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parallel operation of transistor

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eswaramoorthykv

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parallel operation transistor

dear friends,
What will be effect of Vbe in parallel operation of transistor?how it is neglected by connecting resistor at emitter side?
 

betwixt

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parallele transistor

The Vbe voltage is actually the drop across a P-N junction inside the transistor. P-N junctions behave like constant voltage regulators, usually at around 0.6 to 0.7V. In manufacture the Vbe varies slightly from one transistor to another, even if they are the same type. If you put them in parallel, the one with the lowest Vbe will hold the voltage below the level needed for the other(s) to conduct fully.

Putting a resistor in the base pin will isolate the junctions, allowing them to hold their own Vbe independently of each other. Putting resistors in the emitter pin does the same but in a different way. The current through the emitter resistor causes a voltage drop across it which raises the base voltage need for conduction relative to ground (or at least the other side of the resistor if it isn't ground). Vbe stays the same but a higher voltage is needed to drive the transistor.

Which method is used depends on other factors in the circuit.

Brian.
 

senthilkumar.b

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Hi,

As per betwixt statement, there is potential difference between each other. Due to this there should be some circulating current.

while you are going to use the parallel arrangement, that must be power transistor. it should huge current delivering capacity.

In some cases the circulating current may be in 10s of amphere and damage each other. if we provide a small resistor series with emitter, that will drop that small voltage difference and prevent high circulating current.

Its the way to protect power transistor while connecting parallel.

Bye.
 

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