# Finding Q-Point of IRF510

Joined May 11, 2013
2
Hello! I am new to this forum and need some assistance. I looked at the datasheet for IRF510 N-Channel MOSFET Power Amplifier and was wondering how would i be able to determine the Q-Point with large voltage swing? My problem is that I don't know how to read from the datasheet in order to obtain the proper Q-point. Here is the datasheet:
http://www.ee.nmt.edu/~wedeward/EE443L/FA99/IRF510.pdf
If someone can give me some sort of guide on how to obtain the answer, that will be amazing! Thank you so much!

#### aws505

Joined Mar 11, 2013
59
The Q-Point has everything to do with how the transistor is hooked up and (almost) nothing to do with the transistor in question. You need to show us the circuit you intend to use the IRF510 in. For example, the circuit I've attached can have infinitely man Q-Points, all obtainable by selecting the values of R1, R2, RS and RE. The Q-Point generally refers to the DC voltage at the gate of the transistor or the current through the transistor. The way I imagined my circuit would be used is as a Class-A amplifier, such that the transistor is always on and the collector always passes current. A small variation in voltage at the gate then causes a larger voltage variation at the drain. This can be used, for example, as an audio amplifier. You could also set the Q-Point of the transistor such that it acts as a Class-B amplifier, for example, by omitting R1 and CIn. See Wiki's article about biasing.

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#### ScottWang

Joined Aug 23, 2012
7,396
DC Analysis of a MOSFET Transistor Circuit, Q-Point.

Joined May 11, 2013
2
My question was, from the datasheet, how am i able to determine what voltage and what current will give the max power output. I understand how to determine the other components (Rs, Rd, R1 and R2) after I find out what Ids and Vds (the Q-point). I just have trouble understanding how to determine the q-point from the datasheet provided by the manufacturer. Thank you both for your inputs though so far

#### shortbus

Joined Sep 30, 2009
10,044
May be wrong, but for a mosfet, what your looking for is called Vgs or voltage gate to source. This is the usual point that the Ids or amperage drain to source is listed at, on the data sheet.
for a normal Nmos it is 10V. "Logic" level mosfets are at smaller voltages, Vgs.

#### aws505

Joined Mar 11, 2013
59
My question was, from the datasheet, how am i able to determine what voltage and what current will give the max power output. I understand how to determine the other components (Rs, Rd, R1 and R2) after I find out what Ids and Vds (the Q-point). I just have trouble understanding how to determine the q-point from the datasheet provided by the manufacturer. Thank you both for your inputs though so far
Raising the gate-to-source voltage above VGS(TH) will cause the transistor to conduct. For the IRF510, that value is 2V < VGS(TH) < 4V. You may then bias the drain with a current to determine the Q-point. I cannot say where you will get the "max power output" because I don't know how you're using the transistor.

#### shortbus

Joined Sep 30, 2009
10,044
Raising the gate-to-source voltage above VGS(TH) will cause the transistor to conduct. For the IRF510, that value is 2V < VGS(TH) < 4V. You may then bias the drain with a current to determine the Q-point. I cannot say where you will get the "max power output" because I don't know how you're using the transistor.
While using the Vgs(th) will make it conduct(slightly) it is not a good idea to design a circuit using that number. Vgs(th) is used as the shut-off point when designing an audio amplifier.

The Vgs(th) puts the mosfet deeply in the 'linear' area of conduction. This will create high heat in the mosfet, NOT max power output.