Joerg suggested a refined crowbar circuit. Seems that his mail didn't make it to the list. Text below.
- Werner ----- Forwarded message from Joerg Reisenweber <[email protected]> ----- Date: Sun, 29 Jan 2012 14:10:14 +0100 From: Joerg Reisenweber <[email protected]> To: "Undisclosed.Recipients": <@host.almesberger.net> Cc: Werner Almesberger <[email protected]> Subject: Re: [Milkymist-devel] J21: route 5V though jumper ? btw I just thought connecting both VDD rails (3V3 and 5V) to the thyristor via some burst-proof diodes (10A or sth, maybe Schottky), and getting a 2.1V Zener form 5V to 3V3, would not only solve the sync problem (OverVoltage on 5V triggers 3V3 OVP detection via Zener. Then both get crowbarred via their own diode and common thyristor), but also ensure a more sane power-up sequence (Zener working as diode when biased reverse makes sure 5V rail never is significantly lower than 3V3, forward Zener ensures 3V3 comes up in sync with 5V) cheers jOERG ----- End forwarded message ----- _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode
