Diodes & Caps. Do I or not?

[Screech]

I read somewhere that it's a good idea to provide every chip with it's on cap, but I don't remember what would be a good general size or type for all chips.,
What if you had lots of chips and lots of caps? Would they loadup the regulator?. Would a 1 amp voltage reg freek out on startup?

I will be using two 555 timers , six 4066 cmos chips, three LM3914 led drivers, twenty plus leds and few other things. All consuming about 250 Milliamps.


I also read it's a good idea to use diodes to protect chips from reverse voltage.
Do I use them in series or back to front parrallel?
Which diode is suited for this job?

which pics below do I use?
(Only power side drawn)

Can I also use an NPN tranistor as a power switch ,instead of a relay ?


Do i really nead to use the caps and diodes , or is it a whole lot a bull-dust.
What if a cap or diode was to fail?, goodbye to a working circuit?

Thanks

 

[David Bridgen]

If there really is a risk of the supply being inverted then just one diode in series with the regulator, as shown in your 2nd diagram, will be sufficient protection.

10nF across the 555s and 4066s is a good idea. The diodes are not needed.

And yes, an npn as per you diagrams will work.

 

[Screech]

Thanks David,
Do I need protection when the supply is turned off? eg, when relays turn off they produce damaging high voltage that travels back into the circuits.

 

[Nigel Goodwin]

Thanks David,
Do I need protection when the supply is turned off? eg, when relays turn off they produce damaging high voltage that travels back into the circuits.

No, all relay coils should have a reverse connected diode across the coil, this is to protect the driver transistor from the back EMF generated when the relay turns off - no other protection is required.

 

[Screech]

Thanks David,
Do I need protection when the supply is turned off? eg, when relays turn off they produce damaging high voltage that travels back into the circuits.

No, all relay coils should have a reverse connected diode across the coil, this is to protect the driver transistor from the back EMF generated when the relay turns off - no other protection is required.

Cool !
Thanks Nigel, I guess I was worried for nothing.