11 Apr
2012
11 Apr
'12
12:15 p.m.
The basic
specs for the common Motorola MPS-A55 are, in summary:
Polarity: PNP
Power Dissipation Pd: 500 mW
Material: Si (Silicon)
C-E voltage Vceo: 60 V
Current Gain hFE: 50
Package: TO-92
Thanks for helping me decipher the spec.
I have identified some transistors with similar specs (e.g.
http://uk.rs-online.com/web/p/general-purpose-transistor/7390492/), but the current gain hFE is higher at 100. Not sure if it is
better for the hFE to
be higher or lower than the required spec.
It's a very bad idea to assume that hFE will have a particular value, it
varies from transistor to transistor. So a good designer will design his
circuits so that it doesn't matter too much.
In general, and certainly in this application (it's part of the
regulation loop of the bias supply iIRC), the higher the gain the
better. So I think that transistor will be fine.
-tony