Hi, Which Beta or hFE of a specific transistor does CircuitLab use in the calculation of a circuit? For example I have the BC337-40. This transistor has a hFE between 250 and 600.

by JCPStevns
March 22, 2021

Hi @JCPStevns, Beta or hFE varies a lot from transistor to transistor, and even within the operating range of a transistor. I found a BC337 datasheet which lists hFE as Min 250, Max 600, with no Typ specified. This 250-600 range is listed at IC=100mA, VCE=1.0V. When IC=300mA, the hFE is Min 60, with no max specified.

The hFE is further specified by a curve on Figure 3, DC Current Gain. From this curve, we can see that the peak is near IC=100mA, and it's significantly lower at, for example IC=10mA or IC=1mA.

That's a complicated way of saying "it varies a lot". But in general, you will design a BJT circuit that works if the transistor gain is at least some minimum value (for example 250), and design your circuit such that if the actual transistor you're using is better (higher hFE), then it'll still work as performed (while consuming less base current, for example).

You can use CircuitLab's DC sweep or parameter sweep to vary Q1.B_F and see if your circuit still works well with different gains.

by mrobbins
March 22, 2021

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