{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"BUJ303B,127","brand":"NXP Semiconductors","brandSlug":"nxp","productSlug":"BUJ303B127","canonicalUrl":"https://icboms.com/nxp/BUJ303B127","factsUrl":"https://icboms.com/api/mcp/products/BUJ303B%2C127","rawCanonicalId":null},"summary":{"shortDescription":"WeEn Semiconductor BUJ303B,127 NPN power bipolar transistor, 400 V Vce, 5 A Ic, 100 W, TO-220AB through-hole, 150°C junction temperature.","salesMarkdown":"## 400 V Vce, 5 A Ic — the switching transistor for mains-referenced circuits The BUJ303B,127 from WeEn Semiconductor is an NPN power bipolar transistor in a TO-220AB through-hole package. Its 400 V collector-emitter breakdown voltage and 5 A continuous collector current make it a fit for line-voltage switching applications — flyback clamps, electronic ballasts, switch-mode power supply primary-side drivers, and motor control snubbers where a 400 V blocking rating is the minimum for 240 VAC rectified rails. ## 100 W power dissipation — thermal budget for the design Rated for 100 W maximum power dissipation, this part needs a heatsink for any continuous load above a few watts. The TO-220AB metal tab is the primary thermal path — plan for a thermal pad or mica insulator and a properly sized heatsink. The junction temperature limit is 150°C, so derate the power based on the thermal resistance of your mounting arrangement. The Vce(sat) is 1.5 V maximum at 1 A base current and 3 A collector current. That 1.5 V drop at 3 A means 4.5 W conduction loss in the transistor alone — a figure that directly factors into the heatsink sizing and the overall efficiency budget. The DC current gain (hFE) is a minimum of 23 at 800 mA collector current and 3 V Vce. This moderate gain means the base drive circuit must supply roughly 35 mA to saturate the transistor at 800 mA load; at the full 5 A rating the required base current will be higher, so the driver stage needs to be sized accordingly.","metaTitle":"BUJ303B,127 NPN Power Transistor, 400 V, 5 A, TO-220","metaDescription":"BUJ303B,127 NPN bipolar power transistor. 400 V Vce, 5 A Ic, 100 W max. TO-220AB through-hole. Active lifecycle.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Logic ICs"],"specifications":{"Package":"Bulk","Power - Max":"100 W","Mounting Type":"Through Hole","Package / Case":"TO-220-3","Transistor Type":"NPN","lifecycle_stage":"eol_hot","Operating Temperature":"150°C (TJ)","Supplier Device Package":"TO-220AB","Vce Saturation (Max) @ Ib, Ic":"1.5V @ 1A, 3A","Current - Collector (Ic) (Max)":"5 A","Current - Collector Cutoff (Max)":"100µA","DC Current Gain (hFE) (Min) @ Ic, Vce":"23 @ 800mA, 3V","Voltage - Collector Emitter Breakdown (Max)":"400 V"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$0.36","stockQuantity":0,"priceTiers":[{"qty":825,"price":"$0.36000","currency":"USD"}]},"links":{"datasheetUrl":"https://cdn.icboms.com/dbbcfd2a219380dbc60468e2892b0b4f.pdf","sourceUrl":null},"ai":{"faq":[{"question":"Is BUJ303B suitable for 400 V applications?","answer":"Yes. The collector-emitter breakdown voltage is rated at 400 V maximum, which means the transistor can block 400 V in the off state. This makes it suitable for circuits operating on rectified 240 VAC mains (typical peak ~340 V) or other 400 V bus applications, provided the switching and conduction losses stay within the 100 W power dissipation limit."},{"question":"What is the hFE of BUJ303B?","answer":"This is a moderate gain figure typical of a power transistor — the base drive circuit must supply adequate current to saturate the device at the intended load."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/nxp/BUJ303B127","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/nxp/BUJ303B127 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}}