Calculating base current?

MacIntoshCZ · Jan 19, 2021

Hello,
I would like to know how can i calculate base current when base is directly connected to emittor/collector?
Ir1 = 600uA Ib= 2uA
Spice says...
I though current would be splitted in half. But it isnt.
thanks

rjenkinsgb · Jan 19, 2021

I'd expect it to be the collector current divided by the hFE at that current, as long as the overall current is within the transistor continuous rating.

eg. For an hFE of 200, base current 1/200th the collector current.

MacIntoshCZ · Jan 19, 2021

thanks

Nigel Goodwin · Jan 19, 2021

I suspect that while it's nice in theory, in reality it will be FAR different - when you operate transistors near saturation point the gain drops off considerably.

However, why would you want to know? - you're wiring the transistor as a diode - so there is no base and no collector.

MacIntoshCZ · Jan 19, 2021

Nigel Goodwin said:
However, why would you want to know? -

It was strange to me. I supposed that current would flow symetricaly in two different paths (splited in halfs). I am learning at my own, sometimes I just stare blankly into a book... Then i ask here =)

audioguru · Jan 19, 2021

With the base connected to the collector then the emitter current is exactly the same as the collector.
With the base connected to the emitter then the transistor is turned off and does not conduct any current.

rjenkinsgb · Jan 19, 2021

audioguru said:
With the base connected to the collector then the emitter current is exactly the same as the collector.

... exactly the same as the collector plus base.

gophert · Jan 19, 2021

rjenkinsgb said:
... exactly the same as the collector plus base.

Why bother with a 0.5% "error"?

canadaelk · Jan 21, 2021

Hm. So why do we all spend extra money for the digits to the right on our DVMs? E

Nigel Goodwin · Jan 21, 2021

canadaelk said:
Hm. So why do we all spend extra money for the digits to the right on our DVMs? E

We don't

audioguru · Jan 21, 2021

My calculator also has many extra useless digits that I usually round off.

gophert · Jan 21, 2021

canadaelk said:
Hm. So why do we all spend extra money for the digits to the right on our DVMs? E

That's why I usually use the 200v scale - so I don't see all those numbers flashing and moving in the 3rd, 4th and 5th decimal places at lower scales.

Like this one...

JimB · Jan 21, 2021

canadaelk said:
Hm. So why do we all spend extra money for the digits to the right on our DVMs? E

Most of the time the extra digits are not required, but occasionally when they are required the extra digits no longer seem expensive but priceless.

JimB

Calculating base current?

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