"John Robertson" wrote in message
...
Not an expert on instantaneous surges in resistors (you could ask my
daughter - she is in third year physics ;-) but I would suggest that
you consider using Flame-Proof resistors in this application. these
are resistors that open internally and do not burn up your board
when
they fail...sometimes known as a fuse resistor....
John :-#)#
On 24 Nov 2003 22:50:40 -0800, (Jason Hsu)
wrote:
It's part of a design for a T/R sense circuit for a noise
cancellation
device.
I won't bore you with too many details. One thing I noticed in a
design I'm looking at is that 1W resistors could be subject to as
much
as 50W of power apiece during the time it takes for a relay to
respond. This response time is 7msec. The overall duty cycle will
be
low (well under 1%).
Can the 1W-51 ohm resistors handle this 50 RF volts 0-peak (about
50W
PEP) for .007 sec? 50W over .007 seconds is .35 Joules. .35W for
1
second is also .35 Joules, which a 1W resistor should have no
trouble
handling. Can the resistors be damaged during that .007 seconds?
No, it will not be damaged.
Also, how much time does it take to damage a toroid? If it can
handle
X units of flux density continuously, how much flux density can it
handle for .007 seconds with a low overall duty cycle (like well
under
1%)?
This is an entirely different situation. The maximum flux density is
fixed by the core material, and cannot be exceeded, no matter how much
current you feed through the coil.
Jason Hsu, AG4DG
usenet AAAAATTTTT jasonhsu.com