sc4431 is a four terminal device for regulating an isolated power supply with very low output voltage. it is intended to be used as a replacement for three terminal shunt regulators such as sc431l where the output voltage is too low for them to function in conjunction with an opto-isolator. it achieves this by having separate supply and output pins, allowing the output to sink current at voltages as low as 0.2v, while the supply pin still has sufficient voltage for the device to function. in this way, allowing for a 1.6v drop through an opto-isolator diode, regulation down to 1.8v out can be achieved. the sc4431 shunt regulator is available with three initial reference voltage accuracies (0.5%, 1.0% and 2.0%) in the space saving 5-lead sot-23 package. the three voltage tolerances allow the designer the opportunity to select the proper cost/tolerance for their application.