Power dissipation of BJT in linear operation

[mixmaestromark]

Hi all

I am trying to calculate the power dissipation of a high-frequency npn BJT (NE461M02) which is acting as a small-signal amplifier in CB configuration. This is for reliability prediction and I need to calculate the stress on the component.

I have done some googling but I cannot seem to find any useful information on this. If somebody could explain the physics behind power dissipation in a BJT and how I can calculate it I would be very greatful!

Regards
Mark

 

[eklikeroomys]

You would need to calculate the sum of the power dissipations caused by the DC bias point and the rms value of the AC signal

 

[mixmaestromark]

You would need to calculate the sum of the power dissipations caused by the DC bias point and the rms value of the AC signal

Thanks for your reply.

Yes I understand that the dissipation will be a combination of dc and ac, but I would like to know how exactly this is calculated and how the power is actually dissipated within the transistor?

 

[umesh49]

In amplifier operation your collector to emittor votlage and collector current will keep on changing. You need to integrate the multiplication of instantaneous voltage and current and find the average over a full cycle.

 

[FvM]

You have asked for a small-signal amplifier. Then Pv = Vce*Ic + Vbe*Ib.

 

[mixmaestromark]

Thanks guys. I guess the overall dissipation calculation would involve umesh49's integration of ac voltage & current as well as FvM's dc operating point dissipation?

 

[Kral]

The dissipation of an ideal class A amplifier is independent of the AC signal, as implied by FvM's answer. If the amplifier is non-linear, then the dissipation can change with signal. In this case, the calculation is not straight forward, and a simulation would be your best approach to calculating the dissipation.