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.

 

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?

 

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.

 

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.

 

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.

 

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.

 

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.

 

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

 

Many Mosfets do not turn on properly when the Vgs is only 5V. Your Mosfet has no part number for us to see its Vgs specs.

 

Many Mosfets do not turn on properly when the Vgs is only 5V. Your Mosfet has no part number for us to see its Vgs specs.

Thanks for pointing out this issue. If 5V is not enough then what needs to be done to allow the ECU to fully turn the MOSFET on?

 

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"?

 

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?

 

In your second schematic and as long as the external supply’s ground is not tied to the vehicle’s chassis, you don’t need a diode.

 

Thanks to everyone who commented on my question. I learnt something new through the questions that you guys posted.