Why does a transistor heat when base current is high

[pgsabel]

Why does a transistor heat when base current is high

 

[nxing]

when there is more current, it means more electrons are moving and this movement generates lots of heat.

 

[mohammad mokhtar]

Hi
More base current means more collector current and the losses of the transistor
equal to VCE× Ic + Ib × Vbe = Vce × Hfe × Ib + Ib × Vbe
=Ib ( Hfe × Vce + Vbe )
as you see the losses is linearly proportional Ib >
Please put into consideration Hfe is the dc gain and not the ac gain .
Regards

 

[on1aag]

Hi Pgsabel,

It's the product of the base current and the base-emitter voltage that
makes the transistor heat up. If you apply a base current of 50 mA to
a transistor, the dissipation will be: 700 E-3*50 E-3=35 E-3 = 35 mW.
This might not seem much, but if you do that to a small (TO92)
transistor with a maximum dissipation between 300 and 500 mW, you
will feel that it is heating up. The total dissipation of a transistor is the
sum of the base-emitter voltage multiplied by the base current and the
collector-emitter voltage multiplied by the collector current. Bare that in
mind if you don't want to burn your fingers.
The total dissipation of a transistor depends on the size of the die and
the package.

on1aag.

 

[Euler's Identity]

I've never considered IbVbe, but yes, technically, that's power. Rather, I usually only consider IcVce, but yes, technically, a transistor will heat up if you open the collector, which removes the Ic contribution to Ie, proving Ib does contribute.

But, for practical purposes, transistors heat up when you have Ic and a Vce, where, usually, Ic<<Ib. Saturate the device and you'll get minimal heat. Why? Because Vce is low at Vce sat. True, Ic may be high and, therefore, you get heat anyway, but....

Ok engineers, you may commence shootng at me now.

 

[neils_arm_strong]

base cureent increase gives collector current increase and it heats uo the transistor.

 

[the_risk_master]

Does it depend on how the transistor is configured, whether common-base, common-emitter, emitter-follower, etc..?

 

[newelltech]

Everyone has been dancing around the exact answer.

First, if you want to measure the instantaneous DC power dissipated use this:
P = Ib x Vbe + Ic x Vce (NPN or PNP)
This eqn is true regardless of the configuration (common-base, etc).
You can see that usually the Ib x Vbe term is small when a transistor is properly biased for small signal amplification and can be ignored. Notice also that the transistor parameters (hfe, etc.) do not matter. Also, with a linear ac amplifier configuration, the signal does not affect the power dissipation.

With high base current you will have significant dissipation. For example if Ib = 1 A, you may have 1 Watt of dissipation just from the base current.

Some transistors operate in the non-linear region (class AB amps, logic, etc) and the average power will be dependent on the input signal.

 

[archie18]

I would like to know what happens if my base current is higher than collector current.
For e.g if my Ic = 1mA( load resistor=5K) , Vcc=+5V and I am applying 5v to base through 1K resistor.
Under these circumstances will my transistor 2n2222 get burnt/damaged?

 

[yadavvlsi]

More current means more electrons flowing per unit time. So scattering rate will be high, which produce more heat. Also base region is very small compared to collector and emitter. So current density will be high. If base current is high it will reduce the gain of transistor. Base current should be very small to achieve high gain.

 

[KerimF]

newelltech (post #8) has already answered very well the OP question.

For your example on post #9, Vce is very low (say 0.1V):
P_dis = Vce * Ic + Vbe * Ib
P_dis = 0.1*5 + 0.75*(5-0.75)/1 = 0.5 + 3.2 = 3.7 mW
This is rather a very low power dissipation.

Typically, a high base current will damage a saturated transistor (Vce small) not because of the high transistor temperature but because the internal base junction would act as a tiny fuse. On the datasheet, Ib max is usually given too.

 

[yadavvlsi]

I would like to know what happens if my base current is higher than collector current.
For e.g if my Ic = 1mA( load resistor=5K) , Vcc=+5V and I am applying 5v to base through 1K resistor.
Under these circumstances will my transistor 2n2222 get burnt/damaged?

Currents (base, collector) are not solely depends on external bias and resistors. See the basic current equations of transistor.
Bipolar junction transistor - Wikipedia, the free encyclopedia.