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Help with Electric Diagram Mosfet

Started by kurt-olsson, April 18, 2021, 02:21:06 AM

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kurt-olsson

April 18, 2021, 02:21:06 AM Last Edit: April 18, 2021, 02:21:51 AM by kurt-olsson
I have attached my Basic electric diagram on how things are connected.

I having some troubles on how to dim my backlight.

I walt to place a mosfet or a PWM control between my 5V+ and Negative -

This is easy if having seperate negatives. But in my setup all negatives are all connected togheter and therefore i am not sure how to hook it up 100%. I have ideas but would like to confirm on how to use a mosfet modult with my diagram.

I want the 5V+ to be dimmable.


ame

No disrespect, but your diagram is not useful.

Ignoring everything but the 5V system I assume you have something like this:

+5V ---???--->|--- GND

Where ??? is your dimmer circuit, and >| is your LED.

Do your LEDs have a series resistor too? Doesn't really matter.

Anyway, in this case you need a "high side" switching circuit, which in general is harder to build, more costly, and less common than the "low side" driver. I haven't been able to find something suitable with a cursory Google search.

Are you sure you can't rewire things so that you can switch the ground (low side) instead?


kurt-olsson

Non taken, this is a crappy diagram :)

Will try to make another with my mosfet circuit included they way i am thinking of wiring it.

I could seperate the negatives pretty easily but i am also curious to see if my circuit works.

Thanks for the input though, will try to post a new diagram tonight.

ame

Ok, cool.

If you have a MOSFET module in mind please post a link. There are several on AliExpress, but they all seem to be low side switching (because it's easier and cheaper).

kurt-olsson

April 18, 2021, 06:48:49 AM #4 Last Edit: April 18, 2021, 07:03:27 AM by kurt-olsson
I am thinking of these ones.

I will add a heatsink and top it with 4.5Amps. I will install these on a metal plate and check the temperature.
But with many, i can devide all my backlight of around 20Amps in total.

https://www.ebay.com/itm/5pcs-TOP-MOSFET-Button-IRF520-MOSFET-Driver-Module-for-Arduino-ARM-Raspberry-pi-/303931530100?_trksid=p2349624.m46890.l49286

Circuit will be pretty much ->

VIN -> 5V+ from power supply
GND -> - Negative from power supply
V+ -> My 5V+ Backlight positive (bulbs)
V-  -> Connect Negative cable from my Negative Bus where ALL my negatives are connected.

Thats the plan.


My only question left is if i can take BOTH the GND and V- From my negative Bus?

That way i can have all negatives still in one bus






kurt-olsson

April 18, 2021, 08:27:36 AM #5 Last Edit: April 18, 2021, 09:19:44 AM by kurt-olsson
Faulty post

ame

Quote from: kurt-olsson on April 18, 2021, 06:48:49 AMI am thinking of these ones.

I will add a heatsink and top it with 4.5Amps. I will install these on a metal plate and check the temperature.
But with many, i can devide all my backlight of around 20Amps in total.

https://www.ebay.com/itm/5pcs-TOP-MOSFET-Button-IRF520-MOSFET-Driver-Module-for-Arduino-ARM-Raspberry-pi-/303931530100?_trksid=p2349624.m46890.l49286

Circuit will be pretty much ->

VIN -> 5V+ from power supply
GND -> - Negative from power supply
V+ -> My 5V+ Backlight positive (bulbs)
V-  -> Connect Negative cable from my Negative Bus where ALL my negatives are connected.

Thats the plan.


My only question left is if i can take BOTH the GND and V- From my negative Bus?

That way i can have all negatives still in one bus


No, that won't work. That module is a low side switch. Here's a better picture:

https://m.aliexpress.com/item/33059636580.html

You can see from the photo of the underside of the board that V- and GND are not the same. V- on the board goes to the MOSFET which then switches it to ground.

If you Google for IRF520 you should find a bunch of application notes that might help you understand how the MOSFET works for different applications, and how to use it. That module is (probably) the simplest low side switch you could make.

kurt-olsson

April 18, 2021, 09:09:05 PM #7 Last Edit: April 18, 2021, 09:49:36 PM by kurt-olsson
Thanks.

I will prob build my own circuit and keep it simple instead of using modules.

Will put the mosfet between PS Negative and the Negative busses so i can use the Source and Drain of the mosfet just like normal.



Thanks again for sharing your input, really apreciate it.

Thanks

RayS

You may need to separate your (-) connections so they aren't connected.

I went down that road for 2 reasons:

1. Standard 12Vdc LED Dimmers usually don't have a "Common" ground. Sometimes the ground side is PWM'd

2. For Reason #1, when I installed a commercial intercom and keyed the mic, all that PWM noise on (-) traveled through the sim ground and nearly blew my ears off.

My solution was to continue using the cheap LED dimmers you can find on Amazon but isolate the power side. I have about 8 dimmers in my pit, all driven by an isolated 12VDC power supply, where the ground is never shared with any other ground.

All I had to do was remove the potentiometer from the device and run wires to it so I could mount the dimmer control remotely.

You may find that using a COTS dimmer is a cheaper and less frustrating solution:

12VDC LED Dimmers on Amazon



Ray Sotkiewicz

kurt-olsson

Thanks Ray for the input.

I will cut the circuit where the negatives are separated just before returning to the PSU. Not the fancy way i wanted but that will work.

For my LED and MCP dimming i dont have a common negative so there is no problem.

So my solution is basically what you suggest.

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