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The MPSA42 transistor is a well-known high-voltage NPN device favored with its ability to handle demanding switching and amplification tasks. This article will discuss its specifications, pinout, applications, comparisons, advantages, and more.
The MPSA42 is a high-voltage NPN silicon transistor designed for reliable switching and amplification in demanding circuits. With a collector-emitter voltage rating of 300 V and a collector current capacity of 500 mA, it is well-suited for applications that require robust performance beyond what standard small-signal transistors can deliver. Its TO-92 package makes it easy to integrate into compact designs, while its moderate gain and stable operation support both general-purpose and high-voltage signal stages.
You can use the MPSA42 for high-voltage drivers, video circuits, and control stages in power supplies. Despite its small size, it offers dependable thermal performance and switching characteristics when used within its power dissipation limits.
If you are interested in purchasing the MPSA42, feel free to contact us for pricing and availability.
| Pin Number | Pin Name | Function |
| 1 | Emitter (E) | Emits carriers; typically connected to ground or negative side of the circuit. |
| 2 | Base (B) | Controls transistor operation; small current here allows a larger current to flow from collector to emitter. |
| 3 | Collector (C) | Collects carriers; main current flows through this pin to the emitter when activated. |
| Model | VCEO (Max) | IC (Max) | Package |
| MPSA42 | 300 V | 500 mA | TO-92 |
| KST42 | 300 V | 500 mA | SOT-23 |
| MMBTA42 | 300 V | 100 mA | SOT-23 |
| PZTA42 | 300 V | 500 mA | SOT-223 |
| SS8050 | 25 V | 1.5 A | TO-92 |
| BC547 | 45 V | 100 mA | TO-92 |
| 2N3904 | 40 V | 200 mA | TO-92 |
| 2N2369 | 40 V | 200 mA | TO-92 |
| 2N3055 | 60 V | 15 A | TO-3 |
| Parameter | Value |
| Lifecycle Status | Active |
| Mounting Type | Through Hole |
| Package / Case | TO-226-3, TO-92-3 (TO-226AA) |
| Supplier Device Package | TO-92-3 |
| Number of Pins | 3 |
| Polarity | NPN |
| Element Configuration | Single |
| Collector-Emitter Breakdown Voltage (VCEO) | 300 V |
| Collector-Base Voltage (VCBO) | 300 V |
| Emitter-Base Voltage (VEBO) | 6 V |
| Collector Current (IC Max) | 500 mA |
| Max Collector Current | 200 mA (datasheet test condition) |
| Current – Collector Cutoff (ICBO) | 100 nA |
| Collector-Emitter Saturation Voltage (VCE(sat)) | 500 mV @ 2 mA, 20 mA |
| Voltage – Rated DC | 300 V |
| Current Rating | 500 mA |
| Power Dissipation (Max) | 625 mW |
| Frequency – Transition (fT) | 50 MHz |
| Gain Bandwidth Product | 50 MHz |
| DC Current Gain (hFE) | 40 @ 30 mA / 10 V |
| Operating Temperature Range | –55°C to +150°C (TJ) |
| Max Operating Temperature | 150°C |
| Min Operating Temperature | –55°C |
| Moisture Sensitivity Level (MSL) | 1 (Unlimited) |
| Packaging | Bulk |
| Lead-Free Status | Lead Free |
| RoHS Status | RoHS Compliant |
| Dimensions (Height x Width) | 4.7 mm × 3.93 mm |
| Weight | 201 mg |
| Base Part Number | MPSA42 |
| Published | 2009 |
The diagram shows how an MPSA42 NPN transistor can be used as a high-voltage switch, allowing a low-voltage control signal to operate a load powered from a much higher supply. In this circuit, a +5V signal is applied to the transistor’s base through a 1 kΩ resistor, which limits the base current and protects the transistor. When the base receives this +5V drive, the MPSA42 turns on, allowing current to flow from the +48V supply, through the load, and down through the transistor to ground.
This configuration is a low-side switching arrangement, meaning the transistor controls the ground path of the load. The load is connected directly to the high-voltage supply, but it activates only when the transistor provides a return path. Because the MPSA42 supports up to 300V, it safely handles the 48V line while still being triggered by a logic-level signal. This makes it useful for driving high-voltage indicators, relays, or other loads from microcontrollers or low-voltage control circuitry.
The MPSA42 is widely used in high-voltage switching because it can handle up to 300 V across its collector–emitter junction. This makes it suitable for circuits powered by elevated supply rails, such as 48 V or higher DC systems. A low-voltage control signal can activate the transistor, allowing it to safely switch loads that operate at much higher voltages without stressing the control circuitry.
The MPSA42 transistor’s moderate current capability and strong voltage tolerance make it an effective driver for relays, solenoids, and other inductive loads. When paired with proper base drive and protection diodes, it can interface low-voltage controllers with electromechanical components that require higher operating voltages, ensuring reliable activation and isolation.
In mixed-voltage systems, the MPSA42 serves as a practical tool for shifting low-voltage logic signals up to high-voltage domains. With its ability to withstand substantial voltage differences, it ensures safe signal translation between microcontrollers and high-voltage sections of a circuit, preventing direct exposure of sensitive components to dangerous voltage levels.
Older CRT displays and high-voltage video circuits often require transistors that tolerate high voltage and operate at respectable frequencies. The MPSA42 fits these needs well, providing stable amplification and switching performance in circuits where rapid transitions and elevated voltages are common, making it a staple in legacy display repairs.
The MPSA42 is commonly used in power supply startup and control stages, especially in switch-mode power supplies (SMPS). Its high-voltage capability allows it to manage early startup currents, control feedback loops, or drive auxiliary circuitry without failing under the harsh electrical conditions typical of power regulation environments.
With its fast switching speed and high breakdown voltage, the MPSA42 performs well in timing, pulse control, and waveform generation circuits. It can handle rapid transitions without distortion while also surviving high-voltage spikes, making it reliable in precision timing or signal-shaping applications.
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