mosfet help

ccc11223

i have a 12v dc 3A solenoid that i am trying to control using an irf510 mosfet. ive been trying to hook up the mosfet to my homework board, but it is not working. could someone tell me what connections i need to make? and also is controlling the mosfet as simple as sending a either a high or low signal to the gate pin?

oldPGMguy

here's one way

http://www.electro-tech-online.com/electronic-projects-design-ideas-reviews/96886-low-side-battery-mosfet-switch.html

being a switch logic high at the gate turns it on and logic low-0volt turns it off.....

erco

oldPGMguy: That's a nice forum, thanks for sharing the link!

Phil Pilgrim (PhiPi)

ccc11223,

The IRF510 is a poor choice for controlling from a logic level. (You got it at RadioShack, right?) From the datasheet: with 5V on the gate, it can safely sink only 1A. With a 3A load, it will surely overheat. A better choice would be an IRL510, which is fully-characterized at lower gate voltages. An even better choice is the IRF3708. With 5V on the gate, the drain-source resistance is in the single-digit milliohm region.

-Phil

ccc11223

i also have a ULN2803A Darlington Array. would this be able to do the job? if so, what connections do i make on my board?

Phil Pilgrim (PhiPi)

Even though its transistors are bipolar, the ULN2803 datasheet claims that you can safely parallel the 500mA outputs to sink more current. (Typically, with bipolar transistors, this is a bad idea.) So, theoretically, eight outputs in parallel could be used to sink up to 4A. However, at 375mA average per output at 3A total, the saturation voltage will be about 1.6V. Multiply that by 3A, and you get a power dissipation of 4.8W. The limit for this device is 2.5W. So I would say no, the ULN2803 is not a good choice for your app.

-Phil