High side switch for 12 V

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What is the best way to replace a manual switch and a thermostatic switch with switches controlled by AVR? These switches control 12 V signal and/or power (up to 1 A) and I'm not able to put a MOSFET between load and ground, but they do have common ground.

Is it possible to control a MOSFET switch on a high side of a 12 V system with 3.3 V AVR? How?

Using a relay would be straight forward, but I'm trying to keep the power consumption as low as possible. How much would a relay consume?

Are there any other options?

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There is no "best" way... An easy solution would be for your AVR to drive the gate of a N-FET that has its source tied to ground, and its drain pulled to 12V with a resistor. The drain of the N-FET would also be connected to the gate of a P-FET. The source of the P-FET would be held high and the drain would be connected to the load.

When the N-FET gate is high, the FET is on, pulling the P-FETs gate away from its source, turning it on. When the N-FET gate is low, the resistor pulls the P-FET's gate to it's source, turning it off.

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Maybe try optocouplers?

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There are such things as solid state relays that can easily be drive by an avr even a 3V3 one.
Look up Clares optomos range for example.

John

If all else fails, read the instructions.

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Similar to nleahcim, but example with a npn, not nmos driving a P channel mosfet.

No idea on load, inrush currents etc.. you need to watch these specs.

oddbudman

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You could use a bistable relay; it has two coils, one to engage the relay, one to release it. Each coil only needs a short pulse. Disadvantage is that it won't release if power goes away.

Battery powered domestic thermostats usually have this kind of relay to control the central heater furnace.

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What about an infineon profet

/Bingo

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Bingo600 wrote:
What about an infineon profet

That looks very good!

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AnalogicTech has announced the AAT4285, said to be the industry's first integrated slew-rate controlled lHigh side switch capable of supporting 12V operation. By integrating level shift and slew rate control functionality into a single device, the AAT4285 allows designers to reduce power consumption and minimize parts count in various new 12V application.

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mikestrepps wrote:
AnalogicTech has announced the AAT4285, said to be the industry's first integrated slew-rate controlled lHigh side switch capable of supporting 12V operation...

I think others got there first. For example:

http://cds.linear.com/docs/Datas...

Greg