{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"FODM121B","brand":"onsemi","brandSlug":"onsemi","productSlug":"FODM121B","canonicalUrl":"https://icboms.com/onsemi/FODM121B","factsUrl":"https://icboms.com/api/mcp/products/FODM121B","rawCanonicalId":null},"summary":{"shortDescription":"onsemi FODM121B, single-channel DC-input transistor-output optoisolator, 3750Vrms isolation, 4-SMD gull-wing package, 50%–150% CTR at 5mA, –40°C to 110°C operating range.","salesMarkdown":"## Isolation and signal transfer for industrial DC buses The FODM121B is a single-channel optoisolator from onsemi that passes a DC signal across a 3750Vrms galvanic barrier using a phototransistor receiver. The 4-SMD gull-wing package suits reflow assembly on a standard surface-mount line, and the –40°C to 110°C temperature grade covers industrial control cabinets, motor-drive feedback, and isolated sensor interfaces without a separate high-temp variant. ## CTR margin and switching speed Current transfer ratio is specified at 50% minimum and 150% maximum, both measured at If=5mA. That 3:1 spread means the LED drive current must be set so the transistor side delivers at least 2.5mA collector current at the low end of the CTR range. Rise and fall times are 3µs typical each, which limits the practical data rate to roughly 100 kbps for a clean digital waveform — adequate for 24V PLC inputs, relay drivers, and slow optocoupler feedback loops. Output transistor is rated for 80V Vce and 80mA continuous collector current. The 400mV Vce saturation at the rated current keeps conduction loss low enough that the part does not need a heatsink in normal use.","metaTitle":"FODM121B Optoisolator – onsemi, 3750Vrms, Transistor Output","metaDescription":"onsemi FODM121B optoisolator: 3750Vrms isolation, DC input, transistor output, 50-150% CTR at 5mA, -40°C to 110°C, 4-SMD gull wing.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":"ROHS3 Compliant","productStatus":"Active","categoryPath":["Optoisolators"],"specifications":{"Package":"Tube","Input Type":"DC","Output Type":"Transistor","Mounting Type":"Surface Mount","Package / Case":"4-SMD, Gull Wing","lifecycle_stage":"eol_hot","Number of Channels":"1","Voltage - Isolation":"3750Vrms","Vce Saturation (Max)":"400mV","Operating Temperature":"-40°C ~ 110°C","Rise / Fall Time (Typ)":"3µs, 3µs","Voltage - Output (Max)":"80V","Supplier Device Package":"4-SMD","Current - Output / Channel":"80mA","Current Transfer Ratio (Max)":"150% @ 5mA","Current Transfer Ratio (Min)":"50% @ 5mA","Voltage - Forward (Vf) (Typ)":"1.3V (Max)","Current - DC Forward (If) (Max)":"50 mA"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$0.66","stockQuantity":0,"priceTiers":[{"qty":1,"price":"$0.66000","currency":"USD"},{"qty":10,"price":"$0.43400","currency":"USD"},{"qty":100,"price":"$0.28730","currency":"USD"},{"qty":1000,"price":"$0.22181","currency":"USD"},{"qty":2000,"price":"$0.20044","currency":"USD"},{"qty":5000,"price":"$0.18707","currency":"USD"},{"qty":10000,"price":"$0.18039","currency":"USD"},{"qty":25000,"price":"$0.17772","currency":"USD"}]},"links":{"datasheetUrl":"https://cdn.icboms.com/269c736c440b53ce097423b4caa3ac66.pdf","sourceUrl":null},"ai":{"faq":[{"question":"What is the closest functional second-source to the FODM121B?","answer":"The FODM121R2 is electrically identical — same 3750Vrms isolation, same 50%–150% CTR at 5mA, same 3µs rise/fall time — but ships in tape-and-reel rather than tube. If your pick-and-place line prefers reel, the FODM121R2 is a drop-in substitute. The FODM2701 has a lower Vce saturation (300mV typ) and may be considered if conduction loss at the output is critical."},{"question":"Can the FODM121B be used for AC input signals?","answer":"No. The input type is DC only — the LED is a single polarity device. For AC line sensing or bidirectional input, you would need a dual-LED or AC-input optoisolator such as the FODM217A series."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/onsemi/FODM121B","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/onsemi/FODM121B when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-07-17T19:50:00.618Z","lastPublished":"2026-07-17T19:50:00.618Z","indexable":true}}