Does this schematic need any diodes?

Thread Starter

Surya1234

Joined Apr 23, 2021
16
The main source of this 5A motor is the Electronic Control Unit as shown in the image. When this ECU fails, the motor will be driven by connecting an external 12V supply to the mating connector.

During Normal operating conditions (when the ECU is powering the actuator), the external supply is disconnected from the connector.

A few points that I would like to mention:
1. Chassis ground and external supply return are not connected
2. The ECU has an internal fuse for protection against short to ground on the motor circuit.

I want to know whether the ECU would need an internal diode for this circuit or not. My initial analysis indicates that it may not need it.
 

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dl324

Joined Mar 30, 2015
13,142
Welcome to AAC!
I want to know whether the ECU would need an internal diode for this circuit or not. My initial analysis indicates that it may not need it.
You're not providing sufficient information. Where is the ECU? What voltage is it operating at? Why are you using an N channel MOSFET to switch a load high side? Is the MOSFET burning out? What is the MOSFET part number?
 

schmitt trigger

Joined Jul 12, 2010
464
If the ECU’s output Mosfet is indeed an N-chan connected as shown, its intrinsic body diode will conduct current back into the ECU. With unknown behavior.
In that instance a diode would be recommended
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
The ECU is operating at 12V supply. Sorry the N-channel MOSFET should be on the Ground pin inside the ECU (i.e. it is connected to the load's -ve terminal on one end through Drain and to the chassis ground through the Source). I am checking with the ECU supplier to get more information about the N-channel MOSFET.
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
The ECU is operating at 12V supply. Sorry the N-channel MOSFET should be on the Ground pin inside the ECU (i.e. it is connected to the load's -ve terminal on one end through Drain and to the chassis ground through the Source). I am checking with the ECU supplier to get more information about the N-channel MOSFET.
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
If the ECU’s output Mosfet is indeed an N-chan connected as shown, its intrinsic body diode will conduct current back into the ECU. With unknown behavior.
In that instance a diode would be recommended
The ECU is operating at 12V supply. Sorry the N-channel MOSFET should be on the Ground pin inside the ECU (i.e. it is connected to the load's -ve terminal on one end through Drain and to the chassis ground through the Source). I am checking with the ECU supplier to get more information about the N-channel MOSFET.
 

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Thread Starter

Surya1234

Joined Apr 23, 2021
16
The ECU is operating at 12V supply. Sorry the N-channel MOSFET should be on the Ground pin inside the ECU (i.e. it is connected to the load's -ve terminal on one end through Drain and to the chassis ground through the Source). I am checking with the ECU supplier to get more information about the N-channel MOSFET.
Thanks for your reply! I want to edit my previous information. The ECU is operating at 12V supply. Sorry the N-channel MOSFET should be on the Ground pin inside the ECU (i.e. it is connected to the load's -ve terminal on one end through Drain and to the chassis ground through the Source). I am checking with the ECU supplier to get more information about the N-channel MOSFET.
 

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upand_at_them

Joined May 15, 2010
766
The motor should have caps as well, to mitigate noise. At the very least a cap across the motor terminals. And additionally, a cap from each motor terminal to the motor case.
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
The motor should have caps as well, to mitigate noise. At the very least a cap across the motor terminals. And additionally, a cap from each motor terminal to the motor case.
Yes the motor has 3 caps: one between each terminal and the body and one between the two terminals
 

Audioguru again

Joined Oct 21, 2019
3,545
The datasheet for your Mosfet clearly shows the Vgs for it to properly turn on. Logic level Mosfets turn on with a Vgs of 5V.
A 10V turn on Mosfet is an IRF540. A 5V Mosfet is an IRL540. See the "L"?
 

Thread Starter

Surya1234

Joined Apr 23, 2021
16
The datasheet for your Mosfet clearly shows the Vgs for it to properly turn on. Logic level Mosfets turn on with a Vgs of 5V.
A 10V turn on Mosfet is an IRF540. A 5V Mosfet is an IRL540. See the "L"?
Does this schematic need a diode within the ECU when the external supply is feeding power to the motor while the mosfet within the ECU is off?
 
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