1 Answer
In a **BJT** (Bipolar Junction Transistor), **current** refers to the flow of electric charge through its three terminals:
- **Emitter (E)**
- **Base (B)**
- **Collector (C)**
The BJT operates using **both majority and minority carriers** (hence the name *bipolar*), and the currents are related like this:
1. **Emitter current (Iₑ)**:
The current that leaves (or enters, depending on type) the emitter terminal. It's usually the largest current because the emitter is heavily doped to supply charge carriers.
2. **Base current (Iᵦ)**:
A small current flowing into (for NPN) or out of (for PNP) the base. It controls the transistor's operation. The base is lightly doped and very thin, so only a small fraction of the emitter current enters the base.
3. **Collector current (I꜀)**:
The current that flows into (for NPN) or out of (for PNP) the collector. It is almost equal to the emitter current, minus the small base current.
The important relationship is:
\[
I_E = I_C + I_B
\]
In simple terms:
- **Most of the emitter current** (around 95–99%) **becomes collector current**.
- **A small portion** becomes **base current**.
Also, **current gain** (\(\beta\)) is an important property:
\[
\beta = \frac{I_C}{I_B}
\]
where \(\beta\) is typically large (like 100–300 for small-signal BJTs).
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Would you like a quick diagram to make this even clearer?
- **Emitter (E)**
- **Base (B)**
- **Collector (C)**
The BJT operates using **both majority and minority carriers** (hence the name *bipolar*), and the currents are related like this:
1. **Emitter current (Iₑ)**:
The current that leaves (or enters, depending on type) the emitter terminal. It's usually the largest current because the emitter is heavily doped to supply charge carriers.
2. **Base current (Iᵦ)**:
A small current flowing into (for NPN) or out of (for PNP) the base. It controls the transistor's operation. The base is lightly doped and very thin, so only a small fraction of the emitter current enters the base.
3. **Collector current (I꜀)**:
The current that flows into (for NPN) or out of (for PNP) the collector. It is almost equal to the emitter current, minus the small base current.
The important relationship is:
\[
I_E = I_C + I_B
\]
In simple terms:
- **Most of the emitter current** (around 95–99%) **becomes collector current**.
- **A small portion** becomes **base current**.
Also, **current gain** (\(\beta\)) is an important property:
\[
\beta = \frac{I_C}{I_B}
\]
where \(\beta\) is typically large (like 100–300 for small-signal BJTs).
---
Would you like a quick diagram to make this even clearer?