How powering PIC in auto ?

[fratello]

I made some schematics with PIC (12F675=windows closer;16F648A=thermometer/thermostat) and I use them in my car. I powered them like in picture...but, sometimes, without any reason, the PIC's are damaged. If I replace them, in the sames boards, these works fine, for a while...(weeks, even month !) and...collapeses again ! Can somebody sugessting one better metod for powering PIC's in auto environment ? Thanks in advance for every reply and sorry for my poor english. All the best !

[mackrackit]

Can we see the remainder of the schematic?

Yes, that is a very basic power supply as one can get but I will bet you are getting a spike from someplace else.

[Archangel]

I made some schematics with PIC (12F675=windows closer;16F648A=thermometer/thermostat) and I use them in my car. I powered them like in picture...but, sometimes, without any reason, the PIC's are damaged. If I replace them, in the sames boards, these works fine, for a while...(weeks, even month !) and...collapeses again ! Can somebody sugessting one better metod for powering PIC's in auto environment ? Thanks in advance for every reply and sorry for my poor english. All the best !

Hi Fratello,
Maybe you are getting a back EMF from the relays or motors, relays are good for over 100v back emf,also; try some decoupling caps across the motor power leads. I am pretty sure you already are using blocking or snubber diodes, perhaps a faster diode.

[fratello]

Thanks for reply ! This is one of schematic that I use : module for up/down windows of my car. The powering is like in previous post. The capacitors for decoupling (10uF & 100nF) are SMD, near at pins of PIC's.
LE : For relays I use 1N4007.

[fratello]

In previous post VR1 is not correct...

[Gusse]

Hi Fratello,

Can you measure broken PIC's if the IO's have been damaged?
- are input resistances (IO to GND) at the same level as with new PICs?

Is there any possibility that ESD would enter the system when swithes are pressed?

In car environment, you can easily charge up to very high potentials and if you discharge it to switches, PIC it can be damaged.

1) You could add serial resistors to PIC inputs 4 & 5. Already small resistors (~100 ohm) will damp ESD currents.
2) 5.1V zeners could be added next to C1 and C2.
3) Or do both

BR,
-Gusse-

[fratello]

Thank You for reply !
I have just one damaged 12F675; the resistance from pin 4 to GND are about 9k7, from pin 5 to GND are 9k1, with PIC powering with 5V ; PIC outside from module : pin 4 to GND = 16k3 and pin 5 to GND 13k3. What reveals that ?
Unfortunate I don't have now one good 12F675 for measuring the IO resistance; I wait for postal messenger from e-commerce.