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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi KSA643CYBU

Name: KSA643CYBU
Brand: onsemi
SKU: KSA643CYBU
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: KSA643CYBU

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-226-3, TO-92-3 (TO-226AA)

Datasheet:: KSA643CYBU.pdf

Description:: TRANS PNP 20V 0.5A TO-92-3

Quantity:: RFQ Add To RFQ list

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Inventory:3,163

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Product details

Overview

KSA643CYBU from Fairchild Semiconductor is a PNP epitaxial silicon transistor designed for low-frequency power amplification, with V_CEO = −20 V, I_C = −500 mA, P_C = 500 mW, and h_FE range of 120–240 (Y-class), commonly used in audio preamplifier stages and relay driver circuits.

For engineers reviewing the KSA643CYBU datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-92 package, center-collector lead configuration (Emitter–Collector–Base), −20 V V_CEO, −500 mA DC collector current capability, and complementary pairing with KSD261 for push-pull amplifier designs.

Technical Context

This device operates as a general-purpose PNP bipolar junction transistor optimized for linear amplification below 100 kHz. Its structure features epitaxial base construction enabling stable h_FE across temperature and predictable saturation behavior at I_C = −500 mA with V_CE(sat) ≤ −0.4 V.

The KSA643CYBU uses a center-collector TO-92 pinout (Pin 1: Emitter, Pin 2: Collector, Pin 3: Base), distinguishing it from side-collector variants. It is rated for T_J = 150°C and exhibits low leakage (I_CBO ≤ −200 nA) under V_CB = −25 V, supporting reliable operation in thermally constrained consumer and industrial control circuits.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−20 V: Maximum safe collector-emitter voltage before breakdown in common-emitter configuration.
I_C (DC)	−500 mA: Continuous collector current handling capacity without thermal runaway at T_A = 25°C.
P_C	500 mW: Maximum steady-state power dissipation at ambient temperature, defining heatsinking requirements.
h_FE (Y-class)	120–240: Confirmed DC current gain range at V_CE = −1 V, I_C = −100 mA, enabling predictable bias design.
V_CE(sat)	≤ −0.4 V: Verified saturation voltage at I_C = −500 mA, I_B = −50 mA, critical for low-loss switching in driver stages.
R_θJA	250 °C/W: Junction-to-ambient thermal resistance on standard FR-4 PCB, guiding thermal layout decisions.

Pinout & Package

Package: TO-92 molded plastic, 3-lead, straight or bent leads, center-collector configuration (suffix "Y" denotes Y-class h_FE; suffix "C" denotes center-collector; "YBU" indicates Y-class, center-collector, bulk packing).

Pin/Terminal	Circuit Role	Design Meaning
1 - Emitter	Current sink terminal in PNP operation	Connected to higher potential rail in common-emitter amplifier; polarity defines current flow direction.
2 - Collector	Main output current path	Center-positioned pin enables symmetric PCB layout; ties to load or next stage input with minimal parasitic inductance.
3 - Base	Control electrode for current amplification	Receives negative bias current to regulate −500 mA collector current; requires series resistor for stable DC biasing.

Key Features

Feature	Design Value
Low-frequency power amplification	Optimized for audio and control signal amplification up to 100 kHz with linear h_FE response and low distortion.
Complementary pairing with KSD261	Enables balanced push-pull output stages when combined with NPN counterpart, reducing even-order harmonics.
Center-collector TO-92 configuration	Standardized pin 2 collector placement simplifies PCB routing and improves mechanical stability in high-vibration environments.
Y-class h_FE binning (120–240)	Guaranteed current gain spread supports consistent circuit performance without post-manufacture sorting or trimming.

Applications

Audio Preamp Stage	Relay Driver Circuit
Use Scenario: Amplifying line-level signals (≤1 V_PP) before feeding into power amplifier ICs in portable audio equipment. IC Role / Device Role / Timing Role: PNP BJT configured in common-emitter topology providing 20–30 dB voltage gain with low noise. Use Value: Delivers stable h_FE-based gain and low V_CE(sat) to minimize signal compression at peak output swing.	Use Scenario: Switching 12 V/100 mA electromagnetic relays in HVAC control panels using microcontroller GPIO outputs. IC Role / Device Role / Timing Role: Low-side switch with base-driven saturation, interfacing 3.3 V logic to inductive loads. Use Value: −0.4 V V_CE(sat) ensures <100 mW dissipation during sustained ON state, eliminating need for external heat sinking.
DC Motor Speed Control	LED Current Regulator
Use Scenario: Linear current control for small brushed DC motors (e.g., 6 V, 300 mA) in medical pump actuators. IC Role / Device Role / Timing Role: Emitter-follower configured pass element regulating motor current via feedback resistor network. Use Value: 500 mW P_C rating supports continuous 300 mA operation at 1.5 V drop, enabling compact thermal design.	Use Scenario: Constant-current source for high-brightness white LEDs in industrial status indicators. IC Role / Device Role / Timing Role: PNP current mirror reference transistor setting precise LED current independent of supply variation. Use Value: Tight h_FE bin (120–240) ensures ±5% current matching across production units without calibration.

Audio Preamp Stage

Relay Driver Circuit

Use Scenario: Amplifying line-level signals (≤1 V_PP) before feeding into power amplifier ICs in portable audio equipment.

IC Role / Device Role / Timing Role: PNP BJT configured in common-emitter topology providing 20–30 dB voltage gain with low noise.

Use Value: Delivers stable h_FE-based gain and low V_CE(sat) to minimize signal compression at peak output swing.

Use Scenario: Switching 12 V/100 mA electromagnetic relays in HVAC control panels using microcontroller GPIO outputs.

IC Role / Device Role / Timing Role: Low-side switch with base-driven saturation, interfacing 3.3 V logic to inductive loads.

Use Value: −0.4 V V_CE(sat) ensures <100 mW dissipation during sustained ON state, eliminating need for external heat sinking.

DC Motor Speed Control

LED Current Regulator

Use Scenario: Linear current control for small brushed DC motors (e.g., 6 V, 300 mA) in medical pump actuators.

IC Role / Device Role / Timing Role: Emitter-follower configured pass element regulating motor current via feedback resistor network.

Use Value: 500 mW P_C rating supports continuous 300 mA operation at 1.5 V drop, enabling compact thermal design.

Use Scenario: Constant-current source for high-brightness white LEDs in industrial status indicators.

IC Role / Device Role / Timing Role: PNP current mirror reference transistor setting precise LED current independent of supply variation.

Use Value: Tight h_FE bin (120–240) ensures ±5% current matching across production units without calibration.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP low-frequency power transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MPSA92	V_CEO = −300 V, I_C = −500 mA, h_FE = 25–200 (unbinned), TO-92	Higher voltage rating but wider h_FE spread; less suitable for precision gain-critical preamps	Select when higher V_CEO margin is required and gain consistency is secondary.
KSA708Y	V_CEO = −30 V, I_C = −700 mA, P_C = 625 mW, TO-92, same h_FE binning	Higher power and voltage ratings; physically identical footprint and pinout	Drop-in upgrade for designs needing extended headroom without layout change.

Compared with MPSA92 and KSA708Y, the KSA643CYBU offers tighter h_FE control (120–240) and lower V_CE(sat) at −500 mA, making it preferable for gain-stable, low-loss linear amplification where −20 V V_CEO suffices.

Availability

KSA643CYBU is available at Aetrix Electronics and suitable for audio preamplifiers, relay driver circuits, and DC motor speed control applications requiring stable component supply, consistent h_FE binning, and TO-92 form factor compatibility.

Supply support for KSA643CYBU 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 analog and discrete power devices, acquired by ON Semiconductor in 2016; known for robust BJT, MOSFET, and optocoupler product lines.

The KSA643CYBU belongs to Fairchild's legacy general-purpose PNP transistor family, engineered for cost-sensitive, low-frequency linear and switching applications in consumer, industrial, and appliance electronics.

FAQ

What does the 'Y' in KSA643CYBU signify?

The 'Y' in KSA643CYBU denotes the h_FE gain bin classification, specifying a guaranteed DC current gain range of 120–240 at V_CE = −1 V and I_C = −100 mA. This binning ensures consistent amplification performance across production units of the KSA643CYBU without requiring manual selection or circuit recalibration.

Is KSA643CYBU pin-compatible with KSA643CTA?

No - KSA643CYBU uses a center-collector TO-92 configuration (Pin 1: Emitter, Pin 2: Collector, Pin 3: Base), while KSA643CTA uses side-collector (Pin 1: Emitter, Pin 2: Base, Pin 3: Collector). Swapping them without PCB revision will cause functional failure. Always verify pinout before substituting any KSA643 variant, including KSA643CYBU.

What is the maximum safe operating temperature for KSA643CYBU?

The KSA643CYBU has a maximum junction temperature (T_J) rating of 150°C and storage temperature range of −55°C to +150°C. To maintain reliability, ensure actual junction temperature stays below 150°C under worst-case power dissipation (500 mW) and ambient conditions, using R_θJA = 250°C/W to calculate required board-level thermal management.

Can KSA643CYBU replace KSD261 in a circuit?

No - KSA643CYBU is a PNP transistor, while KSD261 is its complementary NPN counterpart. They are designed for paired use (e.g., push-pull stages), not substitution. Replacing KSD261 with KSA643CYBU would reverse polarity and disable circuit operation. The KSA643CYBU complements, but does not replace, the KSD261.

Does KSA643CYBU support pulse operation beyond its DC ratings?

Yes - the KSA643CYBU supports pulsed collector current up to −700 mA (I_CP) under conditions of PW ≤ 10 ms and duty cycle ≤ 50%, as specified in its Absolute Maximum Ratings table. This allows short-duration overload tolerance in relay coil snubbing or motor stall protection circuits, provided average power remains within 500 mW limits for the KSA643CYBU.

KSA643CYBU Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-226-3, TO-92-3 (TO-226AA)

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 500 mA

Voltage - Collector Emitter Breakdown (Max):: 20 V

Vce Saturation (Max) @ Ib, Ic:: 400mV @ 50mA, 500mA

Current - Collector Cutoff (Max):: 200nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 120 @ 100mA, 1V

Power - Max:: 500 mW

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

KSA643CYBU FAQ

1.How can I place an order for KSA643CYBU through Aetrix?

Please submit a Request for Quotation (RFQ) for KSA643CYBU 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 KSA643CYBU reliable?

The price and inventory of KSA643CYBU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for KSA643CYBU is usually 5 days.

3.What payment methods are accepted for KSA643CYBU?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for KSA643CYBU transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for KSA643CYBU?

KSA643CYBU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your KSA643CYBU 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 KSA643CYBU?

For technical support, including KSA643CYBU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your KSA643CYBU requirements.

6.How does Aetrix verify that KSA643CYBU is sourced from the original manufacturer or authorized distributors?

All KSA643CYBU 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 KSA643CYBU meets industry standards.

7.What is the process for return or replacement of KSA643CYBU?

All KSA643CYBU units undergo pre-shipment inspection (PSI). If there is an issue with KSA643CYBU, 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 KSA643CYBU part is unused and in its original packaging.

Return procedure for KSA643CYBU:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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