Can I connect a momentary button between 12V and Pin3 to turn on the load?

(Pin1 and Pin2 may be used in the future to interface a microcontroller to control the load through PWM with a 3.3V signal)

 

Hi Fran,
Why not across pins 3 & 4 for the Momentary Switch?
E

 

Thank you for helping me once again, E.

I should have added that maybe in the future I would use 4.5V or 6V loads. In that case, by bridging Pin3 and Pin4, the voltage divider created by the two 4.7K resistors would put less than 3V on the gate, which maybe wouldnt turn the mosfet fully on, as far as I understand from its specifications.

https://www.infineon.com/dgdl/irlr7843pbf.pdf?fileId=5546d462533600a40153566de53526d8

 

@FranciscoB Is the circuit actually referenced to Earth GND??
Per drawing.

 

hi Fran,
R3 could be a higher value than 4k7, say 10k or 15k.
E

update:
I would ensure that Vgs > 2.5V in order to exceed the min Vgs level.

 

The circuit is battery powered by 8xAA, the load being a small 12V water pump that draws like 500mA. Connected to pin1 and pin2, I have a micro controller powered by a smartphone battery, which actuates the pump for 30 seconds twice a day. It has been running for over 1 year and I have not had to change the 8xAA pack yet.

I want to add a switch to turn on the pump without having to play with the micro controller, ex: I want to adjust the valves along the hose while the pump is running. You can see the series of vases being watered in the attached photo.

 

I would eliminate R5, not really needed as the mosfet is rated 20v at the gate.

 

Thank you for helping me once again, E.

I should have added that maybe in the future I would use 4.5V or 6V loads. In that case, by bridging Pin3 and Pin4, the voltage divider created by the two 4.7K resistors would put less than 3V on the gate, which maybe wouldnt turn the mosfet fully on, as far as I understand from its specifications.

https://www.infineon.com/dgdl/irlr7843pbf.pdf?fileId=5546d462533600a40153566de53526d8

I don't understand this statement, bypassing the output of the coupler is the same as turning it on, will have little or no effect on the divider. (save the small voltage drop)

As to your original question...you can safely bypass the output of the coupler or the MOSFET itself.

 

I tried your suggestions above and the project is working reliably, thank you!

Now, regarding the circuit below, I have a similar question: if I placed a switch connecting 12V (DC Power Supply) and the point behind R3 to turn in on manually, what modification would I need connect a microcontroler to J1? Should I place a diode between the GPIO of the uC and "Trig/PWM" to protect it from the 12V when the switch is pressed?

 

What is the supply voltage for the micro?
Does the micro need to be isolated from the mosfet circuit?

 

The microcontroller unit that can be seen in the attached photo works with 4xAA and the GPIO signal is at 3V3.

It does not need to be isolated, I would be connecting the GPIO to the Trig/PWM pin and gnd to gnd.

 

Need to change that 100K resistor to 100 ohms.
Using a schottky diode will reduce the voltage at the gate to appx 3 volts, which may not be enough to turn the mosfet fully ON.
Will post a circuit later today that will convert the 3.3v to 12 volt.

 

The "k" was a typo, I meant to write 100Ω, sorry

 

Will post a circuit later today that will convert the 3.3v to 12 volt.

 

hi Fran,
An alternative level shifting circuit.
E

 

I may be missing something but...

If you use a DPDT pushbutton you can completely bypass the MOSFET, disconnecting it and replacing it with the 12V.

 

Thank you all, problem solved!