# What is this triple-transistor arrangement called?

For an old Fuji 2DI200D-100 power transistor module, it uses three transistors internally for each half-bridge:

The circuit in question doesn't connect to the middle bases at all, just B1 and B2, so this (dual) triplet is being used solely as two big transistors. Is this called a "triple Darlington pair?" "Darlington triple?" Or is there some other name for this arrangement?

• I've seen it called a "trilington", but I don't think there is any "official" name for it. – Hearth Jul 10 at 17:26
• ”each half of an "H" bridge” For future reference, that’s called a half-bridge. – winny Jul 10 at 17:42

They're called high current triplets.

I don't propose to cover high current followers in any great detail, because they are already explained in various other articles and projects on the ESP website. High current versions are typically used in the output stages of power amplifiers, and can be simple complementary Darlington pairs, Sziklai pairs or in some cases a triple (three devices in cascade), and using various mixtures of NPN and PNP transistors. There are many combinations, and it is hard to provide the detailed analysis that each deserves in a short article.

Instead, I will show some of the common variations, purely for interest's sake. If you want to know more, you will need to perform your own analysis because the choice of transistors determines how well each version will work in any given configuration. The selection of devices depends on the application, frequency range, voltage and current, and given the number of transistor types available, the number of combinations is truly vast.

In the drawings below, resistors between individual transistor base-emitter junctions are not shown. For high-current triples, Q2 could have an emitter-base resistor of around 220 ohms, and Q3 might use 22 ohms, but these values need to be determined by the application and to suit the devices and intended purpose. Higher resistances can increase the turn-off time, and lower values draw more current. This is part of the design process, and each case will be different.

Source: https://sound-au.com/articles/followers.html (section 11)

• You're using the > quotation markdown to incorrectly highlight stuff you've written yourself - unless, that is, you are quoting yourself, in which case you should give attribution! :^) – Transistor Aug 4 at 21:59
• @Transistor Maybe you should read last line I didn't quote: Source: sound-au.com/articles/followers.html (section 11) :-) – Huisman Aug 5 at 5:28
• Ha! Got it, thanks. I thought the reference was for the diagram only. +1. – Transistor Aug 5 at 9:14