Re: LF: Re: Hall Effect for Over-current shutdown?

["Alan Melia" <alan.melia@btinternet.com>]

Hi Stefan that might be taking a bit of a risk! A 100v working FET might be ok at 24 V but the recommended minimum rating is 4 times the DC supply for Class D and E. It does mean you have to put up with higher rds(on) but all design has its compromise somewhere.

 

Alan

G3NYK

----- Original Message -----

From: Stefan Schäfer

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, April 09, 2013 1:27 PM

Subject: Re: LF: Re: Hall Effect for Over-current shutdown?

Hi Warren,

Instead of spending to much effort to the current sensing my advice is to use other FETs. A 500 V FET at 30 V supply voltage is a heavy waste of power in the on resistance. For 30 V and a class D, try e.g. a IRFP3710 or IRFP150N . That should work much better.

73, Stefan/DK7FC


Am 08.04.2013 21:07, schrieb Warren Ziegler:

Hi Alan,

    I've modified the G0MRF amp with the M0BMU output configuration, I'm using a 30V supply.

The G0MRF uses a current sense resistor to shut down the amp quickly in case too much current is being draw.

I've modified the output transformer turns ratio to produce more power at lower supply voltages (I'm using 500V, 55a FETs).

However with the new higher currents and with a new appropriate value sense resistor its developing a LOT of heat (12 W or so) and needs to be heat-sinked.

I'm thinking Hall-effect might be more efficient and produce less heat - I'm pretty sure that others have used Hall effect devices to protect MOSFET amplifier and I'm looking for circuit tips.

73 & Tnx!

Warren

On Mon, Apr 8, 2013 at 2:52 PM, Alan Melia <alan.melia@btinternet.com> wrote:

Ah interesting problem Warren.... why is it over-current?? if it is over-current because a high voltage has welded/melted a short between drain and source, then the protection wont help ....high currents usually lead to excess heating ......but what is the real cause? If you really need DC supply protection would not a high-side current monitor be easier/faster??? The problem then could be there is enough energy stored in the PA choke to zap the FET before, or even if, you can disconnect the supply.

 

OK drive fails permanently on might be a condition it would protect the FETs against with DC coupled drive

 

Alan G3NYK

----- Original Message -----

From: Warren Ziegler

To: rsgb_lf_group

Sent: Monday, April 08, 2013 7:15 PM

Subject: LF: Hall Effect for Over-current shutdown?

Anyone using a Hall effect device for overcurrent sensing and shutdown in a MOSFET amplifer?

--
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1

 

--
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1