Big crowbar module for <4VDC?
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From: Joerg on 17 Dec 2008 18:44 Hello All, After modding a 5V linear to 3.3V I feel a bit iffy about the crowbar, considering the Dollar amount that is going to be connected to it. The original crowbar is partially under (!) a big electrolytic, a bear to modify. Plus it probably isn't a good one to begin with, couldn't see a TL431 in there. So, is there a big old fat crowbar module anywhere that can wrestle an 18A linear supply? The usual OVP modules from Condor and others only have a smallish TO220 SCR in there which would probably go kablouie before it can protect anything. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 17 Dec 2008 19:19 On Wed, 17 Dec 2008 15:44:48 -0800, Joerg <notthisjoergsch(a)removethispacbell.net> wrote: >Hello All, > >After modding a 5V linear to 3.3V I feel a bit iffy about the crowbar, >considering the Dollar amount that is going to be connected to it. The >original crowbar is partially under (!) a big electrolytic, a bear to >modify. Plus it probably isn't a good one to begin with, couldn't see a >TL431 in there. > >So, is there a big old fat crowbar module anywhere that can wrestle an >18A linear supply? The usual OVP modules from Condor and others only >have a smallish TO220 SCR in there which would probably go kablouie >before it can protect anything. All you care about is the I^2*t rating of the fuse versus that of the SCR. Make sure the traces can support the expected crowbar current! In the Master's designs there is only a mild click when the fuse "flashes" ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
From: Jim Thompson on 17 Dec 2008 20:12 On Wed, 17 Dec 2008 15:44:48 -0800, Joerg <notthisjoergsch(a)removethispacbell.net> wrote: >Hello All, > >After modding a 5V linear to 3.3V I feel a bit iffy about the crowbar, >considering the Dollar amount that is going to be connected to it. The >original crowbar is partially under (!) a big electrolytic, a bear to >modify. Plus it probably isn't a good one to begin with, couldn't see a >TL431 in there. > >So, is there a big old fat crowbar module anywhere that can wrestle an >18A linear supply? The usual OVP modules from Condor and others only >have a smallish TO220 SCR in there which would probably go kablouie >before it can protect anything. Second question. You _are_ aware that the crowbar goes on the _input_ side of the linear regulator, aren't you ?:-) Short series loop of input electrolytic and fuse and SCR... phzzzzt ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
From: Michael A. Terrell on 17 Dec 2008 20:18 Jim Thompson wrote: > > On Wed, 17 Dec 2008 15:44:48 -0800, Joerg > <notthisjoergsch(a)removethispacbell.net> wrote: > > >Hello All, > > > >After modding a 5V linear to 3.3V I feel a bit iffy about the crowbar, > >considering the Dollar amount that is going to be connected to it. The > >original crowbar is partially under (!) a big electrolytic, a bear to > >modify. Plus it probably isn't a good one to begin with, couldn't see a > >TL431 in there. > > > >So, is there a big old fat crowbar module anywhere that can wrestle an > >18A linear supply? The usual OVP modules from Condor and others only > >have a smallish TO220 SCR in there which would probably go kablouie > >before it can protect anything. > > All you care about is the I^2*t rating of the fuse versus that of the > SCR. > > Make sure the traces can support the expected crowbar current! > > In the Master's designs there is only a mild click when the fuse > "flashes" ;-) "And let there be light...' If only for a second. :) -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy.
From: Joerg on 18 Dec 2008 12:53
Jim Thompson wrote: > On Wed, 17 Dec 2008 15:44:48 -0800, Joerg > <notthisjoergsch(a)removethispacbell.net> wrote: > >> Hello All, >> >> After modding a 5V linear to 3.3V I feel a bit iffy about the crowbar, >> considering the Dollar amount that is going to be connected to it. The >> original crowbar is partially under (!) a big electrolytic, a bear to >> modify. Plus it probably isn't a good one to begin with, couldn't see a >> TL431 in there. >> >> So, is there a big old fat crowbar module anywhere that can wrestle an >> 18A linear supply? The usual OVP modules from Condor and others only >> have a smallish TO220 SCR in there which would probably go kablouie >> before it can protect anything. > > Second question. You _are_ aware that the crowbar goes on the _input_ > side of the linear regulator, aren't you ?:-) > Ideally yes. Reality, no. Most crowbars are across the output terminals. They do their job because typically the supply is toast anyway if the crowbar has to kick in. IOW one of the pass transistors has fused shut and then it doesn't matter where the crowbar sits. > Short series loop of input electrolytic and fuse and SCR... phzzzzt > ;-) > And that's the problem ... the SCR needs to be huge. There is a really fat one in the supply (>>TO220) but to get there would require major surgery. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |