Introduction
The 2N2907A is a classic PNP bipolar junction transistor widely used in switching and amplification tasks. Thanks to its metal TO-18 package, it offers excellent thermal stability and noise immunity — making it a reliable choice in both hobbyist and professional circuits. This guide covers its key specs, pinout, practical usage, H-bridge example, and replacement options.
2N2907A Transistor Key Features
Transistor Type: PNP Bipolar Junction Transistor (BJT)
Package: TO-18 metal can (high reliability, compact size)
Maximum Collector Current (Ic): 600 mA
Maximum Collector-Emitter Voltage (Vceo): 60 V
Maximum Power Dissipation (Ptot): ~400 mW (depending on heatsinking and ambient temperature)
Transition Frequency (fT): Typically around 200 MHz – suitable for high-speed switching
DC Current Gain (hFE): 100 to 300 (depends on test conditions)
Metal Can Advantage: Enhanced thermal conductivity and EMI shielding
Polarity: Requires negative base-emitter voltage to turn on
Applications: Switching, signal amplification, audio frequency circuits, and general-purpose low-power applications
2N2907A(Metal Can)Transistor Pinout
| Pin Number | Name | Description |
|---|---|---|
| 1 | Emitter | Current flows out; connect to V+ |
| 2 | Base | Controls the transistor switching |
| 3 | Collector | Current flows in; usually to load |
Usage Notes:
- Polarity: As a PNP transistor, the base must be at a lower voltage than the emitter to turn it on.
- Pin Order: Viewed from the bottom (pins down), the pins are numbered clockwise: 1 (Emitter), 2 (Base), 3 (Collector).
- Metal Case: Connected to the collector (Pin 3); keep it from touching other parts to avoid shorts. 2N2907A Transistor Circuit H-Bridge Motor Driver Using 2N2907A
| Component | Type/Function |
|---|---|
| Q2, Q4 | PNP transistors (e.g. 2N2907A) — high side switches |
| Q1, Q3 | NPN transistors — low side switches |
| D1–D4 | Flyback diodes — protect against voltage spikes |
| R1–R4 | ~1 kΩ base resistors — limit base current |
| M1 | DC motor — load driven by the bridge |
Functionality
- Forward Rotation: Activate Q2 + Q3
- Reverse Rotation: Activate Q1 + Q4
- Stop (Brake or Coast): Turn off all or short both sides (not both on same leg!)
Why 2N2907A Is a Good Choice
- Handles up to 600 mA, ideal for small DC motors
- Fast switching (200 MHz) supports PWM and digital control
- TO-18 metal case** improves heat dissipation and blocks EMI
Design Tips & Analysis
- Topology: PNP on top (to V+), NPN on bottom (to GND) — standard H-bridge
- Base resistors (~1 kΩ): Limit current and ensure full switching
- Flyback diodes: Protect against motor-induced voltage spikes
- Metal case = collector: Must insulate to avoid shorts
- Avoid shoot-through: Never turn on both top or both bottom transistors together
- Cooling: Use airflow or heatsink if current >300 mA
- Power stability: Add electrolytic cap across supply to handle spikes
2N2907A Transistors Equivalent
Equivalent Models Overview
| Model | Type | Package | Vceo | Ic Max | hFE Range | Frequency (fT) | Notes |
|---|---|---|---|---|---|---|---|
| 2N2907A | PNP | TO-18 | 60 V | 600 mA | 100–300 | ~200 MHz | Original, metal case, good heat & EMI |
| 2N2907 | PNP | TO-18 | 60 V | 600 mA | 100–300 | ~200 MHz | Same specs, slightly looser tolerances |
| 2N2907AL | PNP | TO-18 | 60 V | 600 mA | 100–300 | ~200 MHz | Low-temp variant, improved stability |
| 2N2906A | PNP | TO-18 | 60 V | 600 mA | ~100–300 | ~150–200 MHz | Slightly older variant |
| KSP2907A | PNP | TO-92 | 60 V | 600 mA | 100–300 | ~200 MHz | Plastic case, same specs, cheaper |
| KTN2907A | PNP | TO-92 | 60 V | 600 mA | 100–300 | ~200 MHz | Similar to KSP, used in Asia |
| MPS2907A | PNP | TO-92 | 60 V | 600 mA | 100–300 | ~200 MHz | Motorola series, common TO-92 version |
| PN2907A | PNP | TO-92 | 60 V | 600 mA | 100–300 | ~200 MHz | Widely used, reliable, same electrical spec |
Replacement Guidelines
Best drop-in (TO-18):
2N2907, 2N2907AL, 2N2906A — Same pinout and metal case. Fully compatible in fit and heat handling.
Equivalent (TO-92):
KSP2907A, MPS2907A, PN2907A, KTN2907A — Same specs, smaller size, less heat dissipation. Good for low to medium power.
⚠️ Notes:
- TO-92 and TO-18 are not mechanically interchangeable. Check layout.
- For current >300 mA, use TO-18.
- If using TO-92, ensure airflow or heatsinking.
Recommended Options
- PN2907A / KSP2907A – Small size, low current
- 2N2907A / 2N2907AL – High frequency or EMI-sensitive
- 2N2907A – Best for near 600 mA continuous load
Conclusion
The 2N2907A remains a solid choice for low-power switching, motor drivers, and analog circuits where thermal stability matters. Whether you're replacing a part or designing from scratch, understanding its equivalents and best-use scenarios helps ensure reliable performance. Consider your power, space, and frequency needs when selecting substitutes — and for demanding loads, stick with the TO-18 original.
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