Kn value of a specific transistor given spec sheet

In summary, you are looking for the K,n value of a specific transistor (2n7000) and you are close, but you don't know what value to use for V,tn to complete the equation and solve for K,n.
  • #1
extremepilot
13
1
Hi,
Working on a project, I am told to find the K,n value of a specific transistor (2n7000), given the spec. sheet. I know K,n can be found from the formula:

I,d = K,n * (V,gs - V,tn)^2

I'm close, from the spec sheet, I can use a V,gs value and a corresponding I,d value, however not sure what value to use for V,tn to complete the equation and solve for K,n. Any help?

Thanks for your time
 
Last edited:
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  • #2
That's a thermal voltage that depends on temperature. It's approximately 26 mV at room temperature.
 
  • #3
That is V,t which is 26mV like you said but what I am looking for is K,n which is in units if mA/V
I believe
 
  • #4
Look up a spice model for the transistor. It should be there. And the units should be A/V^2
 
  • #5
Thanks, tried this - I placed the 2n7000 in the circuit and clicked "Edit Properties" on it but I can't find ANYTHING in the property editor

Any help is appreciated
 
  • #6
Simple google results:

Code:
*ZETEX  2N7000  Spice Mosfet Subcircuit  Nodes D G S  Last revision 11/91
*ZETEX  60V 200mA pkg:TO-92
.SUBCKT X2N7000 3 4 5
M1 3 2 5 5 MOD1 L=1 W=1
RG 4 2 343
RL 3 5 6E6
D1 5 3 DIODE1
.MODEL MOD1 NMOS VTO=2.474 RS=1.68 RD=0.0 IS=1E-15 KP=0.296
+CGSO=23.5P CGDO=4.5P CBD=53.5P PB=1 LAMBDA=267E-6
.MODEL DIODE1 D IS=1.254E-13 N=1.0207 RS=0.222
.ENDS X2N7000


If you are using LTSpice, go to the LTSpice directory and find folder lib/cmp and look under mosfets.
 
  • #7
Thanks. I have no idea what LTspice is, but doesn't look like it's installed on my school's computers. Part of the assignment is to enter these characteristics (K,n V,t W, L etc ) into one of the regular Mosfet Ntype transistor models so it acts as a 2n7000, rather than using the 2n7000 model itself... Waht, is there any chance you could tell me how I would do that? I don't see how to do it at all.
Thanks

EDIT: Seems like I need to use the PSpice model editor, and type in the values of the 2n7000. I'll try and figure the rest out.
Thanks a lot
 
Last edited:

1. What is the Kn value of a transistor?

The Kn value, also known as the transconductance value, is a measure of the current amplification capability of a transistor. It is typically expressed in units of mA/V^2 and can be found on the transistor's spec sheet.

2. How is the Kn value determined?

The Kn value is determined through testing and measurement of the transistor's characteristics, such as the drain current and gate voltage. These values are then used to calculate the transconductance value using the formula Kn = ΔID/ΔVGS.

3. Why is the Kn value important?

The Kn value is important because it helps determine the gain and performance of a transistor in a circuit. A higher Kn value indicates a higher current amplification capability, while a lower Kn value may result in lower gain and overall performance.

4. Can the Kn value of a transistor change?

Yes, the Kn value of a transistor can change depending on various factors such as temperature, voltage, and aging. However, it is typically a stable value and will not change significantly under normal operating conditions.

5. How do I choose a transistor based on its Kn value?

The Kn value is just one of many factors to consider when choosing a transistor for a specific application. It is important to also consider other specifications such as voltage and current ratings, as well as the desired circuit requirements. Consulting the transistor's spec sheet and consulting with a knowledgeable engineer can help in selecting the right transistor for a given application.

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