Load Dump/Transient Protection.
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Posted by AJ on October 26, 2005, 6:05 am
Please log in for more thread options Hi all, I am just looking for some idea's on 24V automotive systems. I have a regulator that I would like to use (LM3488) which has a max input of 40V. To protect against load dump and transients I was thinking of a PolyFuse/TVS arrangement on the input but if the system is to work on 24V I would have to use a 30V TVS which clamps at around 48V, a little high for the input of my regulator! Any ideas? Regards AJ | ||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Posted by John Popelish on October 26, 2005, 10:33 am
Please log in for more thread options AJ wrote: use a 36 volt, 3 watt zener. But with a +-5% tolerance, this means that it might clamp as low as 34.2 or as high as 37.8 volts. The only energy in a load dump is that stored in the inductance of the wiring. There is also a possibility that the alternator will produce its full output into the battery till the regulator recovers, and the worst case for this would be when the vehicle is operating with the battery disconnected. How much current must your regulator deliver? | ||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Posted by Fred Bloggs on October 26, 2005, 2:44 pm
Please log in for more thread options
John Popelish wrote: > AJ wrote:
> >> Hi all,
>> >> I am just looking for some idea's on 24V automotive systems. I have a >> regulator that I would like to use (LM3488) which has a max input of >> 40V. To protect against load dump and transients I was thinking of a >> PolyFuse/TVS arrangement on the input but if the system is to work on >> 24V I would have to use a 30V TVS which clamps at around 48V, a little >> high for the input of my regulator! Any ideas? >> >> Regards >> >> AJ >> > If you really want to clamp the peaks to less than 40 volts, you might
> use a 36 volt, 3 watt zener. But with a +-5% tolerance, this means that > it might clamp as low as 34.2 or as high as 37.8 volts. The only energy > in a load dump is that stored in the inductance of the wiring. There is > also a possibility that the alternator will produce its full output into > the battery till the regulator recovers, and the worst case for this > would be when the vehicle is operating with the battery disconnected. > > How much current must your regulator deliver? What???!!! The load dump scenario is a catastrophic loss of battery connection, the alternator pumps the whole car load up to whatever 60V with allowable 500ms rundown. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Posted by John Popelish on October 26, 2005, 2:28 pm
Please log in for more thread options
Fred Bloggs wrote: >
> > John Popelish wrote: > >> AJ wrote:
>> >>> Hi all,
>>> >>> I am just looking for some idea's on 24V automotive systems. I have >>> a regulator that I would like to use (LM3488) which has a max input >>> of 40V. To protect against load dump and transients I was thinking of >>> a PolyFuse/TVS arrangement on the input but if the system is to work >>> on 24V I would have to use a 30V TVS which clamps at around 48V, a >>> little high for the input of my regulator! Any ideas? >>> >>> Regards >>> >>> AJ >>> >> If you really want to clamp the peaks to less than 40 volts, you might
>> use a 36 volt, 3 watt zener. But with a +-5% tolerance, this means >> that it might clamp as low as 34.2 or as high as 37.8 volts. The only >> energy in a load dump is that stored in the inductance of the wiring. >> There is also a possibility that the alternator will produce its full >> output into the battery till the regulator recovers, and the worst >> case for this would be when the vehicle is operating with the battery >> disconnected. >> >> How much current must your regulator deliver? >
> > What???!!! The load dump scenario is a catastrophic loss of battery > connection, the alternator pumps the whole car load up to whatever 60V > with allowable 500ms rundown. Is that the official definition of a load dump in vehicle applications? Is this documented somewhere? | ||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Posted by Spehro Pefhany on October 26, 2005, 3:40 pm
Please log in for more thread options
On Wed, 26 Oct 2005 14:28:23 -0400, the renowned John Popelish >Fred Bloggs wrote:
>>
>> >> John Popelish wrote: >> >>> AJ wrote:
>>> >>>> Hi all, >>>> >>>> I am just looking for some idea's on 24V automotive systems. I have >>>> a regulator that I would like to use (LM3488) which has a max input >>>> of 40V. To protect against load dump and transients I was thinking of >>>> a PolyFuse/TVS arrangement on the input but if the system is to work >>>> on 24V I would have to use a 30V TVS which clamps at around 48V, a >>>> little high for the input of my regulator! Any ideas? >>>> >>>> Regards >>>> >>>> AJ >>>> >>> If you really want to clamp the peaks to less than 40 volts, you might >>> use a 36 volt, 3 watt zener. But with a +-5% tolerance, this means >>> that it might clamp as low as 34.2 or as high as 37.8 volts. The only >>> energy in a load dump is that stored in the inductance of the wiring. >>> There is also a possibility that the alternator will produce its full >>> output into the battery till the regulator recovers, and the worst >>> case for this would be when the vehicle is operating with the battery >>> disconnected. >>> >>> How much current must your regulator deliver? >>
>> >> What???!!! The load dump scenario is a catastrophic loss of battery >> connection, the alternator pumps the whole car load up to whatever 60V >> with allowable 500ms rundown. >
>Is that the official definition of a load dump in vehicle >applications? Is this documented somewhere? That's what a load dump is. For an official version of a load dump transient, see: ISO 7637-2, Test Pulses 5a and 5b. There is a lot of energy in a load dump event. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com | ||||||||||||||||||||||||||||||||||||||||||||||||||||
>
> I am just looking for some idea's on 24V automotive systems. I have a
> regulator that I would like to use (LM3488) which has a max input of 40V.
> To protect against load dump and transients I was thinking of a PolyFuse/TVS
> arrangement on the input but if the system is to work on 24V I would have to
> use a 30V TVS which clamps at around 48V, a little high for the input of my
> regulator! Any ideas?
>
> Regards
>
> AJ
>
>