11 Apr
2012
11 Apr
'12
3:09 p.m.
On 04/11/2012 06:15 AM, Rob Jarratt wrote:
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 pretty unusual for a circuit design to rely on a specific current
gain (Hfe), because it's not constant. It varies with the voltage
across the transistor, and varies a good amount from transistor to
transistor of the same model. Don't try too hard to match the Hfe.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
I need to replace a transistor in my H7140 PSU for my
PDP11/24. The
transistor is marked GPSA55J3 and the printset identifies it as "XA 55
PNP 500MW SI 60 50 P", it is in a TO-92 package.
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