Control unit for semi-automatic welding with thyristor regulator. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electric welding. Control unit for semi-automatic welding with thyristor regulator. Encyclopedia of radio electronics and electrical engineering

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Consider the scheme of a typical thyristor phase control unit (BFT), which is used to adjust the welding voltage, as well as to adjust the welding wire feed speed. On fig. 18.19, and the BFUT circuit is shown on a unijunction transistor VT3.

Rice. 18.19. Schematic diagram of a typical thyristor phase control unit (click to enlarge): a - on a unijunction transistor; b - on the analogue of a unijunction transistor

The unit is powered by a rectified, but not smoothed voltage of 24 V, which is applied between the 1-2 V terminals of the BFIU. With the help of a parametric stabilizer R6, VD3, trapezoidal pulses with an amplitude of 12 V are formed from this rectified voltage. These pulses are used to power and synchronize with the network of a relaxation generator assembled on elements R4, R5, R7, R8, C1, VT3.

At the end of each half-cycle of the network, due to a pause in the synchronizing trapezoidal voltage, the capacitor C1 is discharged through the transition e-b1 VT3. By changing the value of the resistor R4, it is possible to change the charging time of the capacitor C1, and, consequently, the delay (phase shift) in the formation of the generator output pulse relative to the clock voltage.

After the voltage on the capacitor C1 reaches the threshold of the transistor VT3, the transistor will open. The capacitor is discharged in the circuit: C1, transition e-b1 of the transistor VT3, R7, R8 and transition b-e of the transistor VT2, C1.

Transistor VT2 opens and, in turn, opens transistor VT1. From pin 2 BFUT through an open transistor VT1, resistor R1 and diodes VD1, VD2, the control voltage will go to the control electrodes of the thyristors of the controlled rectifier.

Since the phase of the synchronizing voltage and the voltage supplied to the controlled rectifier are the same, then in this way its output voltage is adjusted.

If the unijunction transistor is not at hand, then it can be replaced by an analog assembled on two conventional bipolar transistors VT3, VT4, which have different conductivity. The scheme of such an option is shown in Fig. 18.19. b.

Author: Koryakin-Chernyak S.L.

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Comments on the article:

Victor
Misprint: on both examples of the circuit, kt502 is direct conduction, not reverse, although the circuit requires a transistor with reverse conduction, I installed kt315 and it works.

Sergei
If it were possible also printed circuit boards.

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