RU1810999C - Transistorized switch - Google Patents

Abstract

The invention relates to electrical engineering and can be used in switching power supplies of electronic devices. The transistor switch contains 1 power transistor (1), 1 control signal driver (4), 1 bias voltage source (5), 1 diode (6), 1 additional transistor (7), 1 resistor (8). 2 ill.

Description

N

fe

Fi8.1

00

about y about y

The invention relates to electrical engineering and can be used in pulsed secondary power sources of electronic devices.

The aim of the invention is to increase the efficiency of the transistor switch by reducing the static losses in the open state to a level close to the saturated mode while maintaining the speed characteristic of the unsaturated mode.

In FIG. 1 shows a diagram of the proposed transistor switch; in FIG. 2 - diagrams explaining the operation of the circuit.

In FIG. 1 and the following notation is adopted in the text: 1 - power transistor, 2 - load, 3 - power supply, 4 - control signal driver, 5 - bias voltage source, 6 - diode, 7 - additional transistor, 8, 9 - resistors . The device comprises a power transistor 1, the collector-emitter junction of which is connected in series with the load 2 and a power source 3, a control signal shaper 4, the first output of which is connected to the emitter of the power transistor 1, and the second terminal is connected in series with the bias voltage source 5 to the power base transistor 1, diode 6, the cathode of which is connected to the collector of power transistor 1, an additional transistor 7, an emitter connected to the anode of diode 6, and a collector to the first (positive) output of the source bias voltage 5, resistor 8, shunt base-collector junction of additional transistor 7. The base-emitter junction of power transistor 1 is shunted by resistor 9.

The device operates as follows.

Suppose first that the resistance of resistor 8 is zero. Obviously, in this case, the additional transistor 7 is a diode, and the power transistor 1 is in an unsaturated mode. If the resistance of resistor 88 is chosen in such a way as to bring an additional transistor 7 to the initial portion of the active region (Fig. 2 a), then due to the insignificant dynamic resistance of the output circuit of transistor 7, the effect of the redistribution of the currents of the base of transistor 1 and the diode is preserved (see Fig. 2 a). In this case, the voltage at the open transistor 1 is higher than in the saturated mode, but significantly lower than with the shorted collector-emitter junction of the transistor 7 (see Fig. 2 b). If the resistance of the resistor 8 is chosen so that the operating point of the transistor 7 has shifted

to the horizontal region (Fig. 2a), the current redistribution effect disappears, but the current continues to flow through the base-collector junction of the transistor 1. With increasing collector current of the transistor 1, its collector-emitter voltage also changes, this leads to a change in voltage at its base, and, accordingly, to a change in voltage at a positive

output of the bias voltage source. In the absence of transistor 7 due to the low dynamic resistance of diode .6, this would lead to a substantial redistribution of currents in the base-emitter and bazacollector circuits and a significant increase in the collector-emitter voltage. When there is a transistor 7 chip with a large output dynamic resistance, the current in the base-collector circuit of transistor 1 is little

from voltage changes at its collector-emitter and collector-base junctions. Therefore, the collector-emitter voltage does not practically differ from the saturated mode. Despite the lack of linear

dependences between the collector current of transistor 1 and diode 6, the presence of current in the base-collector circuit leads to a sharp decrease in excess charge in the collector region, which leads to practical

eliminate the delay when turning off the transistor. The practice of using high-power, especially high-voltage transistors has shown that any circuitry solutions in the base-emitter circuit for forced locking of the transistor do not guarantee that there is no delay in the front of the current drop. The control on both transitions ensures the edge duration is not worse than that of an unsaturated key, while maintaining

low static loss in the open state. It is significant that in this case the difference in the frequency parameters of various transistor instances disappears. Samples with a maximum resorption time and a maximum falling edge are not inferior to the best specimens with an unsaturated mode of operation.

The proposed technical solution was tested on a prototype of a voltage converter with an output power of 200 W. KT840A transistors were tested as power transistors. KT854A, KT839A. The KT646A transistor was used as an additional transistor, but other types of transistors were also tested (KT805A and others).

When using an additional transistor, the voltage on the power transistor in the open state increases

by 0.1 ... 0.2 V., Front of current drop across all samples 0.1 ... 0.2 μs.

In connection with that. that the auxiliary transistor is in active mode, the question arises of the stability of its characteristics. It should be noted that the transistor is under a voltage of about 1.5 V, i.e., in the initial characteristic region. It is known that, on the verge of an open state, transistors lose the spread of the parameter h 21 Oe, which is specified at a higher collector voltage. The batch of KT646A transistors in an amount of 20 pcs was experimentally tested. Verification showed that despite the spread in the parameters of transistors, a positive effect, that is, an increase in speed with a minimum of static losses, is always present.

and

Jk

Redistribution Area / Hike

b%, 5

Unsaturated key / s / shorted nom (short circuit) protection - torus 7

Claims (1)

SUMMARY OF THE INVENTION A transistor switch comprising a power transistor whose collector-emitter junction is connected in series with a power supply and a load, a control signal shaper whose first output is connected to an emitter of a power transistor and the second terminal is connected in series with a bias voltage source to the base of the power transistor. a diode whose cathode is connected to a collector of a power transistor, characterized in that, in order to increase the efficiency, an additional transistor is introduced, the emitter of which is underneath connected to the anode of the diode, a collector connected to the first output of the bias voltage source, and the base through a resistor connected to the collector of an additional transistor. One LAN / pi s / lad # 0go / while corrector is base 8 t, MKC Ftsg. 1 Time to undress / ladies