On 17/02/14 19:31, David Riley wrote: > On Feb 16, 2014, at 11:56 AM, Fabio Battaglia <[email protected]> wrote: > > 5% should be fine; 5% was actually the "expensive" grade of resistor > when these parts were new. 1K, more or less, is generally just a > nominal value unless it's for a termination network (e.g. for SCSI), > in which case you usually want the given value with a 5% tolerance to > match the characteristic impedance of the transfer medium. The > recommended value in the datasheet should probably be fine; you don't > want an output cap that's too big on a 78xx part, because when you cut > off the power supply, you could end up reverse-biasing the regulator > if there's a lot of stored energy in the cap, and my recollection is > that the 78xx regulators don't have much in the way of protection. You > can always drop a diode from output to input to protect it, though > that's obviously not ideal if the PCB doesn't already allow for that. > - Dave Yep, I've seen 7805 being destroyed by reverse voltage caused by a big cap discharging. It shouldn't be an issue on this case though: I don't have the datasheet handy, but I remember that the reccomended value wasn't that much distant from 1.0uF (probably less). 1.2uF just struck me as a weird value though.
While the diode is probably not needed, It might not be a bad idea either if no one advices against: It's not hard to solder on the back of the board and I have plenty of good-enough silicon diodes... -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
