# IEC open-circuit output, L-type (open collector)

Canonical URL: https://eloragrid.ai/symbols/iec-open-circuit-output-l-type
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: OC-L
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Diamond with underline inside the outline at the output
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.

Underlined diamond inside an outline: an open-circuit output that can only drive a low level.

## In plain English

### What does IEC open-circuit output, L-type (open collector) mean?

The underlined diamond marks an output, such as an NPN open collector or an N-channel open drain, that can supply a relatively low-impedance L level when on and is open when off. An external pull-up is needed. TI's public overview notes this output type supports a positive-logic wired-AND connection.

### A simple example

When a variant with a built-in passive pull-up exists, a further mark inside the diamond distinguishes it. Reviewing the exact additional drawing mark tells the drafter whether an external pull-up must be added to the schematic.

### What the drawings help you do

The additional drawing mark does not state the maximum pull-up voltage. Some open-drain outputs tolerate a higher pull-up rail than the device supply and some do not.

### This particular reference

Underlined diamond inside an outline: an open-circuit output that can only drive a low level. The H-type open-circuit output has the line above the diamond and drives a high level only.

### Terms

- Terminal: An identified point where a conductor connects.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Rating: A value stating the conditions for which equipment is specified.

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)


## What it represents

The underlined diamond marks an output, such as an NPN open collector or an N-channel open drain, that can supply a relatively low-impedance L level when on and is open when off. An external pull-up is needed. TI's public overview notes this output type supports a positive-logic wired-AND connection.
When a variant with a built-in passive pull-up exists, a further mark inside the diamond distinguishes it. Reviewing the exact qualifier tells the drafter whether an external pull-up must be added to the schematic.
The qualifier does not state the maximum pull-up voltage. Some open-drain outputs tolerate a higher pull-up rail than the device supply and some do not.

## How to read it

- Underline below the diamond: pulls low only.
- Find the external pull-up on the net.

## Information to show or reference

- Draw the diamond with its underline next to the output.
- Show the pull-up resistor.
- Record the permitted pull-up voltage.

## Important distinction

The H-type open-circuit output has the line above the diamond and drives a high level only.

## Facts

- Drives: Low level only
- Wired connection: Wired-AND in positive logic
- 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. Describes the L-type open-circuit output qualifier and wired-AND capability.

## 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.