# What is the forward beta of the BJT KN2222A?

I don't know what is the forward beta of the bipolar junction transistor KN2222A, I'm an amateur and i don't found the value in the data sheet or i just don't understand where. Please let me know

• Have a look in the datasheet: buchangelec.com/data/transistor/general/2222a.pdf on page 2 there's a section: "DC Current Gain" which is $h_{FE}$ which is also $\beta$. There are mostly minimum values there. For hobby projects you could just assume $\beta$ = 50 and that would fit the needs of 99% of generally used circuits. If your circuit relies on the BJT having a specific value of $\beta$ then you should use a better (less $\beta$ dependent) circuit. Jun 12 '19 at 6:48
• @Bimpelrekkie Thank you! Jun 12 '19 at 6:53
• Each manufacturer who applies such a part number can decide how to answer that question. Sometimes a specification covers multiple manufacturers (2N2222A is such a specification), but probably not KN2222A. Jun 12 '19 at 6:56
• That datasheet is poorly specified. It relies upon $V_\text{CE}=10\:\text{V}$ and it doesn't show the values for different temperatures (which is more important to know.)
– jonk
Jun 12 '19 at 6:57

And for what it's worth there are multiple $$\\beta\$$ factors to consider when designing BJT circuits:

• $$\\beta\$$, $$\\beta_{DC}\$$, $$\h_{FE}\$$ - These refer to the BJT's DC forward current gain when the BJT is operating in forward-active mode (small signal amplification). Used when performing the DC design/analysis.
(n.b. The 'FE' refers to Forward current gain, common-Emitter configuration.)
(n.b. Parameters written with UPPERCASE subscripts typically refer to DC parameters.)

• $$\\beta_{ac}\$$, $$\h_{fe}\$$ - These refer to the BJT's AC forward current gain when the BJT is operating in forward-active mode (small signal amplification). Used when performing the AC design/analysis. Typically, $$\\beta_{ac}\ll\beta_{DC}\$$.
(n.b. Parameters written with lowercase subscripts typically refer to AC parameters.)

• $$\\beta_{sat}\$$ - Refers to the BJT's forward current gain when the BJT is operating in "hard" saturation mode (when the BJT is turned ON fully). Typical values are $$\5 \le \beta_{sat} \le 30\$$ with $$\\beta_{sat}=I_{C(sat)}/I_{B(sat)}=10\$$ being a fairly common value for low power and medium power transistors.
(n.b. Data sheets often use lowercase text for parenthetical text—e.g., $$\I_{C(sat)}\$$, $$\V_{BE(sat)}\$$, etc. This does not indicate or imply that these are AC parameters.)
(n.b. $$\\beta_{sat}\$$ is not an AC parameter because the transistor is not performing small-signal AC amplification when it is operating in saturation mode.)

And as a general rule do not use $$\\beta\$$, $$\\beta_{DC}\$$, $$\h_{FE}\$$ to perform saturation calculations. If you do, the BJT will likely operate in "soft" saturation—i.e., in the transition region between the BJT's forward-active mode and its "hard" saturation (fully ON) mode.