Propeller rebooting - Power Supply Issues

Alex.Stanfield

I need some recommendations on filtering my PSU an avoiding reboots on the propeller protoboard usb.

My project has a propeller proto-board with usb which is fed from a "power module" I built for the high power loads I need to drive. This power module (see schematic) has two linear regulators:
Input PSU -> 7812 -> 7808 -> Propeller protoboard
The input PSUs are notebook PSUs capable of delivering 4.5A@16v

From the 12v rail I'm driving an electric lock with a 10ms pulse. The lock opens fine but then the propeller reboots.
No rebooting happens with the same circuit but no lock attached nor does it happen if powered from a different source. So I'm assuming that the current load of the lock is pulling down the 7808 input or creating enough "noise" there as to reboot the propeller. I still couldn't capture the glitch in the 8v rail on the scope but evidence points me in that direction.

So, how would you filter this? Suggestions on reworking the schematic (and/or PCB) are welcome, specially if not too far off my current design. :cool:

Help and hints are greatly appreciated.

Alex

Leon

Do you have a diode across the solenoid?

You need to pay careful attention to your supplies and grounds. TVSs can help with transients.

Alex.Stanfield

Leon wrote: »

Do you have a diode across the solenoid?

You need to pay careful attention to your supplies and grounds. TVSs can help with transients.

Yes. It's a 1N5819 40v 25A(peak) Schottky across all solenoids.

I'm planning to put one of those schottkys and a big cap between the 7808 and the propeller. I'll give it a try.

I'll need to get lower voltage TVS to try that one. (I have only for 39v on hand)

Thanks Alex

BTW: The ICs are mic4427 fet drivers.

Phil Pilgrim (PhiPi)

Add a diode where indicated here:



and change C3 to 1000 uF or more. This will help to isolate the input to your 8V regulator from fluctuations in the 12V supply.

-Phil

Alex.Stanfield

Phil Pilgrim (PhiPi) wrote: »

Add a diode where indicated here:

and change C3 to 1000 uF or more. This will help to isolate the input to your 8V regulator from fluctuations in the 12V supply.

-Phil

Thanks Phipi, since it's easier right now I'll try that but after the 7808 (which only powers the propeller protoboard)

Will let you know.

Alex

Phil Pilgrim (PhiPi)

If you do it after the 7808, you will need to add another cap (1000+ uF) after the diode. You cannot put the diode between the 7808 and C4.

-Phil

Alex.Stanfield

It's working !!! :cool:

I placed a 1N5819 schottky after C4 and a 4700uF 16V cap after it. No rebooting now ;-)

Phipi, I'll modify the schematic in the final release following your suggestions, but I had it all built and the easiest way out seemed to bring this diode and cap directly in the connector to try it out.

Thanks everyone for the help, this forum is really great to have around !

Alex