# NPN phototransistor

Canonical URL: https://eloragrid.ai/symbols/npn-phototransistor
Publisher: Elora Grid
Updated: 2026-10-14
Lookup label: PHOTO-NPN
Drawing use: Schematic
Reference families: Manufacturer

An NPN transistor whose collector-emitter conduction responds to incident light in the documented detector arrangement.

## What it represents

An NPN transistor whose collector-emitter conduction responds to incident light in the documented detector arrangement.
On a schematic, identify the collector/emitter connections and any accessible base terminal and trace the optical sensing and load circuit. Keep the component tag and signal/reference names consistent across the control drawing, terminal schedule and device documentation.
A phototransistor provides transistor action; a photodiode generates a different detector current response.
Terminal letters describe electrical roles, not package pin numbers. Check the selected public datasheet for the actual pin assignment, polarity and any internally connected terminals before completing the drawing.

## How to read it

- Identify the collector/emitter connections and any accessible base terminal.
- Trace the optical sensing and load circuit.

## Information to show or reference

- Label the collector/emitter connections and any accessible base terminal.
- Cross-reference the optical sensing and load circuit.
- Add the selected device or circuit documentation revision, power/reference connections and project signal convention.

## Important distinction

A phototransistor provides transistor action; a photodiode generates a different detector current response.

## Facts

- Common schematic mnemonic: PHOTO-NPN — descriptive only; project/device documentation defines reference designations.
- Terminal / interface focus: The collector/emitter connections and any accessible base terminal
- Artwork scope: Original educational component glyph; not a certified standard graphic or package pinout.

## Public references

- [BPW77 silicon NPN phototransistor documentation](https://www.vishay.com/docs/81527/bpw77n.pdf) — Vishay. Public primary manufacturer documentation establishes the component function or circuit/topology relationship. Preview geometry and drafting explanations are independently authored.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.