12 V, this turns out to be, in most cases, unacceptable.

The use of power field effect transistors requires a sharp increase in the area of the crystal, since they are approximately 5 times smaller than bipolar transistors in the required area of the crystal for the same current, for a given voltage drop across the key.

In this case, they turn to bipolar composite transistors with a special bias source.

Known key power amplifier [1] with a bias source based on the rectifier, the very presence of which is associated with additional losses.

Known key amplifier [2] in which the bias source is made without the use of a rectifier. Loss reduction is achieved in it due to the complexity of the circuit. One power transistor requires two auxiliary transistors and four windings.

In addition, in key power amplifiers operating in a bridge circuit, there is a problem of “through” currents in the rack.

A key power amplifier is proposed that dramatically simplifies the circuit and limits the “through currents” in the power rack.

This is achieved by the fact that a key power amplifier for bridge semiconductor converters based on composite transistors composed of power and auxiliary bipolar transistors controlled from the transformer windings, the primary winding of which is connected via a bridge circuit between the preliminary and output amplification stages, between the collectors of the power and auxiliary transistors the bias source is turned on, and between the base of the auxiliary transistor and the collector of the power transistor two last sequences coupled feedback diode, and said transformer has two additional windings, each of which is connected between the collectors of the power and auxiliary transistors.

The figure 1 presents a diagram of the proposed key power amplifier in the option of using it in a single-phase converter of constant voltage to sinusoidal alternating voltage.

Forms of currents and voltages in the circuit are presented in figure 2.

The structure of the scheme includes:

one; 2- power switches from a bipolar transistor and a shunt diode;

3; 4 - auxiliary bipolar transistors ;;

5; 6 - transistors preliminary cascade of effort;

7; 8 - feedback diodes;

Tp1 - control transformer;

W ₁ - primary winding, W ₂ W ₃ - windings;

Lf - filter inductance;

Zн - load.

The key amplifier in the output stage of the converter operates as follows.

When you turn on the transistor 6 at the beginning (indicated by dots) of the windings of the transformer Tp1, positive potentials arise, which ensure the base current flows through the transistor 3 and the power semiconductor switch 1.

The bipolar power transistor of the key 1 goes into the saturation region, on its base there is a positive potential relative to the collector, which is summed with the voltage of the base-emitter of the transistor 3, and current begins to flow through the control diodes 7, which reduces the base current of the transistor 3, transferring it to the boundary region with saturation area. As a result, due to the action of the bias voltage on the additional winding W ₅ and regulation of the base current of the transistor 3, the power transistor of the switch 1 goes into the saturation region, minimizing the direct voltage drop between collector and emitter.

When you turn off the transistor 6, due to the reaction of the inductance of the winding W ₁ , the polarity on the windings changes, but while the power switch 1 is in the region of resorption of excess media, it closes the winding W ₁ through the key 5.

As a result, the voltage across the winding W2 is insufficient to turn on the power switch 2, and only as the power switch 1 passes through the active region to the cut-off region, the base current of the transistor 4 and the power transistor of the switch 2 increases, which transfers it to an adjustable saturation region. This dramatically reduces emissions of "through" currents during switching, increases reliability and efficiency

Subsequently, the processes are repeated with the switching of power switches 1 and 2 in turn.

When controlling the transistors of the preliminary control stage with high-frequency modulation of the main frequency, due to the action of the filter Lf, a sinusoidal current and voltage are generated at the load Zн, as shown in figure 2. In practice, the voltage drop across the power switches does not exceed 0.2 ÷ 0.3 Volts, and for each power switch, only one auxiliary transistor and one winding are required.

Sources:

1. (19) SU ₍₁₁₎ 1427530 A1 dated 09/30/1988 Bull. No. 36 Н02М 7/538

2. (19) RU ₍₁₁₎ 86366 U1 dated 08/27/2009 Bull. Number 24

Claims (1)

A key power amplifier for bridge semiconductor converters based on composite transistors composed of power and auxiliary bipolar transistors controlled from the transformer windings, the primary winding of which is connected in a bridge circuit between the preliminary and output amplification stages, and a bias source is connected between the collectors of the power and auxiliary transistors, and between the base of the auxiliary transistor and the collector of the power transistor, two series-connected diode, characterized in that the said transformer is equipped with two additional windings, each of which is connected between the collectors of the power and auxiliary transistors.