Protecting DC-DC Converters from Short Circuits

Outline

• When the output terminal of a DC-DC Converters short circuits for some reason, excessive current flows through the output, causing various kinds of troubles such as fuming, firing, and breakdown. Previously, a short-circuit protection circuit consisting of a transistor, Zener diode, and resistor, etc. was installed to prevent this. However, simply by inserting "POSISTOR^®" into the output side, abnormal current flow when a short circuit occurs can be limited and the DC-DC Converters protected from damage.
• Murata's "POSISTOR^®" for overcurrent protection generates heat by itself due to abnormal current flow during short circuits, increases the resistance of the "POSISTOR^®" to limit the abnormal current flow, and prevents the DC-DC Converters from fuming, firing, or being damaged.
• An appropriate shape of "POSISTOR^®" (discrete type or surface mount type) can be selected according to the circuit current and mounting method.

Circuit example: Protecting DC-DC Converters from short circuits

When the output terminal of a DC-DC Converters shorts out, the output current rapidly increases possibly causing various troubles such as overheating, fuming, or even firing. To prevent this from happening, short-circuit protection comprising a Zener diode, transistor, and resistor has been adopted in many cases. But a simpler and more cost-effective way is required.
Chip "POSISTOR^®" (0603-size chip-type component) presents a solution because it can detect over-current by itself and suppress it to the safe level.

Roles of "POSISTOR^®"

• Increases the resistance of "POSISTOR^®" due to abnormal current flow when short circuits occur on the DC-DC Converters, and limits the abnormal current flow to prevent the DC-DC Converters from fuming, firing, or being damaged.
• Decreases the resistance of "POSISTOR^®" and unlike the fuse, recovers its original resistance when the short-circuiting stops.