Uncategorized

Understanding the curves of a MOSFET

Ask QuestionAsked todayActive todayViewed 33 times2

I am trying to understand the curves of a MOSFET. Sorry if the question is very basic.

Where the red point is is the saturation zone of the MOSFET, therefore the source drain voltage must be 0V because at this point the MOSFET is saturated conduction at maximum current, because on the X axis of the graph called Vds marks 10V for the red point.

enter image description here

transistorsmosfetShareCiteEditFollowFlagedited 4 mins agoJRE46.2k88 gold badges7474 silver badges124124 bronze badgesasked 2 hours agoMario5755 bronze badges

  • 1therefore the source drain voltage must be 0v No, the red dot is at the point where VDSVDS = 10 V, see the X-axis of the graph. The source drain voltage is VDSVDS. Look up when a MOSFET is in saturation, there is an equation which tells you that VDSVDS needs to be larger than a certain value. – Bimpelrekkie 1 hour ago 
  • Ah, let me see. (1) The green region is the “saturation” region. (2) The yellow region is the “linear”, or “ohmic”, or “triode” region. (3) In the saturation region, the thick horizontal (well, slightly tilting upwards) straight lines (well, OK, curves) represent the points in the region of a particular Vgs value. (4) So for example, the curve that the red dot sits represents the points of Vgs = 2.5V. (5) The vertical lines 0, 5, 10, 15, 20 mean the voltage across Drain and Source, Vds. (6) Now the red dot operating point says this: (a) Vds = 10V, (b) Vgs = 2.5V, Id = approx 16A . – tlfong01 1 hour ago    

Add a comment

2 Answers

ActiveOldestVotes1

therefore the source drain voltage must be 0v because at this point the mosfet is saturated conduction at maximum current

No, you have this wrong. Maybe you were perhaps thinking of the BJT saturation region (when the collector-emitter voltage is close to 0 volts)? If so, then you’d be correct but, it’s the other way round for a MOSFET – the channel is saturated rather than the base/collector on a BJT.

From Wiki on MOSFETs: –

enter image description here

ShareCiteEditFollowFlaganswered 41 mins agoAndy aka331k1818 gold badges268268 silver badges577577 bronze badgesAdd a comment0

Question

What do the curves and the red dot represent in the following MOSFET Id vs Vds and Vgs characteristic graph?

mosfet graph

Answer

  1. The green region is the “saturation” region.
  2. The yellow region is the “linear”, or “ohmic”, or “triode” region.
  3. In the saturation region, the thick horizontal (well, slightly tilting upwards) straight lines (well, OK, curves) represent the (connected) points in the region of a particular Vgs value.
  4. So for example, the curve that the red dot sits represents the points of Vgs = 2.5V.
  5. The vertical lines 0, 5, 10, 15, 20 mean the voltage across Drain and Source, Vds.
  6. Now the red dot operating point says this: (a) Vds = 10V, (b) Vgs = 2.5V, Id = approx 16A.

References

(1) Microelectronic Circuit Design, 4th Ed (free eBook) – Richard C Jaegar, Travis N Ballock, McGraw Hill 2011

(2) MOSFET Characteristic Curves (Ohmic, Triode & Saturation Region) (25 min YouTube) – Dr Sunanda Manke, Barkatullah University India 2020sep03

(3) Linear Mode Operation and Safe Operating Diagram of Power-MOSFETs – J Schoiswohl, Infenion, App Note V1.1 2017may


Appendices

Appendix A – Recommended reading list of the Jaeger book

Part 1 Solid State Electronics and Devices

Chapters

  1. Chapter 4 Field-Effect Transistors page 145,
  2. Chapter 5 Bipolr Junction Transistors page 217

Sections

  1. Saturation of the I-V characteristics, Section 4.2.4, Page 154, Fig 4.8
  2. Mathematical Model in the Saturation (Pinch-off) Region, Section 4.2.5, Page 155, Fig 4.10
  3. NMOS Transistor Mathematical ModelSummary (Cutoff region, Triode region, Saturation region, Threshold voltage) Chapter 4, page 160.

Appendix B – Clarifying concepts and terms in MOSFET characteristics graph

Linear Mode Operation and Safe Operating Digram of Power-MOSFETs – J Schoiswohl, Infenion, App Note V1.1 2017may

mosfet concepts and terms

ShareCiteEditDeleteFlagedited 12 mins agoanswered 54 mins agotlfong011,46811 gold badge66 silver badges1111 bronze badgesAdd a comment

Categories: Uncategorized

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.