Ron,
The TIP120 and TIP125 will each dissipate 65 Watts if properly heat
sunk
Their rating is 65W as long as you keep their mounting surface below
25°C. In practice that's usually impossible, so their practical power
dissipation capability is significantly lower. That's why I looked at
transistors with a higher power rating.
On the other hand, if the application is cathode bias of an amplifier,
and just calls for around 1A at 8V, so 8W, the power rating of those
transistors is plenty, of course.
and they are Darlington type with a dc gain of approaching 1,000.
Yes, and being Darlington means that they have a higher and much more
variable base-emitter drop. That's why I try to avoid Darlingtons in
such super-zener circuits. Their voltage stability is less good than
that achieved with a non-Darlington transistor.
Again, in this application probably even with a Darlington the resulting
stability is good enough. But a non-Darlington transistor in this
circuit makes for a more accurate Zener replacement.
Manfred
========================
Visit my hobby homepage!
http://ludens.cl
========================
_______________________________________________
Amps mailing list
Amps@xxxxxxxxxxxxxx
http://lists.contesting.com/mailman/listinfo/amps
|