When the grid voltage is below 220V, the normally closed contact of J1 allows the transformer B to operate in a step-up mode. The output voltage remains under 220V, and J2 connects the 5th pin of the transformer. However, when the grid voltage exceeds 220V, J2 switches to the 4th pin of the transformer.
When the grid voltage goes above 220V, resistor R1 takes a sample, and J1 is activated to connect the transformer’s 5th pin, enabling a step-down function. If the output voltage exceeds the set value, R4 samples the voltage and triggers J2 to close its normally open contact, connecting the 4th pin of the transformer.
Component selection is crucial for the regulator's performance. The power handling capability mainly depends on the core cross-section and the diameter of the enameled wire used in the transformer. The core size is 19×(24–25), and the winding uses high-strength enameled wire with a diameter between 0.27–0.35 mm. The coil can be wound without layers. The first to second winding has approximately 48 turns, the second to third has around 822 turns. From the third to fourth, use 0.41–0.51 mm enameled wire, and each of the fourth to fifth windings should have about 85 turns.
Transistors BG1 and BG3 are typically 3DG type small power transistors, while BG2 and BG4 are PNP silicon medium power transistors. There are no special requirements for resistors or capacitors; standard components can be used.
This design ensures stable voltage regulation under varying grid conditions. Proper component selection and precise winding calculations are essential for reliable operation. The circuit is well-suited for applications requiring automatic voltage adjustment and protection against overvoltage or undervoltage situations. It provides a cost-effective and efficient solution for maintaining consistent power output.
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