Description
The 2N5401 is a high-voltage, low-power PNP bipolar junction transistor (BJT). It is the direct “complement” to the 2N5551. While the 2N5551 is NPN, the 2N5401 features the same high-voltage capabilities but is designed to conduct current from the supply rail (Emitter) to the load (Collector).
Key Specifications
| Parameter | Symbol | Rating |
| Collector-Emitter Voltage | $V_{CEO}$ | -150V |
| Continuous Collector Current | $I_C$ | -600mA (0.6A) |
| Power Dissipation | $P_D$ | 625mW |
| DC Current Gain | $h_{FE}$ | 50–240 (at 10mA) |
| Transition Frequency | $f_T$ | 100MHz |
Why the 2N5401 is Critical
In high-voltage circuit design, you often need to create “push-pull” stages or level shifters. Because the 2N5401 has nearly identical voltage and current ratings to the 2N5551 (NPN), they are frequently used together as a matched pair.
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Push-Pull Amplifiers: When paired with a 2N5551, the 2N5401 allows you to build circuits that can amplify signals across a wide voltage swing while maintaining symmetry.
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High-Side Switching: Because it is a PNP device, it is excellent for high-side switching where the load needs to be connected to ground, and the transistor controls the positive voltage rail.
Practical Implementation
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Level Shifting: If you have a 3.3V or 5V logic signal and need to control a high-voltage rail (e.g., 100V), you can use the 2N5401 in a driver circuit to “pull” the gate of a high-side P-Channel MOSFET.
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Saturation Mode: To use this as a switch, remember that the base must be pulled below the emitter voltage. Because it is a BJT, you should provide a base current that is roughly $1/10^{th}$ of your desired collector current to ensure it is fully “ON.”
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Thermal Limitations: Like the 2N5551, the 2N5401 is housed in a TO-92 package. It is not a power transistor. Attempting to switch 600mA continuously will generate heat that the small plastic package cannot dissipate effectively. For loads nearing 500mA+, ensure the duty cycle is low or use an additional power-stage transistor.
Comparison Summary
If you are designing a high-voltage system, keep these two parts in your component library:
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NPN: 2N5551 (160V, 0.6A)
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PNP: 2N5401 (150V, 0.6A)
Together, they form the foundation for most high-voltage, low-power amplification and switching tasks.
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