# How to get hFE value?

• posted

Hi,

I made a sample circuit and I want to calculate the value of hFE. How can I get the value. I know hFE=Ic/Ib and Ib is (Vcc-Vbe)/Rb which is about 100uA. In order to get Ic, I have to know hFE and a sample circuit is not the same condition from datasheet. If I draw this sample circuit to PSPICE, it give me the Ic so that I can calculte the value of hFE. But how, what, and who know to get hFE without using PSPICE.

+------+-----+ | | | | | | Rb Rc | | | | | /C + +----|B V \\E - | | | | +-----+

Rb is 343k, Rc is 810, Vcc is 35V, and transistor is P2N2222A.

clueless Ken.

• posted

Use 200 for that transistor.

• posted

```--
Measure the voltage on the collector, subtract that voltage from the
supply voltage and divide that by the collector resistor\'s```
• posted

Extrapolate using the data sheet. Which says, btw, that at I(c)=150mA, V(ce)=10V, min hfe=100, max hfe=300. Hence the previous poster's suggestion to use 200.

hfe varies with current, voltage, temperature, etc. Generally highest around the mid-point of voltage and current ranges, lower towards the ends.

• posted

"NoClue"

** Honest at least ....

** You cannot.

Hfe is a variable parameter of *actual devices* - it varies widely from sample to sample and is also significantly affected by the voltage current and temperature levels experienced by that device.

What you have drawn is suitable for TESTING the Hfe figure of individual PN2222 devices - since the base current is fixed and the collector current can be noted from the voltage across Rc.

....... Phil

• posted

The simplest and most accurate way to determine the hFE for the transistor you are using is to simply measure the current flowing through Rc and Rb. Then divide Rc/Rb. You could as suggested else-where measure the voltage across the resistors, however you then open yourself to errors when you remember the tolerance values applied to the resistors.

Chris

NoClue wrote:

• posted
** Top Posting Groper Alert !!

** Better try Ic / Ib.

** With standard 1% resistors and a decent DMM, the result will be within 1% which is likely to be as good or better than using the same DMM as a current meter.

When matching the Hfe of two or more devices, accurate test figures are irrelevant.

...... Phil

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