Timeline for Device shutdown: harm from charged capacitors?
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| May 20, 2014 at 13:00 | comment | added | Spehro 'speff' Pefhany | @Medo42 Yeah, and I would recommend not listening to those people. ;-) Sure, it could be a good idea for a 7812. | |
| May 20, 2014 at 12:58 | comment | added | Medo42 | @SpehroPefhany The ST datasheet agrees with you, but some people still recommend it (elektronik-kompendium.de/public/schaerer/ureg3pin.htm). Anyway, just substitute a 7812 for the sake of this discussion :) | |
| May 20, 2014 at 12:06 | comment | added | Spehro 'speff' Pefhany | @Medo42 Perhaps a nit-pick, but a diode is never required across a 7805. | |
| May 20, 2014 at 12:02 | comment | added | Spehro 'speff' Pefhany | Anything 10n or below is probably safe on a part with a protection network-- it would require 10V/usec to get 100mA. YMMV with RF parts and such like. | |
| May 20, 2014 at 11:57 | comment | added | Daniel | Ugh.. alright, I see your problem. There doesn't seem to be any information in the datasheet which would make this calculation possible. Microchip tends to make pretty rugged parts though, and my gut thought is that it should be ok. But the ideal case would be to drive it from an op-amp to ensure a low impedance for the ADC. | |
| May 20, 2014 at 11:56 | comment | added | Wouter van Ooijen | That depends on the particular chip and pin. Most pins will be fined with normal (let's say =< 1u) values, but I recall the MCLR pin of most (all?) PIC micro-controllers. It is common to connect a large (let's day 22uF) elco for the reset timing, but the pin is not guaranteed to survive that when Vcc drops, so a series resitor was needed. | |
| May 20, 2014 at 11:43 | comment | added | Medo42 | That's exactly why I'm asking though. What constitutes "large" capacitances? Is there a good rule of thumb, e.g. anything below 1uF*5V is probably safe? | |
| May 20, 2014 at 11:40 | comment | added | Daniel | True. But if you had large capacitances or high voltages, I'd say sure, good to be careful, but everybody has caps on the inputs and outputs of ADCs and DACs. | |
| May 20, 2014 at 11:36 | comment | added | Medo42 | As I said, I don't think these particular cases will be a problem, but there are other cases where protection diodes are recommended - e.g. across an 7805, to prevent the input voltage from dropping below the output voltage on shutdown. And damage to components isn't always obvious, it might just cause e.g. increased wear and drift over time... | |
| May 20, 2014 at 11:30 | history | answered | Daniel | CC BY-SA 3.0 |