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MHz Fast H-Bridge or Half Bridge Possibility

Question asked by JB_Tron on Jun 17, 2013
Latest reply on Jun 17, 2013 by RSchnell

Hello,

 

First time posting and I am  not an expert circuit designer.

I found some discussion on driving an H-bridge with the ADuM3220 in the AD forum's and I see the MOSFET gate charge will limit the speed to 1MHz.

As I see it, the H-bridge would allow the us to just use one power source but the load would have to be isolated from ground. A half -bridge would require two power sources but then we could drive each electrode with respect to ground.

 

 

Here is a copy of a technical request I sent to International Rectifier;

Hello,

We have a project I would like to discuss with IR engineers.

The physicists need to convey rare isotopes down a section of beam pipe that has partial pressure. This can be accomplished with a series of electrodes that are rings with 10mm holes spaced about 5mm apart. They are electrically connected in groups of eight and will be driven with eight phases.

Here are the parameters for each phase;

1) Frequency range 300KHz to 3.5Mhz.

2) Amplitude 120Vpp.

3) The load characteristic is essentially an 800pf capacitor.

4) The physics simulations are best with a square wave.

5) To accomplish a 3000V/us slew rate on 800pf would require sourcing 2.4A. (slewrate = I(max)/C)

I expect there may be a FET solution maybe in an H-bridge configuration but I am not very familiar with this, especially for high frequency.

There is an op-amp from Apex (PA107) with great specs. However, at almost $400/ea, that was shot down by the project leader.

I envision having individual power modules mounted near the vacuum feed-through to minimize the effects of stray capacitance, inductance and resistance.

If there are any recommendations for this “DC coupled broadband amplifier” please advise.


This was the response;

Hello John,

 

If I understand your question correctly, you are looking for a way of generating those different phases which will drive the load capacitances. I can suggest you the MOSFET's which have a switching capability of upto 5MHz. But the MOSFET's would require the gate drivers to drive the FET's, but our gate drivers have the capability of switching upto 300KHz only.

 

Here is an application notes on Full bridge : http://www.irf.com/technical-info/refdesigns/irsolwib.pdf

 

I was looking at the Intersil EL7104 for the gate drive.

 

I see from some postings that there are expert designers monitoring these forums.

Any suggestions would be greatly appreciated.

Thanks in advance.

JB

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