Bipolar Junction Transistors (BJTs) look like old-fashioned electronic components, but due to their low cost and superior parameters, they can solve many problems. We can find new applications that were not possible in the past due to the high cost of these components, such as where we can replace higher-power transistors (with or without heat sinks) with multiple parallel-connected transistors in some cases, and Get many benefits from it.
In general, low-power transistors are faster, have higher operating frequencies, lower noise, lower total harmonic distortion, and their The package is more convenient for manual and automatic soldering. Many transistors that dissipate up to around 1W come in packages similar to TO-92. Most of these transistors are relatively inexpensive, can be purchased in large quantities, and are easy to use in packages like the TO-92.
The heat generated from these packages is easily dissipated efficiently by cooling fans or even normal air convection. Additionally, we can take advantage of the large copper surface area around these transistors to increase their power dissipation. There is a lot of heat dissipation information and calculations documented in the data sheets and literature for the different packages of these electronic components, so we won't discuss them in detail here.
Power transistor packages such as TO-126, TO-220 are large and heavy, making it difficult to mount on a PCB, and additional heatsinks are required to exploit the full performance and reliability of these power transistors.
These packages and heatsinks block the flow of cooling air, and the use of additional heatsinks creates mechanical and electrical problems, such as heatsinks that are not very stable in vibrating equipment, they require electrical isolation, etc.
