{"schemaVersion":1,"slug":"iec-backward-diode-backward-unitunnel-diode","name":"IEC backward diode: backward (unitunnel) diode","kind":"symbol","abbreviation":"BACKWARD","aliases":["HDI1_S00648","VDI1_S00648","backward diode Backward (Unitunnel) Diode"],"category":"electronics-components","drawingTypes":["Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"Backward diode form: Backward (Unitunnel) Diode.","description":["A backward diode uses tunnelling behaviour to provide useful conduction at a small reverse bias. Its operating region is different from the forward-conduction region of an ordinary rectifier. This entry identifies the backward (unitunnel) diode form in the publisher's IEC-context family.","A small-signal detector can exploit the low-bias response. Trace the bias and signal polarity in the complete circuit rather than treating the device as a reverse-polarity protection rectifier. ","A backward diode is related to tunnel-device physics; it is not simply an ordinary diode drawn in the opposite direction."],"readingNotes":["A small-signal detector can exploit the low-bias response. Trace the bias and signal polarity in the complete circuit rather than treating the device as a reverse-polarity protection rectifier.","A backward diode is related to tunnel-device physics; it is not simply an ordinary diode drawn in the opposite direction."],"drawingChecklist":["Identify terminal polarity and the required bias region.","Reference the selected component characteristics and package pinout.","Show the surrounding bias and signal-conditioning network."],"distinction":"This entry adds the backward (unitunnel) diode detail to the broader backward diode family. A backward diode is related to tunnel-device physics; it is not simply an ordinary diode drawn in the opposite direction.","facts":[{"label":"Drawing form","value":"Backward (Unitunnel) Diode"},{"label":"Public vendor block names","value":"HDI1_S00648 / VDI1_S00648. Autodesk identifiers, not standards database IDs."},{"label":"Drawing purpose","value":"backward diode"},{"label":"Graphic scope","value":"Independently authored educational illustration; not certified standard geometry, a terminal pinout or a product footprint."}],"references":[{"sourceId":"pub-symbol-semiconductors","relevance":"Public Semiconductor Components table explicitly lists HDI1_S00648 / VDI1_S00648 with this operating or connection form. Vendor graphics are linked, not copied."}],"related":["diode","photodiode","npn-phototransistor"],"artwork":"s28-iec-backward-diode-backward-unitunnel-diode","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","symbolVariant":{"convention":"IEC","form":"Backward (Unitunnel) Diode","reference":"Autodesk IEC-60617 Symbol Preview: Semiconductor Components, HDI1_S00648 / VDI1_S00648. This identifies the publisher's library context; exact IEC graphics and database identities are not asserted."},"plainEnglish":{"title":"What does IEC backward diode: backward (unitunnel) diode mean?","introduction":"A backward diode uses tunnelling behaviour to provide useful conduction at a small reverse bias. Its operating region is different from the forward-conduction region of an ordinary rectifier. This entry identifies the backward (unitunnel) diode form in the publisher's IEC-context family.","example":"A small-signal detector can exploit the low-bias response. Trace the bias and signal polarity in the complete circuit rather than treating the device as a reverse-polarity protection rectifier. ","drawings":"A backward diode is related to tunnel-device physics; it is not simply an ordinary diode drawn in the opposite direction.","terms":[{"name":"Signal","meaning":"Electrical information passed between devices, rather than necessarily the main power supply."},{"name":"Rating","meaning":"A value stating the conditions for which equipment is specified."},{"name":"Schematic","meaning":"A drawing showing function and connections rather than physical appearance."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"AutoCAD Electrical: Semiconductor components","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-AC954072-7314-4682-88AF-38160D61E9A2.htm"}],"detail":"Backward diode form: Backward (Unitunnel) Diode. This entry adds the backward (unitunnel) diode detail to the broader backward diode family. A backward diode is related to tunnel-device physics; it is not simply an ordinary diode drawn in the opposite direction.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/iec-backward-diode-backward-unitunnel-diode","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/iec-backward-diode-backward-unitunnel-diode.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pub-symbol-semiconductors","title":"AutoCAD Electrical: Semiconductor components","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-AC954072-7314-4682-88AF-38160D61E9A2.htm","type":"cad-reference","scope":"Public vendor catalogue naming and functional variants. Vendor block names are not IEC identifiers. Linked for reference; no graphics or CAD files are redistributed.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public Semiconductor Components table explicitly lists HDI1_S00648 / VDI1_S00648 with this operating or connection form. Vendor graphics are linked, not copied."}]}