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Electronics => Beginners => Topic started by: avector on October 19, 2019, 07:22:43 pm

Title: Art of Electronics Bad Idea question
Post by: avector on October 19, 2019, 07:22:43 pm

I recently bought Art of Electronics 3rd Edition, which does not have the "Bad Circuits" from the 2nd Edition. In pursing the material and the website, I came across this "Bad Circuit" for a high side power switch using PMOS:

https://artofelectronics.net/bckt-high-side_power_switch/ (https://artofelectronics.net/bckt-high-side_power_switch/)

I see that the PMOS is going to take a long time to turn off with only ~480uA to increase gate voltage, but I don't see anything fatally wrong with the circuit. Yet everywhere else on the internet I looked used a BJT NPN instead of an NMOS to drive the gate. I was wondering if someone could look up this circuit in the 2nd Edition or if anyone knew more (or saw something obvious I missed)?

Title: Re: Art of Electronics Bad Idea question
Post by: edavid on October 19, 2019, 07:38:48 pm

The maximum V_GS of the P MOSFET is likely to be exceeded.

Title: Re: Art of Electronics Bad Idea question
Post by: Zero999 on October 19, 2019, 08:58:34 pm

Fortunately it's easy to fix by adding another resistor.
[attachimg=1]

Another alternative is a BJT with an emitter resistor.
[attachimg=2]