JohnDW
Automotive
- Jun 26, 2011
- 8
Hi Guys,
I would appreciate your thoughts on the following.
Looking for a gerneral purpose design that will provide protection and 5 volt regulator for use in Automotive microcontroller applications.
The holy grail would have a small foot print on the PCB, pretty bulluit proof and a sensbile cost....and not hyper complex if I can help it!
The system should the usual protection from;
Sustained over current draw
Transient voltage spikes
Sustained over voltage
Reverse Battery
A preposed cirucit built from individual surface mount parts is.
Regulator
Micrel LDO MIC2920A Reg. A 5V 400mA regulator, with reverse protection to -20V, Transient protection to 60V, internal current limiting. Which is a great all round package but I still feel I should provide some front line protection as well. Will also need to provide enough heatsinking on the PCB. It will need the usual caps on the input/ouput but i think I can use 1206 SMD ceramics.
The Front line protection would consist of
Fuse
PTC resettable, 16V, 350mA Hold, 750mA Trip. I would preffer a high operating voltage and PTCs always have a significant gap between the hold and tripping current so you need a serious problem before they will trip But what else to use?
I could use a standard SMD fuse but its 'Return to Base' if any thing happens for repair, which is no good really. And some devices will be potted solid.
Capacitor
A 33uF electrolytic - provides some basic filtering.
But what voltage ?? The lower the voltage gives a smaller the package but I dont want it to pop. The supply will rarely exceed 14V so can I get away with a 25V Cap? Or will a transients blow it ?
Zenner Limiter
18V 3W Zenner Limiter - Anything over ~18v will bleed off, if the over voltage is sustained and excessive, the PTC resettable fuse (FS1) should (eventually!) trip.
In a reverse battery condition the Zenner will conduct forwards and the PTC should trip.
TVS (transient voltage suppressor)
Vishay TransZorb - SMAJ24A 400w, Breakdown 26V, Clamp Voltage 39V. This should catch any of the nasty fast transients.
SO... I'm looking for a robust but realistic design that I can move between various small projects. Is the above overkill / not enough / Just wrong!
Thoughts?
I've not found any 'all in one' protection solutions for automotive applications, anyone heard of one?
Cheers for your input, John.
I would appreciate your thoughts on the following.
Looking for a gerneral purpose design that will provide protection and 5 volt regulator for use in Automotive microcontroller applications.
The holy grail would have a small foot print on the PCB, pretty bulluit proof and a sensbile cost....and not hyper complex if I can help it!
The system should the usual protection from;
Sustained over current draw
Transient voltage spikes
Sustained over voltage
Reverse Battery
A preposed cirucit built from individual surface mount parts is.
Regulator
Micrel LDO MIC2920A Reg. A 5V 400mA regulator, with reverse protection to -20V, Transient protection to 60V, internal current limiting. Which is a great all round package but I still feel I should provide some front line protection as well. Will also need to provide enough heatsinking on the PCB. It will need the usual caps on the input/ouput but i think I can use 1206 SMD ceramics.
The Front line protection would consist of
Fuse
PTC resettable, 16V, 350mA Hold, 750mA Trip. I would preffer a high operating voltage and PTCs always have a significant gap between the hold and tripping current so you need a serious problem before they will trip But what else to use?
I could use a standard SMD fuse but its 'Return to Base' if any thing happens for repair, which is no good really. And some devices will be potted solid.
Capacitor
A 33uF electrolytic - provides some basic filtering.
But what voltage ?? The lower the voltage gives a smaller the package but I dont want it to pop. The supply will rarely exceed 14V so can I get away with a 25V Cap? Or will a transients blow it ?
Zenner Limiter
18V 3W Zenner Limiter - Anything over ~18v will bleed off, if the over voltage is sustained and excessive, the PTC resettable fuse (FS1) should (eventually!) trip.
In a reverse battery condition the Zenner will conduct forwards and the PTC should trip.
TVS (transient voltage suppressor)
Vishay TransZorb - SMAJ24A 400w, Breakdown 26V, Clamp Voltage 39V. This should catch any of the nasty fast transients.
SO... I'm looking for a robust but realistic design that I can move between various small projects. Is the above overkill / not enough / Just wrong!
Thoughts?
I've not found any 'all in one' protection solutions for automotive applications, anyone heard of one?
Cheers for your input, John.
