SU428503A1 - RELAXATION IMPULSE FORMER - Google Patents

Description

one

The invention relates to educational technology, in particular, to an amplifier-driver of output pulses of thyristor transducer control systems, and can be used in control systems of TCOTpiHbiMH 1InvertOr frame and AC-to-DC rectifiers, in frequency converters, etc.

A relaxation pulse former for starting thyristors is known, which contains an avalanche transistor, a charging resistor, a storage capacitor, a pulse transformer, and a load element.

A disadvantage of the known formers is that the output pulses have an overestimated power, a considerable power of the driver control is required, there is no possibility to change the duration of a double amplitude ejection, the pulse has a gentle falling front.

With the aim of forming a two-stage pulse, increasing a1Plipses of ipulses and decreasing the front duration in the proposed pulse shaper, the primary winding of the pulse transformer, the beginning of which through the storage capacitor is connected to the load cell, is connected to the avalanche transistor collector circuit. and the secondary winding is connected to the base via a parallel RC circuit connected in series with the second diode.

FIG. 1 shows the basic electronic circuit of the proposed driver; in fig. 2 - the shape of the output pulse of the imager; in fig. 3 - load diagram of an avalanche transistor.

An avalanche transistor. T is used as an active element of the driver. The diode D of the base B | Klyuchen chain provides a positive bias at the base of the transistor T connected via a resistor Ri to the power source // "i-

in the standby mode, the driving pulses are supplied to the base circuit of the transistor T through a capacitor C and a diode D2. The power source Yap2 and the resistor RZ serve to provide the locked state of diode D2 in the absence of an input signal. The avalanche transistor collector through the resistor R, the transformer Tp is connected to the power supply Yapz- The feedback circuit is formed by the secondary winding W of the transformer Tp, the resistor RA,

capacitor Sd, diode Dz- Parallel

primary winding Wz transformer Tr

A forward-facing diode D4 is connected in the forward direction. Discharge capacitor Cp and

load element ZH is connected parallel to the avalanche transistor T.

Shaper works in the following way.

The circuit works both in auto-oscillator mode and in standby modes, depending on the choice of the initial operating point, respectively: in areas with negative resistance, or with a large positive resistance of the current-voltage characteristic of the avalanche transistor.

Self-oscillating mode. The capacitor Cp is charged before the voltage: At the maximum of the current-voltage characteristics of the avalanche transistor Tt / p (Fig. 3). At time point to (FIG. 2), the transistor G turns on. When the transistor T is avalanched in its collector circuit and, consequently, a current appears in the primary winding Wz of the transformer Tp. In this case, the voltage Ug (t) is applied to the primary winding, and the voltage drop iHa of the transistor T decreases accordingly. The mutual phasing of the windings of the transformer Tr, shown in FIG. 1 is such that an avalanche-like increase in the collector and base currents develops in the circuit. The voltage on the primary winding of the transformer is stabilized at the level of the voltage drop on the directly connected diode D. The voltage drop on the transistor T decreases and on the load increases. At time fi (Fig. 2), the transistor T enters the saturation state. The voltage across the load cell ZH is Uiii. The working point of the transistor in the time interval to-ii (φ, ig. 3) moves along the dynamic load direct fli from point O to point /. (The position of the load voltage is determined mainly by the resistance of the load, as well as the equivalent resistance of the diode D4 and the transformer Tr, by the resistor RZ in the collector circuit of transistor G). Beginning from the moment fi in the scheme, the first pulse pulse pulse is formed. At the same time several processes occur:

the current flowing through the feedback circuit through the capacitor Cz, the diode Dz, the resistor 4 charges the capacitor C2. The potential difference across the capacitor € 2 increases with time, and since it is subtracted from the direct voltage of the secondary winding of the transformer, the Oto / pa Mg - (mz, mi is the number of turns of the secondary Wj

the primary and primary windings of the transformer Tp), then the base current of the unlocking of the booster decreases in time;

on the other hand, the blocking current / bz from the source Isch;

the collector current of the transistor is reduced by iBo time B1 and the discharge of the capacitor Cp through the saturated transistor G to the load element ZH.

The transistor goes out of saturation when the base current

.-

1b - From - 1b „p

where / ККР is the critical value of the collector current at which the transistor T begins to go out of saturation (point a in Fig. 3);

P is the gain of the transistor T In the circuit with a common emitter.

At time 2, the formation of the first pulse pulse is completed, and the trailing edge of the first pulse is formed. The load voltage is UH.

The working point of the transistor T goes over

from point a to point b according to the dynamic loading straight line H2 (Fig. 3). Positive feedback when the transition of the transistor from saturated to active mode is absent. This is both guaranteed by the choice of shunt

0 diode D with a steep branch of the current-voltage characteristic. Therefore, although the current through the diode D decreases, the voltage across it varies slightly, and therefore, the voltage on the secondary voltage of the primary winding W varies only slightly. The capacitor € 2 in the feedback circuit is still charged to

t, 1 o

same level Ug. For example, Iv 2

The effect on load ZH at time t is equal to Utts. In the time interval, the transistor operates in the avalanche mode (in Fig. 3 points b and b). In this time interval, the base current changes its direction, i.e., it is opposite to the base current direction during normal operation. The dynamic load line changes its position during the discharge of the capacitor Cp to the load element ZH. When the load voltage is in its position, the Zz transistor T turns off and enters a cut-off state. At time f4, the formation of the apex of the second pulse is completed. The load voltage narrow equals UH. The transistor T is turned off and the collector circuit current iB decreases.

Capacitor C2 is discharged through a resistor, the diode Dz is then locked by the positive iHDM voltage of the capacitor Cz. The feedback circuit is isolated from the base circuit during the charging time of the capacitor. The power supply source of the IP creates the conditions for switching on the transistor T at a given voltage of the Ipz power source at level 0. As soon as the voltage on the capacitor Cp to 5 is set to 1P | pJ | Egene U trans / source, and the process is repeated.

Standby mode is provided by locking the transistor T with a high voltage power source.

 The resistor can be switched to ground, as shown in FIG. 1 dotted line. The scheme works in a similar way.

The device also works when the transformer Tr is switched on in the e-mitter circuit. Work 5 of the scheme is similar to the one reviewed.

Ztt resistor MLT - 0.5 100 ohm C capacitor 0.5 microfarads.

The dependence of the parameters of the pulse on the nabl. I load element from; the load resistance values of capacitors C2, Cp are given in the tables.

From the tables it can be seen that the duration of the first impulse is /. And it does not depend on the magnitude of the capacitor C capacitance and the load resistance, the duration of the second imvulsum tviz depends on the resistance and the load, however

10 change can be compensated by changing the capacitor capacitance Cp.

abl 2

Subject invention

15

A relaxation shaper for starting thyristors containing an avalanche transistor, a charging resistor, a storage capacitor, a pulse transformer, and a load element differing in that, in order to form a two-step pulse, to increase the amplitude of the pulses and to reduce the front duration, the avalanche transistor circuit is connected first shunted

25 by a diode connected in the forward direction, the primary winding of the pulse transformer, the beginning of which is connected via a storage capacitor to the load element, and the secondary winding is connected to the base

30 through a parallel RC circuit connected in series with the second diode.

i / a 5

Un

Fig 3