What is this element on the far right of schematic described as "270 OHM"? Is this some kind of inductor? What is its purpose in this device (this is a reference design of dc-dc power supply of sim900 taken from its datasheet) and what would be an exemplary part number? power supply section of sim900

  • \$\begingroup\$ It's a relay - google 'relay symbol'. \$\endgroup\$ – Mike Spark Dec 14 '14 at 18:44
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    \$\begingroup\$ "FB" probably indicates a ferrite bead. Not posting as an answer because I'm pretty sure this is a duplicate. \$\endgroup\$ – The Photon Dec 14 '14 at 18:48
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    \$\begingroup\$ possible duplicate of What component is this? \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 14 '14 at 18:49
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    \$\begingroup\$ @rubix_addict In future put hyperlinks in your question, for example to the app note from where you excerpted the schematic and to a page describing what a SIM900 is. Help others and you'll get the help back. \$\endgroup\$ – Adam Lawrence Dec 14 '14 at 18:51
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    \$\begingroup\$ another possible duplicate: Meaning of FB symbol in schematics? \$\endgroup\$ – Nick Alexeev Dec 14 '14 at 23:17

It is a ferrite bead with a 270Ω impedance.

Ferrite beads have a number of symbols in use in schematics. There hasn't been a standardization in the symbol like for other components. Many people treat them like a simple inductor, some like a resistor, some with a special symbol they made for it. Some of the symbols seen include:

enter image description here


It's most likely a ferrite bead for high-frequency suppression, given the fact that the SIM900 you described seems to be a GSM/GPRS phone module doohickey which is likely very sensitive to HF noise.

(Also, the schematic symbol implies 'inductor with something other than an air core'.)

The 270 ohm figure is almost certainly the peak impedance of the bead at its target frequency.


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