Universal thyristor regulator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Universal thyristor regulator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / welding equipment

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The basic circuit (Fig. 1) was developed for a welding rectifier, which allows obtaining a high quality of the welding arc in the current range of 30-160 A when using stainless electrodes. Any transformer with a secondary winding voltage of 28 to 60 V and a current of up to 160 A can be used in the rectifier, incl. conventional transformers with a "hard" characteristic and not quite correctly calculated welding transformers, which, when welding, strongly "sit down" the supply network.

(click to enlarge)

Welding current can be smoothly adjusted by the resistor R5, brought to the front panel of the rectifier. The circuit limits the open circuit voltage of the rectifier to 30-40 V, which ensures safer work of the welder and allows the use of the output filter capacitor C6 with an operating voltage of 30 V.

The introduction of current feedback (the signal is taken from the current sensor R8) limits the short circuit current and stabilizes the welding current in case of voltage fluctuations in the network. This is especially important when working from a "weak" network, which often happens in rural areas and with long lead wires.

If some elements of the circuit are changed, it can be used to create control rectifiers for currents from 1 to 1000 A, for example, car starting chargers, powerful welding rectifiers.

The circuit uses the minimum number of the most affordable and cheapest components, the circuit setup is simple.

The circuit was developed taking into account traditional circuit solutions, taking into account the ease of installation of power elements and the requirements for circuit versatility.

The control bridge rectifier is made on the elements VS1, VS2, VD1, VD4. On the elements R16 R18, R25, VD12, VD13, VT3, a circuit for discharging the capacitor C5 of the sawtooth voltage generator (GPN) at the moment the mains voltage passes through 0 is assembled. signal GPN, and therefore, the opening angle of VS20 and VS24 depends on the voltage at the emitter VT14, which is determined by the signals from the current sensor R4, the output voltage limiting stage (R5, R1 - R2, C5, VD8, VD6, VT11) and the resistance of the resistor R15. R4 sets the initial offset based on VT9 and determines the amount of output current at which the voltage drop across the current sensor R11 is sufficient to open VT2.

When the output voltage rises above the threshold (determined by the position of the trimmer resistor R13), the current of the transistor VT2 through the resistor R6 also opens VT1, while the voltage at the VT5 emitter increases, the opening angle of the thyristors is automatically maintained so that the output current and output voltage do not exceed the set values. Cascade current generator 4 A (on R1, R2, VD16, VD17, VT6) generates the current necessary to open thyristors VS1 and VS2 and decoupling diodes VD7 and VD8. A 20 mA current generator (on R9, R26, VD4, VD5, VT7) and a parametric stabilizer on (R10, VD10) provide a stable voltage.

Capacitor C6 (output filter) together with inductor L1 creates the conditions for stable and "soft" ignition and burning of the welding arc.

The optimal output voltage of the transformer (at the maximum current that the rectifier should provide) is 28-35 V. Transformers with an output voltage of up to 60 V can also be used, but this may worsen the stability of the arc at low output currents. Inductor L1 can be made on any suitable core made of transformer steel with a cross section of 15-25 cm2 with a non-magnetic gap of 0,5 mm; the number of turns is 50-80, the wire cross-section is at least 10 mm2. Capacitor C6 is recruited from electrolytic capacitors with an operating voltage of at least 30 V: with a total capacity of at least 30000 microfarads. Diodes VD1, VD3, thyristors VS1 and VS2 can be used almost any, designed for a current of at least 160 A, by installing them on radiators. When using a transformer having two windings for a voltage of 28-35 V, they are connected in series, the middle point is connected to the connection point of the VD1 VD3 cathodes, and the VD1 and VD3 diodes themselves are excluded from the circuit.

Figure 2 shows the location of the elements, and Figure 3 shows the printed circuit board of the device.

As a current sensor R8, the author used a piece of D3 mm stainless wire folded four times and sandwiched between the terminals. The distance between the terminals is 55 mm. You can use a part of the welding cable as a current sensor, choosing a section of such a length that at the maximum output current the voltage drop across it is approximately 0,3 V. This condition must be observed when choosing other materials and designs for the sensor. Figure 4 and Figure 5 show simplified wiring diagrams for various current sensor designs.

Since the control electronic circuit does not use a separate power source, it is convenient to make the rectifier a separate construct that has two inputs for supplying alternating voltage from a transformer and two outputs for connecting a welding cable, a current regulator and an ammeter on the front panel. As an ammeter, you can use almost any pointer device that measures the voltage on the current sensor R8, if you turn it on through the appropriate damping resistance and calibrate the scale.

For adjustment, the output of the circuit is loaded with a resistance of 10 ohms, with a power of at least 100 W, the resistor R5 is set to the position of minimum resistance, the slider R13 is in the upper position. Turn on the rectifier and check the change in the output voltage when the R13 engine rotates within 24-36 V, if necessary, select R12.

Then the output of the circuit is short-circuited and, by rotating the R5 slider, the change in the output current is checked within 30-160 A (you can measure the current of the primary winding of the transformer by multiplying its value by the transformation ratio).

If, in the position of maximum resistance R5, the output current is higher (lower) than 160 A, the resistance of the sensor R8 is increased (decreased) accordingly, changing the distance between the terminals (the length of the cable section). The limits of output current regulation by resistor R5 are changed by selecting resistor R4. A 10 ohm load is connected, the output voltage is set to 13-30 V with resistor R36, after which the 10 ohm resistor is turned off and the operation of the rectifier is checked in the entire output current range, igniting the welding arc.

When using a circuit for designing devices for cars, transformers are used that provide an output voltage of 160-300 V (for cars with a 18-volt battery) and 20-12 V (with a 30 V battery) at currents of 35-24 A. The inductor L1 is excluded, the capacitance of the capacitor C6 can be reduced to 10000 microfarads, the resistance of the sensor R8 is selected to limit the output current at the level of 160-300 A. By selecting the resistor R12, the open circuit voltage is set to 14 and 28 V, respectively, for 12 (24 V) batteries.

You can apply the circuit in chargers by selecting the desired output current ranges and the voltage limit threshold. Inductor L1 and capacitor C6 are excluded, the current stabilizer in the power supply can be replaced with a resistor, power elements are selected with the appropriate power.

If you intend to use only electrodes for welding, designed to operate on direct and alternating current (for example, ANO-4; ANO-6), you can try to simplify the design by excluding L1, C6 and elements of the voltage limiting circuit.

The elements indicated in the diagram can be replaced with almost any similar ones, taking into account the fact that the elements VT2, VT4, VT6, VT7, VD2, VD6, VD14, VD18 must withstand the amplitude value of the AC voltage supplied to the input. The composite transistor VT6 can be replaced with transistors from the KT829, KT827 series or a pair from the KT817, KT819, KT805 and KT503, KT645 series, etc. When choosing the power elements of the circuit, it is necessary to take into account their allowable operating current and provide the necessary heat sink.

Author: V.N. Capon

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