measuring hfe for a transistor

[Walid]

Hi , I am using a digital multimeter to measure hfe for transistors , but what i noticed was that the hfe value displayed was different when i used a different battery for the multimeter. The older the battery was , the less value for hfe is dislayed. e.g i tried to measure hfe for a certain bjt (BC 548). It gave the value 170 for hfe with old battery. when i used a newer battery it gave 220 for hfe. so what value should i consider in the design?
thanks

 

[BrownOut]

hfe varies widely depending on several factors, one is the input current. 170-222 isn't a bad spread, really. If you design depends on predictable hfe, you might consider a redesign.

 

[audioguru]

Your multimeter reads hFE which is the DC current gain, not hfe which is the AC current gain.
The HFE increases when the collector to emitter voltage is increased due to the Early effect.

Your circuit should be designed so that the entire range of hFE from a certain transistor part number will work.