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Subject: Re: Grounding the Base of Bipolar Transistors

Date: 02/07/03 at 12:59 PM
Posted by: Ron Harrison
E-mail: rmaxh@yahoo.com
Message Posted:

In Reply to: Grounding the Base of Bipolar Transistors posted by Franklin DeMatto on 02/06/03 at 2:18 PM:

Before I answer your question, I want to point out that the base-emitter junction is a diode, so you should have a current-limiting resistor in series with your switching signal source.
There are two reasons for the resistor to ground:
1. Bipolar transistors have leakage current from collector to base. This can cause the transistor to turn on partially, especially at high temperatures, if there is not a path to ground for the leakage current.
2. Bipolar transistors exhibit a phenomenon called base charge storage. Excess charge accumulates in the base region of a transistor when it is saturated, and the transistor will not turn off until that excess charge is swept out.

Ron


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