Optimizing Microcontroller Output Using MOSFETs: Finding the Right Transistor

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The discussion focuses on using MOSFETs to amplify the output from a microcontroller that can only source 25mA per pin, with a need for 120-150mA. The 2N7000 MOSFET is considered, but simulations indicate it may not provide sufficient current at 5V. Participants suggest testing the 2N7000 on a breadboard and consider using a driver IC, like a Darlington 8-channel, as a more efficient solution for managing multiple outputs. The original poster expresses interest in finding PSpice models for the driver IC to facilitate simulations. Overall, the conversation emphasizes the need for reliable alternatives to achieve the desired output current.
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Hi,
I'm working with a microcontroller that outputs 5V, 25mA max from each pin. I need to source 120-150mA. I'm looking at 2n7000 MOSFET for the job. Spice simulations show the output current is 50mA when Vg = 5V (microcontroller output) and about 120mA when Vg = 5.5V. Since I'll be using over 20 pins from the microcontroller, amplifying the output for each pin is impractical. Is there another cheap and reliable MOSFET that can be substituted so this will work?

Thanks
 
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Are you using the transistor as a low-side switch? TO-92 packaged 2n7000s should be able to handle that load quite easily. I'd try it on a breadboard to be sure.

Transistor as a switch (because I'm too lazy to mock it up in Circuit Lab):
http://www.electronics-tutorials.ws/transistor/tran_7.html
 
Is there some reason you are looking to MOSFET? It does not seem to be very high power - and for 20 outputs - that is a lot of descreet components. Did you consider a Driver IC - like this Darlington 8 Channel in one IC... https://www.sparkfun.com/products/312
 
Thanks for the fast replies.

MATLABdude said:
Are you using the transistor as a low-side switch? TO-92 packaged 2n7000s should be able to handle that load quite easily. I'd try it on a breadboard to be sure.

Transistor as a switch (because I'm too lazy to mock it up in Circuit Lab):
http://www.electronics-tutorials.ws/transistor/tran_7.html

The transistor is set up so that the drain is connected to a 5V supply, the source is connected to the load and the gate is connected to the microcontroller. The site you posted has interesting configurations, I'll take a look.
The way I understand how MOSFETs work is the source current depends on how much voltage is put at the gate (in this case the voltage is .5V too low to give the 120mA).

Windadct said:
Is there some reason you are looking to MOSFET? It does not seem to be very high power - and for 20 outputs - that is a lot of descreet components. Did you consider a Driver IC - like this Darlington 8 Channel in one IC... https://www.sparkfun.com/products/312
I didn't search around a lot for driver ICs. That IC you posted looks like it's just what I need, thanks! Do you know if there are PSpice models out there to run simulations with that device?
 
The DS has a schematic for each stage.
 

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