FPF270X Over Current Protection

Using the FPF270X adjustable over-current protection IC can be designed a very simple adjustable current-limiting electronic project .FPF270X provide full protection to systems and loads from excess current conditions.Minimum current limit is adjustable from 0.4A to 2.0A.The input voltage range is 2.8V to 36V. Loads can be activated or deactivated with a low-voltage logic compatible ON pin. Fault conditions can be monitored using the error flag pin and/or the power-good pin.

All devices clamp the load current so that it cannot exceed an externally programmed current level. An over temperature feature provides further device protection in case of excessive levels of power dissipation.
FPF2700 responds to an overload condition that lasts longer than a fixed blanking period by turning off the load, followed by a retry after the auto-restart time.The FPF270X has an adjustable 0.4A to 2.0A minimum current limit set through an external resistor, RSET, connected between ISET and GND.A 4.7 F to 100 F ceramic capacitor is adequate for CIN in most cases. Larger CIN values may be required in high-voltage or high-current applications.

A 0.1 F to 1 F capacitor, COUT, should be placed between the OUT and GND pins. This capacitor helps prevent parasitic board inductances from forcing the output voltage below ground when the switch turns off.
During a hard short condition on the output while operating at greater than 24V VIN, a large instantaneous inrush current is delivered to the shorted output. A capacitor must be placed at the OUTPUT pin, acting as a current source to support the instantaneous current draw (Table 2).

For more details about how to design a protection circuit using FPF270X IC please consult the manufacturer datasheet.

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Simple DC Over voltage Protector Circuit Diagram

A very simple DC over voltage protector circuit is shown below. The transistor is set to monitor the input voltage applied to it from the left, in case the voltage rises above a specified limit, the transistor conducts, providing the required current to the SCR, which instantly fires, shorting the output and thus protecting the load from the hazard. Its also called a Crowbar circuit.
The circuit shown below is very simple to understand and is quite self explanatory.
The working may be understood with the following points:
The supply DC input voltage is applied from the right hand side o the circuit across the SCR.
As long as the input voltage remains under a certain predetermined value, the transistor is unable to conduct and therefore the SCr also remains shut.
The threshold voltage is effectively set by zener diode voltage.
As long as the input voltage stays below this threshold everything goes on fine.
However in case the input crosses the above threshold level, the zener diode starts conducting so that the base of the transistor starts getting biased.
At some point of time the transistor becomes fully biased and pulls the positive voltage to its collector terminal.
The voltage at the collector instantly passes through the gate of the SCR.
The SCR immediately conducts and shorts the input to ground.
This may look a bit dangerous because the situation indicates that the SCR might get damaged as it shorts the voltage directly through it.
But the SCR remains absolutely safe because the moment the input voltage drops below the set threshold the transistor stops conducting and inhibits the SCR from going into damaging extents.
The situation is sustained and keeps the voltage from reaching above the threshold.

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