[SOLVED] Bipolar Junction Transistor Work Flow

[WhyWhy]

Hi guys,

About the transistor, i thought the electron must flow from negative power supply --> emitter --> base --> positive terminal .



But why it also can flow from negative power supply --> emitter --> base --> negative terminal .



I refer from this link:

https://www.allaboutcircuits.com/vol_3/chpt_4/2.html

Regards,
YY

 

[cl10greg]

I am having a difficult time figuring out what you are questioning in here.

I think you are just looking too much into conventional and practical flow of current. The main focus of BJT is to think of them as a diode for the control gate. You need a certain amount of voltage from the base to emitter to complete the conduction path (usually 0.7V either positive or negative depending on NPN or PNP) and allow for current flow. Once the BJT is on, the current flowing into the gate controls the current that flows through the junction. It is essentially a very small resistor so it can support current flow in either direction with a gain that is defined by the part. Please let me know if this helps or if I answered the wrong question.

 

[WhyWhy]

Hi Cl10greg,

I understand need 0.7V at base to help conducting. My question is why the direction of arrow at the picture is from emitter to collector.

 

[cl10greg]

Hi Cl10greg,

I understand need 0.7V at base to help conducting. My question is why the direction of arrow at the picture is from emitter to collector.

Because they are showing the current flow as the actual rather than the conventional. Electrons are flowing from cathode to the anode of the source.

 

[Audioguru]

A long time ago electricity and the beginning of electronics was taught to use "conventional" current flow because they did not know about electrons. The arrow in the transistor is for conventional current flow. Later they discovered electrons and of course they found that conventional current flow is backwards but it was too late to correct it so both current flows have been learned.

I never think about conventional or electron current flow because I know how transistors and things work.

 

[WhyWhy]

Finally i understand.. Thanks cl10greg and audioguru