PNP Transistor (BJT) Symbol
Definition: The PNP Transistor (BJT) symbol represents a bipolar junction transistor with a p-type emitter, n-type base, and p-type collector, defined in IEC 60617-05 and ANSI Y32.2 / IEEE 315-1975, drawn as a vertical line (base) with two diagonal lines for collector and emitter — the emitter line carrying an arrowhead pointing inward toward the base, indicating conventional current flows into the emitter when the transistor is conducting.
Also known as: PNP BJT, PNP transistor, p-n-p transistor, PNP bipolar transistor, 2N2907, sourcing transistor.
What the PNP Transistor (BJT) symbol means
The PNP Transistor (BJT) symbol represents a three-terminal bipolar junction transistor in which the majority charge carriers are holes. The transistor conducts when the base terminal is pulled below the emitter voltage by approximately 0.6–0.7 V, allowing a small base current to control a much larger collector-to-emitter current. In circuit diagrams the PNP symbol signals a current-sourcing switch or amplifier stage that sources current from the positive supply rail through its emitter.
The PNP BJT symbol appears in schematics wherever the design calls for a high-side switch (load connected between collector and negative rail), a complementary pair with an NPN transistor in push-pull or Class-AB amplifier stages, or a current mirror source. Its orientation — emitter toward the positive supply — is the key topological indicator that distinguishes it from the NPN configuration.
How to identify the PNP Transistor (BJT) symbol
The PNP BJT symbol is drawn as a circle (device envelope, optional) containing: a vertical line representing the base connection; a diagonal line from the base line to the upper-right for the collector terminal; and a diagonal line from the base line to the lower-right for the emitter terminal, with a filled arrowhead on the emitter line pointing inward toward the base. The inward-pointing emitter arrow is the definitive identification feature — NPN emitter arrows point outward. The base pin exits left, the collector exits upper-right, and the emitter exits lower-right in the standard orientation used by this symbol (Base x=0, Collector x=50 y=45, Emitter x=50 y=5).
Function in a circuit
A PNP BJT conducts from emitter to collector when a small current is drawn out of the base terminal (base driven below emitter potential by ~0.6 V for silicon). The collector current is approximately hFE (DC current gain, typically 50–300) times the base current. In switching mode the transistor saturates when enough base current is supplied, presenting a low collector-emitter voltage (VCEsat ≈ 0.1–0.3 V). In amplifier mode the transistor operates in the active region, providing voltage or current gain. Power dissipation is IC × VCE and must be managed with heatsinking for higher currents.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-05 (semiconductors) defines the PNP BJT symbol as a base line with two angled branches for collector and emitter, the emitter branch carrying an arrow pointing toward the base. The IEC symbol may include a circle envelope for discrete devices. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315-1975 defines the same three-terminal structure with an inward-pointing emitter arrow for PNP transistors. The ANSI/IEEE symbol is functionally and visually identical to the IEC version; a circle envelope is also optional. |
| Key difference | IEC 60617-05 and ANSI Y32.2 / IEEE 315-1975 use the same glyph for the PNP BJT. The only practical difference is that some ANSI schematics omit the circle envelope while IEC schematics for discrete devices typically include it; the arrow direction (inward for PNP) is identical in both standards. |
Terminals / pins
| Pin | Name |
|---|---|
| base | Base |
| collector | Collector |
| emitter | Emitter |
Typical values
VBE (turn-on): ~0.6–0.7 V (silicon); VCEsat: ~0.1–0.3 V (saturated); hFE (current gain): 50–300 (general purpose); IC(max): 0.6 A (2N2907), 1 A (BC327), 5 A (TIP42); VCEO (collector-emitter breakdown): 40–100 V typical; power dissipation: 625 mW–65 W (TO-92 to TO-3) depending on package.
Where the PNP Transistor (BJT) symbol is used
- High-side switching of loads referenced to the positive supply rail (emitter to V+, collector to load to GND)
- Complementary NPN-PNP push-pull output stages in Class-AB audio amplifiers
- Current mirror source circuits providing stable bias currents in analogue IC design
- Level-shifting and inverting driver stages in microcontroller peripheral circuits
- Relay driver circuits where the PNP sources base current from the logic supply
- Temperature-sensing circuits exploiting the predictable VBE–temperature coefficient (~−2 mV/°C)
Example
In a microcontroller-driven relay circuit, a PNP BJT (2N2907) is connected with its emitter to the 5 V supply, its base resistor driven by a GPIO pin pulled low, and its collector connected through the relay coil to GND. When the GPIO outputs LOW, base current flows out of the base, the transistor saturates, current flows through the relay coil, and the relay closes — a classic high-side PNP switch.
Key facts
- The PNP BJT symbol is identified by the emitter arrow pointing inward toward the base — the mnemonic 'arrow pointing in = PNP' (NPN emitter arrow points outward).
- A PNP transistor conducts when the base is pulled at least 0.6–0.7 V below the emitter voltage (for silicon); base current flows out of the base terminal.
- The three terminals are Base (control input), Collector (output, connected to the load side), and Emitter (connected to the positive supply in a high-side switch configuration).
- Collector current equals base current multiplied by hFE (DC current gain), typically 50–300 for general-purpose PNP devices such as the 2N2907 or BC557.
- The PNP symbol is defined in IEC 60617-05 and ANSI Y32.2 / IEEE 315-1975; both standards use an inward-pointing emitter arrow, with an optional circle envelope for discrete devices.
- PNP transistors source current from the positive supply through the emitter; NPN transistors sink current to the negative supply through the emitter — this is the fundamental topological difference.
- Common general-purpose PNP BJTs include the 2N2907 (0.6 A, 40 V), BC557 (0.1 A, 45 V), and TIP42 (6 A, 100 V).
Frequently asked questions
What does the PNP transistor symbol look like?
The PNP BJT symbol consists of a vertical base line with two diagonal branches: one going to the upper-right (collector) and one going to the lower-right (emitter). The emitter branch has a filled arrowhead pointing inward toward the base line. A circle envelope is optional. The inward arrow is the definitive visual identifier for a PNP device.
What does the PNP transistor symbol mean in a circuit?
The PNP symbol indicates a bipolar junction transistor that conducts collector-to-emitter current when the base is driven below the emitter voltage. The emitter is typically connected to the positive supply, making the PNP a current-sourcing or high-side switch controlled by pulling the base low.
How do you tell a PNP symbol from an NPN symbol?
The emitter arrow direction is the key: PNP emitter arrow points inward (toward the base line); NPN emitter arrow points outward (away from the base). A useful mnemonic is 'NPN = Not Pointing iN' or 'PNP arrow Points iN to base'.
What is the IEC and ANSI standard for the PNP transistor symbol?
The PNP BJT symbol is defined in IEC 60617-05 (semiconductor devices) and ANSI Y32.2 / IEEE 315-1975. Both standards use the same glyph: a base line with collector and emitter branches, the emitter carrying an inward-pointing arrow. An optional circle envelope may be included for discrete devices.
What voltage turns on a PNP transistor?
A silicon PNP transistor begins conducting when the base-emitter voltage VBE reaches approximately −0.6 to −0.7 V (base 0.6–0.7 V below emitter). For complete saturation in switching circuits, the base current should be approximately one-tenth of the desired collector current (IC / hFE rule).
What are the three pins of the PNP BJT symbol?
The three pins are Base (the control terminal, driven by the input signal), Collector (the output terminal, connected to the load), and Emitter (the supply terminal, typically connected to the positive voltage rail in a PNP high-side switch). In the symbol, Base exits left, Collector exits upper-right, and Emitter exits lower-right.
When should I use a PNP transistor instead of an NPN?
Use a PNP transistor when the load must be switched on the high side — between the positive supply and the load. PNP transistors source current from V+ through their emitter, making them natural high-side switches. NPN transistors are more common for low-side switching (load between V+ and collector, emitter to GND) because NPN devices generally offer better current gain and lower saturation voltage in standard silicon processes.
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