Help choosing transistor/mosfet/relay

mosfet relay schematic

I need some help from you guys with a project I'm working on where I want to modify the factory setup of a circuit board and motor that only turns in one direction.

Currently the board sends 2 volts to the motor, which pulls .49 Amps at 2 volts. The board is powered by 9 volts.

I would like to use the board to trigger a transistor/mosfet/relay, which will send 6 volts to the motor. The transistor/mosfet/relay will have to be triggered by only 2 volts. I can use resistors to decrease the 9 volts as necessary (that's no problem). The motor will pull .65 Amps at 6 volts so the transistor/mosfet/relay will have to be able to handle nearly 4 watts.

I know how to set the circuit up. And I know how to calculate which resistor to use to get the 9v to 6v. But I need help picking out a transistor/mosfet/relay that can operate under such stressful conditions (4 watts) but be triggered by such a low voltage (2v).

Thanks,
Chris

choosing a transistor

You will have to put a transistor inverter after the 2 V to get the swing necessary to drive the MOSFET gate. Then you will have to use the opposite 2 V, 0 V signal to turn the motor on/off.

choosing mosfet transistor

red2cwm said:

And I know how to calculate which resistor to use to get the 9v to 6v.

Click to expand...

R = 3 / I

Use transistors if your project requiere fast switching, as PWM.

Bipolars transistors requiere to calculate base resistor according to load current, whereas mosfets are 'simply voltage triggered' : Bipolars are current controled, whereas mosfets are voltage controled.

In summary, Mosfets surely requiere less adaptations than relays ( be careful : inductive load ) and bipolars transistors. Just verify if threshold voltage is en accordance with your signal.

Regards,

Manu

choosing transistor

Hi,

You can also use Optocupler. It will work at 2V if you have the right resistor at the diode side, and drive the motor.

factors to consider when choosing a transistor

gidimiz said:

Hi,

You can also use Optocupler. It will work at 2V if you have the right resistor at the diode side, and drive the motor.

Click to expand...

Yes, great idea, you can use a optocoupler to drive your MosFet, as that schematic :

See You...