The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: Mike Poulton
Subject: Re: Problems with MOSFET drivers
Date: 18 Nov 2002 03:57:25 GMT
Organization: MTP Technologies
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
On 17 Nov 2002, firstname.lastname@example.org (Adam Seychell) said:
> That method of control cannot stabilize to the resonant frequency
> since the magnitude of the current falls off either side of Fo. You
> must have phase information.
> I'd look at getting a CMOS 4046 PLL to lock in on the primary current
> using a current transformer. And limit the VCO to narrow frequency
> range say 500kHz ~ 700kHz.
Why can't primary current be used to stabilize the frequency? As long
as the VCO is limited to a narrow frequency range, it seems like it
would work just fine. I would probably use a microcontroller to read
current and adjust frequency, but there's probably an analog way to do
it as well.
> But first get the gate driving problem fixed and don't even start to
> worry about feed back or loop control. You may need to totally re-plan
> your entire driver/transformer/bridge setup. If you want the ultimate
> gate drive transformer then use 4 windings of RG178 coax over a say
> 30mm E core. Connect all shields together for primary and each inner
> conductor go to a FET. I think the only leakage inductance here will
> be outside connections to the FETs and driver. Put gate resistors
> also, at least while developing. The only disadvantage is reduction in
> efficiency of the bridge but that's not your priority at the moment
> and can be optimised at a latter time. Use 3A SMD schottky diodes
> across the output of driver to supplies in order to stop reverse
> currents (they must be close to the drivers or they have little
> effect). Also dramatically increase your supply coupling from the 100n
> as I thought you mentioned using in one of you other post. Your
> driving more capacitance than that, so how can that amount of supply
> capacitance hold charge ! As I said make sure you read up on all the
> app notes as they go into all this detail.
Most recently, I've been using .1uF across the supply -- plus whatever's
inside that multi-$k lab supply. Should be more than enough, but I'll
add more anyways. The driver outputs are mosfets, so they contain
reverse diodes already. I'll ad external ones, just in case. I'll make
a new transformer from coax -- I have tons of RG178. Looks like it'll
be a few days before I get to work on it, though, since I just got
several large assignments with plenty of time pressure.
Not only do I speak for my company, I AM my company!
Live free or die!
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup