Will ANY MOSFET turn fully on with between 5 to 12v?

[jpanhalt]

In the future I will use the term "fully turned on" to avoid any confusion.

Some people use the term, "hard on," which has fewer words, but creates certain complications for search engines.

John

 

[Ubergeek63]

Hi to all,

After doing some MOSFET research online I realise I don't fully understand how they are turned on. Since all the FETs I have used have always been switching lowish voltages (the most was 30v) I have never come up against what they actually need to saturate with the high voltage ones.

The ones I plan on using are STP9NK60Z N-CHANNEL 600V - 0.85r - 7A and will be switching about 270v dc for a DC universal motor.

I was wondering if I can switch it with the output from a 555 timer for PWM or even from a PIC micro?

Nowhere in the specs does it state the actual voltage or current needed to switch it, and up to now I didn't know it was a concern.

Any help appreciated

Thanks Al

this is a bit late but i do not think it has been covered with simplicity or with the solution to your problem...

the answer is no and the solution is cascode, though you probably still need a gate driver.

A RFP12N10L in the source lead gives you logic level performance if you put 15V on the gate of your other FET but will still need a 1A gate drive for decent switching speeds.

Dan

 

[Jeff Birkle]

High voltage MOSFET switching

So a high side driver would have the same potential as the souce?
Do they have charge pumps in them to reach that?

I'm also still studying the "bootstrap" technic. any comments or good reads?

Would using an N mosfet in this circuit require a driver with charge pump to reach a 4volt higher potential then the source to turn on, and up to -20volts (from source potential) to turn it off?

I have used a 820k resistor between the gate and source of the high side and it switchs off fairly fast. The turn on is a lttle slow though.

Without knowing the rest of the circuit it's hard for you to know but,
It does work, but would this work long term and satisfactory?

Should I start this in another thread so as to not complicate this thread?

Regards
Jeff

 

[WTP Pepper]

This is a circuit I have used to drive power FET gates. It takes a 0-5v squarewave and boosts it to 0-10v. A cheap alternative if you cannot afford logic FETs.

 

[Roff]

This is a circuit I have used to drive power FET gates. It takes a 0-5v squarewave and boosts it to 0-10v. A cheap alternative if you cannot afford logic FETs.

What is the point in having gates in series? To get high current drive, you need gates in parallel. Furthermore, 6 unbuffered inverters in parallel will not be sufficient to drive a power MOSFET.
Am I missing something?

 

[Ubergeek63]

This is a circuit I have used to drive power FET gates. It takes a 0-5v squarewave and boosts it to 0-10v. A cheap alternative if you cannot afford logic FETs.

that is still only maybe 100mA

 

[Ubergeek63]

What is the point in having gates in series? To get high current drive, you need gates in parallel. Furthermore, 6 unbuffered inverters in parallel will not be sufficient to drive a power MOSFET.
Am I missing something?

i was just assuming he meant in parallel...

 

[Ubergeek63]

You might just as well use a REAL gate drive chip to get the 15V@1Apk and float it on a capacitor.

 

[WTP Pepper]

What is the point in having gates in series? To get high current drive, you need gates in parallel. Furthermore, 6 unbuffered inverters in parallel will not be sufficient to drive a power MOSFET.
Am I missing something?

Nope. Apologies. You are correct. They are in parallel for the current drive. A bad hair day, but IIRC it could easily drive a MOSFET gate at a few hundred KHz.