MOSFET - Page 1
Forum section: electronics / beginners

author: misiek303
author_rank: Contributor
timestamp: March 21, 2023, 04:41:33 pm
content: I would like to create a version of the Switch Controller for my motorcycle. This is the link with examplehttps://nwtcycletronic.com/wp-content/uploads/X21-PLUS-P-worksheet.pdfIt has a lot of I/Os. I will be using MEGA 2560, I think it's good enough for the first trial.For the 12V outputs, I believe they use one of the MOSFET's relays. And here are my questions:1. How do you think they achieved such a small footprint, especially with 10-12 output of 12V.The MOSFETS circuits take up a lot of space, especially for 12 of them.2. What MOSFETS could be good for this application. The motorcycle runs on 12V, and it must support a 55W load.3. Is there anything else I could use for this application? - the other day I found anAutomotive 8ch Low-sideswitch.https://www.rohm.com/products/power-management/ipds/smart-low-side-switch-ics/bd8lb600fs-c-product#productDetail.But I don't think I will be able to purchase it in a few quantities.4. From the X21 diagram you can see that lights are connected to X21 to get the 12V and to the GND.You can't do it in MOSFET, as far I understand you can hook up the light to the LOAD of MOSFET and 12V. So I don't understand how it works.What do you think, can you help to select a proper MOSFET or other switches?Thanks

author: Eraldo
author_rank: Regular Contributor
timestamp: March 21, 2023, 05:45:11 pm
content: First of all I would suggest on watching a few videos on how mosfets work and the different types out there but I'll give some simple answers to your question.1) as you said the circuit achieves those switchings with mosfets. Mosfets are great as switches because of their low internal resistance. Because of that they dissipate very low energy when on. So that means you can go quite small with mosfets as long as the load isn't huge. The ones inside are smd ones and propably in a dpak package(quite small).But even though there are 12 outputs it doesn't mean they are using the same caliber mosftets since the load on some of those outputs is quite small.2) the most important aspect here is the type of mosfet you use. Either N channel or P channel. In this application it doesn't matter but the one being used is propably an N channel one because of their lower resistance compared to the other one. As for the specific model it's fine as long as the gate voltage is 5V or lower (since if it's higher you can't controll it with an arduino) and the voltage/current is not under the level of your load. Something like STP55NF06L works fine (not sure how common it is). Or find another replacement for it. (Make sure to search on how to connect a mosfet in a circuit becase it's different for N channel and P channel mosfet3) that chip is quite low power so good luck driving a 50w lamp with it (it has a max current of 1 amp)4)what is there you don't understand. Mosfets in this case are acting as switches. In the case of N channel one you connect the source to ground and the drain to 12 v. The gate is then controlled by the arduino.In the first place why are you trying to build something like this. Are you trying to learn about the circuit or learn more about mosfets. Since in your post it sounded like you wanted to build one and connect it to your motorcycle (which is a very bad idea). If it's the latter just buy a proper one and change it to the mechanic.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 21, 2023, 06:18:15 pm
content: You can get a 20A MOSFET in an SO-8 package. As long as you can manage the heat generated by the MOSFET life's good.Read up on heat sinking.It looks like they are using "high-side" switching. For that you have two options; P-channel MOSFETS or N-channel types and an auxiliary high voltage generator.The latter technique is not uncommon in automotive applications.If you make a good choice of MOSFET and give it the right level of gate drive it will only dissipate a few 100mW.eg SI4459BDY with its gate pulled at least 4V below Vsource. A simple npn transistor switch will do that for you.You will likely need some protection to your MOSFET switch against over current and over voltage.

author: misiek303
author_rank: Contributor
timestamp: March 21, 2023, 06:42:00 pm
content: Thank you for your answers.I few reasons why I want to do it.- The X21 comes as a kit which I don't want and need. They don't sell them individually, they are designed and programmed for the specific kit. Once you spend $300 and want to change controllers, you're done, can't do it.- X21 is locked in a specific configuration. I am a software Engineer and I think I could do better for my self.- I have an idea to expend this board with other features like, BL to change the configuration fro the phone app. Add alarm logic etc.So I would like to take this opportunity to learn and to create some DIY Switch Controller projects and possibly I will get some community attention that is looking for something like that as well not spending $300+.pt 4. I looked at this MOSFET and circuithttps://protosupplies.com/product/d4184-mosfet-control-module/The way a LOAD is connected is between 12V of the battery source and the MOSFET LOAD. In my case, I need to connect to the GND and the 12V output. But you already gave me some homework to do.Also question about the above MOSFET. They say:"This MOSFET module with optoisolation uses theD4184 N-Channel logic compatible MOSFETwith low Rds(on) for moderate to higher current low-side switching applications." but also say "This biases the gate at 50% of the power supply voltage which turns on the MOSFET. If a 12V power supply is used, the gate will be at 6V."So I don't think it is aLogicas I will need at least 6V to turn it on. I will research the types you mentioned in your respond soon.Thank you

author: mariush
author_rank: Super Contributor
timestamp: March 21, 2023, 06:45:04 pm
content: You'll also want to read about input capacitance and how it affects things .. some mosfets have a lot of capacitance, so they'll pull some current for that microsecond or whatever when you turn them on and the atmega chip may not be able to handle it, and you'd also need to have discharge resistors or some other method to turn them offI don't think you need mosfets that powerful that you'd need mosfet drivers but you never know.If you want to, see video below, where he goes through selecting mosfet and mosfet driver to pwm a high power light and adjust brightness -- as your application will mostly be just blinking lights for turn signals and maybe low bright/high bright for stop lamp I don't think you need to complicate yourself with driversI quite like mosfets likeAON7524orAON7528but Vds of 30v may be a bit low for auto/motorbike.There's 40v ones likeAON6236or soic 8 ones likeAO4484and of course, higher voltages as well...There's also mosfet arrays, for example seeAON7804, 2 n-channel mosfets rated for max 30v and 9A each.... orAO4882, 2 independent n-channel mosfets, 40v max and 8A each.

author: misiek303
author_rank: Contributor
timestamp: March 21, 2023, 07:58:37 pm
content: I found this articlehttps://circuitjournal.com/which-mosfet-should-you-use-with-arduinoPretty cool explanation, but it still confuses me which type do I need.From his explanation looks like I need a P-type, because, when LOAD is connected to the GROUND, the Gate can have a lower Voltage than the VCC ( good for Arduino )Selecting N type, if I wish to connect Load to the Ground I need a higher V on the Gate to turn it on.Is this right what I am saying?( my application it's all about the connection Load to the Ground )

author: Terry Bites
author_rank: Super Contributor
timestamp: March 22, 2023, 10:20:52 am
content: The mosfet module uses low side switching. That makes things a bit easier.mariush points out thta you will need to drive the mosfet with enough current to get it to swich properly.Gate drivers are easy to use. If you small package sizes there are plenty of options. Prices start from about $0.50.You can get dual an quad devcies. Its generally more ecconomical to use multichannel drivers.One thing to watch out for in automotive electonics is the phenomenon of "load dump". When load is removed from the alternator its terminal voltage can rise well above 12V.This surge voltage can reach 100V or so untill the regualtor can get it under control. It takes about half a second for this to happen. Mean time your project has been fried.Load dump most commonly occurs when the starter motor current drops off after cranking or the battery is disconnected from the charging circuit.You may have built in protection in your car or bike. Its a good idea to add it to your project. The most common aproach is to put a TVS diode across the rails. A series polarity protection diode will help be needed too.

author: Eraldo
author_rank: Regular Contributor
timestamp: March 22, 2023, 08:20:33 pm
content: Quote from: misiek303 on March 21, 2023, 07:58:37 pmIf you are using N type mosfet you need to connect the mosfet to the ground (source) and the lamp is connected directly to the 12V and the other lead (drain) of the mosfet.Just search on how to drive an N channel mosfet with an arduino and you'll find a schematic.

author: misiek303
author_rank: Contributor
timestamp: March 27, 2023, 03:35:32 am
content: I attached a circuit. I maybe close the solution. As a reminder, my goal is to use the microcontroller Atmega 2650 to turn on 12V high-load devices on my motorcycle, like all none LED lights or even the starter ( motor ).So the requirements are:1. High-side configuration to allow the lights and everything else to the GND2. 12V lights and starter potently up to 6A3. turn on/off from microcontroller( I have no clue how to show this picture here, sorry )I also wonder if I should use an optocoupler to fully protect the circuit.Can you have a look and advice, please?Also what kind of MOSFET would you recommend - if I could find an array configuration that would be awesome for a small foot print.Thank you