# Hall effect for over current protection

Discussion in 'General Electronics Discussion' started by snakub, Feb 16, 2012.

1. ### snakub

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Feb 16, 2012
I am not new to electronics but I don't know Jack Schmidt about SMPS's. I am looking to build a step down dc to dc converter from 250 volt dc to 5 to 12 volts at 100 amps. For over current I am thinking of using cycle by cycle protection using this hall effect sensor http://www.lem.com/docs/products/lf%20306-s%20e.pdf and a nand gate. Pwm is sent through the nand gate as normal until a particular current is reached and a positive voltage is sent to the other lead of the nand gate shutting off current for sometime. My questions about this current sensor is on the data sheet what is meant by with 12 volts and with 15 volts on the first page? Is this the required supply voltage to the sensor or can a lower voltage like 5 volts be used? If voltage out of the sensor is proportional to the amount of current in the sensor how do I make sure that the nand gate shuts off at the desired voltage say if I am using 5 volts to supply the sensor but I want the nand to shut off at 2.5 volts or 150 amps of current? And can a toroid withstand 100 amps? How big would it and the wire and core have to be?

Last edited by a moderator: Feb 17, 2012
2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
You will note that the device requires +/-12 to +/-15 volts. Look a few lines lower.

So a single ended 5V rail is *way* out of the question.

3. ### snakub

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Feb 16, 2012
Ah! Thank you for clearing that up. Someone else mentioned on another forum that these sensors are not fast enough to do cycle by cycle over current protection. Although I don't know about that though because I have seen plenty of motor controller and charger projects using hall effects at 16 to 32 khertz. So to do the whole +- thing would I have to have something like a small dc to dc power source http://www.datasheetarchive.com/7A5U12-12-datasheet.html But I can remember when I had this very sensor hooked up to an arduino and and it reading value from 0 to 1028 when a magnet was brought near it and that was on 5 volts idk. What would you recommend for current sense to turn on the nand gate at a certain value? Are there nand gates that turn on when a certain voltage is reached?