Thanks to all for the comments. Your stories reminded me of an audio amp
oscillating in the 20 MHz range caused by PCB layout. A cap here and a
cap there fixed it. But that was a product that expected and needed EMC
testing. This "passive" thing may not be as passive as I thought. And
thanks to John who reminded that immunity testing will also be required.
As always, the list comes through to remind of things forgotten. Thank you.
Scott
On 7/12/2013 8:26 AM, Russell Beattie wrote:
Scott
I have also had the same experience with a similar simple circuit
going into oscillation on a vehicle and causing all sorts of problems
- at around the 60 to 70 MHz range.
Russ Beattie
*From:* Derek Walton <lfresea...@aol.com>
*To:* don_borow...@selinc.com; emc-p...@ieee.org
*Cc:* sdoug...@radiusnorth.net
*Sent:* Friday, July 12, 2013 11:12 AM
*Subject:* Re: EMC Required?
HI Scott,
I'd like to reinforce what Don has said. I flew to Scotland in the
early days of CE with a product that should have aced emissions and we
were worried about susceptibility. It failed emissions and passed
susceptibility. The 3 transistor circuit was singing away around 70 MHz.
I'm always reminded of the old saying "we test to confirm our design
is good"
Cheers,
Derek.
-----Original Message-----
From: Don_Borowski <don_borow...@selinc.com>
To: emc-pstc <emc-p...@ieee.org>
Cc: Scott Douglas <sdoug...@radiusnorth.net>
Sent: Fri, Jul 12, 2013 9:16 am
Subject: Re: EMC Required?
Scott-
I have seen some really simple circuits using common, cheap
transistors that had unwanted oscillations in the range of 100 to 200
MHz, which failed radiated emissions.
The most recent one was similar to your circuit, though in the
opposite direction -- a simple circuit with a few transistors driving
the LED of an optocoupler for low speed digital data. The fix was
simple (a small resistor in series with the base lead of the bipolar
transistor driving the LED), but the test was essential, as the
circuit otherwise performed without a problem.
Don Borowski
EMC Compliance Engineer
Schweitzer Engineering Labs
Pullman, WA, USA
From: Scott Douglas <sdoug...@radiusnorth.net
<mailto:sdoug...@radiusnorth.net>>
To: "emc-p...@ieee.org <mailto:emc-p...@ieee.org>" <emc-p...@ieee.org
<mailto:emc-p...@ieee.org>>
Date: 07/12/2013 06:46 AM
Subject: EMC Required?
Sent by: emc-p...@ieee.org <mailto:emc-p...@ieee.org>
Hi folks,
Consider a simple circuit. IR diode, a transistor or two, some resistors
and caps. Receives input from IR remote, converts to electrical and
sends down a wire. No clock in the thing so you could call is passive.
But does it need EMC testing for US or EU? The IR signal will be in the
35-50 kHz range so pulses down the wire will be the same. Does this make
it fit within the realm of EMC required? The device is sold by itself
without other products, but is always connected to something else in
use. Something else could be a wide variety of anything. I think of it
like a stand-alone audio speaker. Purely a passive device that is driven
by signals that fall within the EMC required realm. So do you do EMC
or not?
Looking forward to your opinions on this.
Scott
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