TL431 as Constant Linear Voltage Regulator
Category: Linear Power Supplies
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed and simulated in Proteus 7.10. In this circuit you will learn that how LM431 or TL431 can be used as constant linear voltage regulator. This is a very simple circuit and working of this circuit is given below. 1. TL431 is a 3 terminal device. Pin 1 is Reference, pin 2 is anode and pin 3 is cathode. 2. The maximum sink capability of TL431 is 100mA. 3. In this circuit a TL431, a variable resistor of 1K, a series resistor of 100ohm and two resistors R1 1k ohm and R2 10k ohm are used to make potential divider for reference pin. 4. The input of this circuit is varies from 3V to 12V and desired output is 2.75V (see animation) 5. The formula of calculating output voltage is Vo = (1+R1/R2)*2.5V after puting values of R1 and R2 we get Vo = (1+0.1)*2.5V = 2.75V, which can be seen in animation 6. The current flowing through resistor R3 can be calculated as I = (Vin - Vo)/R For max. Vin = 12V I = (12 - 2.75)/100 = 92.5mA and for min. Vin = 3V I = (3 - 2.75)/100 = 2.5mA Applications: 1. This circuit can be used to understand the working of TL431. 2. This circuit can be used as low power constant linear voltage regulator. 3. This circuit can be used as zener diode.