Thought experiment for those with time on their hands :-)

Bipolar transistors are current amplifiers, so it almost always makes 
sense to operate them with base current less than collector current - 
usually much less . Some high voltage applications have forced Betas 
not much more than 1 as the switched power (HV x Ic) is >> the 
switching power Ib x Vbe.But, just sometimes, in low voltage 
applications it can be useful to have base current > collector 
current.

I have just designed a circuit with a small signal PNP bipolar 
transistor with a forced Beta of about 0.5.

Suggest why?

Supply voltage is about 12 Volt. Transistor current is around 0.5 mA 
(so base current is about 1 mA). (Final collector and base currents 
may be reduced but this works OK for now).

The purpose of this 'challenge' is to

- Point out that some strange configurations may sometimes be useful.

- Point out one such.

- See if anyone else comes up with anything interesting.

I'll be away for a few days so may not comment further till early next 
week.


        Russell McMahon


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