Circuit diagram of adjustable voltage power supply made with TL431

　　Circuit Overview:

　　Precision voltage reference IC TL431 is a common precision voltage reference IC, which is widely used. Its output voltage can be adjusted up to 36V continuously, the working current range is as wide as 0.1--100mA, the typical value of dynamic resistance is 0.22 ohms, and the output noise is low. Figure 1 shows a voltage reference and a driving field effect tube K790 as an adjustment tube to form a voltage-stabilized power supply with large output current (about 6A), simple circuit and safety.

　　working principle:

　　The 220v voltage is stepped down by transformer B, rectified by D1-D4, and filtered by C1. In addition, D5, D6, C2, and C3 form a voltage doubler circuit (making Vdc=60V), Rw and R3 form a voltage divider circuit, T1431 and R1 form a sampling amplifier circuit, 9013 and R2 form a current limiting protection circuit, field effect tube K790 is used as an adjustment tube (can be directly used in parallel), and C5 is an output filter circuit. The voltage stabilization process is: when the output voltage decreases, the potential of point f decreases, and the voltage of point e increases after internal amplification of T1431. After adjustment by K790, the potential of point b increases; conversely, when the output voltage increases, the potential of point f increases, the potential of point e decreases, and the potential of point b decreases after adjustment by K790. Thus, the output voltage is stable. When the output current is greater than 6A, the transistor 9013 is cut off, so that the output current is limited to within 6A, thereby achieving the purpose of current limiting.