High Voltage Regulated with Foldback Current Limiting Circuit Diagram

This is a High Voltage Regulated with Foldback Current Limiting Circuit Diagram. The Foldback is a current limiting feature (a type of overload protection) of power supplies and power amplifiers. When the load attempts to draw over current from the supply, foldback reduces both the output voltage and current to well below the normal operating limits.

 High Voltage with Foldback Current Limiting Circuit Diagram

Under a short circuit, where the output voltage has reduced to zero, the current is typically limited to a small fraction of the maximum current.This circuit use a TMOS MTM7N45 (Q2) is used as a series pass element in a linear high voltage supply that accepts +275-V unregulated and produces 250 V regulated with foldback current limiting. 

A 15-V zener, Dlf provides the dc reference for operational amplifier Ul, whose other input is obtained from a fraction of the output voltage. Ul drives Q3, which drives the gate of Q2. Foldback current limiting is achieved by Rl, R2, R3, R4, Ql, and D2.