What Is SOT-23 Package?
The most common SOT are SOT-23 variations. The SOT23-3 package is very popular and a common package for transistors, and is also used for diodes and voltage regulators. Small Outline Transistor (SOT) packages are very small, inexpensive surface-mount plastic-molded packages with leads on their two long sides. Due to their low cost and low profile, SOT’s are widely used in consumer electronics.
The SOT-23 and the SC-70 packages are two of the most widely used SOT packages today. Note that aside from these two, there are many other SOT package types used in the IC industry.
SOT-23-3 Package
What is the significance of numbers (2,3) mentioned in SOT23? While some packages do have numbers that mean something, the TO, DO, and SOT series are simply serial. SOT-23 is just package number 23 in the JEDEC SOT specifications. There’s no significance to the numbers beyond that. You may occasionally see SOT-23-3 or SOT-23-5 or SOT-23-6; these do have significance, as the last digit is the number of pins on the package. Sometimes SOT-23-5 gets referred to as SOT-25, as well, but this is generally considered incorrect. Similarly for SOT-23-6 being called SOT-26.
A small outline transistor (SOT) is a family of small footprint, discrete surface mount transistor commonly used in consumer electronics. The most common SOT are SOT23 variations, also manufacturers offer the nearly identical thin small outline transistor (TSOT) package, where lower height is important.
In the beginning of the surface mount era was SOT 23, which had three pins. It was used mainly to replace the very popular TO-18 and TO-92 3 pin leaded transistor packages, the name means Small Outline Transistor. As such, three pins in a triangular configuration was easy to read, as it echoed the three pin leaded package.
As densities increased, it was noticed that the SOT 23 had ‘missing leads’, and the package could be increased to up to 6 leads without increasing significantly the area it consumed. 5 leads was an especially useful package, as it permitted a single op-amp or single 2-input logic gate to be implemented. So SOT 23-5 and SOT 23-6 were born.
Where a manufacturer’s data sheet covers only single transistors, they tend to use only the original SOT 23 designation. Where a manufacturer is providing (let’s say) diodes, diode pairs and diode triples in 3 and 6 pin versions of the SOT 23 package, they’ll sometimes refer to the 3 pin version as SOT 23-3 to distinguish it from the SOT 23-6, but sometimes just call it SOT 23. It’s up to the manufacturer.
Note that SOT-23 and SOT 23-3 are just names, they don’t have any definition. They have just entered the language through use and custom. JEDEC formally standardizes dimensions, its TO-236AB package outline is the JEDEC title for what is known as SOT 23 and SOT 23-3.