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High Speed Switching of NPN and PNP Transistors

IP.com Disclosure Number: IPCOM000079116D
Original Publication Date: 1973-May-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Guha, SK: AUTHOR [+2]

Abstract

The circuits of Figs. 1 and 2 are capable of switching 1-2 amperes through high-current transistors (NPN or PNP), at a repetition rate of approximately 0.5-1 MHZ.

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High Speed Switching of NPN and PNP Transistors

The circuits of Figs. 1 and 2 are capable of switching 1-2 amperes through high-current transistors (NPN or PNP), at a repetition rate of approximately 0.5-1 MHZ.

In Fig. 1, a small logic signal (0.5V 0.3 ma) turns on a high-current NPN transistor which delivers a collector current of 1.2 amperes to a coil. When an UP level signal is applied at the input, T1 turns ON and T2 turns OFF. Since T1 turns ON, T3 turns ON rapidly and supplies large drive current to the base of the high-current NPN transistor T5 and thus turns ON T5 quickly. Since T2 is OFF, the base current of T4 is zero. So T4 is OFF.

When a :DOWN level signal is at the input, T1 turns OFF and T2 turns ON. When T1 turns OFF, T3 turns OFF also. Since T2 turns ON, T4 turns ON hard as the collector current of T2 is the base current of T4. Since T4 turns ON hard, it provides an excellent low-impedance path to ground for the base charge of T5 (the high-current NPN device) and, therefore, turns OFF T5 fast. When most of the base charge of T5 has gone to ground, the base current of T4 (also the collector current of T2) diminishes and T2 saturates heavily, and the collector of T2 stays at -0.3 volt.

When T5 is turned ON, T4 is OFF providing the base of T5 with a very high impedance to ground, thus allowing all the collector current of T3 to go to the base of T5 and turn ON T5 hard.

When T5 is turning OFF, T4 is ON hard providing the base of T5 with a very low imp...