PIC power supply circuit

[milen]

I am thinking to build my power supply circuit based on L78M05CV ic.
Does this ic has any protection agains harmful voltage spikes (normal thing in car electrical environment) and I just need to add 0.1uF and 0.33uF ceramic capacitors, or do I need to build more complex circuit with big electrolytic capacitor on the input side and possibly a 15V reversed biased zener? If I need to add extra capacitor and zener will the below circuit be fine?

Also what should be the value of capacitor near the MCUs vcc and gnd pins? Someone suggested me to use 100nF, but those capacitors are to big to be solder below the MCU (on the 28DIL socket).

 

[(*steve*)]

Somebody has posted a very similar question here https://www.electronicspoint.com/linear-voltage-regulator-t215373.html which has answers that may be relevant to your question.

And another thing, Circuits are often drawn with the input on the left and the output on the right. At first glance I wondered why you had a zener and a fuse on the output.

The zener and fuse combination you have here is probably not a good idea for a car. You'll basically blow the fuse if there is any prolonged input voltage above 15V, same will happen if you accidentally reverse the polarity. Whilst that will provide protection, it will be damn annoying.

The circuit, as it is currently designed, will be a race between the zener blowing to protect the fuse, or the fuse blowing to protect the zener. Murphy generally wins in these cases and you're likely to find that the zener has a pretty short life if there are frequent spikes unless your power leads have significant resistance.

Better protection circuits will withstand and suppress spikes without blowing fuses or stressing components.

Most 100 nF capacitors are small. I have some that are about 1mm x 2mm (and they're not the smallest ones!) -- are you sure you haven't selected 100 uF, or a capacitor with a very high voltage rating?

100 nF = 0.1 uF