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Re: Power Supply Design - Input Protection Scheme
Posted: Mon Dec 31, 2012 12:30 pm
by DaWaN
TheRevva wrote:
The way I 'read' the schematic, it will protect the +5vSwitched from over voltage (and, as has been mentioned, the 5v6 Zener looks somewhat superfluous now).
However, it will NOT protect the +5vTPS and +5vAux lines at all.
Correct, as the +5V TPS and +5V AUX lines go directly to the connector to the EMS. From the connector these two lines directly power sensors on the engine.
You do not want any kind of crowbar in this situation as current would only be limited by external fuses.
The internal 5V is protected by this circuit and if someone connects 12V to those external lines the polyfuses protect the EMS from damage.
If external sensors break from 12V...that is out of the scope of the EMS.
TheRevva wrote:
Thus, if some IDIOT (like me) somehow connected +battery to the +5vTPS line, this line WOULD shoot up to battery (and therefore the actual TPS wiper input would jump up accordingly possibly causing the TPS analog input protection to activate.
(The TPS would still function, but it would be 'read' as full scale from about 5/12 of its wiper travel through to WOT)
I'm not 100% certain what is connected on the +5vAux line. My 'assumption' is that it's for external Hall Effect / Opto sensors.
As far as I'm aware, the majority of such sensors will quite happily survive on full battery voltage and for those that cannot, it's NOT the fault of the EMS!!!
Furthermore, I understand that most such sensors use an open collector type output and as such they would not affect the corresponding EMS input.
However, there _are_ some sensors with internal pull ups that might feed +battery back into the unit (thereby activating the OVP on the associated input)
Both digital and analog inputs have their own OVP
Re: Power Supply Design - Input Protection Scheme
Posted: Tue Jan 01, 2013 1:58 am
by Dan
Yep DaWan is correct. I should be testing in the next 24hours or so
Re: Power Supply Design - Input Protection Scheme
Posted: Fri Jan 04, 2013 2:34 am
by Dan
Testing is still to be done, i have been busy with other matters. I hope to have it done soon though as i have all the required components now.
Re: Power Supply Design - Input Protection Scheme
Posted: Sat Jan 05, 2013 11:38 am
by Dan
Testing has commenced!
Re: Power Supply Design - Input Protection Scheme
Posted: Sat Jan 05, 2013 1:41 pm
by Dan
Testing completed.
It has been concluded that the proposed 431 + PNP clamp be set to 5.1V and the linear reg configuration stays as it currently is via the schematics.
Re: Power Supply Design - Input Protection Scheme
Posted: Sun Jan 06, 2013 5:28 am
by DeuceEFI
I can confirm that the circuit as designed in Dan's last post with the picture of the TL431 and the PNP transistor (minus the 5.6v zener) does indeed keep the 5v supply at a safe level (I measured 5.4vdc on the rail) when I applied 12vdc to the 5vdc rail.
Re: Power Supply Design - Input Protection Scheme
Posted: Sun Jan 06, 2013 9:27 am
by Dan
Did you use it with the pnp clamp? What voltage did you tie the ref pin of the 431 to? As I drew it in my last schematic post in this thread is incorrect as that was with 2.5v at the ref pin. The solution is to set the ref pin to 2.6v so that the clamp triggers at 5.1v. I am keen to Skype with you Andy if you need further clarification? Either that or wait for the next push of RavAGE schematics which should be in the next 24hours.
Re: Power Supply Design - Input Protection Scheme
Posted: Sun Jan 06, 2013 1:26 pm
by Fred
Andy, how did you apply 12V to the rail? Directly? Or through a resistor? If directly, it's amazing that it didn't let smoke out. If through a resistor 5.4 is pretty high, though it depends how low of a value you used. If through standard 470ohm input current limit on an ADC then that's not really acceptable as it would mean 5.7 on the pin. Or did you mean on the pin, in which case you got 5.1 on the rail. Help, I'm lost! :-)
+1 re 5.1 vs 5.0 setting, too.
Dan, I dunno about 24hours, I only got to bed at nearly 5am, so I'm running low on time today too. But before the end of the week for sure, and the sooner the better. Will advise.
Re: Power Supply Design - Input Protection Scheme
Posted: Sun Jan 06, 2013 10:20 pm
by TonyS
5.4V is about as low as you can go. Any lower and you run the risk of trying to regulate the regulator (the regulator output voltage may be as high as ~ 5.30V).
Thanks,
Huff
Re: Power Supply Design - Input Protection Scheme
Posted: Sun Jan 06, 2013 10:23 pm
by Dan
regulator output voltage is approx 5.02V when using correctly spec'd resistors (attention paid to tolerance)
should never ever get to 5.30V.