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How to calculate the saturation of a transistor?
Divide the maximum collector current (I C) by the minimum current gain (h FE) at that collector current. For example, say I C (max) = 30 mA and h FE (min) = 83 at I C = 30 mA. The result is that I B (nominal) is about 360 µA. Multiply I B (nominal) by a “saturation factor” – a number between 2 and 10 – to ensure that the transistor saturates.
How is the saturation of a BJT determined?
Saturation (for a BJT) is defined in several ways, but generally it relates to the collector-emitter voltage V CE. Here is an LTSpice simulation of a 2N4401 transistor driving a 160 ohm load with a 5V supply, which corresponds to about 30 mA collector current with the transistor turned ON.
Why do you need a saturated switch on a switch?
When you’re switching a load ON and OFF, you want to saturate the switching device in the ON state, because you want to minimise V CE, to maximise the voltage across the load. This circuit is then called a “saturated switch”.
What’s the maximum possible current in a collector circuit?
But at a certain point, the collector current starts to become limited by the collector circuit. With a 5V supply and a 160 ohm resistor, the maximum possible current is 31.25 mA.
What’s the maximum possible current of a transistor?
With a 5V supply and a 160 ohm resistor, the maximum possible current is 31.25 mA. The transistor wants its collector current to increase, because its base current is continuing to increase, but it can’t, because the collector circuit is limiting the current.
What are the rules of thumb for transistor action?
Some useful “rules of thumb” which help in understanding transistor action are (from Horowitz & Hill): A base emitter voltage VBEof about 0.6 v will “turn on” the base-emitter diode and that voltage changes very little, +/- 0.1v throughout the active range of the transistor which may change base current by a factor of 10 or more.