Foldback (power supply design)
Encyclopedia
Foldback is a design feature that functions as follows. When overcurrent is drawn by the load, the supply reduces output voltage
and current
to well below the current limit. This approach has been used in power supplies and power amplifiers.
The prime purpose of foldback current limiting is to keep the output transistor
within its safe power dissipation limit. An output transistor that can handle the power dissipation of supplying the current limit at the rated voltage will dissipate more power if it supplies the same amount of current into a short circuit
, since the voltage drop across the transistor is greater. A simple current limit would therefore expose the transistor to risk of failure, or require a larger transistor. Foldback keeps the output transistor within its power dissipation limits under fault
or overload
conditions.
Foldback also reduces power dissipation in the load in fault conditions, which can reduce the risks of fire
& heat damage.
Many power supplies employ simple current-limiting protection; foldback goes one step further by reducing the output current limit linearly as output voltage decreases.
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
and current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
to well below the current limit. This approach has been used in power supplies and power amplifiers.
The prime purpose of foldback current limiting is to keep the output transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
within its safe power dissipation limit. An output transistor that can handle the power dissipation of supplying the current limit at the rated voltage will dissipate more power if it supplies the same amount of current into a short circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
, since the voltage drop across the transistor is greater. A simple current limit would therefore expose the transistor to risk of failure, or require a larger transistor. Foldback keeps the output transistor within its power dissipation limits under fault
Fault
Fault may refer to:*Fault , planar rock fractures which show evidence of relative movement*Fault , in dog breeding, is an undesirable aspect of structure or appearance that indicates the dog should not be bred...
or overload
Overload
-Bands:* Overload * Overload * Overload -Albums:*Overload *Overload *Overload -Songs:*Overload , a dance song by Voodoo and Serano...
conditions.
Foldback also reduces power dissipation in the load in fault conditions, which can reduce the risks of fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
& heat damage.
Many power supplies employ simple current-limiting protection; foldback goes one step further by reducing the output current limit linearly as output voltage decreases.