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The NTE123AP is an NPN small-signal transistor known for its versatility, solid performance, and compatibility with many common electronic circuits. This guide explores the transistor’s pinout, specifications, application examples, circuit usage, CAD models, and more.
The NTE123AP is a versatile NPN small-signal transistor designed for audio amplification and general-purpose switching. It comes in a compact TO-92 package and offers reliable performance in low-power circuits such as pre-amplifier stages, signal drivers, and control applications. With a collector-emitter voltage rating of around 40 V and a collector current capacity up to 600 mA, it provides more headroom than many basic small-signal transistors, making it a solid choice for hobby and light-commercial designs.
Because of its good gain characteristics and stable frequency response, the NTE123AP can be substituted in circuits that originally used transistors like the BC547, provided its pinout is matched correctly. This makes it useful for repairs, upgrades, or custom builds where a dependable and easily sourced NPN transistor is required.
If you are interested in purchasing the NTE123AP, feel free to contact us for pricing and availability.
| Pin Number | Pin Name | Description |
| 1 | Emitter (E) | Emits carriers; usually connected to ground or negative supply in NPN circuits. |
| 2 | Base (B) | Controls transistor switching and amplification; receives the input signal. |
| 3 | Collector (C) | Collects carriers; typically connected to the load or positive supply in NPN circuits. |
| Equivalent / Alternative | Pinout | VCEO (Max Voltage) | IC (Max Current) | Notes |
| BC547 | C–B–E | 45 V | 100 mA | Very common general-purpose NPN; lower current rating than NTE123AP. |
| BC548 | C–B–E | 30 V | 100 mA | Similar to BC547 but slightly lower voltage rating. |
| 2N2222 / PN2222A | E–B–C | 40 V | 600–800 mA | Very close electrical match; good high-current alternative. |
| 2N3904 | E–B–C | 40 V | 200 mA | Widely used; slightly lower current capability. |
| S9014 | E–B–C | 45 V | 100 mA | Common in small-signal circuits; lower current limit. |
| MPS2222A | E–B–C | 40 V | 600 mA | Another robust substitute with similar specs. |
| Specification | Value |
| Transistor Type | NPN |
| Package | TO-92 |
| Pinout | 1: Emitter, 2: Base, 3: Collector |
| VCEO (Collector–Emitter Voltage) | 40 V |
| VCBO (Collector–Base Voltage) | 60 V |
| VEBO (Emitter–Base Voltage) | 6 V |
| IC Max (Collector Current) | 600 mA |
| Power Dissipation (Pd) | ~625 mW |
| DC Current Gain (hFE) | ~100–300 |
| Transition Frequency (fT) | ~250 MHz |
| Operating Temperature | –55°C to +150°C |
The circuit shown is a regulated 12-volt battery charger built around the LM350 adjustable voltage regulator. The input passes through a 1N5401 diode for reverse-polarity protection before reaching the LM350, which controls the charging voltage through its adjust pin. A pair of resistors sets the regulator’s output level, ensuring the battery receives a stable and safe charging voltage.
To improve current handling, the circuit uses a BD140 PNP transistor that works alongside the LM350 to supply additional charging current when needed. A small NPN transistor - originally a BC547 but replaceable with an NTE123AP - acts as a sensing and control device. It monitors the regulator’s output and helps drive the BD140 while also controlling the indicator LED. The LED provides a simple visual cue to show that charging activity is taking place.
Capacitors placed at the input and output of the LM350 help smooth the supply and stabilize the regulator. Additional resistors around the transistors define biasing and ensure the circuit responds properly as the battery voltage rises. Overall, the design provides a reliable way to charge a 12-volt battery using a simple linear regulator with added current boost and visual indication.
The NTE123AP is commonly used in low-power audio amplifier stages, such as pre-amplifiers and driver circuits. Its stable gain and low noise characteristics help boost weak audio signals without introducing distortion. This makes it ideal for small radio receivers, microphone amplifiers, and compact speaker systems.
Because it supports up to 600 mA of collector current, the NTE123AP functions well as a general-purpose switch. It can drive relays, LEDs, buzzers, and other small loads in digital circuits. When the base receives a small control voltage, the transistor quickly switches on or off, making it useful for automation, microcontroller interfaces, and logic-level control circuits.
The transistor can be used to regulate or boost current in linear regulator circuits. It often works alongside voltage regulators or sensing components to stabilize output current, protect circuits from overload, or assist in power management. Its versatility allows it to handle moderate current levels while maintaining predictable behavior.
In oscillator or timing applications, the NTE123AP performs well due to its gain and frequency response. It can be used in RC or LC oscillators, tone generators, and simple waveform-shaping circuits. Its predictable response helps maintain stable oscillation frequency, which is essential in timing, signal generation, and communication circuits.
Thanks to its availability and wide operating range, the NTE123AP is often used in hobby electronics, repairs, and breadboard experiments. Its forgiving electrical ratings make it suitable for learning transistor biasing, building small amplifiers, or replacing damaged NPN transistors in various consumer devices. It's a practical all-around component to keep in a parts kit.
Versatile small-signal performance, suitable for both audio amplification and switching applications.
High collector current rating (up to 600 mA), allowing it to drive loads that many TO-92 transistors cannot.
Good gain range (hFE 100–300), providing stable amplification in low-power stages.
Wide availability and easy replacement for common NPN types like BC547, 2N2222, or 2N3904.
High transition frequency (fT ~250 MHz) makes it suitable for audio, RF, and general-purpose signal circuits.
Compact TO-92 package, ideal for breadboards, prototyping, and tightly packed PCBs.
Operates over a wide temperature range, providing reliability in different environments.
Not a power transistor, despite its relatively high current rating; unsuitable for high-wattage applications.
Limited thermal dissipation due to its small TO-92 package—heat buildup must be managed.
Maximum voltage rating (VCEO 40 V) may be insufficient for higher-voltage circuits.
Pinout varies from some equivalents, which can cause wiring mistakes if not checked.
Performance depends on proper biasing, so incorrect bias can result in distortion or low gain.
Not ideal for precision or high-stability analog circuits, where specialized transistors are preferred.
NTE Electronics is known for its broad manufacturing and distribution capabilities, offering a wide range of electronic components such as semiconductors, resistors, capacitors, relays, and hardware parts designed for both repair and new design applications. The company focuses on providing dependable, easy-to-source replacement parts that match or exceed the specifications of discontinued or hard-to-find components. NTE supports consistent quality control, clear cross-reference resources, and extensive stocking of equivalents for thousands of electronic devices, making them a trusted supplier in maintenance, prototyping, and small-scale production.
The NTE123AP is a flexible component suitable for a wide range of low-power electronic designs. Its balanced specifications, practical TO-92 packaging, and compatibility with popular transistor types make it an excellent choice for repairs, upgrades, or new circuit builds. With clear advantages in audio, switching, regulation, and hobby applications. By understanding its capabilities, limitations, and suitable alternatives, you can confidently integrate the NTE123AP into your projects and achieve consistent, reliable results.
NTE123AP Datasheet.pdf
RoHS Statement.pdf
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