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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Powerful controlled rectifier on thyristors, 220 / 0,5-15 volts 6 amperes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters A controlled rectifier on thyristors - elements with a high power gain, allows you to get high currents in the load with little power spent in the thyristor control circuit. The first two figures show variants of thyristor-based rectifiers that provide a maximum current in the load up to 6 A with a voltage adjustment limit from 0 to 15 V (Fig. 1) and from 0,5 to 15 V (Fig. 2).
During one half-cycle, a positive voltage relative to the cathode is applied to the anode of the thyristor. Until a positive signal of a certain amplitude is applied to the control electrode from the trigger circuit, the thyristor does not pass current in the forward direction. Through some arbitrary delay angle a, a positive trigger signal is applied between the voltages on the control electrode and the cathode, causing current to flow through the thyristor and, accordingly, through the load. When the polarity of the voltage on the anode of the thyristor is reversed, the latter closes regardless of the magnitude of the control voltage, while the other arm of the circuit begins to work similarly to that considered earlier. By adjusting the turn-on delay angle a with respect to the applied voltage, it is possible to change the phase ratio of the beginning of the current flow and the applied voltage and adjust the average value of the rectified load current (voltage) from maximum (a = 0) to zero (a = Pi). The turn-on delay angle of thyristors D1 and D4 is changed by potentiometer R1. Diodes D2, D3 protect the value of control (start) from negative voltage at a time when the voltage at the anodes of the thyristors is negative. To obtain wide adjustment limits a (0 = Pi), RC circuits are used. In the rectifier (Fig. 2), the thyristor and the trigger circuit operate both in positive and negative half-cycles, the capacitor discharge time is reduced, which leads to a decrease in the range of angle a and, accordingly, to a decrease in the voltage regulation limits on the load. To eliminate this phenomenon, diode D3 is included.
Thyristors for the rectifier (Fig. 1) it is desirable to choose with a close resistance value of the control electrode - cathode section. If it is not possible to select the same thyristors, then the circuit can be balanced using additional resistance. To do this, turn on the equivalent load and change the resistance value of the potentiometer R1 to set the maximum current. Turning off the thyristor control circuits one by one, the current of each rectifier arm is measured. Variable resistance of 10 com. connected in parallel to the control electrode to the cathode of the thyristor through which a larger current flows. By changing the value of this resistance, the same current readings are achieved. Given the spread of thyristor parameters, it is necessary to correct the resistances of resistors R1 and R2. Initially, R1 is taken slightly larger than calculated, and R2 is determined as the residual resistance of the potentiometer R1, provided that its change does not increase the load current. The maximum value of R1 is limited by the resistance at which the load current is zero. Structurally, thyristors must be placed on radiators with an area of 50 sq.cm (Fig. 1), 250 sq.cm - (Fig. 2). In all variants, a transformer assembled on a conventional USh35x55 core was used. For winding, a wire of the PEV brand was taken. The primary winding contains 550 turns, the wire diameter is 0,55 mm. Secondary winding data: for the option in Fig. 1 - the number of turns is 2x60 with a PEL wire with a diameter of 1,35 mm; for the option in Fig. 2 - the number of turns is 2x64 with a PEL wire with a diameter of 1,35 mm.
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