Pump Control Circuit

[rocky79]

Hello,
Can anyone tell me if this circuit will works. The idea here is that i have a digital logic 3.3 v signal to the input "pump" When the Input is 3.3v i want the pump to turn on. and when it's 0 v the pump should turn off. Now the supply to the Pmos is Gnd and -12 v. Will it work?

Thanks

[ImaBiggles]

Hello,
Can anyone tell me if this circuit will works. The idea here is that i have a digital logic 3.3 v signal to the input "pump" When the Input is 3.3v i want the pump to turn on. and when it's 0 v the pump should turn off. Now the supply to the Pmos is Gnd and -12 v. Will it work?

Thanks

why do complicated? as simple solid state relay will work. what the current requirements of the pump?

[rocky79]

why do complicated? as simple solid state relay will work. what the current requirements of the pump?

It's not complicated, it's a simple transistor. Transistors are more reliable than relays. No moving parts.

[Acetronics]

Hi, Rocky

:eek: Your diode has to be reversed ( here, its MTBF is limited to ...µs !!! )

:o Depending on the motor size, use a 1N4004 ( or + ) , 1N5404, or BY 29-200 ( TO 220 case )

;) I'd add a 1MOhm resistor between the Opto transistor Base and Emitter, to be sure of the off position ... ( try never to let the base unconnected ... )

Alain

[z-matrix]

for 12V DC, use irfz44 ;)

that is an n-fet
cheap, and can take much current with no heat sink (10A without sink).

it will be similar, just connect source to negative and the load negative to drain.

instead of the 1N400x series, i whould recommend a fast diode,
like an 1n5819 schottky in "REVERSE" polarity connected in parallel with the motor, so it can damp inductive kickbacks.
that can take a continuous 1A easily that should be enough for an 5-10A motor, but if you need reliability, use MBR2045 or similar diodes (these can handle 10A continuous easily with a small heatsink).

[ImaBiggles]

It's not complicated, it's a simple transistor. Transistors are more reliable than relays. No moving parts.

Nope, not talking about a traditional relay, the solid state flavor which is a potted circuit as in:
http://www.uoguelph.ca/~antoon/circ/solidstate.html
a more robust flavor of your circuit. Of course you can build it too - for high amp applications it can save money (and there is the DIY fun aspect of it too)

low amp flavors (<2amp) can be had for a dollar or two and often can be scrounged up from old boards. higher amp one <$10. I stacked a couple before to increase amp capacity and it worked fine (of course if one failed, itll smoke the board so I dont recommend that for critical applications)

[rocky79]

Hi Alain,
Oops i didn't realize that the diode is connected in reverse. Do i need one anyways? since the Pmos has built in diode from Drain to source.

Karim

Hi, Rocky

:eek: Your diode has to be reversed ( here, its MTBF is limited to ...µs !!! )

:o Depending on the motor size, use a 1N4004 ( or + ) , 1N5404, or BY 29-200 ( TO 220 case )

;) I'd add a 1MOhm resistor between the Opto transistor Base and Emitter, to be sure of the off position ... ( try never to let the base unconnected ... )

Alain

[Acetronics]

Hi, Karim

If your supply line impedance is low enough ... theoretically no ... but...

a "Transil " diode ( acts like a High surge energy Zener ) like 1N6286A or BZW 06-xx would be a better solution to protect the Mosfet from overvoltage, when in OFF state.

As an example, with a small boat electric motor ... I measured more than 100 volts peaks at switchoff with a 2N3055 !!! mosfets DO NOT like overvoltage ...

Alain

[vintage1]

It appears to me that the variable resistor is redundant, the diode is back to front ad the circuit will turn OFF when 3.3v is applied..

[Acetronics]

Heuuuuuu

Vintage ... your pseudo is well chosen , but sometimes you should leave " The Lord's Wineyards " ... :D

Have a second look to Karim's work ... please. :rolleyes:

Alain

[vintage1]

Ah, Positive earth. Muy bad ;)

That takes care of the diode, the invert sense and the P channel FET.

Variable resistor still redundant tho. ;)

[Acetronics]

Ah, Positive earth. Muy bad ;)


Variable resistor still redundant tho. ;)

:D

Not Really : permits to trim the slew rate for Fet conduction control ... to limit inductive spikes generated by the motor.

No way for you to get out from here, tho ;)

Alain

[rocky79]

Thanks Alain for defending my design ;) its simple and it works.