Foldback in power supply

Foldback is one of the important feature in power supplies. Foldback option in power supplies can be related to frequency or current limiting. Foldback is one of the dominant feature found in linear mode power supplies. In switching mode power supplies, under over current conditions, the switching frequency is limited to have a very low duty cycle. There are two basic types of current limiting circuits that are most commonly used in linear regulators, Constant Current Limiting and Voltage-Dependent Current Limiting. Constant Current Limiting is used in the case where the load current specifications of the regulator is low. If the load current specification is high, current fold back is used.

Current limiting is basically done when the load tries to draw over current which is beyond the capability of the regulator or power supply. This can be said as over current protection. The over current condition generally happens in a scenario where the load is shorted to ground and there is a sudden current draw. Under foldback condition, the otuput voltage and current are reduced a limit which helps circuit tor educe any damage. the importance of foldback is that both voltage and current are reduced to a safe limit. The main disadvantage with foldback option is that it is not completely self-recoverable. Here self-recovery talks about power supply coming back to normal working condition without any latch up of the circuit. This means that foldback option has some hysteresis built into it.