Transistor Operation

1. Cut off (no collector current), useful for switch operation.
   截止（无集电极电流），适用于开关操作
2. In the active region (some collector current, more than a few tenths of a volt above the emitter), useful for amplifier applications
   在放大区（某些集电极电流， emitter 电压高于几 tenths 伏）, 适用于放大器应用
3. In saturation (collector a few tenths of a volt above emitter), large current useful for "switch on" applications.
   在饱和区（集电极略高于发射极几十分之一伏），有较大的电流，适用于'导通'应用。

Collector Current Determination

The base-emitter voltage V_BE can be considered to be the controlling variable in determining transistor action. The collector current is related to this voltage by the Ebers-Moll relationship (sometimes labeled the Shockley equation):

where T = absolute temperature T = 绝对温度 k = Boltzmann's constant k = Boltzmann 常数 e = electron charge e = 电子电荷 其中

Base-Emitter Junction Details

1. A base emitter voltage V_BE of 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.
   当基极-发射极二极管的发射极电压V_BE约为0.6 V时，该二极管会被“导通”，且在此晶体管的活动范围内，该电压变化非常小，小于±0.1 V，这种变化可能使基极电流增加10倍或更多。
2. An increase in base-emitter voltage V_BE by about 60 mV will increase the collector current I_C by about a factor of 10.
3. The effective AC series resistance of the emitter is about 25/I_C ohms.
   发射极的有效交流串联电阻约为25/I_C欧姆。
4. The base-emitter voltage V_BE is temperature dependent, decreasing about 2.1 mV/C
   基-射极电压V_BE具有温度依赖性，约每下降2.1 mV/C
5. The base-emitter voltage V_BE varies slightly with the collector-emitter voltage V_CE at constant collector current I_C : ΔV_BE ≈ -0.001ΔV_CE.
   基-射极电压V_BE在集电极电流I_C恒定时，随着集电极-射极电压V_CE略有变化：ΔV_BE ≈ -0.001ΔV_CE。
基极-发射极电压V_BE增加约60 mV时，集电极电流I_C将增加约10倍。

Transistor Action

More about transistor regions

Collector Current

Normal transistor action results in a collector-to-emitter current which is about 99% of the total current. The usual symbols used to express the transistor current relationships are shown.

The proportionality β can take values in the range 20 to 200 and is not a constant even for a given transistor. It increases for larger emitter currents because the larger number of electrons injected into the base exceeds the available holes for recombination so the fraction which recombine to produce base current delines even further.

Use of the Current Gain

Any circuit that depends on a specific value of the current gain β is a bad circuit because that value varies for a given transistor as well as between different transistors of the same type.