Preface

During this period of time, I came into contact with Based on triode 、 Voltage regulator diode realizes voltage reduction and voltage stabilization Circuit . When you are familiar with circuits and reading articles , I found many articles about Triode linear voltage stabilizing circuit The principle of is not introduced in detail 、 An incorrect question .

This paper first introduces the design of triode Input / Output characteristic curve , And use on this basis Multisim Build a triode voltage stabilizing circuit , Finally, the voltage stabilizing circuit is Principle analysis .

One 、 Triode input / Output characteristic curve

1. Input characteristic curve

When the common emitter of the triode is connected , Voltage between collector and emitter $U_{CE}$ When maintained at different voltages , reflect $U_{BE}$ And $i_B$ A series of curves of the relationship , Called triode Common emitter input characteristic curve .

In general , When $U_{CE}\ge 1V$ when , The collector junction is in the reverse bias state , here $U_{CE}$ Increasing pair of $i_B$ The impact is very small , therefore $U_{CE}\ge 1V$ The later common emitter input characteristic curve is similar to $U_{CE}＝1V$ The characteristic curves of are basically coincident .

therefore , The device manual of triode usually only gives one $U_{CE}\ge 1V$ Input characteristic curve of , As shown in the figure above .
The mathematical expression of the input characteristic curve is ：
$$i_B=f(U_{BE}{|}_{U_{CE}=oftenCount})$$
The input characteristic curve of triode is very similar to the volt ampere characteristic curve of diode , There is also a dead zone ; The dead time voltage of the silicon tube is about 0.5V, The dead time voltage of germanium tube is about 0.2V. After conduction , Silicon tube $U_{BE}$ about 0.5V, Germanium tube $U_{BE}$ about 0.3V.

2. Output characteristic curve

1） Cut off zone
The cut-off area is $i_B=0$ The area below the characteristic curve of . In the cut-off area , Transistor's Both the transmitting junction and the collector junction are in the reverse bias state , The collector has only a very weak current $I_{CEO}$ adopt , At this time, the triode loses its amplification function .

2） Saturation zone
When the voltage applied to the triode emitter junction is greater than $PN$ Junction conduction voltage , And when the base current increases to a certain extent , The collector current no longer increases with the increase of the base current , But it is near a certain value and no longer changes , At this time, the triode loses its amplification effect on the current , The voltage between collector and emitter is very small , The conduction state between collector and emitter is equivalent to that of switch . This state of triode is called saturation conduction state .

In the saturation zone , Corresponding to different $i_B$ The characteristic curves of values almost coincide . here ,$U_{CE}$ smaller ,$i_C$ Although increase , but $i_C$ Little increase ,$i_B$ Lose right $i_C$ The ability to control . When saturated , Transistor's The emitter junction and collector junction are in the forward bias state . The voltage between the collector and emitter of the triode is called Set - Radiation saturation pressure drop , Write it down as $U_{CES}$. In small and medium power silicon tubes , Usually $U_{CES}＜0.5V$.

3） Zoom in
When the voltage applied to the triode emitter junction is greater than $PN$ Junction conduction voltage , And at a proper value , Transistor's The emitter junction is forward biased , Collector reverse bias , At this time, the base current controls the collector current , Make the triode have the function of current amplification .

In the magnifying area , The characteristic curve is similar to a cluster Parallel equidistant The parallel lines of ,$i_C$ The amount of change and $i_B$ The amount of change basically maintains a linear relationship , here $\Delta i_C=\beta \Delta i_B$, And $\Delta i_C＞＞\Delta i_B$,$\beta$ Is the current amplification factor of triode .

meanwhile , In this area, the control effect of collector voltage on collector current is very weak , When $U_{CE}\ge 1V$,$U_{CE}$ The increase of is difficult to cause $i_C$ An increase in . here , if $i_B$ unchanged , Then the triode can be regarded as a constant current source .

Two 、 Triode voltage stabilizing circuit and principle analysis

1. Triode series voltage stabilizing circuit

This article is based on Multisim Built by triode 、 Zener diode 、 resistance 、 A triode series linear voltage stabilizing circuit composed of capacitance and other vertical components , The implementation will 12V The DC voltage passes through the triode 、 Voltage stabilizing diode and other components are reduced to 5V, Power the load . For the convenience of observation , choose LED The lamp （ red ） As a circuit load , Its working voltage is 1.66V, electric current 5mA. Its basic circuit topology is shown in the figure below ：

resistance R1 And zener diode D1 Form a basic voltage stabilizing circuit , The voltage is stabilized at... Through the zener diode 5.6V; The zener diode is connected with the base of the triode , Emitter output , Form a simple triode Emitter follower ; here , The emitter voltage changes with the base voltage , namely $U_E=U_B-U_{BE}$, among $U_{BE}$ Is the tube voltage drop between the base and emitter . According to the follower principle, we can generate the required voltage , The output voltage of the simulation circuit in the figure is theoretically 5V.

Multisim Simulation results , As shown in the figure below ：

From the simulation results, it can be seen that the voltage stabilizing diode in this circuit stabilizes the voltage at 5.602V, The final output voltage of the circuit is 4.889V（5.602V - $U_{BE}$, Silicon tube 0.6V~0.7V）, And the output voltage waveform is stable , The function of the circuit is basically realized .

2. Analysis of voltage stabilization principle

The following is about power supply changes and load changes , The output voltage adjustment process of triode series linear voltage stabilizing circuit is analyzed in detail .

1） Constant load , Input voltage $U_{in}$ Reduce
When the load does not change , Input voltage $U_{in}$ Less hours , Output voltage $U_{out}$ There is a downward trend . Due to the existence of Zener diode , The base voltage of the triode remains unchanged . here , The base - Emitter voltage $U_{BE}$ increase . from Input characteristic curve You know ,$i_B$ With $U_{BE}$ To increase with . Triode emitter junction forward bias , Collector reverse bias , be in Zoom in , Yes $\Delta i_C=\beta \Delta i_B$, namely $i_C$ increase . And because the circuit is a triode series voltage stabilizing circuit , The loop current is the same ,$U_{out}=i_C\ast R_{load}$,$U_{out}$ increase .

2） Constant load , Input voltage $U_{in}$ increase
When the load does not change , Input voltage $U_{in}$ increases , Output voltage $U_{out}$ There is an increasing trend . Due to the existence of Zener diode , The base voltage of the triode remains unchanged . here , The base - Emitter voltage $U_{BE}$ Reduce . from Input characteristic curve You know ,$i_B$ With $U_{BE}$ To reduce by . Triode emitter junction forward bias , Collector reverse bias , be in Zoom in , Yes $\Delta i_C=\beta \Delta i_B$, namely $i_C$ Reduce . And because the circuit is a triode series voltage stabilizing circuit , The loop current is the same ,$U_{out}=i_C\ast R_{load}$,$U_{out}$ Reduce .

3） Input voltage $U_{in}$ unchanged , Load reduction
Input voltage $U_{in}$ unchanged , When the load is reduced , Output voltage $U_{out}$ There is a downward trend . Due to the existence of Zener diode , The base voltage of the triode remains unchanged . here , The base - Emitter voltage $U_{BE}$ increase . from Input characteristic curve You know ,$i_B$ With $U_{BE}$ To increase with . Triode emitter junction forward bias , Collector reverse bias , be in Zoom in , Yes $\Delta i_C=\beta \Delta i_B$, namely $i_C$ increase . And because the circuit is a triode series voltage stabilizing circuit , The loop current is the same ,$U_{out}=i_C\ast R_{load}$,$U_{out}$ increase .

4） Input voltage $U_{in}$ unchanged , Increased load
When the input voltage $U_{in}$ unchanged , When the load increases , Output voltage $U_{out}$ There is an increasing trend . Due to the existence of Zener diode , The base voltage of the triode remains unchanged . here , The base - Emitter voltage $U_{BE}$ Reduce . from Input characteristic curve You know ,$i_B$ With $U_{BE}$ To reduce by . Triode emitter junction forward bias , Collector reverse bias , be in Zoom in , Yes $\Delta i_C=\beta \Delta i_B$, namely $i_C$ Reduce . And because the circuit is a triode series voltage stabilizing circuit , The loop current is the same ,$U_{out}=i_C\ast R_{load}$,$U_{out}$ Reduce .

summary

1） This paper introduces the characteristics of triode Input / Output characteristic curve ;
2） be based on Multisim A series linear voltage stabilizing circuit of triode is built ;
3） The design of triode series linear voltage stabilizing circuit is described in detail Output voltage adjustment process ;

The above is the whole content of this article , I hope this paper can be helpful for you to understand and use the triode series linear voltage stabilizing circuit .
Of course , If there is any mistake or imprecision in the content of this article , Please also point out in time , thank you ！

Reference resources

Triode series voltage stabilizing circuit - regulated power supply - Electronic enthusiast network ;
Triode regulated linear power supply - CSDN Blog ;
Diagram of characteristic curve of triode ;