In any electronic design, the protection systems have an important role. Unforeseen accidents are common in industrial equipment or those operated by many people. A short circuit or overload is not required (or expected) can destroy a power system and, at worst, can cause serious accidents. The integrated circuit is a NIS5112 electronic fuse (electronic fuse ) ideal for automotive applications and for all that you need a utility power 12Volts. Despite having an SOIC8 package, SENSEFET technology allows NIS5112 working with currents up to 5A. in developments where space, reliability and low cost are important.
The application and development of protection systems in electronic equipment are not as easy as people may believe. Almost daily operational problems occur in household products (TV, DVD Player, Videogames, etc) and people are always convinced that there is a fuse what is broken or loose some cablecito "that's out there. The classic fuse is encapsulated in a glass bulb with two metal caps that serve as a connection is broken props and sometimes very rare. It is necessary within the team there is a very important circuit for the fuse is damaged and thus protect the circuit power, otherwise they break a lot of things in any device before it is destroyed fuse . We could add further that faults that are raised within the team broken components. And when it comes to a point of mass destruction where shorts are serious , Makes his entrance scene fuse savior for the team not ignite or explode (because the break has already occurred). That is, the fuse classical, in most cases, provides limited protection. True preventive action is carried out by intelligent circuits every team has developed and, of course, those who can design from NIS5112 use.
The integrated circuit is a ON Semiconductor sold in a SOIC8 package. The salient features of this component are many and the attempt to describe in the text of this article along with accompanying videos. Among these qualities, the first is the possibility that gives you the NIS5112 to adjust the working current or action and protection through a simple resistance and low power dissipation of a preset (adjustable resistor). In the circuit shown above, found in component data sheets, you can see the resistance of 56 Ohms as the manufacturer offers reference circuit demonstration raised. Depending on the resistance value it, you get the current job or action electronic fuse. In data sheets are no formulas or calculations to determine the appropriate value (resistance) depending on the current work ( protection) to be taken. Only found a chart (Fig. 2, p. 4) which are two specific curves. A " Ilimit_SS ," the action current of the fuse on the basis of the current limiting resistor or "sensing." The other, " Ilimit_OL , "the overload current to fuse acting.
Understanding this chart will allow us to access all the possibilities offered by the NIS5112 . Ilimit_OL is the curve that represents the current at which the circuit detects an over-consumption and act accordingly. That is, a value between 3.5 A and 5.5 A, according limiting resistor. That is, as the chart shows, with a current limiting resistor of 75 ohms the fuse will act at 4 amps power disconnecting the load. This disconnection (as seen in the second video) may be temporary or permanent. That is, if the length of time the problem occurs is of short duration, fuse automatically resets . On the contrary, if we have a long-term problem over time, fuse cut power to the load permanently and we can only restore power disconnecting and reconnecting circuit (the classic "off and on again" ).
other hand, the curve Ilimit_SS offers information on what will be the starting current (start) that we can get in terms of the current limiting resistor. That is, according to the value we assign to the current limiting resistor, fuse or circuit feed will prevent this action to find a load (use the connection time) outside the values \u200b\u200bset at the beginning of the design. As in the previous curve, we can deduce that: with a current limiting resistor of 330 Ohms, the NIS5112 only allow circuits that consume power roughly 500mA. If the initial current exceeds this value, the electronic fuse not allow the passage of food coming from the source connected to the network or from a battery . Thus, the curves should be reason to the functioning of NIS5112 and to take full advantage of it. Let's see how it behaves with a direct short.
Continuing with the description of the features of the NIS5112 , we have the possibility to work with voltages between 9 and 18 volts for proper operation with transient values \u200b\u200b(in spikes) up to 25Volts (1ms). The maximum voltage delivered to the fuse circuit that will work 15Volts. And all excursions above this value will be "cut " at that level. This property makes it ideal for automotive applications, where power 12Volts is a common denominator between the operating circuits. On the other hand, the maximum current rating as the NIS5112 allow to drain on a circuit will be 5.3 A, according to their datasheet, and transients may reach values \u200b\u200bof up to 25A. The following circuit is the one you showed in the video, with the difference that in our case, working with input voltage from a battery of 12Volts , we do not include C4 and C3 in the assembly. In addition, the type of load that the test did not warrant inclusion of these capacitors needed. We advise to place, so you must not stop where it says install the schematic.
Thanks to technology SENSEFET , you can have a MOSFET transistor power with temperature protection, for that matter, has the ability to protect itself. Equipped with a very low driving resistance (30 milliohms ), the transistor provides the NIS5112 the advantage of stop functioning when the temperature has crossed a threshold of risk. In the second video you can see a sequence where this situation arises. When the load resistance puts the fuse to the limit of its current setting, the temperature starts to increase, the MOSFET performance begins to decrease, the LEDs light up less, and temperatures in a few moments enough to level the NIS5112 activate your self-protection system. This maximum temperature is 135 ° C. And only if low 40 ° C, the integrated circuit will be operational to continue their work. That is, if the situation does not change the circuit, the device is self-protected indefinitely until we realize that an overload condition is occurring in the circuit to energize when the payload we want to feed. Watch the video, especially when the LEDs on and try to finish off.
Finally, we find the pin Enable / Timer makes the NIS5112 behave like a real ignition key. With a logic high, enabling us to ensure the integrated circuit. And with a logic low disables operation placing it as an open key. In the event that you are not applying any logic state and placed there a capacitor, be obtained a time delay to activate the voltage output. This delay is associated with the capacitor value connected there. That is, if all highlight the virtues of NIS5112 here you think of few, you can use it as a key to turn on (or not) sub-systems that work with 12Volts. And you can even set a small delay of activation. The pin dV / dt (associated in the operation to pin Enable / Timer ) has connected a capacitor that determines the speed at which the SENSEFET goes to a full conducting state. Observed in this data sheet is expressed as an upslope before the step pulse voltage input. The capacitor placed on this pin determines the growth rate of this ramp.
care Perform circuit development, is well studied and optimized the basic general idea of \u200b\u200bany good designer. This search for the details that "make a difference " implies the inclusion of an appropriate system of protection against damage that may make operating an entire production line or an entire section of a manufacturing plant instrumentation. The damage caused by a design fails when you least expect can be avoided with appropriate safeguards. NIS5112 is an integrated circuit designed for this purpose. And the benefits are also important, vital to care for and maintain all types of protected circuits. An electronic fuse you can program in its current capacity and that can be used as switch "is the heart of the integrated circuit and transforms it into a precious element in any development. We invite you to tell your experiences fuse and your impression on this IC in Electronics Forum arg.
Source:
http://www.neoteo.com/Portada/tabid/54/id / 21737/pg/0/cp/1/Default.aspx
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