8.7.2. Emitter Current and Collector Current Ratio (α)

Now coming to the other important parameter which is the ratio of the collector terminal current and the emitter terminal current, where we know that the emitter terminal current can be expressed.

Now we do have the other parameter apart from β , we do have collector current divided by emitter terminal current which is denoted by α.

In a bipolar junction transistor (BJT), the two key currents are the collector current (IC) and the emitter current (IE). The ratio of these two currents is represented by α (alpha). This ratio is crucial because it indicates how effectively the transistor can amplify current.

The emitter current can be represented in relation to the collector current and the base current (IB) as follows: IE = IC + IB. This equation shows that the total emitter current is the sum of the current flowing to the collector and the current going into the base.

Think of a BJT like a water faucet. The collector current is like the water flowing out of the faucet (the main output), while the emitter current represents the total water flow coming from the source (including a small trickle going into an extra pipe, symbolizing the base current). The ratio α tells us how much of the total water (emitter current) is actually flowing out of the faucet (collector current). A high α value means most of the water is being used effectively, which is what we want.

That can be expressed in terms of β and this expression can be easily found that, if we write the expression of emitter current which is collector current plus the base current.

The parameter α can also be related to another important parameter in BJTs, known as β (beta), which is the current gain of the transistor. The relationship is defined mathematically as α = β / (β + 1). This relationship is significant because it helps us understand how changes in transistor characteristics can affect amplification.

In simpler terms, a transistor's ability to amplify a signal efficiently is influenced by both α and β. A higher β usually indicates a stronger transistor that can produce a higher collector current with a smaller base current.

Imagine α as a sports team, where β represents the star players. A team with a few star players (high β) but most of the players (base current) need training (lower efficiency) might not perform well overall. However, if the team works together effectively (high α), even with fewer exceptional players, they can still win games, just like a transistor can amplify signals effectively with a good balance of collector and emitter currents.

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