# IEC open-collector buffer (rectangular form)

Canonical URL: https://eloragrid.ai/symbols/iec-open-collector-buffer
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: 1
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: 1 element with the underlined-diamond open-circuit (L-type) output qualifier
Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier. The counterpart is the matching functional concept; no equivalence of every detailed standard graphic is asserted.
Related representation: [Open-collector buffer](https://eloragrid.ai/symbols/open-collector-buffer)

IEC buffer with an underlined diamond at the output, showing an open-collector or open-drain stage.

## In plain English

### What does IEC open-collector buffer (rectangular form) mean?

The underlined diamond inside the outline marks an output that can pull to a low level but needs an external pull-up to produce a high level. TI's public explanation describes this as suitable for a positive-logic wired-AND connection. The 1 additional drawing mark makes the element non-inverting overall.

### A simple example

Open-collector outputs are used for shared alarm lines, level shifting to a higher pull-up voltage, and driving small relays or indicator lamps. The pull-up resistor or load must be shown on the drawing, together with its supply, because the element cannot produce a high level by itself.

### What the drawings help you do

The symbol does not state the maximum sink current or the maximum voltage the output may be pulled to. Those limits are device data and govern whether a relay coil or lamp can be connected directly.

### This particular reference

IEC buffer with an underlined diamond at the output, showing an open-collector or open-drain stage. An overlined diamond is the H-type open-emitter output, which sources current and needs a pull-down.

### Terms

- Coil: A wound conductor that can produce a magnetic field when energised.
- Terminal: An identified point where a conductor connects.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf)
- [SN74LS07 — open-collector output buffers](https://www.ti.com/lit/ds/symlink/sn74ls07.pdf)


## What it represents

The underlined diamond inside the outline marks an output that can pull to a low level but needs an external pull-up to produce a high level. TI's public explanation describes this as suitable for a positive-logic wired-AND connection. The 1 qualifier makes the element non-inverting overall.
Open-collector outputs are used for shared alarm lines, level shifting to a higher pull-up voltage, and driving small relays or indicator lamps. The pull-up resistor or load must be shown on the drawing, together with its supply, because the element cannot produce a high level by itself.
The symbol does not state the maximum sink current or the maximum voltage the output may be pulled to. Those limits are device data and govern whether a relay coil or lamp can be connected directly.

## How to read it

- Find the pull-up resistor or load and its supply rail.
- Check whether several outputs are wired together.

## Information to show or reference

- Show the underlined diamond next to the output.
- Draw the pull-up and label its supply.
- Note the sink current and voltage limits where a load is driven directly.

## Important distinction

An overlined diamond is the H-type open-emitter output, which sources current and needs a pull-down.

## Facts

- Output qualifier: Diamond with underline (L-type open circuit)
- External part required: Pull-up resistor or load
- Wired connection: Positive-logic wired-AND
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Defines the open-collector output qualifier and its wired-AND capability.
- [SN74LS07 — open-collector output buffers](https://www.ti.com/lit/ds/symlink/sn74ls07.pdf) — Texas Instruments. Manufacturer open-collector buffer documentation.

## 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.