Timeline for What are the fundamentals behind this p-channel MOSFET / driver circuit?
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 13, 2021 at 7:47 | comment | added | user57037 | @frr oh, yeah that is true. If anything gets damaged it will probably be the GPIO in this case. I guess maybe I was thinking more in general, you don't want to apply 3.3 V to an NPN transistor base when the emitter is grounded. | |
| Nov 13, 2021 at 7:01 | comment | added | frr | Regarding the R55 being possibly omitted - it would be the Arduino's TTL output, rather than the 2N3904 base, that I'd worry about :-) Not sure if the Arduino's outputs are short-circuit-safe... otoh the general-purpose discrete BJT should survive a couple milliamps of base current. | |
| Nov 13, 2021 at 6:23 | history | edited | user57037 | CC BY-SA 4.0 |
added 68 characters in body
|
| Nov 13, 2021 at 6:17 | comment | added | user57037 | Oh, sorry. 0.6 V is the voltage drop from base to emitter of a typical BJT. It could be a bit higher or lower depending on ambient temperature and how much current you run through it. Usually people use 0.6 or 0.7 V for this type of calculation. | |
| Nov 13, 2021 at 5:51 | comment | added | Jordan Sheinfeld | I forgot , where did the 0.6v value is coming from in your calculation ? | |
| Nov 12, 2021 at 19:35 | comment | added | user57037 | You have a very wide range of acceptable values for R55, but it should be there to avoid excessive current in the base or 2n3904. It is possible that 2n3904 could be damaged if R55 is 0 Ohms or 100 Ohms or something like that. Anything over 1 k will probably protect it. You could substitute a low-power mosfet instead of 2n3904. For example BSS138, and in that case, 0 Ohms would be OK (R55 would not be needed). | |
| Nov 12, 2021 at 19:25 | comment | added | Jordan Sheinfeld | Amazing, thanks! Is neglecting R55 at all can damage 2n3904 in any way ? or what are the implications ? | |
| Nov 12, 2021 at 19:03 | history | answered | user57037 | CC BY-SA 4.0 |