Power Supply Regulators Unit 6 – Three-Pin IC Regulator
Exercise 2 – Current Regulation and Power Efficiency
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate three-pin IC current
regulation and determine IC power dissipation. You will verify your results with a multimeter.
DISCUSSION
- An LM317 can be configured as a constant current source (current regulator).
- RP is selected for a specific current output and the reference voltage of the IC is essentially
constant. - Current regulation is maintained by the combined internal reference voltage and op amp
producing a constant voltage across RP. - Current regulation and voltage regulation depend on a constant voltage across RP.
- Voltage regulator configuration uses the programming current flowing through R 2 to set the
circuit output voltage. Once set, the output voltage is constant and the output current varies
depending on the load resistance. - Current regulator configuration uses the programming current as the circuit constant current
output and flows through R 2. Output current is constant and the output voltage varies
depending on the load resistance. - Power is dissipated by the regulator. Power = VD x IRL (where IRL = VREF/RP or IK of the
circuit). - Power consumed by the IC regulator is not available to the load. Therefore, power efficiency
is less than 100%. - Power efficiency is the power consumed divided by the line power. Multiply by 100 to obtain
percentage. %PE = (PLOAD / PLINE) x 100.