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HF gate driver schematic

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brundle

Wed Dec 19 2007, 06:15AM

Registered Member #355 Joined: Thu Mar 30 2006, 01:42PM
Location:
Posts: 3

Hello@all,

I am searching for a circuit for a HF for gate driver to approx. 27 MHz.
Have anyone the schematic from the FPS-4N evaluation board.

see:

OR:
Have anyone a good alternative schematic for HF gate drivers?

I want to drive a class-e amplifier with a commen Mosfet like IRFP460 or IRF840

with best regarts

brundle

J. Aaron Holmes

Wed Dec 19 2007, 11:21AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

brundle wrote ...

Have anyone the schematic from the FPS-4N evaluation board.

Have you asked the manufacturer?

brundle wrote ...

I want to drive a class-e amplifier <snip>

You mean Tesla coil, right?

There are other forums/web sites for talking about amplifiers...

Cheers,
Aaron, N7OE

brundle

Wed Dec 19 2007, 12:07PM

Registered Member #355 Joined: Thu Mar 30 2006, 01:42PM
Location:
Posts: 3

[..]Have you asked the manufacturer?[...]
Good idea. I will contact the manufacturer.

[..]You mean Tesla coil, right?

[...]
right. A class-e Mosfet based Tesla Coil

ragnar

Wed Dec 19 2007, 12:35PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

brundle wrote ...

Hello@all,

I am searching for a circuit for a HF for gate driver to approx. 27 MHz.
Have anyone the schematic from the FPS-4N evaluation board.

see:

OR:
Have anyone a good alternative schematic for HF gate drivers?

I want to drive a class-e amplifier with a commen Mosfet like IRFP460 or IRF840

with best regarts

brundle

I would be more inclined to help you if you A) read the board rules, and didn't beg others for schematics without showing the effort you have put in, and B) didn't scream the thread title in caps.

You will have great difficulty driving an IRFP460 at 27MHz, even if you had the special low-charge version of the die.
The IRF840 is a lot more feasible.

Look at the application examples for the DEIC420 gate-driver chip. It will do what you need, but we don't plan to design and execute your whole project for you.

Steve Conner

Wed Dec 19 2007, 12:55PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Also be aware that no matter how hard you drive the gate, no polysilicon gate MOSFET will work efficiently at 27MHz. The physics of the device just won't allow it. You might as well buy the metal gate MOSFET evaluation board from IXYS.

HV Enthusiast

Wed Dec 19 2007, 04:12PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

That datasheet is way old.

The new manufacturer is IXYS RF.

They have several series of RF Frequency Gate Drivers (i.e. DE515 series) and RF MOSFETs for pulsed / switching applications.

We have used them extensively in our work in high power Class Phi (E/F) converters.

They are NOT cheap though. Plan on spending upwards of $25.00 each for the gate drivers and even more for the MOSFETs.
And you'll need a good RF approach to use them properly.

brundle

Thu Dec 20 2007, 06:30AM

Registered Member #355 Joined: Thu Mar 30 2006, 01:42PM
Location:
Posts: 3

OK I have developed a totem pole HF gate driver with zetex transistors.
The first stage is a TTL based crystal oscillator.
The second stage is a level shifter from TTL to 12V
The third stage is a totem pole buffer with zetex high current transistors
The fourth stage is biasing the Mosfet to Vgsth (approx. 3V)

But at 13.56MHz the buffer voltage brake down to approx. 4V

Then I have found the FPS-4N evaluation board.
How do the schematic work?

I looks like multiple totem pole stages (right?)

OK, if it is not possible to drive a common mosfet @27.12MHz
I will be satisfied with 13.56MHz.

I want to drive a Tesla Coil with a ISM frequency.

But let us discuss about the FPS-4N evaluation board schematic:
How could it be, that this board is able to drive a Mosfat @ 27.12MHz
Did they use multiple totem pole stages?

Marko

Thu Dec 20 2007, 10:24AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Some hints you might use:

-It is hard to get a TTL oscillator to put out 50% duty cycle, so it is preferable to use 2x or4x higher frequency, and then divide it by 74 bistable. This will always give you good 50% duty cycle waveform. But it may be troublesome if you want to use a specific frequency and a crystal oscillator.

-I found out that simply using a BS170 with a 50-100 ohm drain resistor makes a very good level shifter for this case. You connect the gate directly to logic output. Drain resistor needs to be small enough to provide enough current; it will get hot and needs to be rated for few watts. If you have some small P channel mosfets you can use one in push-pull with BS170 (much better than a resistor).

-I had good performance of emitter follower push-pulls up to 8Mhz, so 13Mhz doesn't look too unrealistic.
The push-pull alone without any biasing worked well.

I'm not sure how all of your DC blocking caps will behave.. it might not matter with a fixed oscillator, but they will need a number of cycles before voltage 'sets' down to wanted level...
And during these cycles your mosfet may be constantly on! I'd keep the DC block cap no but few times bigger than gate capacitance, no matter of little voltage drop on it.

If you are going to drive the mosfet significantly negative this way you'll need higher supply voltage than 12V for the driver in order to keep it on.

- Other thing you might consider is resonant gate drive - in series with gate you use an inductor tuned to resonance, and a resistor which you use to adjust Q -
this saves lots of power and makes gate drive much easier.
You may need only few volts to drive the gate fully, depending on Q you set.

Waveform is sine wave but still it can be more than good enough for those frequencies where mosfet delays are biggest factor anyway.

- you may use a smaller class E stage to drive the big one, and etc.

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