Understanding Pinout Diagram of Mosfet - Page 1
Forum section: electronics / beginners

author: The13thParish
author_rank: Contributor
timestamp: July 07, 2021, 07:35:39 am
content: Dear all,I have a schematic from which I am building a circuit. There are two MOSFETS required for which I have found an equivalent part number (and datasheet) on Mouser to the one indicated on the schematic. I've posted the schematic and pinout side-by-side in the attached image.Comparing the schematic with the pinout from the datasheet, I'm a little confused by the difference in symbol between the two. Can anyone guide me through which pins from the datasheet (D1, D1, S1, G1 for the p-channel and D2, D2, S2, G2 for the n-channel) correspond to the ones in the schematic? In particular, I am confused by the "hook" looking pin on the schematic which doesn't look like anything from the datasheet.Any tips or pointers, even general ones, are gratefully received.All the best,Ryan

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2021, 08:42:08 am
content: A MOSFET only has three connections to the semiconductor junction: gate, source and drain. Quite often there will be multiple pins to the same part of the semiconductor junction, to reduce the resistance.The IRF7105, has an N-channel and P-channel MOSFET, in the same package.Ignore the hooks, it's just the style of symbol used in the schematic.For the P-MOSFET, pin 1 on the IRF7105, goes to #2 on the schematic and pin 7 & 8 on the IRF7105, to #5 schematic. Now figure the rest out yourself.

author: David Hess
author_rank: Super Contributor
timestamp: July 07, 2021, 05:08:01 pm
content: I do not think the hooks correspond to anything in the MOSFET structure, unlike the other side where the arrow is. It does not seem to represent the construction of a dual gate MOSFET.There is a fourth connection at the arrow which represents the substrate but in almost all MOSFETs it is shorted to the source as shown by the symbol. There are 4-pin MOSFETs which make the substrate connection available separate from the source but this has nothing to do with the gate.

author: The13thParish
author_rank: Contributor
timestamp: July 14, 2021, 09:47:03 pm
content: Pin 1 doesn't belong to the p-channel mosfet, but the n-channel one.At any rate, am I correct to assume that the source and drain for the p and n-channel are reversed (the gates remaining the same)? I notice that many diagrams switch the positions such that the drain position for the n-channel is the source position for the p-channel and conversely. The pinout diagram for the IRF7105 however has the source and drain in the same position as labelled by the S and D pins.All the best,Ryan

author: The13thParish
author_rank: Contributor
timestamp: July 14, 2021, 10:11:32 pm
content: OK, now I see that the symbol for the p-channel is often (in other places) shown vertically flipped. I think I've solved this problem. What all these shenanigans have highlighted is that I need to do more reading . . .All the best,Ryan

author: Zero999
author_rank: Super Contributor
timestamp: July 15, 2021, 10:34:47 am
content: Quote from: The13thParish on July 14, 2021, 09:47:03 pmYou're right. I should have said N-channel MOSFET. The fact you've spotted my mistake shows you understand it.