IRFU9020, How fast?

[slopagafud]

How fast can a IRFU9020 be switched? Im looking to get a 9v,30khz pulse.

 

[Hero999]

Yes, look at the datasheet, it will tell you how long it takes for the MOSFET to turn on and off.

 

[Nigel Goodwin]

30KHz isn't really particularly fast, but you may have to take precautions to switch an FET that quick.

 

[slopagafud]

Yes, look at the datasheet, it will tell you how long it takes for the MOSFET to turn on and off.

Im not so good at reading the datasheets yet, Im pretty new to all this. Im sure they look more intimidating than they really are, but I start going crosseyed before I figure anything out.

 

[I²R]

Im not so good at reading the datasheets yet, Im pretty new to all this.

**broken link removed**

 

[slopagafud]

30KHz isn't really particularly fast, but you may have to take precautions to switch an FET that quick.

Precautions? Please explain.

Ps. thank you I2R I will read that when I have a little more time.

 

[Nigel Goodwin]

Precautions? Please explain.

FET's aren't as wonderful as people seem to think, to switch them fast you have to inject considerable current in the gate - to charge and discharge the gate capacitance. If you don't, it will switch slowly, get hot, and die!.

 

[Hero999]

However at 30kHz it shouldn't be a problem, an astable 555 timer is all you nead.

 

[slopagafud]

However at 30kHz it shouldn't be a problem, an astable 555 timer is all you nead.

Im using a PicAxe 08M, instead of the 555. Im just playing around with different configurations, trying to learn the how, what, and why of different components.

 

[mneary]

You need more than 5V to properly turn the gate on.

 

[I²R]

You need more than 5V to properly turn the gate on.

On what do you base this assertion?

 

[Hero999]

The IRFU9020 is not a logic level MOSFET.

Given the worst case senario, only a few mA will flow when the gate is biased at 5V.

Also, this is a p-channel MOSFET and therefore needs a level shifter to work from a 5V PIC, if the voltage it's switching is >5V (which it is).

 

[mneary]

On what do you base this assertion?

The data sheet. The relevant chart is "typical saturation characteristics" since the OP intends to use it as a switch. Note that this is "typical" and could be plus or minus 1 volt (e.g. you could be facing the 4V or 6V curve) depending on where your gate threshold is relative to "typical". This assumes that your PIC is putting out 5V with no losses.

**broken link removed** should really be titled "How to Read an Op Amp Data Sheet" because it doesn't say anything about MOSFETs. I'm surprised that you expected it would help the OP.

And, as Hero mentioned, it's a p-channel MOSFET.

Any questions?

 

[I²R]

**broken link removed** should really be titled "How to Read an Op Amp Data Sheet" because it doesn't say anything about MOSFETs. I'm surprised that you expected it would help the OP.

It'll help him get a handle on reading data sheets in general, which was the only point. I couldn't find a tutorial specifically addressing MOSFET data sheets. Instead of complaining, perhaps you can supply one.

 

[mneary]

I did supply a tutorial in the relevant area; saturation characteristics. Since there appear to be none on the net, I wrote it myself.

If you need any other part of the MOSFET data sheet explained, just ask. But I don't intend to write a complete tutorial.

 

[slopagafud]

The IRFU9020 is not a logic level MOSFET.

2 questions, 1)Any suggestions off the top of your head of a MOSFET I can use? 2) How would one go about finding the correct part w/o having to go through a million datasheets?

 

[mneary]

I buy some of my stuff from ebay sellers. In this case I would simply search for logic mosfet. You'll notice that logic level mosfets are more expensive than the others, but they save the hassle of boosting the drive voltage.

You need to decide what current you need, and how many parts. Also surface mount, or not?

 

[Hero999]

You don't need a logic level MOSFET.

As this is a p-channel MOSFET so you need a MOSFET driver to convert the 0-5V pulses to 0-9V pulses.

If you just used a logic level p-channel MOSFET then it would never turn of, it will stay on when the PIC's output goes high.

Also, what power supply are you using?

If it's just a 9V battery, the voltage will quickly drop to 7.5V and it might not work.

 

[slopagafud]

I am using a regular old 9v batt

 

[Hero999]

How much current are you planning to draw?

If it's over 100mA or so then I strongly advise using a larger battery like six AA cells.