Off state: the transistor is in off state, and Vce is approximately equal to the power supply voltage.
Amplification state: the triode is in current amplification state, 0V.
Saturation state: the triode is completely on, Vce≈0V.
The method for judging which state the triode works in is divided into:
1. Current judgment method:
Ic _ max & gtIb*β？ Amplification state
Ic_max≤ Ib*β？ saturation condition
Ic_max=Ib*β=0？ Cut off state
2. Voltage judgment method:
Uce & gt0.3V？ Amplification state
Uce=0.3V？ saturation condition
Uce=Vcc？ Cut off state
1? Triode amplifier circuit (signal triode)
The typical characteristics of triode amplifier circuit are: icmax >; β*Ib, that is to say, no matter how the Ib current changes, β*Ib will not exceed the maximum value of Ic, and the state at this time is the amplification state.
First of all, it is clear that when the transistor is saturated, Vbe=0.7V and Vce=0.3V. Because β will change with the change of temperature and humidity, it is assumed that β= 100, which is convenient for calculation.
Then Ic max=(5V-Vce)/R 1. First, the current required by the Ic is determined according to the load. Assuming that IC needs 47mA, ICMAX = (5VCE)/r1= 47ma. When VCE is minimum, IC can reach the maximum current value, that is, icmax = (5v-0. R 1 =100Ω, determine the Ic current value and the resistance value of R1,and see how Ib is calculated. Because β= 100 and Ic=β*Ib, we can calculate that Ibmax=47mA/ 100=0.47mA, that is, at 0.47mA, the transistor is in the amplification state.
Determine the resistance of R2, because when the transistor is turned on, Vbe=0.7V, the input is a 3V square wave signal, and Ib max=(3v-Vbe)/R2=0.47mA, and R2=4.89K At this time, the transistor is in a critical saturation state, so we choose a commonly used nominal resistance 10K, that is, R2 =1. Ic max meets the requirements, so far all the parameters of the triode amplifier circuit have been obtained, and the resistance selection in the actual design needs to be far from the critical saturation state.