Klaus said:
Hi
This patent is from 1989 and I just stumbled accross it:
www.microdesign.dk/tmp/ReverseProtectionPatent_US5546264A1.pdf
Can this be true that the patent office has appointed this patent? For
sure there must be lots of prior-art out there with the excact same
circuit?
Would you ignore this patent and use the circuit configuration anyway?
Thanks
Klaus
You've got two ways of proceeding:
a) You can try to invalidate the patent. Finding
prior art--published, used or sold--dated at
least a year before the patent application was
filed, Dec. 22, 1994--does that.
If you find it, and it really describes *exactly* what's
patented here, the patent's invalid. If you find
prior art that is something that would make this patent
"obvious" to someone "skilled in the art" of electronic
design, the patent's also invalid, but those requirements
are subjective; the invalidation is not a given.
You could then ask the Patent Office to formally cancel
that patent by filing a request for reexamination based
on the new evidence. I wouldn't bother if you find
identical art. You might consider it if you find prior art
that suggests but is not identical to the patented invention.
Depends on your comfort level, confidence, etc. It
costs $2k to file, and you'd probably need a patent
attorney to handle it.
b) You can use another circuit.
It's important to remember the only thing patented is
exactly what's in the claims.
To infringe a claim your device has to include EACH
and EVERY element described in the claim; (if you
didn't use as many elements you'd have done the same
thing with a simpler circuit and would have grounds for
patenting an improvement; if you use distinctly
different elements, or in a different configuration,
your device is novel, and not infringing.)
These guys claim 1) a back-to-back zener AND 2) a MOSFET switch
in 3) the positive supply line in each of their five claims.
You could make a different circuit not including all those
elements and not infringe, IMHO.
Here's some prior art:
The following appears in Bob Pease's "Troubleshooting
Analog Circuits", (c) 1991, ISBN 0-7506-9184-0, p164:
.----------.
| |
V+ >-----+-----------| Vcc |
| | |
.-. | |
| | R1 | |
| | 1M | |
'-' | |
| | |
| | |
|____. | |
- - - Q1 | |
| ^ | | |
0V >----' '-+-------| GND |
'----------'
He wrote there: "I recently invented a circuit
(Ref. 1) to fulfill the request of a customer.."
Ref. 1 refers to Pease, Robert A., "Protection Circuit Cuts
Voltage Loss," Electronic Design, June 14, 1990, p77.
Obviously, you could safely use Bob Pease's circuit
(assuming it hasn't been patented by someone else
before Bob Pease published it!)
HTH,
James Arthur
