Speed-up for Darlingtons

Darlingtons are useful devices because they have a pleasantly high gain. A disadvantage however, is that they are much slower than normal transistors, something that becomes even more of an issue if the two base-emitter resistors have relatively high values. The reason is that the charge in the base can be dissipated only slowly. In reality this can only happen in the base/emitter junction itself or via the relatively high base-emitter resistor (R2). There is not much that can be done with ready-made ‘three legged’ darlingtons, but with do-it-yourself darlingtons both base connections are readily accessible, which makes it possible to apply ‘minor surgery’ in the interest of a little improvement.