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

[Warren Ziegler <wd2xgj@gmail.com>]

Hi Stefan,

     I think you are advocating higher voltage and lower current to decrease loss in the FET due to the on resistance which is a good idea.

But  what I am looking for is for  over-current protection which would be valuable in any class-D design regardless of the choice of FETs. As Alan has pointed out the wrong output impedance can cause the amp to draw large currents. I am now using a current sense resistor but I was thinking that Hall Effect might be more efficient.

73 Warren

On Tue, Apr 9, 2013 at 8:27 AM, Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de> wrote:

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

 

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