Minimum and maximum current needed to base of bc547.

What is the minimum and maximum current required for base in BC547? for conduction

Hi,

you ask very basic questions.
A forum can´t replace school or reading books.

--> your question can´t be answered.
For both base_currents you are asking for you need to define I_C and V_CE first.

And if you know I_C and V_CE then you can find the answers in the datasheet.
That´s what datasheets are for.
And to answer the question the professionals need to read datasheets, too.

Klaus

KlausST said:

Hi,

you ask very basic questions.
A forum can´t replace school or reading books.

--> your question can´t be answered.
For both base_currents you are asking for you need to define I_C and V_CE first.

And if you know I_C and V_CE then you can find the answers in the datasheet.
That´s what datasheets are for.
And to answer the question the professionals need to read datasheets, too.

Klaus

Click to expand...

sir, i am really very sorry but actually i get confused when in a graphical analysis of base current over emitter current was given by taking base current as 20uA ,30uA and what i knew that minimum amount will be at least in mA thats why to clear it i asked this question. i referred data sheet , and i fount it was in mA. yes definitely that graphical representation example of base current may be shown just as an example,..but to get it confirmed whether there is any significance of this example or not.

by the way the this forum title named as Elementary electronics question..,so m sorry if i had done a blunder. but i must advice the elementary word should be replaced by advance in the forum title

There is no minimal current. BJTs doesn't have threshold voltage or current. The base current is exponential function of the Vbe. If Vbe is higher than 0V current can flows into the base and into the collector too (Ic=hFE*Ib).
Maximum Ic is in the datasheet. If you divide it down with the actual hFE you will get the maximum base current.

Hi,

sir, i am really very sorry but actually i get confused when in a graphical analysis of base current over emitter current was given by taking base current as 20uA ,30uA and what i knew that minimum amount will be at least in mA thats why to clear it i asked this question. i referred data sheet , and i fount it was in mA. yes definitely that graphical representation example of base current may be shown just as an example,..but to get it confirmed whether there is any significance of this example or not.

by the way the this forum title named as Elementary electronics question..,so m sorry if i had done a blunder. but i must advice the elementary word should be replaced by advance in the forum title

Click to expand...

No, this section is not for advanced questions. It is for elementary questions. But before you ask a question you need to study how things work.
There is school, there are books, there is the internet, there even are online video tutorials..they all teach you...go through them first.

We like to help - but we need to see that the poster tried to solve things on his own. Show what you have done (or found out) so far.
This I´m missing with your posts. I only see very short unelaborated questions.

****
Now to your post #3:

I´ve told you to decide I_C and V_CE first.
This is what I expect from you. Without these values you can´t go on.

You say "for conduction". But this is a word you can´t calcualte with. You need values. First.

The designer (you) need to specifiy the meaning of "conduction" by giving I_C and V_CE.

I_C:
* If you want to drive a MOSFET then 1uA is sufficent to drive the gate. So I_C = 1uA may be considerend as ON condition.
* If you drive a LED, then you don´t see nothing with 1uA. 1uA is surely considered as OFF condition.

Similar with V_CE.
* Drive a LED with 1V then it is considered OFF
* drive a BJT with 1V then it surely is considered ON

No need to go through the datasheet without I_C and V_CE.
I want to lead you through this step by step. The problem is if you don´t follow my steps (stand still, turn right or left, going multiple steps)... it´s impossible for me to help.


Klaus

RAHUL_KUMAR said:

What is the minimum and maximum current required for base in BC547? for conduction

Click to expand...

Rahul Kumar, please note that there is no REQUIRED base current at all.
The transistor needs a certain base-emitter voltage (in the vicinity of 0.6...0.7 volts) - and, as a result, there is a base current which is not wanted or desired, but it cannot be avoided.
For designing the bias voltage divider you can/must take this base current into consideration - however, this current is - more or less - a kind of deficiency.
The most important quantity is the base-emitter voltage Vbe, which sets the collector current according to the known Shockley equation (exponential relation between Vbe and Ic).

Each design of an amplifying transistor stage starts with the selection of a suitable collector current Ic.
From this, the corresponding base current Ib is found by Ib=Ic/beta.

Added:
Please post a link to the datasheet you use. There are many BC547 datasheets.
I recommend to link directly to a manufacturer, there you find the latest datasheets.

Klaus

You might look at the hFE-vs-Ic curve, to see what
range of Ic delivers a tolerable beta, and then do the
figuring for Ib at that point (bearing in mind that the
curves a vendor shows, are what they want to show -
and nowhere near the worst case).

Things like beta rolloff at low currents are way outside
the simple closed form solution and want graphical or
simulation methods. Same for operating above knee
current at the other end.

Rahul, you said, "conduction". But a linear amplifier is in conduction and a turned on transistor switch is also in conduction but it is saturated, it is not linear.
Instead of saying "conduction" you should say "linear" or "saturated" which are completely different. When a transistor is linear then the base current is calculated from the collector current and from the range of hFE listed.

A transistor with a low hFE is not sensitive (needs high base current) but a transistor with a high hFE is very sensitive (needs low base current). You can buy a BC547A which has low hFE, a BC547B which has medium hFE or a BC547C which has high hFE. A BC547 with no letter has a wide range of hFE. hFE is used for a linear transistor, usually an amplifier.
A transistor that is a saturated switch usually has its base current 1/10th the collector current even if its hFE is very high, although European transistors usually have their saturation specified with the base current 1/20th the collector current.
The graphs on a datasheet are usually for a "typical" device that has medium spec's. If you design a circuit using typical spec's then the circuit might not work if the transistor has minimum or maximum spec's so you should design so that any transistor that has minimum to maximum passing spec's will work.