Heating Elements via Mosfet + NPN-Transistor

[kobito]

Hello, first post here ever.

I wanna use gpiopins to turn on and off 4 devices via a mosfet-npntransistor circuit.

The Devices:
3x heatingelement 24V 1.25A
1x Pressurepump 12V 4A

See Screenshot

For 12V Pump, just change 24V to 12V and Heizin_3 to Pump_in

I wanna use this circuit so the mosfet doesnt get the 3V from the Gpio but 12V to fully close. If i output 3.3V on the NPN-Transistor the 12V will go to ground and the Mosfet will let the 12 or 24V through.

For the Mosfetresistor:
I=U/R= 12V/1000Ohm = 0.012A = 12mA
P= 12V*12mA = 144mW

NPN-Transistor-resistor for 12V pump:
-> 12mA
hFE: 300 at Ic (Datasheet PBSS4440D)
hFE/3.3(Safety): 300/3 = 100
Ib: 12mA/100= 0.12mA
(3.3V) 10% tolerance -> 2.97V - 0.8V(BE) -> ~2.17V
R=2.17V/0.12mA =18083.3ohm-> ~17500ohm
P = 3.3V*0.12mA = 0.396mW

data-mosfet:
BUK6Y14-40PX
40V VDS
64A ID
VGS 20V

data-npn-transistor:
PBSS4440D,115

I did it like this. If I connect the 12V and 24V to the curcuit

Even without putting 3V on the GPIO pins the heating elements turn on and the pump gets like 0.9V.

Please Help me
ty in advance

[anon57585045]

Please edit your post to embed the images instead of links to possibly unsafe external sites.

[kobito]

how can i do this ? i tried to upload the images but I am not allowed to do this as a new member

EDIT: you can only do one

[anon57585045]

I think the last time I did that, I just pasted the image using copy and paste.

[TomGeorge]

Hi, @kobito
Welcome to the forum.
Please read the post at the start of any forum , entitled "How to use this Forum".

How to get the best out of this forum

See also FAQ - Arduino Forum for general rules on forum behaviour and etiquette. Hello, Welcome to the Arduino Forum. This guide explains how to get the best out of this forum. Please read and follow the instructions below. Being new here you might think this is having rules for the sake of rules, but that is not the case. If you don’t follow the guidelines all that happens is there is a long exchange of posts while we try to get you to tell us what we need in order to help you, which is fru…

You should be able to EXPORT a jpg from the CAD that you are using.

Thanks.. Tom...

[anon57585045]

I hope you know, the MOSFET source and R2 positive bias, must be the same voltage for this to work... as you drew it, the MOSFET gate source voltage will be non-zero in quiescent mode.

[kobito]

So what do I have to change.
For the pump the 12V for R2 and the Source of the MOSFET is the same.

For the 24V i didnt do it. So i just apply 24V at R2 and i am fine ?

So the 12V pump should work fine ??? but iam getting there 0.9V there

[anon57585045]

@kobito

So i just apply 24V at R2 and i am fine ?

Yes. Unless there is more you are not telling me.

[kobito]

well no, but why i am getting some leakvoltage at the pump ?
there i got 12V at R2 and Source

[anon57585045]

You can't drive both 12V and 24V loads from the same circuit. I hope you are not trying to do that. It would be best if you could correct the drawing, and post it again. Specify which device we are talking about so there is no confusion about that.

If you're asking about the pump circuit, post only that.

[kobito]

So this is the whole curcuit, i wanna run
(didnt include the gpiopins(Heiz-3-3V,Heiz1-3V,Pump-1-3V) etc
3x Heatingelement(24A 1.25A, so a total of 3.75A) (heizin_1 to heizin_3)
1x pressurepump (12V,4A)

I got a 12 Pinheader for it to apply to my board

Input
24V 3.75A
12V 4A

[anon57585045]

Your pump circuit is correct so it should work. The others are wrong, needs 24V to R1,2,3.
I suggest looking at your power and ground connections to the board. Are all grounds common? Including microprocessor ground?

Have you measured the voltage on the collector of T4?

Also, a pin header for 4A currents? Sounds a little inadequate.

[kobito]

I am using the Molex 0430451210 for 8.5A max per Contact

So why i am i getting 0.9V at the pump if i just plug in 12V ?
I didnt connect the gnd of the microprocessor to 12v gnd and 24v gnd

[anon57585045]

@kobito

I didnt connect the gnd of the microprocessor to 12v gnd and 24v gnd

Then how on earth would T4 get its base current? All grounds must be connected in order to bias the driver transistor properly.

Electricity travels in a circle...

[kobito]

yep i am dumb ty alot,

so 24v at r1,2,3 and all gnd connected

[anon57585045]

Give it a try and post the result for anybody that reads this.

[kobito]

check will do that in a couple of minutes!

[TomGeorge]

Hi,

@kobito

data-mosfet:
BUK6Y14-40PX
40V VDS
64A ID
VGS 20V

Looking at this circuit;
Remember this is a P-CH MOSFET.

When T3 is OFF, the gate will be at 12V and the source will be at 24V.
This means the gate will be at -12V with respect to the Source, so the Q1 will be ON.

When T3 is ON, the gate will be at GND, this will make the gate at -24V with respect to the Source so Q1 will be ON, or fail.
WHY?
Because Vgs of -24V exceeds the spec Vgs of -20V.
At no time will Q1 be OFF.

Tom...

[kobito]

So I would need 24V at the gate, but also would need a Mosfet that has VGS of -25V or more

[kobito]

Sooooo
I found 12V Heating plates, these should work fine then right?