Timeline for What is the reason to put two MOSFETs in a series connection?
Current License: CC BY-SA 4.0
18 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Feb 5, 2021 at 0:12 | vote | accept | Ernte1893 | ||
| Dec 6, 2020 at 10:53 | answer | added | Saadat | timeline score: 1 | |
| Dec 3, 2020 at 21:00 | history | tweeted | twitter.com/StackElectronix/status/1334603366421422090 | ||
| Dec 3, 2020 at 18:43 | comment | added | Chris Stratton | It looks like this is a little pony power supply to feed a low voltage on-off switch, I'd check that the 5.6 volts is actually DC not AC for some reason of failure. Unless this is part of a protection circuit too(?) I'd seriously consider just replacing it with some other relay drive FET, or even just bridging the relay contact and giving the product some other power switch, eg, plug it into a power strip with a switch. | |
| Dec 3, 2020 at 18:39 | comment | added | Bruce Abbott | What signal is on 'ACRY' | |
| Dec 3, 2020 at 18:34 | comment | added | Ernte1893 | @ChrisStratton: I added the schematics of the power supply part of the amplifier in my original thread. Unfortunately, I cannot find the datasheet of the relay and therefore, I do not know how big the supply voltage is supposed to be. The working circuit is directly connected to the 230V AC. Hence, it's function is to power up the complete amplifier (the 230V AC are leading directly to a transformer to the the main board). Does that answer your request in any way? | |
| Dec 3, 2020 at 18:33 | comment | added | SteveSh | One reason to put two FETs in series is fault tolerance/single point failure mitigation, though I'd be surprised to see that in a consumer level product. The question to ask would be "if I only have a single FET and it shorts drain to source, what are the consequences." | |
| Dec 3, 2020 at 18:27 | history | edited | Ernte1893 | CC BY-SA 4.0 |
added 290 characters in body
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| Dec 3, 2020 at 18:01 | comment | added | Chris Stratton | @Ernte183 please show the surrounding circuitry in particular the actual ground path as Andy asked, specify what the supply voltage to the relay is, and explain what the function of the relay in the amplifier is. | |
| Dec 3, 2020 at 17:56 | comment | added | Chris Stratton | I'm not saying it makes sense to me either, however, the FET does not have a resistor. It could be that they think it's okay to actually use the built in breakdown diode thingy routinely not just for pre-assembly ESD (pretty oddly, NEC states the leakage current for the test condition of applying the absolute maximum!) and this somehow works with DB16. | |
| Dec 3, 2020 at 17:48 | comment | added | Andy aka | @ChrisStratton without a gate source resistor (or defined gate source leakage or defined diode leakage), the circuit makes no more sense to me. | |
| Dec 3, 2020 at 17:43 | comment | added | Chris Stratton | @Andyaka "can be replaced with any resistor self-contained type transistor" is a Japanese to English mistranslation of what replaces what, to quote the NEC application guide for these "in applications, such as interfacing small signals, where the MOS FET is used in a low current region, the MOS FET can smoothly replace the existing transistors containing resistors." datasheetarchive.com/pdf/… The gate protection diode thingy is also mentioned. | |
| Dec 3, 2020 at 17:30 | comment | added | Chris Stratton | One strategy, at least if the surrounding circuitry can be sufficiently understood to validate it, might be to use a single more robust modern logic-level FET... | |
| Dec 3, 2020 at 17:30 | comment | added | Andy aka | Look at the first page bullets @ChrisStratton - I don't know if this constitutes an inbuilt resistor but it sounds like one and the circuit would need it. | |
| Dec 3, 2020 at 17:27 | comment | added | Chris Stratton | @Andyaka what "resistor"? There's some sort of bidirectional breakdown diode thing between gate and source on the data sheet, likely an early form of ESD protection as unprotected gates of early FET's were notorious for ESD damage in handling. | |
| Dec 3, 2020 at 17:24 | history | edited | Chris Stratton | CC BY-SA 4.0 |
series, not serial
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| Dec 3, 2020 at 17:14 | comment | added | Andy aka | It does look odd - the MOSFETs have an in-built gate-source resistor too - another odd-ball thing to have. Are you absolutely positive that GND connects where you show it? | |
| Dec 3, 2020 at 17:07 | history | asked | Ernte1893 | CC BY-SA 4.0 |