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High current through base of transistor

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rai.abhishek

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Hi to all,

I was working on the attached circuit. My aim is to make sure that transistor Q2's base terminal gets about 1A current.
If anyone can please let me know whether this will happen in the attached circuit then it will be highly appreciated.
 

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Yes, with a suitable series resistor value (about 4.3 ohm).
 

Okay sir,

What will happen if I reduce the value of the resistor. Say I make it 2ohms.
 

For an exact answer, you need to consult the transistor datasheet and find out the actual Vbe values. In a rough estimation, the current will double according to ohms law. There's no circuit means to regulate the current.

May be you are intending something different, but you didn't yet tell what you want to achieve.
 

For the record, D1 will compensate for the transistor voltage drop, as you say, but will spoil a lot of the benefits of the regulator's performance.

That probably isn't the end of the world here but I'd recommend having a look at a regulator with a separate load voltage sense pin. It'll be readily available and be a better learning circuit, which may be beneficial. I'm sure other posters will suggest one.
 

There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. This page is mostly about NPN transistors and if you are new to electronics it is best to start by learning how to use these first.
 

@ FvM,
I want to make a voltage source of 5V to supply more that rated current of 7805 ic. I found this circuit on the net and I want to take advice how transistor Q1 help in achieving high current at the output of 7805 ic.

Moreover I would like to know names of the simulation softwares where I could check this circuit.(PSpice 9.1 don't have 7805 ic in its library)
 

Current booster cicrcuits can be found in the datasheet of industry standard voltage regulators, I think also for 7805. A general drawback of many of this circuits is that they miss the short circuit and overtemperature protection of the basic regulator.

Different 7805 models are provided in recent PSPICE version e.g. in opamp.lib, if they are missing in V9.1, you can download manufacturer models.
 

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