Protector for current limited power supplies - uses changing resistance of diode in output current path to produce rapid recirculating current at high output

摘要

The power dissipation of the pass element (1) in a series regulated power supply rises to high levels under feedback current limiting. This occurs when over current protection is provided by comparison of load current (R1,Rs) against ballast current (R1,R2) voltage dividers in each current path. By inclusion of a non-linear element (7) such as a diode, in the output current path (R7,Rs) the voltage at the over current comparator (6) input reflects the change in impedance of the diode as it moves from heavily conductin to lightly conducting. This allows a rapid initial current foldback, so reducing pass element dissipation; and as the current falls the diode resistance increases, so the current changes little. The current limiter is linked to the ballast resistor by two diodes which are connected to the bases of two transistors. A capacitor is connected in parallel to R1, to accelerate current limitation provided by the transistors.