DC/DC Converter Application Note
Protection Circuits (Latch Type/Reset Type/Fold back Type)
Operation of over current protection by circuit type
There are three kinds of current limit protection circuits used in Ricoh DC/DC converters, Latch type, Reset type and Fold back type.
- A Latch type protection circuit latches the power MOSFET to the OFF state during an excessive high load in case it persists for a specified time (the protection delay time). The circuit can be released by changing the IC into the standby mode and back to the active mode by the CE pin, or by turning the power off and back on. There are some products which an adjustable protection delay time by a capacitor connected to the DLY pin (DELAY pin).
- A Reset type protection circuit controls the power MOSFET to the OFF state during an excessive high load in case it persists for a specified time (the protection delay time). The circuit is automatically released after removal of the excessive load and by triggering the soft start operation. The protection delay time is fixed within the IC.
- A Fold back type protection circuit decreases the oscillator frequency when the output voltage decreases below the preset value. Therefore the minimum ON duty decreases and the inductor ripple current increases. As a result the output current decreases. The protection is automatically released after the excessive load is removed.
Products Supporting Latch Type Protection Circuit
Products Supporting Reset Type Protection Circuit
Products Supporting Fold Back Type Protection Circuit