OC-BUF
Open-collector buffer
Provides a logic output through a transistor pull-down stage requiring the documented external load or pull-up.
Schematic
IEC · 1
IEC open-collector buffer (rectangular form)
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.
- 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.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A) · SN74LS07 — open-collector output buffers
IEC · 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.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · 1
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.
A distinction that matters
An overlined diamond is the H-type open-emitter output, which sources current and needs a pull-down.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
Defines the open-collector output qualifier and its wired-AND capability.
SN74LS07 — open-collector output buffers
Manufacturer open-collector buffer documentation.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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