# Mosfet driver question

Discussion in 'The Projects Forum' started by Nubz, Apr 12, 2015.

1. ### Nubz Thread Starter New Member

Apr 12, 2015
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0
Hello everybody. I need some sort of variable frequency astable to drive a total of 12 mosfets (2 sets of 6 mosfets each). I use them as switches. Only one set at a time must be on. Indeed this can be acomplished with a classical astable, however I would like to have a delay between the two on times.

So I would like to have the following in sequence:
1. Set 1 (6 mosfets) turn on then off
2. Small delay (to compensate for mosfet turn off time)
3. Set 2 (6 mosfets) turn on then off
4. Small delay (to compensate for mosfet turn off time)
5. Repeat

The reason for the delay is to avoid a short, between the td(off) and td(on) among the two sets creating a shoot-through condition.
The mosfet is irf8010pbf.
When the mosfets switch, I want them fully on just like a physical switch. The mosfets will swich Vds 50V through a relatively small resistance. (I will implement cooling method if needed)
I will supply any voltage necessary for this driver. Idealy the frequency range of the driver shoud be very wide from as low as possible to the limit of mosfet switching or driver capability.

What is the most power effective solution? Or any solution for that matter.

2. ### crutschow Expert

Mar 14, 2008
13,056
3,245
Driving a MOSFET to its maximum frequency requires a very large gate drive current and will significantly affect the type of driver you need.
What is the maximum frequency you really need?

3. ### Nubz Thread Starter New Member

Apr 12, 2015
8
0
Let's say upper range 1-2 Mhz would be good enough starting from 60Hz. I don't have a fixed upper limit it can be more or less. It can be as low as 500Khz, but the more the merrier.
The idea is that I want to also experiment with resonating inductors (and yes I will implement protection for the transistors). That's the reason for the high frequencies.

4. ### Papabravo Expert

Feb 24, 2006
10,177
1,799
The easiest way to accomplish your goal is with a microcontroller. If you don't want to use one of those devices then a Finite State Machine would be my second choice. MOSFETS are generally not interchangeable. Each one has it's own quirks. In order to define the requirements for a driver we need to know which MOSFETS you have in mind. Achieving a switching frequency of 1-2 MHz. may be a challenge.

5. ### Nubz Thread Starter New Member

Apr 12, 2015
8
0
The mosfet I have in mind is irf8010pbf. Interesting suggestions. I don't have any experience with either, but I will look into Microcontrollers and Finite State Machines. Thank you. In the meantime, more ideas are welcome. I was wondering if there is any way to combine astables or make multiple phase astable to get the job done. hmmm....

6. ### Papabravo Expert

Feb 24, 2006
10,177
1,799
That is precisely what the Finite state machine is designed to do, to effectively make a multiphase machine that will run multiple drivers in parallel.

Here is a link to the datasheet:
http://www.irf.com/product-info/datasheets/data/irf8010pbf.pdf

Some things to note:
1. Vgs ≥ 10V to turn the device fully on. You can't use logic level devices to drive the gate.
2. Qg is 81 Typ. and 120 Max nC. That is a great deal of gate charge to overcome.
3. Ciss is 3830 pf

In short driving this thing at high speed like 2 MHz. is going to be a problem in my estimation.

Last edited: Apr 13, 2015