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onsemi BD157STU
- Part No.:
- BD157STU
- Manufacturer:
- onsemi
- Category:
- Single Bipolar Transistors
- Package:
- TO-225AA, TO-126-3
- Datasheet:
-
BD157STU.pdf
- Description:
- TRANS NPN 250V 0.5A TO-126-3
- Quantity:
- Payment:
- Shipping:
Inventory:6,191
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Product details
Overview
BD157STU from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for low-power fast-switching output stages in TV and radio audio amplifiers. It features a collector-emitter voltage rating of 250 V, DC current gain (hFE) of 30–240 at IC = 50 mA, and continuous collector current of 0.5 A in TO-126 package.
For engineers reviewing the BD157STU datasheet, pinout, applications, or equivalent options, key selection criteria include VCEO = 250 V, IC = 0.5 A, hFE range, TO-126 thermal performance, and safe operating area (SOA) compliance for linear/audio switching use cases.
Technical Context
The BD157STU operates as a medium-voltage, medium-current NPN bipolar junction transistor optimized for linear and switching operation in audio output stages. Its design supports VCEO = 250 V and VCBO = 275 V, with guaranteed hFE ≥ 30 at IC = 50 mA and VCE = 10 V.
Thermal derating begins at TC = 25°C with PC = 20 W, dropping linearly to zero at TC = 150°C. The device exhibits ICBO ≤ 100 µA at VCB = 275 V and IE = 0, confirming stable cutoff behavior under high-voltage bias conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCBO | 275 V - maximum reverse-biased collector-base voltage before breakdown; defines safe operation in common-emitter amplifier configurations with high supply rails. |
| VCEO | 250 V - maximum collector-emitter voltage with base open; sets upper limit for output stage swing in TV/radio audio applications. |
| IC (DC) | 0.5 A - continuous collector current; determines usable output power level in Class-A/B audio drivers without forced cooling. |
| hFE | 30–240 - DC current gain at VCE = 10 V, IC = 50 mA; enables predictable base drive sizing for stable bias networks. |
| PC (TC=25°C) | 20 W - maximum power dissipation at case temperature 25°C; requires heatsinking for sustained operation above ~5 W. |
| VEBO | 5 V - emitter-base breakdown voltage; constrains allowable base drive swing and prevents reverse-bias damage during signal transients. |
Pinout & Package
BD157STU is housed in a TO-126 plastic package with integral metal tab for heatsink mounting. Pin 1 is Emitter, Pin 2 is Collector (connected to tab), Pin 3 is Base - standard configuration for medium-power BJT output devices.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (Emitter) | Current sink terminal | Reference node for bias network; connected to ground or emitter resistor in common-emitter amplifier topologies. |
| 2 (Collector) | Current source terminal | Electrically tied to metal tab; must be insulated from heatsink unless circuit design permits common-collector connection. |
| 3 (Base) | Control input terminal | Receives forward-bias current to modulate collector current; requires series resistor to limit IB ≤ 0.25 A per absolute max rating. |
Key Features
| Feature | Design Value |
|---|---|
| Low-power fast switching | Optimized minority-carrier lifetime for <1 µs turn-off in audio output stages, reducing crossover distortion. |
| TO-126 package with metal tab | Enables direct mechanical and thermal coupling to heatsinks while maintaining electrical isolation via mica washer or sil-pad. |
| Guaranteed hFE range | 30–240 at standardized test conditions ensures consistent gain matching across production lots for bias stability. |
| High VCEO/VCEO ratio | VCEO/VCEO = 250 V / VCBO = 275 V ≈ 0.91 - indicates robust internal epitaxial structure suitable for inductive load switching. |
Applications
| TV Audio Output Stage | AM/FM Radio Power Amplifier |
|---|---|
Use Scenario: Final output driver in analog CRT television audio circuits delivering up to 5 W into 8 Ω speaker loads. IC Role / Device Role / Timing Role: NPN BJT configured in Class-AB push-pull pair to amplify line-level signals with minimal THD. Use Value: VCEO = 250 V accommodates flyback-induced voltage spikes from speaker impedance mismatches and transformer-coupled outputs. | Use Scenario: Medium-power audio power amplifier in portable AM/FM radios operating from 9–12 V supplies. IC Role / Device Role / Timing Role: Single-ended Class-A or Class-AB output transistor driving 4–8 Ω speakers directly. Use Value: hFE ≥ 30 ensures reliable base drive from low-current preamp stages without requiring Darlington configuration. |
| Intercom System Driver | Public Address Pre-Output Stage |
Use Scenario: Voice signal amplifier in wired intercom systems with 100–500 m cable runs and reactive loads. IC Role / Device Role / Timing Role: Linear output device buffering op-amp stage and driving long-line capacitance. Use Value: IC = 0.5 A and SOA curve support transient current surges during voice peaks without secondary breakdown. | Use Scenario: Pre-output gain stage feeding a higher-power final amplifier in distributed PA systems. IC Role / Device Role / Timing Role: Voltage-controlled current source providing stable gain before final power stage. Use Value: VEBO = 5 V and IEBO ≤ 100 µA ensure immunity to reverse-bias leakage in multi-stage cascaded designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar NPN audio output transistor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MJE15030 | VCEO = 300 V, IC = 8 A, TO-220 package; higher power rating and larger footprint. | Designed for high-fidelity audio power amplifiers requiring >10 W output; not drop-in due to different pinout and thermal mass. | Select when upgrading from BD157STU for higher output power and improved SOA margin; requires PCB layout change. |
| BD139 | VCEO = 80 V, IC = 1.5 A, TO-126; lower voltage rating but higher current capability. | Targeted at low-voltage audio amplifiers (≤24 V rails); unsuitable for 110–240 VAC-derived supplies used in CRT TVs. | Choose for cost-sensitive, low-voltage consumer audio where VCEO ≥ 250 V is not required; same package but not electrically interchangeable. |
Compared with BD157STU, MJE15030 offers greater voltage headroom and current capacity but demands mechanical redesign, while BD139 provides higher DC current in identical TO-126 form factor yet lacks the 250 V VCEO needed for legacy TV line-powered audio stages.
Availability
BD157STU is available at Aetrix Electronics and suitable for TV audio output stages, AM/FM radio power amplifiers, intercom system drivers, and public address pre-output stages requiring stable component supply and long-term industrial availability.
Supply support for BD157STU 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
Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.
The BD157STU belongs to Fairchild's legacy NPN audio transistor family, engineered specifically for reliability and linearity in analog broadcast equipment output stages operating from high-voltage DC rails.
FAQ
What is the maximum collector-emitter voltage rating for BD157STU?
The BD157STU has a maximum collector-emitter voltage (VCEO) rating of 250 V at TC = 25°C. This rating applies with the base terminal open and defines the upper voltage limit for safe operation in common-emitter configurations. Exceeding this value risks avalanche breakdown and permanent device failure. The BD157STU datasheet confirms this parameter under "Absolute Maximum Ratings" with test condition IC = 1 mA, IB = 0.
Is BD157STU suitable for switching power supply applications?
No, BD157STU is not recommended for switching power supply applications. It is explicitly characterized as a low-power fast-switching output transistor for TV and radio audio amplifiers-not for high-frequency PWM or SMPS topologies. Its SOA curves, storage time, and lack of specified switching times (ton/toff) indicate optimization for linear/Class-AB operation, not hard-switching duty cycles above 20 kHz.
What is the pin configuration of BD157STU in the TO-126 package?
The BD157STU uses standard TO-126 pinout: Pin 1 is Emitter, Pin 2 is Collector (internally connected to the metal tab), and Pin 3 is Base. This configuration is confirmed in the Fairchild BD157/158/159 datasheet Rev. A1, June 2001, under "Package Dimensions" and "Pin Identification." Proper heatsink isolation is required since the collector is electrically active on the tab.
Does BD157STU have a specified pulse current rating?
Yes, BD157STU has a specified pulsed collector current (ICP) rating of 1.0 A under pulse test conditions: pulse width = 300 µs and duty cycle = 1.5%. This rating allows short-duration current surges beyond the 0.5 A DC limit, supporting audio peak handling in TV and radio output stages. The datasheet notes this value is valid only under the stated pulse conditions and does not extend to continuous operation.
What is the DC current gain (hFE) range for BD157STU?
The BD157STU exhibits a DC current gain (hFE) range of 30 to 240, measured at VCE = 10 V and IC = 50 mA. This wide gain spread reflects process variation across production lots and necessitates design margining in base bias networks. The minimum hFE of 30 ensures functional operation even in worst-case units, while typical units deliver higher gain for improved efficiency in linear amplifier stages.
BD157STU Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- -
- Package/Case:
- TO-225AA, TO-126-3
- Packaging:
- Tube
- Product Status:
- Obsolete
- Transistor Type:
- NPN
- Current - Collector (Ic) (Max):
- 500 mA
- Voltage - Collector Emitter Breakdown (Max):
- 250 V
- Vce Saturation (Max) @ Ib, Ic:
- -
- Current - Collector Cutoff (Max):
- 100µA (ICBO)
- DC Current Gain (hFE) (Min) @ Ic, Vce:
- 30 @ 50mA, 10V
- Power - Max:
- 20 W
- Frequency - Transition:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- TO-126-3
BD157STU FAQ
1.How can I place an order for BD157STU through Aetrix?
Please submit a Request for Quotation (RFQ) for BD157STU 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 BD157STU reliable?
The price and inventory of BD157STU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD157STU is usually 5 days.
3.What payment methods are accepted for BD157STU?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD157STU transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for BD157STU?
BD157STU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your BD157STU 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 BD157STU?
For technical support, including BD157STU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD157STU requirements.
6.How does Aetrix verify that BD157STU is sourced from the original manufacturer or authorized distributors?
All BD157STU 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 BD157STU meets industry standards.
7.What is the process for return or replacement of BD157STU?
All BD157STU units undergo pre-shipment inspection (PSI). If there is an issue with BD157STU, 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 BD157STU part is unused and in its original packaging.
Return procedure for BD157STU:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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