Timeline for Why does MOSFET N back to back switch work?
Current License: CC BY-SA 4.0
13 events
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| Mar 16, 2023 at 6:14 | comment | added | mrbean | @hacktastical Let's say the same back-to-back configuration was used on the low-side, where the drain of the right FET was connected to ground and the drain of the left FET was connected to load. Would the gate voltage of the right FET only need to be above gate-to-drain voltage to turn on? Or would you also need to ensure the gate was above Vgs? I noticed, that the source is one body diode above ground so would gate need to be higher than source still? Or would the right FET turn on with just a high enough gate-to-drain voltage. Would you still need a charge pump? | |
| Feb 22, 2023 at 1:42 | history | edited | hacktastical | CC BY-SA 4.0 |
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| Feb 21, 2023 at 22:46 | history | edited | hacktastical | CC BY-SA 4.0 |
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| May 6, 2022 at 5:12 | vote | accept | Łukasz Przeniosło | ||
| May 6, 2022 at 0:49 | comment | added | hacktastical | Yes, exactly. There’s such a thing as a 4-terminal FET with a separate body connection. | |
| May 5, 2022 at 21:04 | comment | added | Łukasz Przeniosło | @hackstical ok, got it. So while FET is symmetrical in build, the only thing differentiating the drain from source is the body diode direction and removing it would leave the FET fully symmetrical? | |
| May 2, 2022 at 17:28 | history | edited | hacktastical | CC BY-SA 4.0 |
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| May 2, 2022 at 17:26 | comment | added | hacktastical | The definition of ‘source’ and ‘drain’ is arbitrary: it depends on how the FET is biased. The slide deck explains this as it shows how the FET behaves in its different biasing states. It’s really about the substrate vs. gate voltage and how it forms the channel underneath it. | |
| May 1, 2022 at 9:22 | comment | added | Łukasz Przeniosło | thank you for the reference. However I could not find there the info about the issue at hand- it is always referenced as gate voltage vs source voltage still. | |
| Apr 30, 2022 at 17:19 | comment | added | hacktastical | This slide deck may help: alan.ece.gatech.edu/ECE3040/Lectures/… | |
| Apr 30, 2022 at 17:09 | comment | added | hacktastical | FETs are at their basis symmetric devices. The body diode only comes about because of tying the source to the body, forming a parasitic p-n junction. | |
| Apr 30, 2022 at 5:54 | comment | added | Łukasz Przeniosło | Thabks for the answer. I did not know about this phenomena. I was convinced that only by taking the gate higher than the source the transistor turns on (bo matter the 2 direction co ductivity). In here my explanation was that the M1 body diode that has leakage current, which causes the M1 source to be VIN - drop, and thats why it works. Could you give some references on the draid biasing? | |
| Apr 29, 2022 at 22:33 | history | answered | hacktastical | CC BY-SA 4.0 |