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kalee20 · 9th Dec 2017, 2:52 pm

Agree with Mark!

Voltage gain is sensibly independent of hfe, when measured actually on the base, but the loading effect of poor hfe on the generator, will result in a lower signal on the base.

What's wrong with just DC measurements - a 4.7k base resistor from a variable voltage source to drive the base, and a current meter in series with say 100 ohms (for protection) from a 12V supply. Twiddle the base supply for a 10mA collector current, and the hfe calculation is simple.

The transistor may need to be kept cool for this, as leakage current increases with temperature. But a quick trial will determine this.

Argus's method is good in that the transistor's operation is stabilised, but it does need some means of determining the actual (AC) base current to work out hfe.

9th Dec 2017, 2:52 pm	#24
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Matched Transistors Agree with Mark! Voltage gain is sensibly independent of hfe, when measured actually on the base, but the loading effect of poor hfe on the generator, will result in a lower signal on the base. What's wrong with just DC measurements - a 4.7k base resistor from a variable voltage source to drive the base, and a current meter in series with say 100 ohms (for protection) from a 12V supply. Twiddle the base supply for a 10mA collector current, and the hfe calculation is simple. The transistor may need to be kept cool for this, as leakage current increases with temperature. But a quick trial will determine this. Argus's method is good in that the transistor's operation is stabilised, but it does need some means of determining the actual (AC) base current to work out hfe.