Automotive 12V switch for microcontroller - Page 1
Forum section: electronics / beginners

author: misiek303
author_rank: Contributor
timestamp: March 27, 2023, 04:18:30 pm
content: HiI let myself start a new thread with fresh information. I need help reviewing the attached circuit.The goal is to use it in a motorcycle with GND/chassis to control all 12V lights and start the bike. The requirement is to use mosfet in high-side configuration so I could still have all lights connected to the GND/chassis. I added also an optocoupler for extra protection.I don't know what the resistor values would be yet and also what PNP transistor and NPN mosfet to use. I am very open to recommendations.Thank you guys

author: BillyO
author_rank: Super Contributor
timestamp: March 27, 2023, 05:38:59 pm
content: As it stands, it looks okay. Not sure why you need such a low value resistor pulling the MOSFET gate up. Anyway, a 2N2222 should work fine as the transistor. The MOSFET should be able to handle the current of the light and be given sufficient heat sinking. If it is an incandescent light, remember they have very high inrush current - 10 times (or more) their running current. The circuit driving a starter solenoid will need a freewheel diode down at the solenoid.!N4001 diode would be fine for D25 (why do you want it at all?). !N4007 seems like overkill unless you have them lying around.

author: misiek303
author_rank: Contributor
timestamp: March 27, 2023, 06:03:32 pm
content: I updated the resistors, but I still don't know what the exact values should be.Regarding the flyback diode for the starter solenoid case, I thought this is what D24 is for, can you tell where the diode should be?Any recommendation regarding MOSFET's choice?Thanks

author: inse
author_rank: Super Contributor
timestamp: March 27, 2023, 06:22:56 pm
content: D25 is not so good, you might not be able to get sufficient base current.As your light switch does not require ultrafast turn off, remove it and drive the transistor into saturation.By the way, if you are using an optocoupler for safety, then connect the cathode to the Arduino GND, not chassis.

author: BillyO
author_rank: Super Contributor
timestamp: March 27, 2023, 06:49:33 pm
content: Quote from: misiek303 on March 27, 2023, 06:03:32 pmI would put the diode as close to the solenoid as possible.Again, the MOSFET depends on the continuous and surge currents it needs to deal with. What is the total wattage of your lights? Are they LED or incandescent? What is the current draw on the starter solenoid?

author: misiek303
author_rank: Contributor
timestamp: March 27, 2023, 07:19:31 pm
content: The light bulbs are about 55W that I need to support. I will convert them to LED but I would like to have this option to support at least 55W. I don't know how much solenoid draws yet but I assume a lot.

author: misiek303
author_rank: Contributor
timestamp: March 27, 2023, 07:25:49 pm
content: Quote from: inse on March 27, 2023, 06:22:56 pmThe circuit will share a GND with the chassis. But the optocoupler will be physically connected to Arduino GDN. I wonder if that makes any difference actually. Can you explain why ?Thanks

author: inse
author_rank: Super Contributor
timestamp: March 27, 2023, 07:31:48 pm
content: You are creating a kind of loop which is sensitive to EMI.And if you have a bad ground at the arduino, the opto coupler becomes your GND connection and funny things will happen.

author: Benta
author_rank: Super Contributor
timestamp: March 27, 2023, 09:38:11 pm
content: Don't understand why you don't just use Infineon ProFETs. They're built and intended for automotive use. Much simpler.

author: BillyO
author_rank: Super Contributor
timestamp: March 27, 2023, 09:42:24 pm
content: Quote from: inse on March 27, 2023, 07:31:48 pmRight. I missed that.The whole idea of using an optocoupler is the complete isolation. The Arduino GND absolutely has to be the return for the isolator LED. And the Arduino ground should not be the motorcycle ground.

author: langwadt
author_rank: Super Contributor
timestamp: March 27, 2023, 10:01:01 pm
content: Quote from: Benta on March 27, 2023, 09:38:11 pmand protected against most faults and abuse

author: inse
author_rank: Super Contributor
timestamp: March 28, 2023, 03:37:14 am
content: Too simple and reliable solution 🤓

author: misiek303
author_rank: Contributor
timestamp: March 29, 2023, 02:54:38 am
content: ProFets. That's what I was looking forI found a promisingBTS7005-1EPPfet, it may be overkill and here I need some advice. I draw a circuit based on the datasheet and some online examples (attached)https://www.infineon.com/dgdl/Infineon-BTS7004-1EPP-DataSheet-v01_10-EN.pdf?fileId=5546d4626102d35a016147550a725555It is 1-channel only, ideally, I would like to use 4 channels to reduce footprint. There is only one 2ch with this FET series. But it can handle about half of the power.It's this one:bts7008-2epzhttps://www.infineon.com/cms/en/product/power/smart-power-switches/high-side-switches/profet-plus-2-12v-automotive-smart-high-side-switch/bts7008-2epz/I found also 4ch but not sure if my application is good for this one:bts7200-4epahttps://www.infineon.com/cms/en/product/power/smart-power-switches/high-side-switches/profet-plus-2-12v-automotive-smart-high-side-switch/bts7200-4epa/Can you advice please ?