N type Mosfet power

Thread Starter

denison

Joined Oct 13, 2018
252
Hi All, The Ltspice simulations software has a list of N type mosfets. Most of these are for 20 volt gate to source maximum. I need a 30v maximum. Does anybody know if any of them are for 30v? The list on Lt spice is so large that it would take me ages to find one that had a 30v GS. They do not show the gate to source voltage.
 

DickCappels

Joined Aug 21, 2008
7,954
In my limited experience exceeding the VGS of a MOSFET model in LTspice does not hurt anything, though the turning delay may be shorter in the simulation than in real life.

Why not try it and see for yourself?You cannot break anything.
 

Thread Starter

denison

Joined Oct 13, 2018
252
In my limited experience exceeding the VGS of a MOSFET model in LTspice does not hurt anything, though the turning delay may be shorter in the simulation than in real life.

Why not try it and see for yourself?You cannot break anything.
yes Dick I will try that. As long as the results seem reasonable it may give a fair approximation of a real life 30v maximum VGS mosfet. I have on order a BUK456-60 which is a 30v. I am using 24v.
 

ronsimpson

Joined Oct 7, 2019
1,630
Why do you need 30V on the Gate? (24) Can you post a circuit of the Gate parts? It may be that with a simple change we can use lower voltage parts.
 

Thread Starter

denison

Joined Oct 13, 2018
252
In my opinion the best option would be to clamp the gate voltage to under 20, that gives you a much wider range on MOSFET choices. (in real life)
yes I could do that. But I am using 24 volts in my application and everything else is working on a 24v supply so that changes would need to be made to other parts of the circuit. The circuit functions better on higher voltages. The easiest option is to use a higher GS voltage MOSFET.
 

Thread Starter

denison

Joined Oct 13, 2018
252
Why do you need 30V on the Gate? (24) Can you post a circuit of the Gate parts? It may be that with a simple change we can use lower voltage parts.
I am using a 24 volt power supply. Yes I could use lower voltages but the circuit works better on higher voltages. I also have found a fixed 24 volt regulator. Can't take the voltage too high for the op-amps I am using.
 

Papabravo

Joined Feb 24, 2006
17,240
The BUK456 appears to be obsolete and I cannot find a model.
I would check www.onsemi.com
They seem to have Pspice models which should work for you for their active parts.
 
Last edited:

ScottWang

Joined Aug 23, 2012
7,080
Maybe you can using two resistors as the voltages divider to reducing the Vgs input voltage to match the simulation component or the real component of N type MOSFET needed.

Like two 10K or 15K resistors.

Edit:
Or using a 2.4K resistor in series with a 15V(or 12V) zener diode, the two pins of zener diode connects to the Vgs of MOSFET.
 

Thread Starter

denison

Joined Oct 13, 2018
252
Maybe you can using two resistors as the voltages divider to reducing the Vgs input voltage to match the simulation component or the real component of N type MOSFET needed.

Like two 10K or 15K resistors.

Edit:
Or using a 2.4K resistor in series with a 15V(or 12V) zener diode, the two pins of zener diode connects to the Vgs of MOSFET.
Thanks Scott. A voltage divider will do it with 2 resistors. The Vgs is not a critical part of the circuit. The critical part is source to drain and this voltage wont be exceeded. This is part of the circuit. I didn't want to use a transistor because of the on voltage drop. The on voltage drop of a Mosfet is negligible.
 

DickCappels

Joined Aug 21, 2008
7,954
You may need a compensation capacitor to compensate for the gate input capacitance. It is probably safe to try it with just resistors but check the gate drive with a scope just to be sure.
 

ScottWang

Joined Aug 23, 2012
7,080
Thanks Scott. A voltage divider will do it with 2 resistors. The Vgs is not a critical part of the circuit. The critical part is source to drain and this voltage wont be exceeded. This is part of the circuit. I didn't want to use a transistor because of the on voltage drop. The on voltage drop of a Mosfet is negligible.
You can check some types often used below:
N and P type MOSFET Components Simple Data.
 

Thread Starter

denison

Joined Oct 13, 2018
252
You may need a compensation capacitor to compensate for the gate input capacitance. It is probably safe to try it with just resistors but check the gate drive with a scope just to be sure.
You are right there Dick. They can be a bit tricky that way. The input capacitance can hold the mosfet on when it should be off.
 

DickCappels

Joined Aug 21, 2008
7,954
That and the input capacitance can slow switching times if not compensated. I do not know what effect the reverse transfer capacitance will have but since that capacitance can be quite large and slow things down a lot (Think Miller capacitance) it would probably be a good idea to use low value resistors in your gate drive voltage divider.
 
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