Power Supply Regulators Unit 6 – Three-Pin IC Regulator
Exercise 1 – Regulator Operation & Voltage Regulation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate and measure the voltage
regulation of a three-pin IC regulator. You will verify your results with a multimeter.
DISCUSSION
- The circuit configuration produces an adjustable output voltage.
- A specific programming current (IP) is provide by the selection of R3.
- Circuit output voltage is varied by R2.
- At the desired output voltage, V+ and V- are equal. VR3 equals VREF, the zener diode voltage.
- Output voltage is defined by: VO = 1.25 x [1 + (R2/R3)]
- The value 1.25 is the nominal reference voltage and minimum output voltage for this
regulator type. - An opposing offset voltage (equal magnitude and opposite polarity), which cancels the
circuit reference voltage is used to force the output voltage to zero.