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

[wolf_dl4yhf <dl4yhf@freenet.de>]

Hi Warren,

Indeed it requires a few milliseconds (the small reed relay contacts can switch at one or two hundred Hertz) but you don't need to shut off the MOSFET within a few thousand cycles of the carrier frequency - the FET will have to tolerate short pulses of overcurrent anyway.

All the best,
  Wolf .

Am 09.04.2013 17:02, schrieb Warren Ziegler:

Wolf, interesting idea, but doesn't contact closure take about 10ms?

73 Warren

On Mon, Apr 8, 2013 at 4:18 PM, wolf_dl4yhf <dl4yhf@freenet.de> wrote:

.. or wind a few turns of fat copper wire around a 'reed relay' contact tube. Virtually no voltage loss then. I used this for a power supply, but it would work for the DC current feed inside a PA as well. IIRC, the product of number of turns * Amperes was about 50 for the contact to close.

73,
   Wolf .

Am 08.04.2013 21:39, schrieb Alan Melia:

Ah yes that is Class D and can go that way if mis-matched......that is a lot of power in a sensing resistor! I guess a Hall effect device or even a temp sensor would do that job. I think in over current condition a lot of power is dissipated in the devices. High side sensors should be available at 30v The sheets I have seen, suggest they require some assistance above about 40v.

 

Alan

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

From: Warren Ziegler

To: rsgb_lf_group

Sent: Monday, April 08, 2013 8:07 PM

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

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