Current overload protection circuit - small brush motor

[Bicky22]

Hi,

I am a Mech-E trying to design a current overload protection circuit to a small 24VDC brush motor.

The idea is simple, if the motor draws 2-3A, the circuit trips and shuts off power to the motor.

My problem is that it needs to be both auto resetting and work at high temperature (20 - 125 C). Ideally a PTC fuse would be great however with the temperature derating and the non-linearity, they are not consistent enough for my application.

My parameters are 24VDC, 1A hold, 2-3A trip, temperature range from 20-125C, trip time < 2 seconds, simple PCB circuit.

Does anyone have any thoughts on other ways I can go about designing this circuit?

Best Regards.

 

[itsmoked]

See the last page of this electronic circuit breaker compendium:
ECB

Or

ECB2

Or

Roll your own using a very small PIC microcontroller sensing the current and controlling a FET. It would allow special handling of over-currents.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

125C is VERY difficult for anything on a PCB... 125F is doable, but not a lot of PCB components are rated for that. MIL spec maybe, but not COTS. The first IC I looked at on that site from Keith is rated at 85C operating temperature. That's actually fairly good, but you are a long ways from 125C.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[itsmoked]

Good point Jeff! I totally missed that.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Bicky22]

Thank you very much. I appreciate the response.

I think a microcontroller may be the way to go. I will follow down that path for now.

Just to check my understanding: In the second link,ECB2, the Simple Electronic Circuit Breaker. The MOSFET opens (trips) when current flows from the Emitter to the Base of the PNP, so to adjust the trip current you can vary R2. Correct?

 

[itsmoked]

Yes.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Bicky22]

Thank you very much for the help.

On the ECB2 the Simple Electronic Circuit Breaker: How do I calculate the required current flowing through the Source and the Drain of Q1 that would cause enough of a voltage potential across R2 to turn Q2 on and trip Q1?

 

[benta]

Check the Infineon ProFET series and other of their automotive series of power switches. Or NXP. Or...

 

[Bicky22]

Can someone point me in the right direction in terms of analytically analyzing this circuit?

I have the circuit working just as I want it to with R2 = 12K ohms. With my background being mechanical, I’m not sure what approach to take when proving this circuit.

Any help would be appreciated.

Best regards.