Ok, I will reread about inductors in the ebook.

My transistor is acting strange, when it is getting 3.3v from my uC, it is (at first) not turning on all of the way and then after ~ 1/2 second it will turn on fully. It also seems to be inconsistent to where it will sometimes turn on fully immediately.

I want to determine whether this inconsistency is software or hardware related ... my transistors Vg(th) is 1.2(min), 1.6(typ), 2.0(max)

http://www.infineon.com/dgdl/IPP_B_...a4339&fileId=db3a304412b407950112b42a72ce4342

Being that a FET is a voltage controlled device, can I give the gate 3.3v at 1 uA and still see the same performance as 3.3v at 20mA?

 

Forget about the threshold voltage when the Mosfet is barely turned on (it is almost turned off) with a current of only 2mA. The Mosfet is spec'd with a Vgs of 4.5V and 10V which is when it is completely turned on.

The Mosfet does not have a spec when its gate is only 3.3V. There is a graph of a "typical" device that conducts about 60A when its gate is 3.3V and the junction is at 25 degrees C but you cannot buy a "typical" device (you get what they have) and cannot control the temperature.

The current is not gate current (which is zero), it is drain-source current.

 

Thanks for the reply AG,

Based on your second paragraph, do you suggest I incorporate a BJT with the emitter going to the FET gate?

Forget about the threshold voltage when the Mosfet is barely turned on (it is almost turned off) with a current of only 2mA. The Mosfet is spec'd with a Vgs of 4.5V and 10V which is when it is completely turned on.

The Mosfet does not have a spec when its gate is only 3.3V. There is a graph of a "typical" device that conducts about 60A when its gate is 3.3V and the junction is at 25 degrees C but you cannot buy a "typical" device (you get what they have) and cannot control the temperature.

The current is not gate current (which is zero), it is drain-source current.

 

The Mosfet needs a gate voltage of at least 4.5V to turn on. Adding an bjt emitter-follower with 3.3V on its base makes the gate voltage only about 2.7V which is much too low.

 

I mentioned gate drivers in my prior post.

It's no wonder you are having problems; trying to drive a MOSFET with a large gate charge, like those you linked to, directly from a uC with a low Vdd, and you are begging for melt-downs.

You need to get the gate(s) over 4.5v in order to turn them fully ON.

You would have saved a LOT of time if you had posted the Vdd of your uC earlier on, and the fact that you are trying to switch the gates directly from the uC's I/O pins.

It's not going to work well at all.

This is why I don't really like replying to your posts, as you omit a great deal of information by failing to include (a) schematic(s) of your circuit(s). It wastes your time and mine. I just don't have time to waste.

 

Ok, well I will not bother you again then, thanks for the information.

I mentioned gate drivers in my prior post.

It's no wonder you are having problems; trying to drive a MOSFET with a large gate charge, like those you linked to, directly from a uC with a low Vdd, and you are begging for melt-downs.

You need to get the gate(s) over 4.5v in order to turn them fully ON.

You would have saved a LOT of time if you had posted the Vdd of your uC earlier on, and the fact that you are trying to switch the gates directly from the uC's I/O pins.

It's not going to work well at all.

This is why I don't really like replying to your posts, as you omit a great deal of information by failing to include (a) schematic(s) of your circuit(s). It wastes your time and mine. I just don't have time to waste.

 

Thanks AG!

As I was progressing through this post I have tried many different ways, first using a BJT, then using the uC directly and then trying an opto coupler ... and was trying to figure out my best option with experimentation.

I'm going to continue to experiment a little more and maybe use a PNP with 5v or 13v at the emitter. Hopefully that will work well with my circuit.

The Mosfet needs a gate voltage of at least 4.5V to turn on. Adding an bjt emitter-follower with 3.3V on its base makes the gate voltage only about 2.7V which is much too low.