TECHFORUM
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94 August 2009
>>> QUESTIONS
Lead Connections
Of 280 Amps MOSFET
The MOSFET leads in a TO-220
package to carry about 280 amps look
small — about 1 sq mm cross section —
though short length.
What is the best way to connect
the drain and source terminals/leads
and what size heatsink is required to
250 watts for a 2,500 watt inverter?
#8091 Mohammed Ahmad
Mississauga, Ontario, Canada
SMPS Ripple Scrubber
What remedies might there be to
further scrub the ripple from an otherwise very competent SMPS? As I am
learning, they are smart little buggers,
and simply throwing a farad or two
worth of mondo blue caps between it
and my headphone amplifier is not a
remedy. I would like to stay outside
of the unit itself. Any suggestions or
references would be appreciated.
#8092 Bruce Seidner
Knoxville,TN
Battery Powered
Hand/Foot Warmer
I help coach a high school ski
racing team. As a consequence, I spend
a lot of time standing in the snow and
my hands or feet sometimes get cold. I
would like to have a circuit to build a
battery powered hand/foot warmer.
Ideally, the circuit would regulate the
power output of the resistor to maintain
a preset temperature measured with a
thermistor. The preset temperature
point should be variable and able to be
adjusted at any time. I plan to use four
AA NiMH batteries in series.
Energy = 2600 mAh x 4 x ( 4 x1.5V) =
15.6W-hr
If I want it to last eight hours at
100% duty cycle:
Average Power =
15.6W-hr / 8 hr = 2W
Average current = 2W/6V = 333 mA
Resistor = 6V/333 mA = 18 ohms
It would also be nice to have
an ON LED, and an LED that indicates
when current is flowing to the
resistor would help in adjusting the
temperature set point.
#8093
Mark Smith
Corvallis, OR
HVAC Controls On A Computer
What do they have that will tie
HVAC controls on a computer for
home and commercial applications?
#8094 Paul Finnigan
Arlington,VA
Heart Rate Monitor
I need to build a heart rate monitor
to see when my wife's heart rate gets
too high. I have the standard finger
model, but I would like something that
uses chest probes and I could record
the actual signal.
