High Current, Low Voltage "circuit protection" - Page 1
Forum section: electronics / projects

author: andrewTK
author_rank: Newbie
timestamp: November 09, 2020, 07:54:55 pm
content: I am creating a circuit for a DIY neopixel (2812b) controller, My power supply is rated for 5v 60A (though I doubt it actually is capable of 60). Also I'm making the lightshow specifically tailored so not all of them are on at the same time. There will be around 1000 LEDs on this circuit. I am monitoring amperage using an ads1115 which is being polled by a "watchdog" MCU. I would like a way giving the MCU the ability of enabling/disabling power. I have been looking at different n-channel mosfets and it seems difficult to find a logic level mosfet that is suitable for this use case.Should some kind of voltage step up ic be used to get min resistance from the normal mosfet?Is a mosfet even the correct component for this application?Clearly I've got a lot to learn when it comes to higher current stuff.Also it'll be a 4 layer board, 1 layer devoted to this high current bus.

author: jbb
author_rank: Super Contributor
timestamp: November 09, 2020, 11:01:24 pm
content: 60A is quite a bit. 5V / 60A is equivalent to about 0.08 Ohms load resistance, so your connector / protector / PCB / wire resistance needs to be much lower. In fact, voltage drop in your power distribution could be a giant problem for you, so do some analysis now.MOSFETs are probably a good tool for this job. Some quick thoughts:* the ‘current rating’ on a MOSFET datasheet is a filthy lie. Ignore it and look at the resistance* N Channel MOSFETs have better on resistance than P Channel MOSFETs if similar cost* you’ll need to drive NCh FETs with voltage above the 5V rail. There are definitely driver chips which can do this...* you will need to parallel several MOSFETs to get the resistance down* how about splitting the power output into multiple banks?* Analog Devices, Texas Instruments and others make Electronic Fuse (EFuse) chips which are designed to monitor a shunt resistor and cut power with a big MOSFET switch, which sounds a lot like what you want.

author: andrewTK
author_rank: Newbie
timestamp: November 09, 2020, 11:11:35 pm
content: Actually I'm totally fine with breaking it into banks, I plan on 8 zones as far as current sensing goes, so It may be wise to go with more, however, I would like to turn all on or off with 1 pin if that is possible. At that point would want to rate for 30 amps a piece (but should only take around 15amps max).

author: S. Petrukhin
author_rank: Super Contributor
timestamp: November 10, 2020, 12:33:06 am
content: Quote from: andrewTK on November 09, 2020, 11:11:35 pmThe easiest way is to use photodiode optocouplers (photovoltaic). They include several photodiodes in series so that they produce a high enough voltage (up to 30V) to saturate the gate.http://toshiba.semicon-storage.com/ap-en/semiconductor/product/optoelectronics/detail.TLP3924.html

author: David Hess
author_rank: Super Contributor
timestamp: November 10, 2020, 03:44:51 pm
content: Quote from: jbb on November 09, 2020, 11:01:24 pmThere are plenty of low threshold voltage single parts now which meet the requirements. For instance the TO-220 Vishay SUP40012EL-GE3 is 2 milliohms with a Vgs of 4.5 Volts. The International Rectifier IRL60SL216 does even better.