Circuit help - 1mA output @ 4V to drive a relay for 5-10A motor

Thread Starter


Joined Feb 15, 2015
I have a QProx™ QT140 / QT150 and I am driving it with a 5V supply so the output pins provide 1mA @ Vdd-.7 which is ~4V.

I want to drive a 5A motor with one and a 10A motor with the other. These are window motors for a car window. The problem is, I need help designing the circuit to take the 1mA and activate a relay. Can anyone here help? I was thinking about using an NPN transistor and diode but I forgot how to spec these. Any help would be appreciated!

Thread Starter


Joined Feb 15, 2015
Thank you for clarifying. No the motors will not be in a car. We just have the motors laying around and wasn't sure if that would change something. The control circuit can be for any motor really. I just need them to activate a 5A and 10A load.



Joined Feb 19, 2010
I have not done it myself, but from reading here over the past couple of years, to channel 5A and 10A currents you will need to use a FET, NPN generally is not build to handle such large currents.


Joined Sep 17, 2013
I want to drive a 5A motor with one and a 10A motor with the other.
Are those the free-running (no load) currents or the stall (start-up) currents?
By 'drive' do you mean just start and stop, or do you envision speed control and reversing control?


Joined Oct 2, 2009
Interfacing the chipset to a high current driver, I would recommend opt0-isolation.

The output pins can sink 5mA @5V, so that is enough to drive the input LED of an opto-isolator with nothing but a series current-limiting resistor to +5V.

If you wish not to opto-isolate, and drive the gate of an NFET directly, the 1mA source and 5mA sink is enough to do that if the NFET is of the high-current, logic gate type.


Joined Nov 18, 2012
Here is one way of approaching the motor control
Note: The control and power will have to have a common ground

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