Using TL431 as a high-power adjustable voltage stabilized power supply

 　　The precision voltage reference IC TL431 is in a T0-92 package as shown in Figure 1. Its performance is that the output voltage is continuously adjustable up to 36V, the operating current range is as wide as 0.1.100mA, the typical dynamic resistance value is 0.22 ohms, and the output noise is low. Figure 2 is a typical application of TL431, in which the output voltage V at both ends of pins ③ and ② is V=2.5(R2+R3)V/R3. If you change the resistance of R2, you can change the output reference voltage. Figure 3 shows a stable voltage power supply with large output current (about 6A), simple circuit and safety, which is formed by using it as a voltage reference and driving an external field effect transistor K790 as a regulating tube.

　　working principle

　　As shown in Figure 3, 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, and the field effect transistor K790 is used for adjustment. tube (can be used directly in parallel) and C5 is the output filter circuit, etc. The voltage stabilization process is: when the output voltage decreases, the potential of point f decreases. After T1431 internal amplification, the voltage of point e increases. After adjustment by K790, the potential of point b increases. On the contrary, when the output voltage increases, the potential of point f increases. , the potential of point e decreases, and after adjustment by K790, the potential of point b decreases. This stabilizes the output voltage. 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. Except for the 2W resistor R1 and 5W resistor R2, there are no special requirements for other components in this circuit. The component parameters are shown in Figure 3.