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Understanding triode principle


The source of amplified output is power supply connected to collector. We consider it as a pool connected to a collector. The more collector damper is open, greater will be water flow (Ic); base current (Ib) For example, amount of force with which we push collector gate, push harder (Ib becomes larger), collector gate opens more, and water flow (Ic) becomes larger, this is control of base current collector current our thrust is always When thrust (Ib) reaches a certain value, collector gate opens completely to maximum, and our thrust can no longer be linearly related to water flow, and at same time triode saturates with time.

1. Closing Status

Vbe< Triode turn-on voltage (silicon tube is typically around 0.6). At this time, it is equivalent to not pushing gate, gate is closed and no water flows out (Ic is approximately 0 and there is a leakage current).

2. Zoomed State

The emitter junction is forward biased and collector junction is reverse biased. At this time, this is equivalent to a strong pressure on gate (but gate is not at its maximum), and water flows out, and amount of water flow is regulated only by draft.

3. Saturation

The emitter junction is forward biased and collector junction is forward biased (this needs to be checked). At this time, amount of water flow is controlled by two factors, first is thrust (Ib), and second is maximum opening of the gate (Vse).

(Note: resistance value in picture above is written carelessly)

In common-emitter amplifier circuit, as Ib increases, Ic increases, Vce gradually decreases, gradually enters saturation region from gain region, β decreases, and gain of circuit deteriorates.

With exception of environmental factors, a triode can enter saturation in two ways:

(1) The AC signal amplitude is too high. At peak, Ic is too large and Vce is too small.

(2) Increasing amplifier circuit and selected supply voltage is unreasonable.

Therefore, when designing amplifier circuit, we need to design parameters according to input signal in order to avoid tube from saturating during operation.