Triode design, understanding saturation, linear region and cut-off region

First of all, it needs to be clear that the working state of the triode is determined by the peripheral circuit . That is, simple application is the matching and selection of resistance and power supply .

The design idea should be ：

First of all ： according to ube and ib Characteristics of （ It is called input feature in the book ）, As well as their own power supply and resistance circuit , This circuit is linear , The intersection of two curves can be clearly determined ibe and ube.

The second step ： because be The working characteristics of are determined . , in turn, Uce and Ic The relationship between （ It is called output characteristic in the book , With IB Different curves are also different ）, Then from the external current voltage relationship , This relationship is also determined by external resistance and power supply . The point obtained by the intersection of two curves is the only working point .

summary ： The circuit around the base determines Ibe,ibe Determine the output curve , The external circuit determines the operating point . As shown in the figure above , left ：BE And peripheral circuits form a loop , They are input characteristics and peripheral linear circuit characteristics , Intersection determination Ube and Ib. On the right side ：CE And peripheral circuits form a loop . Decibels are output characteristics and characteristics of peripheral linear circuits , The intersection determines the working point .

In practical engineering , When a triode is used as a switch , We expect him to work in saturated areas , And be moderately saturated , Therefore, we hope that the base resistance needs to be small . In this way, the intersection of our output linear curve and output characteristics is usually in the so-called saturation region . This area is characterized by Uce Very small , In other words, it's like direct conduction .

If the resistance is not designed properly , The base current is very small , Then the external output curve is more likely to intersect in the linear amplification area . The frequency energy consumption is also high . Easy to burn pipes .

Practical analysis ： As follows PWM Output transformer conversion voltage A circuit that enhances driving capability , It is called class B complementary symmetric circuit in the book （ It is generally called totem pole ）.pwm15 It's a 0-5 V square wave voltage ,

  At first glance ,Ice and Uce It's a straight line of ratio , It's not right for you to intersect ,Uce It's always been 5v, At this time, it is also said that saturated work Uce Very small , It can be turned on when the switch , I can't tell , It's neither funny nor funny ！

  Don't worry , You have to think about the actual process , How can there be no drive resistor in the drive ？

This picture should be redrawn ：

 

The author thought about this picture for a long time . There are the following doubts ： First of all , We need to get what we expect Ib, But the loop equation here has now become the following form ：

 ​​​​​​​ It's not a simple change Rb You can adjust it linearly .

second ： This connection is no longer the common shooting connection mentioned in the book , Also use the above analysis （ It is also based on the common shooting method ） Is it appropriate ？ Especially input characteristics , The output characteristics are tested in the common firing method .

Third ： According to the connection method , Only in the unique input characteristic curve , The common shot connection method is as follows ：

  Let's look at the circuit that puzzles me , If we knew

 

 

 

 

 

At this time, it can prove the above analysis  .