Power Supply Regulators Unit 4 – Voltage Feedback Regulation
Exercise 3 – Active Foldback Current Limiting
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate the foldback current
limiting protection circuit of a series voltage feedback regulator. You will verify your results
with a multimeter.
EXERCISE DISCUSSION
- Active foldback current protection requires a sensing transistor and current-sensing resistor
to detect a current overload. - The sensing transistor is cut off (does not conduct) when no overload exist and conducts
when a current overload occurs. - Exceeding specified load current causes the circuit output voltage and current to decrease.
- On the VOLTAGE FEEDBACK REGULATION circuit block, transistor Q2 and resistors
R3, R4, and R5 create the foldback network. - During normal operating conditions, Q2 is reverse-biased and does not conduct.
- When the load current through R5 (a current sensing resistor) is large enough to generate a
voltage drop that forward biases Q2, the circuit enters the foldback current-limiting mode.