From: Fred Bloggs
User-Agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0
X-Accept-Language: en-us, en
Subject: Re: Limiting total wattage for a constant-current dummy load?
Date: Sat, 09 Nov 2002 17:20:33 GMT
NNTP-Posting-Date: Sat, 09 Nov 2002 09:20:33 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
John Muchow wrote:
> I've got a 1.2-50V (approx.), 0 -10A constant current dummy load
> circuit (MAX480 op-amp, ICL8069 reference, and IRF540 for the load)
> working beautifully, but I have a problem I can't seem to find a
> solution for.
> I'm limited to about 50 watts for the load right now with the single
> MOSFET device and heat sink I'm using now. But, I can use the load
> with a current "setting" and load voltage that can significantly
> exceed the 50 watt limit if I'm not careful to figure out the wattage
> in advance.
> How can I allow both extremes of current/voltage (10A at up to 5V, or
> 1A(at up to 50V) to flow in this circuit but still limit the overall
> wattage dissipated? I can easily control the current to limit it to
> 10A through the IRF540, but I'm stumped as to how to use the voltage
> to determine the wattage the load would have to dissipate *before* I
> start the darn thing up.
> I'd love have an LED come on that told me "power is too high" if I
> selected a current level that would exceed 50 watts (or any arbitrary
> value) with the voltage present at the MOSFET load.
> Can anyone point me in the right direction? I couldn't find any info
> on the IR, National, Zetex, TI, Fairchild, or Linear Tech. web sites.
I would use a GMR sensor to perform the instantaneous power computation
in analog in such a way that it allows any current setting you program
up to 50W , and this power limit can be programmable too, then cuts in
and limits the current if and when the dummy load reaches the maximum
power setting. See GMR Sensors Manage Batteries, Ramirez&Pelegri at :