Hameedulla-Ekhlas
Senior Member
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Greeting all,
Can any body explain me the surge or inrush current in diodes.
Can any body explain me the surge or inrush current in diodes.
That inrush is a result of the capacitor charging, and is not related to the diode. What they are saying is that you must figure out how large that inrush can be, and make sure you select a diode that can survive that much current.Look at point number five it says regarding to surge or inrush current.
But I would not describe that as a surge or inrush current. I would use those terms for a motor or transformer, something that has a winding that permits very high initial currents but that will "eventually" (i.e., within a fraction of one second) create a counter-emf that reduces the current to "normal" values. When you apply a very small voltage to a diode, smaller than the "forward voltage - on the order of 0.3 to 0.7 volts, no current will flow. Apply more voltage than that, and current will flow. It will continue to drop the same small voltage, but otherwise acts as if it were a wire with no resistance. There is no surge or inrush. Current is either zero, or it is a value that is determined by the rest of the components in the circuit.
What they are telling you is that the diode has a maximum amount of peak current that it can handle before it gets damaged. When an inrush current flows through the diode, it can cause it to heat up.I have attached the lecture file and it shows the circuit.
Look at point number five it says regarding to surge or inrush current.
In the output there is a capacitor. It says that when we close the switch at positive zero the voltage across the capacitor is zero and in the input there is full current. This current it says is a inrush or surge current and diode should withstand this large current.
I dont know is it normal current when switch closes or surge current. Inrush or surge current is much higher than normal current.
I have not heard regarding this before. If you have any farther information or other please I want to know.
That inrush is a result of the capacitor charging, and is not related to the diode. What they are saying is that you must figure out how large that inrush can be, and make sure you select a diode that can survive that much current.
There you go. H-E, think of it like making sure a conductor is big enough to handle the peak load. The conductor does not create the load or current and neither does the diode. They are just conduits, so to speak.That inrush is a result of the capacitor charging, and is not related to the diode. What they are saying is that you must figure out how large that inrush can be, and make sure you select a diode that can survive that much current.
What they are telling you is that the diode has a maximum amount of peak current that it can handle before it gets damaged. When an inrush current flows through the diode, it can cause it to heat up.
In some circuits you will see a series resister in line with the diodes. This helps reduce the amount of inrush current seen by the diode.
There you go. H-E, think of it like making sure a conductor is big enough to handle the peak load. The conductor does not create the load or current and neither does the diode. They are just conduits, so to speak.
Add: LEDs are a different story, but that is not the type diode under discussion in the lecture.
Recall from school that the capacitor charge is an exponential function where the current increases sharply at first then gradually levels out as the capacitor gets charged.Yes mivey, Capacitor starts charging after positive zero time. I only want to know since we close the switch and in positive zero the voltage is also zero across the capacitor so in this positive zero time why inrush current occurs and why it is not a normal current.
Yes mivey, Capacitor starts charging after positive zero time. I only want to know since we close the switch and in positive zero the voltage is also zero across the capacitor so in this positive zero time why inrush current occurs and why it is not a normal current.
Recall from school that the capacitor charge is an exponential function where the current increases sharply at first then gradually levels out as the capacitor gets charged.
Normally charge current is V/R*e^(-t/RC). Here we have practically zero "R" so the voltage is applied in a huge step across the capacitor which results in a very steep charging current curve.
Diodes have a single cycle surge current rating usually denoted by Itsm or Ifsm and a related i^2t value.Greeting all,
Can any body explain me the surge or inrush current in diodes.