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onsemi 2N4921
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- Part No.:
- 2N4921
- Manufacturer:
- onsemi
- Category:
- Single Bipolar Transistors
- Package:
- TO-225AA, TO-126-3
- Datasheet:
-
2N4921.pdf
- Description:
- TRANS NPN 40V 1A TO-126
- Quantity:
- Payment:
- Shipping:
Inventory:4,101
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Product details
Overview
2N4921 from onsemi is a medium-power plastic NPN silicon transistor designed for driver circuits, switching, and amplifier applications. It features 40 VCEO, 1.0 A continuous collector current, 30 W total power dissipation at TC = 25°C, low 0.6 VCE(sat) at IC = 1.0 A/IB = 0.1 A, and TO-225 package. It is used in industrial relay drivers and DC-DC converter switch stages.
For engineers reviewing the 2N4921 datasheet, pinout, applications, or equivalent options, key selection considerations include VCEO rating, safe operating area (SOA) curves, thermal resistance (RJC = 4.16°C/W), saturation voltage under high-current drive, and Pb-free RoHS-compliant packaging.
Technical Context
The 2N4921 operates as a general-purpose bipolar junction transistor with fixed NPN polarity and base-emitter forward bias control. Its electrical behavior is defined by DC current gain (hFE = 40–150 at IC = 50 mA to 1.0 A), fT = 3.0 MHz, and Cob = 100 pF - indicating suitability for low-to-moderate frequency switching up to ~1 MHz with controlled turn-on/turn-off timing.
Thermal performance is governed by junction-to-case conduction (RJC = 4.16°C/W max), requiring thermal compound for optimal heat transfer. Safe operating area is limited by second breakdown and thermal constraints, with derating starting above 25°C at 0.24 W/°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCEO | 40 Vdc - maximum collector-emitter voltage before breakdown under open-base conditions; defines upper rail limit in switching applications. |
| IC (continuous) | 1.0 Adc - rated DC collector current; supports load switching up to ~12 W at 12 V with adequate heatsinking. |
| PD @ TC = 25°C | 30 W - total power dissipation capability when case temperature is maintained at 25°C; requires active thermal management above ambient. |
| VCE(sat) | 0.6 Vdc max at IC = 1.0 A/IB = 0.1 A - low saturation voltage minimizes conduction loss in saturated-switch mode. |
| hFE | 40 min at IC = 50 mA/VCE = 1.0 V - ensures reliable base drive design margin for linear and switching amplification. |
| fT | 3.0 MHz - usable for audio-frequency amplification and PWM switching below 500 kHz with predictable gain roll-off. |
| RJC | 4.16°C/W max - junction-to-case thermal resistance; mandates thermal interface material for sustained >5 W operation. |
Pinout & Package
2N4921 is housed in a TO-225 package (Case 77-09, Style 1), featuring a metal tab connected to the collector and three leads arranged in line: Pin 1 = Emitter, Pins 2 & 4 = Collector (dual-collector configuration), Pin 3 = Base.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Pin 1 | Emitter | Main current exit path; referenced to ground or low-side return in common-emitter configurations. |
| Pins 2 & 4 | Collector | Parallel-connected collector terminals; reduce current density and improve thermal distribution across package. |
| Pin 3 | Base | Control input for bipolar conduction; requires current-limited drive (IB ≤ 1.0 Adc) to avoid damage. |
Key Features
| Feature | Design Value |
|---|---|
| Low saturation voltage | VCE(sat) ≤ 0.6 V at full 1.0 A load enables <1 W conduction loss in high-current switching. |
| High safe operating area | SOA curves validated to 150°C junction temperature support robust pulse handling without second breakdown. |
| Thermal performance | RJC = 4.16°C/W allows direct mounting to heatsinks with thermal compound for stable 10–20 W continuous operation. |
| Pb-free & RoHS compliant | G-suffix indicates lead-free termination and compliance with EU RoHS Directive 2011/65/EU. |
| Complementary PNP pairing | Designed as NPN counterpart to 2N4920G, enabling matched push-pull output stage implementation. |
Applications
| Industrial Relay Driver | DC-DC Converter Switch |
|---|---|
Use Scenario: Driving 24 VDC industrial relays with coil currents up to 800 mA in programmable logic controller (PLC) output modules. IC Role / Device Role / Timing Role: NPN switch operating in saturation mode to close relay coil circuit; base driven by microcontroller GPIO via current-limiting resistor. Use Value: Low VCE(sat) reduces relay coil power loss and self-heating; SOA integrity ensures reliability during inductive kickback events. |
Use Scenario: High-side or low-side switching element in 12 V to 5 V buck converter operating at 100 kHz. IC Role / Device Role / Timing Role: Power transistor in non-synchronous rectification stage; switched by PWM controller with base current limiting. Use Value: 3.0 MHz fT and fast storage/fall times (<1 µs) support clean switching transitions; 30 W PD accommodates transient overload conditions. |
| Audio Power Amplifier Stage | Motor Control H-Bridge Leg |
Use Scenario: Output stage in Class AB audio amplifier delivering up to 5 W into 8 Ω speaker loads. IC Role / Device Role / Timing Role: Linear amplification device biased in active region; paired with complementary 2N4920G for push-pull topology. Use Value: hFE ≥ 40 at 50 mA ensures stable bias point; low VBE(sat) improves thermal tracking between NPN/PNP pairs. |
Use Scenario: One quadrant of an H-bridge driving brushed DC motors in automated gate systems (12–24 V, ≤1 A). IC Role / Device Role / Timing Role: Low-side switching transistor controlled by isolated gate driver; collector tied to motor winding and emitter to ground. Use Value: Dual-collector pins (2 & 4) lower effective current density and improve thermal spreading during stall-current events. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar NPN power transistor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 2N4922G | Higher VCEO = 60 V; otherwise identical package, pinout, and thermal specs. | Supports higher bus voltages (e.g., 48 V industrial systems); same SOA and switching speed. | Select 2N4922G when operating above 40 V supply rails while retaining mechanical and thermal compatibility. |
| MJD122G | TO-252 (DPAK) package; VCEO = 100 V; hFE = 30–120; RθJC = 3.0°C/W. | Surface-mount alternative with superior thermal resistance but different footprint and soldering process. | Choose MJD122G for space-constrained PCBs requiring SMT assembly and higher voltage margin, accepting layout redesign. |
Compared with 2N4921, 2N4922G offers extended voltage headroom without changing board layout or thermal design, while MJD122G provides better thermal performance and voltage rating at the cost of through-hole-to-SMT conversion and requalification.
Availability
2N4921 is available at Aetrix Electronics and suitable for industrial relay drivers, DC-DC converter switches, and audio amplifier stages requiring stable component supply and long-term obsolescence management.
Supply support for 2N4921 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.
The 2N4921 belongs to onsemi's legacy general-purpose power transistor family, engineered for robustness in industrial control, power conversion, and electromechanical interface applications where reliability under thermal stress is critical.
FAQ
Is 2N4921 still recommended for new designs?
No - the official onsemi datasheet marks 2N4921G as discontinued and states it is "not recommended for new design." However, Aetrix Electronics maintains inventory and supports legacy system repair, replacement, and long-life production programs with full traceability and obsolescence mitigation planning for 2N4921.
What is the maximum junction temperature for 2N4921?
The 2N4921 has an operating junction temperature range of –65°C to +150°C. Its safe operating area curves (Figure 5) are explicitly defined for TJ(pk) = 150°C, and thermal derating begins at 25°C case temperature, reducing power by 0.24 W per °C above that point.
Does 2N4921 have a built-in base-emitter resistor?
No - the 2N4921 is a standard discrete NPN bipolar transistor without integrated base resistors. External base current limiting must be provided in circuit design; typical drive uses a series resistor sized to deliver ≥100 mA base current for full 1.0 A collector conduction.
Can 2N4921 replace 2N2222 in high-current applications?
No - while both are NPN transistors, 2N2222 is rated for only 800 mA IC and 500 mW PD, whereas 2N4921 handles 1.0 A continuously and 30 W with proper heatsinking. Substituting 2N4921 for 2N2222 requires verifying PCB layout, thermal path, and drive capability - it is not a drop-in replacement.
What does the 'G' suffix mean in 2N4921G?
The 'G' suffix in 2N4921G denotes a Pb-free, RoHS-compliant version with matte tin lead finish. It reflects onsemi's environmental compliance program and matches the mechanical and electrical specifications of the legacy 2N4921 part, except for termination plating.
2N4921 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- -
- Package/Case:
- TO-225AA, TO-126-3
- Packaging:
- Bulk
- Product Status:
- Obsolete
- Transistor Type:
- NPN
- Current - Collector (Ic) (Max):
- 1 A
- Voltage - Collector Emitter Breakdown (Max):
- 40 V
- Vce Saturation (Max) @ Ib, Ic:
- 600mV @ 100mA, 1A
- Current - Collector Cutoff (Max):
- 500µA
- DC Current Gain (hFE) (Min) @ Ic, Vce:
- 30 @ 500mA, 1V
- Power - Max:
- 30 W
- Frequency - Transition:
- 3MHz
- Operating Temperature:
- -65°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- TO-126
2N4921 FAQ
1.How can I place an order for 2N4921 through Aetrix?
Please submit a Request for Quotation (RFQ) for 2N4921 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for 2N4921 reliable?
The price and inventory of 2N4921 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 2N4921 is usually 5 days.
3.What payment methods are accepted for 2N4921?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 2N4921 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 2N4921?
2N4921 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 2N4921 order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for 2N4921?
For technical support, including 2N4921 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 2N4921 requirements.
6.How does Aetrix verify that 2N4921 is sourced from the original manufacturer or authorized distributors?
All 2N4921 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that 2N4921 meets industry standards.
7.What is the process for return or replacement of 2N4921?
All 2N4921 units undergo pre-shipment inspection (PSI). If there is an issue with 2N4921, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The 2N4921 part is unused and in its original packaging.
Return procedure for 2N4921:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
2N4921 Tags
-
MMBT3906LT1G
onsemi
-
MMBT3904-7-F
Diodes Incorporated
-
MMBT3904LT1G
onsemi
-
MMBT3906-7-F
Diodes Incorporated
-
MMBT3904-TP
Micro Commercial Co
-
MMBT2222A-7-F
Diodes Incorporated
-
BC846BLT1G
onsemi
-
BC847B,215
Nexperia USA Inc.
-
SMMBT3904LT1G
onsemi
-
MMBT2222A-TP
Micro Commercial Co
-
MMBTA06LT1G
onsemi
-
MMBT2222ALT1G
onsemi
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