A friend of mine recently asked me if I knew that there are two package types for humble TO220 devices. I didn’t understand what he meant. He then asked if I had heard of single gauge and dual gauge TO220 packages. Nope still no idea. Finally, he asked if I had seen TO220 voltage regulators such as a 78L05 device with a thin heatsink?

Yes, I had seen these before, in fact I have a couple. I hadn’t really paid a lot of attention to the first time I had seen one of these components with a thin heatsink. I thought that it was perhaps a counterfeit device. That is not the case (excuse the pun). A thinner heatsink is a type of TO220 package.

Below are two TO220 devices, a 7812 12V regulator manufactured by On Semiconductor and a TIP31 NPN transistor from ST Microelectronics. A quick glance and their shape is instantly recognisable.

When they are more closely compared, the difference in the dimensions of their heatsinks becomes obvious.

This document from On Semiconductor explains how they would be transitioning to single gauge packaging for many of their devices. Also, a ST Microelectronics datasheet for their L78S series of voltage regulators provide part numbers and mechanical drawings for the two different package types.

On Semiconductor’s documentation states that there is insignificant difference in performance of the single and dual gauge heatsinks. ST Microelectronics does not detail any difference in the thermal resistance to air of the two different gauges.

Comparing the two different gauges with my samples, the single gauge heatsink can be bent out of shape by hand. This would make a single gauge device prone to damage if mounted to a heatsink that wasn’t secured to a PCB or chassis. Perhaps an advantage of the single gauge TO220 package is that it is faster to solder to a PCB heatsink.

In summary, the different TO220 package types have heatsinks with the following thicknesses:

• Single gauge = 0.5mm
• Dual gauge = 1.2mm

If you are purchasing a large quantity of TO220 devices or need mechanical strength, double check the datasheets and product codes to ensure you order the correct gauge you require.