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

[Warren Ziegler <wd2xgj@gmail.com>]

Thank you Rik, good ideas!

Warren

On Mon, Apr 8, 2013 at 4:12 PM, Rik Strobbe <Rik.Strobbe@fys.kuleuven.be> wrote:

Hello Warren,

 

that should be possible, I have used a A1302 Hall sensor as a "no contact" >100A current monitor.

The sensor was just some mm away from the wire and was calibrated once using a (expensive) amp. meter.

At lower currents it might be better to let the wire run a small loop with the sensor inside.

The output voltage is proportional to the magnetic field (= current through wire) with a offset voltage of 2.5V (at 5V supply voltage).

Just be sure to get a linear Hall sensor (not the latch type) and be aware that most Hall sensors are rather slow (some 10..100us response time). So at 136kHz it will resond to the average current rather than peak currents.

 

73, Rik  ON7YD - OR7T

 

 

---

Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Warren Ziegler [wd2xgj@gmail.com]
Verzonden: maandag 8 april 2013 21:07
To: rsgb_lf_group
Onderwerp: 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