The shunt type regulators are connected in parallel with the load, deflecting the current to behave like a variable resistor and thus keep the voltage in the circuit constant. The circuit shown in the figure is suggested by Fairchild (www.fairchild.com) and can drain currents from 1 to 100 mA with a programmable output voltage up to 36 V. The output voltage is programmed by the resistive network formed by R1 and R2. The LM431sa integrated circuit is supplied in a SOT89 enclosure. In this circuit, the Vref voltage is 2.5 V and the dynamic output impedance is 0.2 ohms.
