Re: Parallel Port Propeller (ParPortProp) Boards Available

[Sergey <skis...@gmail.com>]

Dave,

It seems that such protection is not required for LM3940, at least its
datasheet doesn't mention anything about it (but it does for LM340/
LM78xx devices... even then the diode is only necessary in certain
conditions, generally speaking in the case where input voltage falls
very fast, for example if input gets short circuited to the ground)

LM3940 application note says following regarding output capacitor:

MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain stability is 33 μF
(this value may be increased without limit). Larger values of output
capacitance will give improved transient response.

Thanks to Bill Lewis for pointing that out :-)

Best regards,
Sergey

On Jul 29, 9:39 pm, vk5dg <vk...@internode.on.net> wrote:
> Hello Sergey,
>
> With such a large capacitance on the regulator output, it might be wise to
> put a
> reverse diode across the regulator (cathode on +5v side, anode on 3v side)
> so it
> can discharge with little or no load when powering down.
>
> Regards
>
> David