High side switch

Using Arduino Motors, Mechanics, Power and CNC
1

Hi guys and gals,

Been lurking for a long time, just decided to sign up :slight_smile:

Can anybody point me in the right direction for a high side switch for loads up to about 30A in an automotive environment?
I have read that a p channel fet isn't a great idea in automotive environments, not really sure why.

Maybe something similar to this http://www.st.com/web/en/resource/technical/document/datasheet/CD00233832.pdf but with a higher rating.

Any help appreciated, thanks

2

Going to need a good heatsink; power dissipated will be 30Ax30Ax0.009ohm = 8.1W.
Aduino output can't control it directly, will need a good driver in front to make it turn on/off quickly.

Good automotive relay might be better.

3

Thanks CrossRoads, I was hoping you'd pitch in. That looks fairly suitable. Perhaps I should elaborate more on what I want to do.

I'm thinking of building a power distribution module, similar to
a motec pdm (http://www.motec.com.au/pdm15/pdm15overview/)
or racepak's smart wire (http://www.racepak.com/Components/Smartwire.php) system.

Although it will be slightly more lo tech. I'd just buy one of those but I only need a few outputs as its going in a offroad vehicle, with minimal accessories.

I am trying to shy away from relays, as I want something more compact, lighter and reliable.

30A is a safety net, everything will be between 10-20A.

4

Why not just have a decent toggle switch per output? You need a switch anyway to select on/of per output, yes? Make it a good switch and skip the transistors.

5

Err good point haha not entirely sure why I didn't think of that. I just like building new things

Thanks

6

spol:
Can anybody point me in the right direction for a high side switch for loads up to about 30A in an automotive environment?
I have read that a p channel fet isn't a great idea in automotive environments, not really sure why.

Well an n-channel MOSFET is even worse in that case!

p-channel MOSFETs have poorer specs than n-channel, but since automotive
circuits are always ground-return-via-chassis you have to use high-side switching
so p-FETs are a natural solution.

The tricky bit is protection circuitry, not the actual switching. You'd like
your high-side switch to survive a short-circuit load, work when the battery voltage
has dropped to 8V (starter motor active), handle a battery voltage spike of 30V
without dying.

This is where integrated high-side switches come in - typically they use an n-channel
because they add a charge-pump circuit to generate the gate drive supply above the
positive supply on-chip...
for instance: http://uk.farnell.com/infineon/bts6133d/ic-profet-p-to252-5/dp/1440811