I need help with PIC power supply circuit

[nikens]

PIC power supply circuit

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?
**broken link removed**
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).

 

[karesz]

PIC power supply circuit

Halo Nikens,
for automotive apps is these IC a little bit too old, then the transient suppressions are so 35 years ego not a subject...
I think is better to select actuell types from LT/TI ST ... their are developed especially for automotive apps.
Of course you can try it with such discrete suppressors_minimum zeners- but transient dedicated supression components are better_check pls i.e. Farnells sortiment.
Todays CMOS ICs are pro package to bypass with a 47-100nF & you have place_take pls a small ceramic C(encapsulated Chip C, it measures only ca. 5x5x2mm) if possible SMD_can be on solder side!
https://octopart.com/c317c103k5r5ta-kemet-91278
https://datasheet.octopart.com/MD015E104MAB-AVX-datasheet-13899.pdf
https://datasheet.octopart.com/06035C104KAT2A-AVX-datasheet-5383.pdf
K.
Dont forget pls sufficient cooling to apply, in a car is very hot & your dissipation & lot of vibrations!:-( Car electronics isnt simple to design.

 

[IanP]

Re: PIC power supply circuit

The 7805 regulator is as good as any other voltage regulator (who cares about its age) and it can be easily used in automotive applications ..
Just take certain precautions (as you would do with other voltage regulators) and you should be fine ..
First of all, you need something to take care about overvoltage spikes, and a small resistor (I’d say Rin~4.7Ohm or PTC) together with an RF-choke (~100uH) followed by a Zener diode (or Transient Voltage Suppressor) should do just that ..
Use C1≥220uF and C3≥10uF, they also have to be accompanied by 100nF at each side ..
Then install a couple of 100nF somewhere in the vicinity of your PIC ..

In addition, if there is anything else in your circuit that may draw some current, consider a heatsink for the 7805 voltage regulator ..

Rgds,
IanP