Author Topic: High side switching of 0.1V to 24V with max 30A.  (Read 1740 times)

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Offline PeterFW

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High side switching of 0.1V to 24V with max 30A.
« on: April 07, 2016, 10:11:44 pm »
Hello!
I would like to marry a current sensor with a high side switch to disable the load when a set current limit is reached.
The caveat is, i would like to use the parts i have to finally get rid of all the crap that accumulated, and not order new stuff.
The sensor is a INA226 from TI, it has a open drain output that signals when a set current limit is reached.

The voltage can be within 5A at 0.1 to 24V, 20-30A at 12V or 5A at 24V, it powers a electrolysis cell, resistive load for the most part.

So... the simplest solution would be a relay (and i use one at the moment), but i would like to use something solid state that does not need an extra power supply to only use the 3.3V or 5V logic level that drives the INA226.

Automotive High Side switches i could find all have a undervoltage feature.
A suitable FET i can not find that i can get, i could parallel a bunch of smaller FETs.

What are your thoughts?
 

Offline T3sl4co1l

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Re: High side switching of 0.1V to 24V with max 30A.
« Reply #1 on: April 07, 2016, 10:21:48 pm »
There are high side switches with current sense, e.g. VN5025AJ.  Matter of fact, that might be the slam-dunk part you were looking for.

Ed: oh, down to 0.1V? Well, you can always power the "-V" from -5V, say. Which would screw with your logic levels, but that's not terrifying (use a single BJT or FET to invert +3.3 or 5V logic to -V).

If you're also wanting to do that with existing parts, you'll have to tell us what all you have / have access to, and how big you were expecting it to be (or not).  Which seems to clash with the "get rid of all the crap that accumulated" part, so I don't understand.

Also, don't forget the comparator and latch (RS or monostable), otherwise it just oscillates forever.  If you've already solved this problem, then you've probably done that, but just making sure...  :-//

Tim
« Last Edit: April 07, 2016, 10:25:55 pm by T3sl4co1l »
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Offline PeterFW

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Re: High side switching of 0.1V to 24V with max 30A.
« Reply #2 on: April 07, 2016, 10:26:54 pm »
Hello and thanks for your reply!

There are high side switches with current sense, e.g. VN5025AJ.  Matter of fact, that might be the slam-dunk part you were looking for.

The first thing i looked for were automotive high side switches, all the ones i found suitable had a undervoltage feature.
The VN5025AJ has one as well, at min 3.5V wich would be a problem since i will have loads at around 0.5V but maybe lower.

Greetings,
Peter
 

Offline T3sl4co1l

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Re: High side switching of 0.1V to 24V with max 30A.
« Reply #3 on: April 07, 2016, 10:44:52 pm »
So how about a charge pump?

Tim
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Offline PeterFW

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Re: High side switching of 0.1V to 24V with max 30A.
« Reply #4 on: April 09, 2016, 10:05:37 pm »
Hello and thank you everyone for the replys!
I have thought about the whole thing a bit, when i stick to a relay i need more voltage annyway. The ones i currently use that are happy with 3-5V on the coil do not handle enough current, the big ones want more coil voltage.

So i might as well use that to switch the FET...
Gonna sleep a bit more over that and for now, stick with my low current design.

Greetings,
Peter
 

Offline Simon

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Re: High side switching of 0.1V to 24V with max 30A.
« Reply #5 on: April 14, 2016, 11:39:23 am »
To completely turn on a P-channel MOSFET configured as a high-side switch, you should connect the gate to ground. Are you doing that?

wrong. You need to bring the gate 10V negative of the source. Say you use a 30V supply putting the gate to ground on a high side mosfet will likely blow it.
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