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Why the snubber circuit is necessary for inductive load and not for resistive load.

What is the back EMF?. When we connect the inductive load how the back emf affect the switching device. how to protect the switching device from the back EMF. Please tell me the operation of that protection circuit.

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  • \$\begingroup\$ Have you tried searching the internet for "back EMF" and "snubber"? This question does not show any research effort. \$\endgroup\$ – Phil Frost Nov 11 '13 at 12:42
  • \$\begingroup\$ we are doing home automation project in that we connect resistive and inductive load. we need to measure the FAN back emf. so give me the guidance for how to measure the back emf. Using multimeter can we measure it? \$\endgroup\$ – kalis Nov 20 '13 at 8:53
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First you got to know how an Inductor works. An Inductor prevents sudden change in Current. Assume you have an inductor is series with a switch and to GND. Now when switch(which is a switching device like a MOSFET) is closed, the current rises and attains a stable value across inductor, through switch and to GND.

Suddenly if the switch is now opened, then as we know the current cannot change in the inductor fast enough(due to its property), there is a high voltage generated across the Open terminals of the Switch(faradays Law). This voltage may become high enough to damage the switch.

To provide this current a route to flow, we hook up a snubber circuit.

To answer your question about why only inductive loads. It is because resistors do not block current from changing too fast, so no voltage is generated, so it does not have that issue.

Back EMF for Inductors: As the magnetic field in the inductor grows, it induces a current that works to counter the source battery generated current. It is said to be generating a BACK EMF, and it does so, till the current does not reach a steady value. TO Protect it an inductor from damaging a switching device, we connect a snubber/protection circuit, allowing current to flow through it, thus preventing a high voltage across switching device.

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