Is it appropriate to call BJT current controlled?

[gauthamtechie]

Is it a misnomer to call a transistor(BJT) a current controlled?
http://amasci.com/amateur/transis.html
The website above posts a strong argument that they're "voltage" controlled

 

[Claude Abraham]

All OEM, On Semi, Fairchild, Texas Instruments, Intl Rectifier, etc., refers to a bjt as current controlled. They grow the silicon crystals in the oven, they implant the ions into the material forming n and p layers, diffuse dopants, etc. A bjt if you wish to get down to the microscopic level, i.e. semiconductor physics, is truly a charge controlled device. But when viewing the device externally as a black box, the current control model is accurate unless you start operating the device at very high speeds. The internal stored charge can bottleneck the speed, and the charge control model is much more accurate.

Current control model works well to a limited extent, if the speed is moderate, and the device is in the active or cut off region. In saturation, esp w/ fast switching, charge control provides very good results.

This topic has been beaten to death, I suggest you search my post history and you will find dozens of pages on this. The critics insist a bjt is voltage controlled but none of them have semiconductor physics background, few have more than a mere bachelor degree, I will elaborate, but the arguments have already been presented and no use repeating them. Again, I will clarify if needed. Regards.

 

[MrAl]

Hello,


Ha ha, not this again

The bottom line is that a person very knowledgeable in transistors will know how to handle any model of the transistor you care to throw at them, be it current controlled, voltage controlled, charge controlled, or whatever else you can come up with. So the bottom line is know how to handle all the ways of looking at the bipolar transistor and you'll do well in any discussion or practical circuit analysis.

Each bjt model is used when that model is most appropriate to the application under consideration.

 

[Claude Abraham]

That is why I asked the OP to parse through my posting history and ask a specific question if clarification is needed. I don't want to have another back and forth shouting match. Any time a device is labeled as current controlled, a small but vocal minority insists that it be defined as voltage controlled, despite the OEM saying current controlled. So this issue will never die because a few just don't accept current control period. Thanks for your input and thanks for not feeding a potential monster.

 

[Ratchit]

gauthamtechie,

Is it appropriate to call BJT current controlled?

Is it a misnomer to call a transistor(BJT) a current controlled?
http://amasci.com/amateur/transis.html
The website above posts a strong argument that they're "voltage" controlled

Yes, a BJT is a voltage controlled current source. Here is why. Both the Ic and Ib are dependent on the Vbe of the transistor in a exponential manner. Dividing the Ic by the Ib cancels out the exponential relationship, and makes the Ic appear to be linear with respect to Ib. However, it is Vbe that is controlling both Ib and Ic. Therefore Ib is an indicator of Ic, not a control of Ic. This linear relationship is handy for design, but it does not prove that Ib is controlling Ic. We can delve into that more if you want. It involves diffusion of the charge carriers into the N-P slabs.

Some folks say that because the big semiconductor manufacturers refer to their products as "current controlled", that is what a BJT is. However, when the physics of the BJT are looked at, it is seen that Vbe truly controls the BJT when operated in the active region.

Ratch

 

[Nigel Goodwin]

Pointless thread locked - moderator!