TL431 high precision adjustable power supply

Filter 18.432M

The TL431 is a widely used precision adjustable voltage reference IC, known for its high accuracy and reliability. It allows for continuous adjustment of the output voltage up to 36V, with a broad operating current range from 0.1mA to 100mA. The device features a low dynamic resistance (typically 0.22 ohms) and minimal output noise, making it ideal for a variety of applications. Figure 1 shows a high-current power supply circuit capable of delivering around 6A. This design uses the TL431 in combination with an external field-effect transistor (K790) to achieve stable and safe operation. The circuit is simple yet effective, ensuring both performance and safety.

Figure 1 **Working Principle:** As illustrated in Figure 3, the circuit begins by stepping down the 220V AC input using a transformer (B). The rectification is done through a full-wave bridge (D1-D4), and the DC voltage is then filtered by capacitor C1. Additionally, D5, D6, C2, and C3 form a voltage doubler circuit, which boosts the DC voltage to approximately 60V. A voltage divider consisting of Rw and R3 provides a reference signal to the TL431 (T1431), while R1 is used for feedback and amplification. The 9013 transistor and R2 work together as a current-limiting protection mechanism. The K790 FET acts as the main regulator, and multiple units can be connected in parallel for higher current capacity. Capacitor C5 serves as the final output filter. The voltage regulation process works as follows: when the output voltage drops, the voltage at point f decreases, causing the voltage at point e to rise due to internal amplification within the TL431. This increases the voltage at point b after the K790 adjusts accordingly. Conversely, if the output voltage rises, point f increases, leading to a drop in point e and a corresponding decrease in point b. This ensures that the output remains stable. When the output current exceeds 6A, the 9013 transistor turns off, limiting the current to 6A and protecting the circuit from overloads. In terms of component ratings, resistor R1 is rated at 2W, and R2 is rated at 5W. All other components do not require special specifications, and their values are detailed in Figure 3.